SBPMat BRAZIL-MRS

2nd Brazilian MRS MeetingOctober 26-29, 2003

Symposium F:

Supramolecular Materials for ElectronicAnd/or Optical Applications

Symposium Organizers:____________________________________________________

Roberto Mendonça Faria (USP-São Carlos)

Elizabeth Andreoli de Oliveira (USP)

Leni Akceruld (UFPR, LACTEC)

Marco Cremona (PUC-Rio)

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INVITED PRESENTATIONS

F-I1 FIRST-PRINCIPLES ANALYSIS OF OPTOELECTRONIC PROPERTIES IN SEMICONDUCTING POLYMERS: THE ROLE OF SOLID-STATE PACKING G. Bussi, A. Ferretti, A. Ruini, E. Molinari, INFM, Modena, Italy, and M.J. Caldas, Instituto de Física da USP, SP, Brazil

Ordered films of organic conjugated polymers offer an ideal scenario for the study of electronic and excitonic confinement, being composed of quasi-one-dimensional systems arranged in a three-dimensional crystalline environment. Sofar, experiments are usually interpreted in terms of a single-chain model, therefore neglecting any effect of solid-state arrangement and interchain interaction. We investigate the effect of solid-state chain packing on both optical and transport properties for a prototype polymer, poly-para-phenylenevynilene (PPV), in the two different crystalline packings most often found in real films, herring-bone (HB) and pi-stack. We start from a density-functional theory calculation, for the crystalline system. The optical behaviour is then explored through an ab-initio scheme based on the Bethe-Salpeter equation, that allows us to include electron-hole interaction. We find that the details of crystalline arrangement can alter dramatically the optical properties, leading to a rich excitonic structure involving direct (with electron and hole on the same chain) and charge transfer excitons. Indeed, in the case of HB PPV, the optical inactivity of the lowest component crucially quenches the photoluminescence efficiency. Transport properties have been investigated by converting the band-structure results to a tight-binding formulation. This approach provides a first-principles determination of the transfer integrals, which are found to be a crucial quantity to assess the impact of crystalline aggregation on conduction properties; in particular, we obtain a clear difference in the effect of HB versus pi-stacking.Our results suggest that control of interchain interaction and solid-state packing can be a tunable parameter for the design of efficient optoelectronic devices.

F-I2 SELF-ASSEMBLED MONOLAYERS AS INTERFACES OF MOLECULAR OPTOELECTRONIC DEVICESF. A. Nüesch, Laboratory of Optoelectronics of Molecular Materials, Institute of Materials, EPFL, 1015 Lausanne, Switzerland

Optoelectronic and electronic devices such as light emitting diodes, photodiodes or transistors are traditionally made from inorganic materials such as silicon or gallium arsenide due to their unparalleled performance. Only recently, the commercialisation of organic light emitting devices has swept away the fear that organic materials would lack the stability required for device manufacture and reliability. As a matter of fact, polymer transistors can now exhibit charge carrier mobilities of the same order of magnitude as amorphous silicon. To achieve such high performances, it is necessary to control the growth of the organic films and to study the electric contact to the device electrode. It appears that the interface between electrode and organic film is crucial for charge injection into organic materials. In this work, a strategy is developed, which utilises self-assembled monolayers attached to the device electrodes. Different grafting methods are elaborated and discussed. In particular, the role played by the electrical dipole, conjugation and polarizability of the grafted molecules is elucidated.

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F-I3 SUPRAMOLECULAR SYSTEMS FOR MOLECULAR ELECTRONICS AND OPTICAL DEVICES.O.L. Malta, Departamento de Química Fundamental-CCEN-UFPE. Cidade Universitária, Recife-PE, 50670-901, Brazil.

Supramolecular chemistry provides the way to obtain nano-objects that present high functionality, based on the assembly of molecular units. In these nano-objects, or supramolecular systems, the bonding between the molecular units is rather weak and has a low covalent character. Modeling and manipulating these systems become facilitated by the low energy involved in breaking and forming bonds between the molecular units, making them adequate and efficient molecular complexes to be used in nanodevices. They are of particular interest in molecular electronics and in the design of high performance optical materials based on coordination compounds of transition metal and lanthanide ions. In this thirty minutes talk we will present and discuss, through a few examples, some of the basic aspects of the role played by supramolecular systems in these two subjects, with emphasis on the molecular shuttle switch and on lanthanide complexes for electroluminescent materials.Financial support: CNPq, RENAMI, IMMC

F-I4 FINE CONTROL OF PHOTOLUMINESCENCE IN NANOSTRUCTURED LAYER-BY-LAYER FILMS OF PPVOsvaldo N. Oliveira Jr.,Valtencir Zucolotto, Ângelo D. Faceto, Felipe R. Santos, Francisco E. G. Guimarães, IFSC, Universidade de São Paulo, USP, CP 369, 13560-970, São Carlos, SP, Brazil IFSC/USP, São Carlos/SP, Brazil.

Layer-by-layer (LBL) films are exploited to control the photoluminescence (PL) of poly(p-phenylenevinylene) (PPV) in an unprecedented way. This was achieved by controlling the Förster energy transfer between PPV layers (donors) and layers of a commercial azodye, Brilliant Yellow (BY) (acceptors). Energy transfer was controlled by inserting spacing layers of inert polymers between PPV and BY layers and by photoaligning the BY molecules via trans-cis-trans isomerization with a linearly polarized laser. The intensity of the polarized PL could be varied almost continuously by changing the time of photoalignment. PL was quenched in PPV/BY films with no spacing layers, but increased with the number of spacing layers. Further increase in PL was obtained by photoaligning the BY molecules perpendicularly to the PPV molecules that adopt a preferential orientation in the LBL films. This occurs because Förster transfer is directional, dipole-dependent, being maximum for BY molecules aligned parallel to the PPV molecules. PL polarized parallel to the excitation direction increases up to 4 times the initial value. The precise control of emission offered by the LBL films may be used in smart devices, where the luminescence properties of PPV are combined with the birefringence characteristics of azobenzene-containing materials. Acknowledgment: FAPESP and CNPq.

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F-I5 PHOTOPHYSICS OF SEMICONDUCTING POLYMERS STUDIED BY ULTRAFAST SPECTROSCOPYP. B. Miranda, Instituto de Física de São Carlos, Universidade de São Paulo, C.P. 369, São Carlos – SP, CEP 13560-970

Semiconducting polymers form a relatively new class of materials with important emerging applications in electronics and optoelectronics. The current state of polymer electronics was made possible by more than two decades of intense investigation, from which much has been learned about their electronic structure, elementary excitations and the role played by polymer morphology and impurities. Although considerable progress has been made in recent years towards applications of luminescent conjugated polymers, a few outstanding issues on their photophysics have profound implications for device development and optimization. In this talk I will review some of these open problems and how they have been investigated by time-resolved spectroscopy in the ultrafast timescale (from a few fs to hundreds of ps). Emphasis will be given to recent studies of excitation energy transfer, charge-carrier photogeneration and formation of triplet states. Both homogeneous polymers and guest-host systems will be considered.

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ORAL PRESENTATIONS

F-O1 HIGHLY EFFICIENT POLY(3-METHYLTHIOPHENE)-BASED PHOTOVOLTAIC DEVICES PREPARED ONTO TIN-OXIDE/SULFONATED-POLYANILINE SUBSTRATES.R. Valaski, R. L. Lessmann, L. S. Roman, I. A. Hümmelgen DF/UFPR, C. P. 19044, 81531-990 Curitiba PR, Brazil, R. M. Q. Mello, L. Micaroni, DQ/UFPR, C. P. 19081, 81531–990 Curitiba PR, Brazil.

We investigate the photovoltaic potential of SPAN/PMT (SPAN: sulfonated polyaniline; PMT: poly(3-methylthiophene)) bilayers galvanostaticaly deposited onto tin oxide films (TO), the transparent electrode. TO films are produced by chemical vapour depositon method. Electrochemical polymerization has some advantages like easy thickness control, doping e and dedoping processes. Besides, the production of bilayer polymer devices using chemicall methods may be difficult due to constraints imposed by solvent compatibility limitations. SPAN films present high transparence in the visible range of spectra and ohmic contacts with metal and TO electrodes. PMT films have a high absorption coeficient in the visible range of the spectrum and have good stability at environmental condictions. Our devices were made in the TO/SPAN/PMT/Al sandwich structure, with differents thickness of PMT films, whereas the SPAN film thickness was mainted constant, 120 nm. The measurements were made with illumination through TO and Al electrodes. These devices presented an increase of efficiency with the increase of PMT films thickness till 171 nm. After this value the efficience started to decrease. The best results were obtained with a PMT thickness of 171 nm and illumination through TO electrode: incident photon to collected electron efficiency of 18 %, power conversion efficiency of 1.2 %, open circuit voltage of 0.71 V, short-circuit current density of 0.16 A/m2 and fill-factor of 31%. (at monochromatic radiation of = 580 nm and I = 2.3 W/m2, for all data).

F-O2 NMR CHARACTERIZATION OF THE LECTROLUMINESCENT MATERIAL Poly[(9,9-dihexylfluorenyl-2,7-diyl)-co-(1,4-vinylenephenylene)]L. Akcelrud, Departamento de Química – UFPR, A. Glogauer, Departamento de Química - UFPR , A. R. M. de Oliveira, Departamento de Química - UFPR, R. Ferracin, Instituto de Tecnologia para o Desenvolvimento - LACTEC and A. G. Ferreira Departamento de Química – UFSCar

Electroluminescent polymers are macromolecules that can emit light when an electrical field is imposed, in the same way as conventional inorganic semiconductors or the more recent low molecular weight organic molecules do. Among the additional advantages found with polymers for potential technological applications is the possibility of fabrication of large area displays by means of the usual techniques of thin film processing as dipping or spin coating. The synthesis of these polymers is much more involved than those employed in conventional polymers, however. In the majority of cases the monomers are not available commercially and therefore have to be prepared in a series of steps prior to the polymerization. The characterization of these monomers, as well as of the final product is a most important issue, since a high regularity is a main requirement for the electro-optical performance of the electroluminescent polymer. In this communication we describe briefly the synthesis, and the NMR characterization of poly[(9,9-dihexylfluorenyl-2,7-diyl)-co-(1,4 vinylenephenylene)] which structure is similar to the extensively explored poly(phenylene vinylene) (PPV) with an additional fluorene moiety, which should impart better optical and thermal resistance characteristics.LACTEC, UFPR, CNPq/ Instituto do Milênio em Materiais Poliméricos – IMMP, CAPES.

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F-O3 EXCITON FORMATION IN OLEDS AS OBSERVED BY EDMRG. B. Silva, C. F. O. Graeff, DFM-FFCLRP-USP, Av. Bandeirantes 3900, 14040-901 Ribeirão Preto, Brasil; F. Nüesch, L. Zuppiroli, LOMM-IMX-EPFL, CH-1015 Lausanne, Switzerland.

In this work the injection, transport and recombination properties of tris-8-hydroxynolate-aluminum (Alq3) diodes in different structures, such as ITO/CuPc/-NPD/Alq3/LiF/Al, ITO/BAC10/Alq3/-NPD/Ag and Al/LiF/Alq3/LiF/Al, were investigated by electrically detected magnetic resonance (EDMR). In an EDMR experiment, microwave-induced changes in the conductivity are measured as the sample is subjected to a swept dc magnetic field. The measurements were done using a X-Band (9 GHz) and a K-Band (24 GHz) spectrometer at room temperature. In the case of CuPc/-NPD/Alq3 device, the EDMR signal is quenching, typically 10-5 in amplitude and is composed by two gaussian lines. The predominant line has a linewidht of 16 G and its g-factor decreases from 2.0046 to 2.0041, as the voltage increases, while the second one has a g-factor = 2.0035 and its linewidth increases from 20 to 35 G. The spin dependent process observed in these measurements is assigned to exciton formation due to spin-1/2 particles resonance. In this case the process occurs through two molecules: a cation (Alq+ or NPD+) and an anion (Alq-). Thus, the predominant line arises from cations and the broad gaussian line from anions. The EDMR signatures of cations and of anions are also found at ITO/BAC10/Alq3/-NPD/Ag and at Al/LiF/Alq3/LiF/Al devices, respectively, in which only holes or electrons are injected into the organic layers.

F-O4 MOLECULAR ORGANIZATION IN LANGMUIR-BLODGETT FILMS OF PPV DERIVATIVES M. Ferreira, D. T. Balogh, C. C. Olivati, R. M. Faria and O. N. Oliveira Jr., IFSC/USP, 13560-970, São Carlos/SP, Brazil; Ricardo F. Aroca, University of Windsor, N9B 3P4, Windsor/On, Canada; Carlos J.L. Constantino, DFQB/FCT/UNESP, 19060-900, Presidente Prudente/SP, Brazil

The molecular organization of poly[(2-methoxy-5-n-hexyloxy)-p-phenylenevinylene] (OC1OC6-PPV) and poly-[(2-methoxy-5-n-octadecyl)-p- phenylenevinylene (OC1OC18-PPV) in Langmuir-Blodgett (LB) films have been investigated using FTIR spectra recorded for both transmission and reflection modes considering the surface selection rules and some key vibrational modes. The bands at 970 cm-1 (vinylic C-H wagging) and 854 cm-1 (aromatic C-H wagging), whose induced molecular dipoles are perpendicular to the plane containing the aromatic and vinylic groups (in a planar trans form), are stronger in the transmission mode and weaker in the reflection mode. This shows that OC1OC6-PPV molecules must be anchored to the substrate by the side chain with the aromatic ring practically perpendicular to the substrate. This is confirmed by the Raman spectrum in which a distortion of the vinylene group was observed and by surface enhanced fluorescence (SEF) on an LB monolayer deposited onto Ag nanoparticles. On the other hand, the OC1OC18-PPV has presented a random molecular organization in the LB films. Acknowledgements: FAPESP, CNPq, IMMP/MCT.

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F-O5 THIN FILM OF CARBON NITRIDE AND SILICON NITRIDE AS A BARRIER COATING FOR PLEDs USING LOW TEMPERATURE PLASMA DEPOSITIONA.M. Nardes, E.A.T. Dirani, A.M. Andrade, F.J.Fonseca, EPUSP, Universidade de São Paulo, São Paulo, SP, Brazil; R.Bianchi , IFSC, Universidade de São Paulo, SP, Brazil; FMFT, Pontifícia Universidade Católica de São Paulo, SP, Brazil

Light-emitting diodes based on conjugated polymers (PLEDs) have potentially significant future applications in displays. The stability of devices can be improved by stripping off oxygen and moisture vigorously. Based on that, a PLED must be encapsulated to reduce failure due to moisture or oxygen in the system. Silicon nitride and carbon nitride are widely used in many electronic devices of compound semiconductors (primarily in GaAs and InP) manufacturing for the wireless applications, including devices passivation of metal-semiconductor field effect transistors, high electron mobility transistors (HEMTs), hetero-junction bipolar transistors (HBTs), masking layers, dielectric layers for metal-insulator-metal (MIM) capacitors and encapsulation to protect against the environmental induced degradation or mechanical scratches. In this work a PECVD system was used to deposit silicon and carbon nitrides at low deposition temperatures (around 100ºC) in order to encapsulate PLEDs. Mechanical and optics results concerning the films and electrical characterization concerning the polymeric device are show. Preliminary tests indicate that the film is sufficiently impermeable to moisture and oxygen for application to moisture-sensitive display applications.

F-O6 CONVERSION REACTION OF A POLYSULFONIUM PRECURSOR INTO POLY (p-PHENYLENEVINYLENE) FILMS STUDIED BY ELLIPSOMETRY SPECTROSCOPYR.F. Bianchi, D. Gonçalves, R.M. Faria, Instituto de Física de São Carlos, Universidade de São Paulo, São Carlos - SP, Brazil, E.A. Irene, Department of Chemistry, University of North Carolina, CB #3290, Venable Hall, 27599-3290, Chapel Hill - NC, USA

Poly(p-phenylenevinylene) (PPV) and derivatives have been extensively investigated as active layers in light-emitting devices (LEDs) mainly because of a wide range of emission colors and ease of processing. The precursor route is the most commonly used method of preparing PPV films. Flexible PPV films can be promptly obtained by thermal conversion of a water-soluble precursor, poly-p-xylylidene tetrahydrothiophenium chloride, PTHT. In the present study, our attention focused on the optical properties of PTHT and PPV films on Au-coated substrates as measured by spectroscopic ellipsometry (SE). Fourier transform infrared spectroscopy (FTIR) was used to verify structural differences in the polymer chain such as C=C groups (due to an increase of conjugation) and C=O (due to effects of degradation) groups. Fapesp and Millennium Science Initiative/MCT sponsored this work.

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F -O7 INFLUENCE OF THE OPTICAL EXCITATION ON THE ELECTRICAL PROPERTIES OF POLYMERIC LIGHT-EMITTING DIODES R.F. Bianchi, E.L. Queiroz, L. F. Santos, F.T. Reis and R.M. Faria, Instituto de Física de São Carlos / USP, CP 369, 13560-970, São Carlos, SP, Brazil

Since the electroluminescent properties of poly(p-phenylenevinylene) (PPV) were first reported in 1990, this polymer and its derivatives have been used as active materials in light-emitting devices. Although a large number of papers have focused on the electrical properties of PPV, the transport and injection mechanisms involved are still not completely understood. Frequency-dependent conductivity is a powerful technique that can be used to investigate bulk conduction and injection processes in polymeric electronic devices. In this work we have observed the influence of optical excitation on the complex conductivity of a PPV derivative, the poly[(2-methoxy-5-hexyloxy)-p-phenylenevinylene] (MH-PPV), in ITO/MH-PPV/Al and Au/MH-PPV/Au structures. The measurements were carried out at room temperature, under vacuum and illumination intensities varying between 0 and 250 mW/cm2. The results were interpreted using the random free energy barrier model, which is based on a random distribution of energy potential barriers in a disordered system. The fitting parameters have shown that the metal/polymer interfaces act as a light intensity dependent RC circuit in series with the polymer bulk. This work is sponsored by FAPESP, Brazil

F -O8 AFM STUDIES OF LANGMUIR-SCHAEFER AND LANGMUIR-BLODGETT POLY(5-AMINO–1-NAPHTHOL) FILMS R.L. Moreira, B.R.A. Neves, C.P.L. Rubinger and L.A. Cury, Depto. de Física, UFMG, C.P. 702, 30123-970 Belo Horizonte, MG, Brazil; C.A. Ferreira and A. Meneguzzi, Depto. de Materiais, UFRGS, 90035-190 Porto Alegre, RS, Brazil

In this work we used atomic force microscopy (AFM) to show that ultrathin Poly(5-amino-1-naphthol) (PAN) films can be transferred onto Si substrates through Langmuir-Schaefer (LS) technique or by combining this technique with the Langmuir-Blodgett (LB) one. Since potential applications of this material are in the fields of molecular electronics and anti-corrosive coatings, well adhered films of controlled thickness are suitable. The AFM tip was used to perform nano-indentation nano-delamination of the polymeric film. By adapting a model for indentation of bulky continuous elastic polymers to our nanometric-scale system, we could estimate the critical interfacial shear strength for the PAN/Si interface. The obtained results indicate that the films are indeed well adhered to the substrate. We also show that multilayer PAN films obtained by an appropriated association of the LS and LB methods were very smooth and uniform, with approximately 5 nm thickness per transferred layer.

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F -O9 ABSORPTION AND EMISSION LINE SHAPE OF POLY(P-PHENYLENE VINILENE) THIN FILMS: AN EXPERIMENTAL AND THEORETICAL STUDY.M. Veríssimo-Alves, DF, Universidade Federal de São Carlos, CP 676, 13565-905, São Carlos, SP; A. Marletta, FaFis, Universidade Federal de Uberlândia, CP 593, 38400-902, Uberlândia, MG; R. M. Faria, F. E. G. Guimarães, IFSC, Universidade de São Paulo, CP 369, 13660-970, São Carlos, SP

Optical properties of PPV films depend on the processing techniques and chemical synthesis routes. Molecular packing and structural defects can change electron-phonon coupling and reduce the effective conjugation length N of the polymeric chain. Here we present experimental and theoretical investigations on the absorption and emission line forms of PPV films produced by the cast, spin-coating (SC), self-assembly (SA) and Langmuir-Blodgett (LB) techniques.Absorption spectra are well described by a gaussian distribution of N, with 3 > N > 15. SC, SA and LB films, processed at 110oC, show a shift of the center of the distribution to larger N, and better resolution of emission spectra than films produced by the cast technique. The dependence of the band gap Eg and the dipole moment µ on N are obtained through DFT calculations for isolated PPV chains up to N = 12 using the SIESTA method. Vibrational frequencies and eigenmodes of the oligomers are obtained in order to calculate the dependence of the Huang-Rhys factor on the chain length. Using the theoretical functional forms for these parameters, we fit the absorption spectra and discuss the influence of packing in thin PPV films.

F -O10 FIELD DEPENDENCE OF THE MOBILITY IN DISORDERED ORGANIC MATERIALSJ. A. Freire, Departamento de Física, Universidade Federal do Paraná, Caixa Postal 19044, 81531-990, Curitiba-PR, Brazil.

The mobility of charges in disordered organic materials, measured by time-of-flight experiments, often exhibit an exponential dependence with the square-root of the applied field besides a temperature dependence consistent with a thermally activated process. This is observed in a wide variety of materials and the physics behind the field dependence is still not very clear. It is widely believed that in these materials the transport occurs via thermally activated hops between localized electronic states whose energy is not well defined due to conformational and positional disorder of the molecules. Some attempts to explain the observed field dependence have relied on the charge interaction with the random dipoles present in the material or in the existence of correlations between the molecular orbital energies while assuming a simple Arrhenius form for the hopping mechanism. Here I will discuss the possibility of this dependence be due to the formation of polarons. This will be done in the context of a master equation where the hopping rate between sites takes the form of the small polaron hopping rate of the Holstein model.

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F -O11 HIGHLY DISPERSIVE TIME-OF-FLIGHT SIGNALS IN DISORDERED ORGANIC MATERIALSJ. A. Freire, Departamento de Física, Universidade Federal do Paraná, Caixa Postal 19044, 81531-990, Curitiba-PR, Brazil.

The mobility of charges in disordered organic materials is usually measured by time-of-flight experiments. In these experiments electron-hole pairs are photo-created inside the material and are drifted by an applied bias. As the charges move inside the material a time-dependent current signal can be measured in the external circuit that connects the electrodes. In an ordered system the signal shows a plateau and the time when the current reaches half the plateau value is identified as the average transit-time. When the system is disordered, like what happens in many organic materials used for device applications, the signal shows no plateau and to extract the average transit time is a difficult task. I will show how to build a simple one-dimensional master equation model of the time-of-flight experiment where the charges move by thermally activated hopping between sites whose energy are distributed according to a Gaussian. An exact expression for the average transit-time can be obtained together with the current signal. The signal shows two distinct power-law regimes and we analyze the dependence of the powers with the disorder and with the applied field. More importantly, we observe that the field dependence of the exact transit-time, that ultimately determines the field dependence of the mobility, is directly related to the easily measured crossover-time of the two power-law regimes.

F -O12 CONDUCTING POLYMER IMAGESR. A. de Barros, and W. M. de Azevedo Departamento de Química Fundamental; CCEN-Universidade Federal de Pernambuco, Cidade Universitária CEP: 50740-540, Recife, PE, Brazil.Conducting polymers still attract attention nowadays, and the reason for that in part are due to their intriguing physical properties and the real potential for application in several research areas of advanced technologies. Nevertheless in the market today, there are not many examples of conducting polymer devices, and the reason for that seems to be related with poor polymer processability. For that reason a great effort has been put on the development of new synthetic route and process to produce more processable polymers. Recently we develop a non conventional synthetic route to obtain conducting polymer using light as a catalyst instead of conventional oxidative reagents to induce polymerization of aniline in aqueous solution. In this work we present a straightforward method to produce optical images and read only memory (ROM) devices using the extension of this non conventional route. The optical information storage is done on a thin film of PVA doped with aniline acid solution and transition metals salts in a way that resembles the traditionally photographic process. In the region where the light strike the composite polymer an image appear as results of polymerization of aniline by the transition metal induced by the light. After that, the composite polymer is treated with a reducing solution and water in order to fix the image and extract the unreacted reagents.

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F -O13 POLY(METHYL METHACRYLATE) RELAXATIONS PROBED BY ANTHRYL GROUPS COVALENTLY- LINKED TO THE MAIN CHAINJ.F. Deus, PIPE, UFPR; W. A. Corradini, T.D.Z. Atvars, UNICAMP, Inst. de Química; G. P. Souza and L.Akcelrud* LACTEC, Centro Politécnico UFPR, CEP 81531-990, Curitiba/PR

Poly(methyl methacrylate) (PMMA), poly(9-anthryl methyl methacrylate)(PMMAnt) and poly(MMA-co-MMAnt) were prepared, the copolymers contained one anthryl unit interspersed between each 2, 4, 10, 25,35 and 98 MMA mers. DSC data revealed that the copolymer’s glass transition temperature decreased gradually as the spacing between the anthryl groups increased, up to a point where the presence of these groups was no longer detected. This corresponded to a spacing of 50 MMA mers, where Tg was the same as the pure PMMA, thus establishing the length of chain segment involved in the glass transition of PMMA. In this composition (one anthryl per 98 MMA mers) the DMA spectrum was identical of the pure PMMA. The and relaxations were observed and assigned to the glass transition and to the rotation of the ester groups. By varying the DMA frequency the energy of activation for the two transitions was calculated from the Arrhenius equation . The fluorescence emission of the copolymer was registered with variation in temperature, allowing the determination of the relaxations by this method. Apart from the and previously found, another relaxation,, was detected, and was assigned to the onset of rotation of the methyl groups.

F -O14 VOLTAGE CONTROLLED COLOR OLED USING (Sm,Eu) DIKETONATE COMPLEXES BLEND.R. Reyes, M. Cremona, DF-PUC-Rio Rua Marquês de São Vicente, 225 Rio de Janeiro, RJ, Brazil; E.E.S. Teotonio, H.F. Brito, IQ-USP, São Paulo, SP, Brazil; O.L. Malta, DQF-UFPE, Recife, PE, Brazil.

Organic electroluminescent devices (OLEDs) have attracted strong industrial interest driven by the huge market potential of this recently developed technology. The emission wavelength of the OLEDs can be changed by using different combinations of organic and doping emitting materials. In this work, a lanthanide complexes blend was used to obtain a voltage-controlled color OLED. The device was formed by a 50 nm thick film of MTCD, working as a hole transporting molecular layer, a 50 nm thick layer of the lanthanide complexes blend, [SmxEuy(TTA)3(TPPO)2], working as light-emitting layer and by 50 nm thick layer of tris 8-hydroxyquinoline aluminum (Alq3), which is the electron transporting layer. The devices were grown onto glass substrates coated with indium tin oxide (ITO) layer and aluminium thick (150 nm) cathode. The electroluminescence of the device showed the characteristics narrow emission lines from Eu and Sm ions and the peaks intensity ratio is determined by the applied voltage. Continuous EL tuning emission was obtained varying the applied bias voltage from 8 to 22 V, changing the color emission from red to orange-yellow. Furthermore, an EL broad band peaked about 575 nm was observed and identified as the electrophosphorescence from the TTA-ligand.

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F -O15 NANOSTRUCTURED MANIPULATION OF A DEVICE PERFORMANCEA. Riul Jr, C.J.L. Constantino, P.A. Antunes, J.A. Giacometti, Depto de Física, Química e Biologia, FCT-UNESP, CP 467, 19060-900, Presidente Prudente/SP, Brazil

Nanostructured thin films of several organic materials, including perylenes and electroactive polymers, have been effectively applied as taste sensors. The Langmuir-Blodgett (LB) and self-assembly techniques permit an advantageous supramolecular architecture and thickness control of the materials composing individual sensing units of an “electronic tongue”, enabling a unique handling in the electrical response performance of the device. For instance, tripling the LB film thickness leads to a decrease of half of the observed electrical signal in the same sample analysis. Therefore, a high sensitivity is achieved by the nanostructured manipulation of different materials and noticeable results could be obtained in the detection of tastants, contaminants, and also in the differentiation of complex liquid systems. In addition, one might choose specific transducing materials envisaging a better device performance for a particular application. We will summarize here the main results obtained up to date in such technological application throughout the use of ultra-thin films of several materials.

F -O16 PHOTOABSORPTION AND PHOTOEMISSION INVESTIGATION OF ORGANIC COMPOUNDS USED IN OLEDs.W.G. Quirino, C. Legnani, M. Cremona, - Departamento de Física, PUC-Rio; M. L. M. Rocco, D. E. Weibel, G.V. Mota - Departamento de Físico-Química, IQ, UFRJ

In this work, photoabsorption and photoemission spectroscopy were used with the objective of characterizing the electronic structure of some organic compounds used in organic electroluminescent devices (OLEDs). The investigated compounds in form of thin films were: TPD, Alq3, NPB, MTCD and rare earth complexes as ([Eu(TTA)3(TPPO)2] and [Sm(TTA)3(TPPO)2]), deposited on ITO substrates. The measurements were accomplished using the SGM (250 - 1000 eV) line of Synchrotron National Laboratory (LNLS), covering the valence area as well as different internal shells (C1s, N1s, O1s, Al2p, Eu4d, etc). Furthermore, these films were irradiated for some minutes in the zero order of the same line (no-monochromatic light) and their photoabsorption and photoemission spectra were measured again to study the degradation induced by the exposition to the intense radiation. In the case of MTCD films, for example, the results show that the C photoemission signal is 20-30% lower after irradiation, while the valence signal decreases ~ 50% and the N signal practically vanishes, suggesting that the decomposition in these material happens mainly for the N desorption.

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F -O17 PHOTO-OXIDATION EFFECTS ON THE THERMOMECHANICAL PROPERTIES OF CROSSLINKED HIGH DENSITY POLYETHYLENE USED IN ELECTRICAL COVERED CABLES M. Munaro , G. P. Souza and L. Akcelrud, Instituto de Tecnologia pra o Desenvolvimento – LACTEC, Centro Politécnico da UFPR, Caixa Postal 19067, CEP 81531-990, Curitiba, Brazil

The growing employment of polymeric materials, mainly polyolefines as insulating materials for electrical and telephone cables is due to the good dielectric properties of these materials in combination with their mechanical, thermal and chemical resistance. To further enhance its performance regarding thermal distortion, polyethylene can be crosslinked giving rise to a three dimensional network, the XLPE. When LDPE is used as the starting material, the number of interconnected chains is larger in comparison with the polymer obtained from HDPE, due to the greater number of crosslinking sites (tertiary carbon atoms preferentially) in LDPE than in HDPE, resulting in a higher crosslinking density. On the other hand, HDPE is more prone to induced crystallization in operating conditions, leading to the rise of significant internal stresses, which are deleterious to the mechanical and chemical stability. Nevertheless, XLPE cables manufactured from HDPE are found in operation, and this was the motivation of this study. Scanning electrical microscopy, tensile essays, and oxidation temperature were used to examine XLPE obtained from HDPE , used as cover layer in electrical cables exposed to wheathering, during two years. A high level of shrinkage was observed in the cover with accentuated degradation. The effects of the residual internal stresses, originated during processing and developed during use, combined with photo-oxidation were correlated with the degradation processes.

F -O18 STEADY-STATE PHOTOCURRENT SPECTROSCOPY IN POLYMERIC LIGHT-EMISSION DIODESL. F. Santos, F. T. Reis, R. F. Bianchi, T. Cazati and R. M. Faria, Instituto de Física de São Carlos, Universidade de São Paulo, C.P. 369, 13560-970, São Carlos, SP, Brazil

Steady-state photocurrent spectra were carried out in ITO/poly[2-methoxy,5 ethyl (2’hexyloxy)-p-phenylenevinylene] (MEH-PPV)/Al (Au) structures in the 300-900 nm range. The photocurrent spectra presented a polarity and amplitude applied bias dependence, which suggests the existence of an intrinsic electric field, determined by the difference between the work functions of the electrodes, as well as a field dependence of the free charge carrier generation rates. The obtained results reveal built-in voltages of –0.2 V and +0.6 V for samples with Au and Al electrodes, respectively. Current density-voltage curves show that an excitation wavelength dependent photovoltaic effect takes place at the electrode/polymer interfaces, while a photoconduction process may occur in the bulk. The experimental results can be semi-quantitatively explained by a model which takes into account the optical density of the device structure, the excitonic dissociation energy and the migration and/or diffusion of the photo-generated charge carriers in the conjugated polymer (Acknowledgments to Fapesp and Millennium Science Initiative – Brazil).

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F-O19 ELECTRICAL CHARACTERIZATION OF ELECTRODEPOSITED POLYPYRROLE THIN FILMSM. S. Meruvia, I. A. Hümmelgen, Departamento de Física, Universidade Federal do Paraná, Caixa Postal 19044, 81.531-990, Curitiba, Brazil; R. C. Macanhan, R. M. Q. Mello, Departamento de Química, Universidade Federal do Paraná, Caixa Postal 19081, 81.531-990, Curitiba, Brazil.

Organic semiconductors are used as optoelectronic materials due to its energy gap corresponding to light energy in the visible range of the spectrum. In spite of this characteristic, these materials usually present quite low mobilities, imposing constraints to desired applications. Since charge transport, response time, series resistance and efficiency in optoelectronic devices strongly depends on charge carrier mobilities, materials with high mobilities are highly desirable. In this work we report the investigation of the electrical characteristics of electrochemically synthesized polypyrrole (PPy) using Au/PPy/Al devices The analysis of these data allowed us to determine, by adjusting the space-charge-limited current model, the mobility of positive charge carriers, (1.0 ± 0.5) 10-2

cm2·V-1·s-1, at room temperature. This value is quite high and uncommon value for non-oriented conjugated polymers.

F-O20 OPTICAL, ELECTRICAL AND TOPOLOGICAL PROPERTIES OF MULTI-LAYERS PPV FILMSM. L. Vega, L. H. Libardi, R. F. Bianchi and R. M. Faria; IFSC - USP, CP 369, 13560-970, São Carlos-SP, Brazil; A. Marletta, Faculdade de Física - UFU, CP 593, 38400-902, Uberlândia-MG, Brazil.

The development of new techniques and process to analyze the surface of conjugated polymer thin films has been explored in the literature due to the technological interest of this materials as active layer in flexible displays. The recent results of Atomic Force Microscopy (AFM) show the viability to apply this technique to analyze these soft materials. In this work we present a systematic study of topology, optic and electric properties of multi-layer poly(p-phenylene vinylene) (PPV) films, spin-coated on indium thin oxide (ITO). The PPV films were obtained using the precursor polymer thermal converted at 200°C under vacuum. The aluminum was evaporated on the films as a cathode electrode. The current vs. voltage curves display an enhancement in the operated voltage with the increase in the film thickness, or the number of deposited PPV layers. The photoluminescence spectra present a decrease in the vibronic region associated with film disorder and/or intrinsic structural defects and the effective conjugation length rise with the number of PPV layers. The AFM images were used to analyze the height and the distance between peaks. In the histograms we observe a reduction on the peak heights and the distance between peaks. These results indicate that the surface are more homogeneous with the PPV layer deposition, enhance the optical and electrical properties. This work was financial supported by Brazilian agencies Fapesp and CNPq.

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F-O21 MODELING ELECTRICAL CHARACTERISTICS OF POLYMER/C60 PHOTOVOLTAIC DEVICESM. Koehler, Departamento de Engenharia Elétrica, Universidade Federal do Paraná, 81531-990 Curitiba, Brasil; L. S. Roman, Departamento de Física, Universidade Federal do Paraná, Caixa Postal 19044, 81531-990 Curitiba , Brasil and Laboratory of Applied Physics, Department of Physics, Linköping, University,S-58183 Linköping ,Sweden; M. G. E. da Luz, Departamento de Física, Universidade Federal do Paraná, Caixa Postal 19044, 81531-990 Curitiba , Brasil; O. Inganäs, Laboratory of Applied Physics, Department of Physics, Linköping, University,S-58183 Linköping ,Sweden

We investigate the transport properties of organic photovoltaic devices formed by a heterojunction of a semiconducting polymer and C60. We measured the current-voltage (I-V) characteristic of diodes with variable C60's layer thicknesses and using light of different wavelengths. The I-V measurements are explained using an analytical model which assumes that the photogenerated charge carriers in the polymer layer are created at the heterojunction and that the C60 layer behaves like a photoconductor under illumination. The model also assumes that there is a surface charge Q accumulated at the hereojunction which controls the magnitude of the open-circuit voltage Voc. When Q=0 C/m2, Voc = Vbi, the built-in voltage. With increasing Q, however, Voc becomes increasingly lower than Vbi. The model reproduces the variation of the open-circuit voltage with the variation of the thickness of the C60 layer observed in the experimental data. We fit the experimental I-V characteristics using the electrical conductivity of the fullerene layer as fitting parameter and show that the values of the conductivity are related to the fullerene's optical absorption coefficient for each wavelength. This result implies a large contribution of the C60 film to the diode's photocurrent.

F-O22 IONIC CONDUCTION INFLUENCE ON THE ELECTRICAL PROPERTIES OF POLYMERIC LIGHT-EMITTING DEVICESL. F. Santos and R. M. Faria, Instituto de Física de São Carlos, Universidade de São Paulo, CP 369, 13560-970,São Carlos, SP, Brazil; L. M. Carvalho, Instituto de Macromoléculas Prof. Eloísa Mano, UFRJ, Rio de Janeiro, RJ, Brazil

In this work, the influence of ionic conduction on the electrical properties of poly(2-methoxy-5-(2’-ethyl-hexyloxy)-1,4-phenylene vinylene) (MEH-PPV)/Lithium salt mixtures was studied by dc current-voltage (I-V) and ac impedance measurements. It was observed that ITO/MEH-PPV:(CF3SO3)Li+/Au devices, which initially present almost symmetrical I-V curves at room temperature, exhibit a rectifying behavior after cooling from 340 down to 200 K with an external applied dc voltage. The results show that this rectifying behavior is stable until temperatures around 300 K, with the forward/reverse direction determined by the polarity of the bias applied during the cooling process. This effect suggests that the transport of Li+ ions occurs through the conjugated polymer layer at high temperatures, giving rise to ionic charge density buildup at the polymer/electrodes interfaces, which becomes “frozen” at lower temperatures. The bias dependence of the conductivity/capacitance-frequency curves confirm the formation of depletion regions in the vicinities of the polymer/electrodes interfaces. (Acknowledgments to Fapesp and Millennium Science Initiative/CNPq – Brazil)

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F-O23 CONFORMATIONAL ORDER OF MEH-PPV IN SOLUTIONS AND IS SOLID STATET. D. Z. Atvars, R. F. Cossiello, IQ – UNICAMP, Cx Postal 6154, CEP 13083-970, Campinas, Brazil

Organic polymers may undergo electro and photoluminescence properties. Currently, these polymers are being used for the manufacture of light emitting diodes (PLED). Among these polymers, the poly[2-methoxy-5-(2’-ethylhexyloxy)-1,4-phenylenevinylene (MEH-PPV) with a red emission has been employed in devices. In this work we reported the photophysical properties influenced by solvent cage and we followed the aggregations phenomena of the MEH-PPV of three different molar masses (51, 86 and 125 kg.mol-1). In solutions, the fluorescence spectra are dependent on the concentration and shift to red in higher concentrated samples. In addition, the spectral profile is also changed, due to the efficient self-absorption and re-emission and aggregation processes. Emission spectra of films produced by casting of chloroform or toluene solutions are morphologically and photophysically dissimilar. They maintain the same conformational order of the macromolecules present in solutions. Films prepared by different techniques are also morphologically different, as we observed for films prepared by casting and spin-coating. Annealing can stabilize those macromolecular conformations although it has to be performed under special conditions: absence of oxygen. Microfluorescence spectroscopy is a useful technique to evaluate the efficiency of the annealing process

F-O24 UV-VIS SPECTROSCOPY and BAM OF OC1OC6-PPV IN LANGMUIR MONOLAYERS M. Ferreira, D. T. Balogh, L. Misoguti, C. R. Mendonça, R. M. Faria, O. N. Oliveira Jr. IFSC/USP, 13560-970, São Carlos/SP, Brazil

Langmuir films from a luminescent polymer, poly-[(2-methoxy-5-n-hexyloxy)-p-phenylenevinylene] (OC1OC6-PPV), a derivative of poly(p-phenylenevinylene) (PPV) were investigated using polarized UV-VIS spectroscopy and Brewster angle microscopy (BAM) at the air-water interface. Measurements were taken at various surface pressures for films spread on a pure water subphase. In situ spectroscopy was employed to probe the molecular level ordering of the polymer, which was also denoted in Langmuir-Blodgett films. At large areas per molecule, absorbance is very small but not zero, as polymer aggregates are formed immediately after spreading, which was confirmed by a non-zero surface potential at such areas. The intensity of the maximum absorbance at ca. 500 nm increases upon compression as the density of chromophores increases. The absorption spectra for light polarized parallel to the direction of the barrier compression (0) exhibited higher intensity than that recorded at 90o, indicating a preferential alignment of the film-forming molecules parallel to the barrier. The dichroic ratio (A ///A) is ca. 3. The film morphology, according to BAM images, evolved upon compression from a pattern of irregular domains of different sizes, characteristic of random aggregates in the so-called gaseous phase. In the liquid-condensed phase the film becomes homogenous with no aggregates. Acknowledgements: FAPESP, CNPq, IMMP/MCT

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F-O25 OPTICAL PROPERTIES OF A SINGLE MICROSPHERE OF CONJUGATED POLYMER ENCAPSULATED BY POLYVINYL ALCOHOLE. E. Silva, L. A. Cury, L. O. Ladeira, N. B. Viana, O. N. Mesquita, Depto. de Física, UFMG, C.P. 702, 30123-970 Belo Horizonte, MG, Brazil, and Luiz G. Guimarães, Departamento de Física Nuclear, Instituto de Física, Universidade Federal do Rio de Janeiro, C. P. 68528, 21945-970 Rio de Janeiro, RJ, Brazil

Optical properties of a single fluorescent microsphere formed by the poly(2-methoxy,5-(2'ethylhexoxy)-p-phenilene vinylene) MEH-PPV conjugated polymer encapsulated by polyvinyl alcohol (PVA) are presented. An experimental setup coupling optical fibers to a microscope have enabled us to obtain the emission and transmission spectra for a single microsphere. We were also able to measure the evaporation rate for microspheres with different diameters. Quality factors, of the order of 104 to 105, were estimated for microspheres radius ranging from 12 to 17 m, which strongly indicate that PVA/MEH-PPV microspheres are potential candidates for high gain spherical cavity lasers.

F-O26 SUPRAMOLECULAR ORDERING IN NONLINEAR OPTICAL THIN FILMS BASED ON A SPECIALLY DESIGNED NONLINEAR OPTICAL CHROMOPHORE.A. N. Rashid and P. Gunter. Nonlinear Optics Laboratory, Institute of Quantum Electronics, Swiss Federal Institute of Technology, ETH-Hönggerberg, CH-8093 Zürich, Switzerland

Thin films based on acentric supramolecular assemblies of organic conjugated molecules are very attractive for a multitude of information processing and photonic applications. Thin films based on acentric supramolecular assemblies of organic conjugated molecules are very attractive for many of the applications that are sought. One of the major obstacles in the development of these technologies is the ability to grow macroscopic supramolecular assemblies in the form of thin films that maintain a noncentrosymmetric structure over thicknesses suitable for optical applications.In this contribution, a simple and effective method will be described for the growth of acentric supramolecular self-assembled thin films with stable directional ordering perpendicular to the surface of the substrate. This method, which involves the evaporation under vacuum of well-designed molecules onto cleaned amorphous glass substrates, takes advantage of the control offered by vapor deposition techniques over the thickness of the films grown while directional hydrogen bonding ensures that the acentric ordering is maintained over a large thickness. With this method, thin films with nonlinearities in the order of 7 pm/V with an almost perfect molecular ordering over thicknesses of the order of 1 µm have been grown. Experiments that show that these films can support waveguding will also be presented.

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POSTER PRESENTATIONS

F-P1 THERMALLY SWITCHED POLYMER-DISPERSED LIQUID CRYSTALS OBTAINED BY POLYMERIZATION-INDUCED PHASE SEPARATION OF EBBA-PS-EPOXY SOLUTIONSC.E. Hoppe; M. J. Galante; P. A. Oyanguren; R. J. J. Williams, INTEMA, University of Mar del Plata and CONICET, 7600 Mar del Plata, Argentina

Polymer-dispersed liquid crystals (PDLC), consisting on a dispersion of LC-rich domains in a polymer matrix, are potential materials for electrooptical devices such as reflective displays, optical switches, and variable transmittance windows. The aim of this study is to generate a thermally switched PDLC by phase separation during polymerization of initial homogeneous mixtures composed of reactive polymer precursor, LC and a thermoplastic polymer (TP), as an additional component. They were prepared by matching the refractive index of the polymer with those of the TP and the LC in the isotropic phase. The strategy was based on selecting polystyrene (PS) as the TP-modifier due to transparent multiphasic blends can be generated by reaction-induced phase separation of a PS solution in an epoxy monomer and a tertiary amine. PDLC systems based on a 50 wt % solution of N-4-ethoxybenzylidene-4´-n-butylaniline (EBBA) containing 1-5 wt % PS in an epoxy monomer (diglycidylether of bisphenol A, DGEBA) were analyzed. The polymerization-induced phase separation was performed at 80°C, using a tertiary amine as initiator (benzyldimethylamine, BDMA). Films of variable thickness and composition were prepared. Changing the temperature of the resulting films across the isotropic-nematic phase transition reversibly switched the film from opaque to clear. The response of the films in transmission-temperature curves is presented.

F-P2 ORIENTED GROWTH OF LiTaO3 THIN FILMS BY POLYMERIC PRECURSOR METHODA. H. M. González, A. Z. Simões, M. A. Zaghete, J. A. Varela, CMDMC Laboratory, Rua Prof. Francisco Degni s/n, PO Box 355, Araraquara, São Paulo, Brazil.

Lithium tantalate (LiTaO3) thin film was prepared using polymeric organic solution. The 10-layered film was deposited on (0001) sapphire substrate by dip coating process. The coated substrate was thermally treated at 600°C for 3 h under oxygen atmosphere to reach the crystallization stage. The crystallization process of thin film was analyzed by X-ray diffraction (XRD) and the results revealed the growth of highly oriented film. The surface morphology was observed with an atomic force microscope (AFM) and the studies showed that the lithium tantalate thin film exhibited a smooth, dense and homogeneous surface. UV-visible optical transmittance was measured in order to obtain the optical properties and the thickness of the film. The refractive index estimated confirmed the good quality of this film.

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F-P3 CONDUCTIVITY OF POLY(p-HYDROXYSTYRENE) AND POLYANILINE BLENDSE. M. Gonçalves 1 , J. C. Moreira1, R. K. Onmori2 and S. H. Wang1

1Department of Metallurgical and Materials Engineering, Polytechnic School, University of São Paulo, Brazil, Av. Prof. Mello Moraes 2463, Cidade Universitária, São Paulo, SP, CEP 05508-9002Department of Electronic Systems Engineering, Polytechnic School, University of São Paulo, Brazil, Av. Prof. Luciano Gualberto 158, Cidade Universitária, São Paulo, SP, CEP 05508-900

Blends of DBSA-doped polyaniline (PADB) and poly(p-hydroxystyrene) (PHS) of various compositions were prepared from N,N-dimethylformamide solutions. Freestanding films of blends were obtained by casting, which were characterized by conductivity measurements, optical microscopy (OM), Fourier transform infrared spectroscopy (FTIR) and wide-angle X-ray diffraction (WADX). For PADB concentrations from 1% to 5% the films have shown a variation of conductivity from about 10-6 to 10-4 S/cm. For low concentration of the PADB (< 5%), the secondary doping, resulting from the addition of PHS, is the responsible for the increase in the conductivity. For PADB concentrations from 10% to 50% the films have shown an increase of conductivity from 10-7 to 10-3 S/cm and for values higher than 50% was observed a non-uniform PADB dispersion. For these films the conductivity was approximately 101 S/cm in the high concentration zones, 10-4 to 100 S/cm at the interface and from 10-6 a 10-5 S/cm in the low concentration zones. The presence of the PADB in the blends generated some clusters, which could be observed by an optical microscope.

F-P4 ENERGY TRANSFER PROCESS AND SURFACE ENHANCED LUMINESCENCE NEAR THE METAL/POLYMER INTERFACEC.A.M.Borges R.M. Faria and F.E.G.Guimarães, Instituto de Física de São Carlos, Av. Trabalhador São-carlense, 400, São Carlos-SP, Brazil

We report the change of photoluminescence (PL) quantum efficiency of ultra thin poly(p-phenylene vinylene), PPV, films near the metal /polymer interface. In the experiment, 1.5 nm thick PPV layers were self-assembled on metal films (Au, Al) of different thicknesses (10 to 200 nm), which were deposited on glass substrates. An optically inert spacer based on PDAC/PSS bilayers was used to separate the metal from the PPV active layer. We show that PPV emission is strongly quenched for spacer thicknesses less than 10 nm. Above this value, however, the PPV emission is efficiently enhanced for metal thicknesses above 70 nm. The maximum luminescence enhancement (about 160 higher than the luminescence of PPV film without spacer) is reached for spacer separation of 150 nm. Further increase of spacer thickness cause the drop of luminescence intensity toward the values of PPV intensities on glass. Atomic force microscopy revels that the metal surface structure (size of metal islands and roughness) is correlated with the emission properties. The above results are interpreted in terms of competition between local field enhancement and loss of excitation by energy transfer to surface plasmons of the metal that are in resonance with polymer states.

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F-P5 ELECTROCHEMICAL COPOLIMERIZATION OF ANILINE AND LUMINOLT.P. Mendonça; E. De Robertis; A.J. Motheo, Grupo de Eletroquímica Interfacial, Instituto de Química de São Carlos - USP, Av. do Trabalhador São Carlense, 400, CP 780, 13560-970, São Carlos-SP, Brazil.Luminol has been the most important and earliest reagent used in electro-chemiluminescence (ECL). In a recent work, the redox behavior of luminol in acidic solution was studied and it was observed that it can polymerize on the surface of electrode by constant potential electrolysis (E=1.2 V vs. SCE) or cyclic voltammetry from -0.20 to 1.2 V (vs. SCE). On the other hand, polyaniline (PAni) is a conducting polymer that has been widely investigated aiming towards potential applications including for sensors. The aim of this work is to establish the conditions for the copolymerization of aniline and luminol in order to analyze the application of this material as ECL sensor. The copolymer films were grown on platinum by cyclic voltammetry from 0.5 M sulfuric acid aqueous solution containing different ratios of the monomers. The resulting films were characterized by electrochemical response, IR and UV-visible spectroscopies. All the films obtained presented electroactivity however, for aniline concentrations higher than 10 -3 M, their characteristics resemble the PAni. A strong dependence of the electrochemical response with the film thickness was also observed.

F-P6 ELECTRICAL PROPERTIES AND MORPHOLOGY OF POLY(P-PHENYLENE) FILMS AND COPOLYMERS C. Eiras 1 , M. Foschini1, M. A. Pereira-da-Silva1, C. J. Constantino and D. Gonçalves1

1-Instituto de Física de São Carlos, Av. Trabalhador Sãocarlense 400 CP 369,13560-970 São Carlos S.P. (Brazil); 2-Unesp, CP 467, 19060-900, Presidente Prudente, SP, Brasil

Poly(p-phenylene) (PPP), poly(p-phenylene-pyrrole) (PPP-Ppy), and poly(p-phenylene-3-methylthiophene) (PPP-PMet) films were electrochemically polymerized on indium-tin-oxide glass (ITO) electrodes in a non-aqueous medium using cyclic voltammetry. The PPP, PPP-Ppy and PPP-PMet films were prepared in a CaCl2 salt atmosphere using a glove box to reduce air humidity. The low air humidity obtained during the electrochemical measurements allowed us to control the polymer growth. The morphology of the films was correlated to their values of thickness and roughness as measured by AFM. The optical properties of PPP and derivatives films were investigated by UV-VIS, and their electrochemical response by cyclic voltammetry. The ionization potential and electronic affinity of the films were calculated by taking the onset values of the oxidation and reduction potentials obtained by cyclic voltammetry. The values of energy gap (E g) of the copolymer films were in agreement with those ones extracted from the UV-VIS spectra. Raman spectroscopy was used in order to structurally characterize the PPP and derivatives films.

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F-P7 ELECTRIC FIELD EFFECTS ON LDPE THERMAL PROPERTIESR. Robert1, G.P. Souza2, L. Akcelrud3; 1-Depto. Eng. Eletrica UFPR, 2- Instituto de Tecnologia para o Desenvolvimento, (LACTEC), 3- Depto. Química da UFPR

The thermal and dynamic mechanical behavior of polarized LDPE was investigated, by applying electric fields in the range of 5.37 to 31.7 MV/m, during 2.75 to 43.5h. The polarization strongly affected DSC and DMA spectra, indicating that a new and more ordered phase is formed, which disappears gradually after the removal of the electrical field. A shift of –21.3 0C was found in the DMTA spectra for the Tg of the polarized material, and no changes could be found in comparing the results of WAXS analyses of the original and treated materials. Very similar effects were observed with mechanical loading of the materials, leading to the conclusion that the amorphous phase of LDPE might be orienting under high electric fields in a similar manner.

F-P8 CONTRIBUTIONS OF INTERFACE AND BULK EFFECTS TO AC CONDUCTIVITY IN POLYMER LIGHT-EMITTING DIODESE. L. Queiroz, R. F. Bianchi, R. M. Faria, Instituto de Física de São Carlos / USP, CP 369, 13560-970 São Carlos SP, Brazil.Alternating conductivity and current vs. voltage (I vs. V) measurements for poly[(2-methoxy-5-hexyloxy)-p-phenylenevinylene] – MEH-PPV light-emitting diodes were carried out in samples with different electrodes (ITO, Au, Al and Cu). I vs. V measurements reveal that in forward bias mode, ITO/MEH-PPV/(Au or Al) devices present similar and lower operation voltage (V0) values, while ITO/MEH-PPV/Cu the higher one. However, in reverse mode, V0 is bigger, lower is the work function of the metal. The real and imaginary components of alternating conductivity present the typical behavior of disordered material: while the imaginary component ever grows as a function of the frequency, the real component was observed to be frequency-independent for lower frequencies, and vary as a power-law in the high frequency domain. However, the dc conductivity is lower for ITO/MEH-PPV/Cu, and higher for ITO/MEH-PPV/Al. These results suggest that the electrical performance of the devices may be dictated by the bulk and the MEH-PPV/electrode interface. The Random Free energy barrier model is presented and the calculated the real and imaginary components of AC conductivity in good agreement with experimental data. The bulk and the interface contributions are obtained. (Fapesp, Capes and IMMP/MCT sponsored this work)

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F-P9 POLYMERIZATION OF ANILINE and 3-methylthiophene ON GOLD AND SILVER ELECTRODES modified with DODECANETHIOL SELF-ASSEMBLED MONOLAYERs M. G. Xavier & D. Gonçalves; Instituto de Física de São Carlos, Av. Trabalhador Sãocarlense 400 CP 369, 13560-970 São Carlos S.P. (Brazil)

Polyaniline and poly-3-methylthiophene films were electrochemically synthesized on Au and Ag electrodes before and after modifying their surfaces with self-assembled monolayers (SAMs) of dodecanethiol. The integrity of the SAMs on the Au and Ag electrodes was studied by cyclic voltammetry in an aqueous K4Fe(CN)6/KCl solution. The surface analysis of the modified electrodes was carried out by contact angle measurements and AFM, and by obtaining electrochemical parameters such as the electroactive surface coverage. Meanwhile the modified SAMs/Au(Ag) electrodes showed blocking characteristics, the polymer growth was not inhibited in the presence of the SAMs on the electrode surface, but, on the contrary, it was promoted at higher polymerization rates and more negative oxidation potentials. Acknowledgement: CNPq and IMMP.

F-P10 CORRELATION BETWEEN THE POLARIZATION OF THE EMITTED LIGHT AND THE MORPHOLOGY OF PPV FILMST. Cazati, F. G. Guimarães & R. Faria, Instituto de Física de São Carlos, Universidade de São Paulo, São Carlos - SP, Brazil

We studied photoluminescence properties of poly(p-phenylene vinylene) (PPV) films built by different techniques: simple casting, spin-casting and Langmuir-Blodgett. While films made by spin-casting exhibited a great disordered morphology, those prepared by LB technique presented a high degree of anisotropy, being the molecules oriented mainly along the dipping direction. We observed, as a consequence for oriented films, higher anisotropy in the UV-Vis absorption or emission spectra when the light beams, absorbed or emitted, were detected with polarization parallel and perpendicular to the orientation of the molecules in the film. To explain the results we used the Föster theory, based on dipole-dipole interaction, always taking into account the molecular orientation of the films.

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F-P11 EFFECT OF GAMMA IRRADIATION ON OPTICAL PROPERTIES OF POLY(P-PHENYLENEVINYLENE) SOLUTIONSE. A. B Silva.;. C F. O. Graeff.; . P Nicolucci;. T. G Netto; Faculdade de Filosofia Ciências e Letras de Ribeirão Preto, Univ. São Paulo, Ribeirão Preto- SP/Brazil; R. F Bianchi; R. M. Faria, D. T. Balogh; Instituto de Física de São Carlos, Univ. São Paulo, São Carlos-SP, Brazil

Conjugated polymers have nowadays a vast field of technological applications, however there are still few applications of them in medicine as sensors and detectors of ionizing radiation, for example. In this work we use a conducting polymer: poly[2-methoxy,5-(2-ethyl-hexyloxy – p - phenylenevinylene] (MEH-PPV) for the detection of ionizing radiation, by means of spectroscopic methods such as: (Uv-vis) absorption, photoluminescence (PL) and (FTIR) infrared absorption. The samples have being prepared in films, deposited by spin-coating as well as in solution dissolved in CHCL3. We have found that oxygen plays an important rule in the process of photo-degradation of the material exposed to ionizing radiation. It was found a displacement in the absorption band proportional to radiation dose absorbed from 493 nm up 467 nm for a dose between 0 and 45Gy. This displacement is followed by other changes in the UV-VIS absorption spectra, attributed to the replacement of C=C by C=O bonds. Both FTIR absorption and photoluminescence spectroscopy confirmed this substitution. These results suggest the potential of this material as ionizing radiation detectors.

F-P12 THIN COPOLYMER-BASED SEVEN-SEGMENT LIGHT-EMITTING DISPLAYR. Lessmann, I. A. Hümmelgen, Group of Organic Optoeletronic Devices, Departamento de Física, Universidade Federal do Paraná, Caixa Postal 19044, 81531-990 Curitiba, PR, Brazil. 

Seven-segment displays are used to show numerical quantities in electronic equipment, being present in most of the low-end electronics. In this contribution we demonstrate a novel organic light emitting display made with poly(1,10 – decanedioxy – 2 – methoxy - 1,2 – phenylene - 1,2 – ethenylene - 3,6 – dimethoxy - 1,4 – phenylene - 1,2 – ethenylene – 3 – methoxy - 1,4 - phenylene), OPPVDBC, and a hole injection layer (SPAN: sulfonated polyaniline or PEDOT:PSS: poly(3,4 - ethylenedioxythiophene) : poly(styrenesulfonate). The general device structure is FTO/SPAN(or PEDOT:PSS)/OPPVDBC/Ca (or Al). FTO, fluorine-doped tin-oxide thin films are transparent (transmittance > 80 % in the visible region of the spectrum) conducting, showing low film resistivity (~ 15 /□) and high chemical stability. A photolitographic process was used to pattern the FTO (anode). Electronic transport curves and electroluminescent spectra were obtained for determining turn-on and operating voltage of the device.

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F-P13 SAXS STRUCTURAL STUDY OF NEODYNIUM-DOPED LUMINESCENT POLY(OXYETHYLENE)/SILOXANE HYBRIDS I. C. Correia Vilela, V. de Zea Bermudez, Universidade de Trás-os-Montes e Alto Douro, Quinta de Prados, Portugal; K. Dahmouche, C.V Santilli, Instituto de Química, UNESP, C.P 355, Araraquara-SP, Brazil; N. J. O. Silva, L. D. Carlos, Departamento de Física, Universidade de Aveiro, Portugal; A. F Craievich , Instituto de Física/USP, SP, Brazil

The structural features of two families of transparent and flexible sol-gel derived poly(oxyethylene)/siloxane hybrids doped with neodymium triflate, Nd(CF3SO3)3, were investigated by Small-Angle X-ray Scattering (SAXS). Their organic/inorganic matrix is a siliceous network to which short oligopolyether chains are covalently bonded to both ends by means of urea and urethane linkages, respectively. The SAXS patterns of the undoped di-ureasils exhibit a strong interference peak located at medium q-range which reveals the existence of a spatial correlation between the siloxane nanoclusters grafted to the polymer segments. The introduction of Nd3+ ions in such hybrids leads to the appearance in SAXS patterns of an additional scattered decreasing intensity at low q-range which reveals the existence of a two-level hierarchical structure: the primary level consists of small and spatially correlated siloxane nanoclusters and the secondary level corresponds to large domains, in which the siloxane clusters are located, surrounded by a depleted polymeric phase. A theoretical function was used to fit the experimental scattering curves and to determine the structural parameters corresponding to each level. The di-urethanesils hybrids exhibit quite different behavior since the two-level hierarchical structure already exists in the undoped sample. In both families, the increase of Nd3+ content leads to a decrease of the correlation peak intensity, suggesting that the cations interact mainly with the ether-type oxygen atoms of polymer chains. The determination of the structure of both type of composites allowed us to get a better understanding of their luminescent, ionic conduction and thermomechanical properties.

F-P14 THE EFFECT OF ULTRASONIC VIBRATION IN CONDUCTING POLYMER SOLUTIONW. M. de Azevedo, A J. H. de Oliveira Luna, Departamento de Química Fundamental, CCEN-UFPE 50670-901, Recife, Pernambuco, BrasilPropagation of an ultrasonic wave in liquid generates the formation of cavitations bubbles which can grow and implode under periodic variation of the pressure field. In solution, implosion and fragmentation of the bubble which collapses are the center of high energy phenomena, this rapid formation, growth, and implosive collapse of the gas vacuoles generates short lived (ns), localized “hot spots” whose peak temperature and pressure have been calculated to reach as high as 10000 0C and 10000 atm respectively. Although ultrasound has been known for more than 80 years, its application to chemical reactions has not been investigated thoroughly, and in some case has been used in chemical labs without more concern, just as a tool to speed up solubility. In this work we wish to report the unexpected effect found in conducting polymer solution when treated with ultrasound. From the spectroscopic analysis we observe that absorption spectra of undoped polyaniline dissolved in DMSO, completely change after interaction with ultrasound radiation. The characteristic absorption transition at 620 nm gradually disappears, indicating that a redox process is taking place. On the other hand in the infrared region the absorption transition at 3500 cm -1

characteristic of water vibration decrease it intensities, as an indication of water sonolysis is taking place producing radical species such as H, OH, and HOO.which can interact and modifier the oxidation state of the polymer. Based in these observations we propose a mechanism to explain the polymer color changing induced by ultrasonic waves.

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F-P15 CORRELATIONS BETWEEN MORPHOLOGY, PHOTO AND ELECTROLUMINESCENCE PROPERTIES OF POLY(METHYL METHACRYLATE-CO-9ANTHRYLMETHYL METHACRYLATE)J.F. Deus, PIPE - UFPR, Curitiba/PR; M.L. Andrade, T.D.Z. Atvars, UNICAMP, Inst. de Química, Campinas/SP; and L.Akcelrud* LACTEC, Centro Politécnico UFPR, CEP 81531-990, Curitiba/PR

A series of poly(methyl methacrylate-co-9-anthryl methyl methacrylate) was prepared in which anthryl groups interspersed between each 2, 4, 10, 25 and 35 methyl methacrylate mers was prepared. The effect of the proximity of the chromophores in the photophysical properties was studied in dilute and concentrated conditions, showing that the association of anthryl groups giving rise to aggregates or excimers is strongly dependent on the chain conformations. The photophysical properties of cast-films of largely spaced copolymers are characterized by two decays: one of the isolated chromophore (longer decay rate and vibronically structured emission) and another of aggregated species (faster decay with some broadening of the red-edge of the emission band). Copolymers with chromophores separated by two or four methyl methacrylate units presented the highest degree of association and were the only electroluminescent materials. The proximity of anthryl moieties and the conformation of the polymer chains are important factors governing excimeric-like emission and film properties of anthracene containing polymers used in technological applications.

F-P16 CORRELATIONS BETWEEN NANOMECHANICAL PROPERTIES AND COMPOSITION OF POLY(METHYL METHACRYLATE-co-9-ANTHRYLMETHYLMETHACRYLATEJ.F. Deus, PIPE, UFPR; A.C. Tavares, C.M. Lepienski, Dep. de Física, UFPR; and L.Akcelrud*

LACTEC, Centro Politécnico UFPR, CEP 81531-990, Curitiba/PR

The proximity of anthryl groups is an important factor opto-electronic and film properties of anthracene containing polymers used in technological applications. The anthryl groups were interspersed between an average of 4, 10, 25 and 35 methyl methacrylate mers. It was observed that the effect of anthryl groups is more pronounced in viscosity measurements than in hardness and elastic modulus. The inclusion of anthryl groups in amounts in the order of 4% is responsible for increases of about 20% in hardness and in viscosity. These results were related to a decrease in the chain mobility, which is corroborated by the significant increases in the glass transition temperature with small amounts of anthryl groups.

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F-P17 POLYANILINE/POLYURETHANE NETWORKS: CORRELATIONS BETWEEN MORPHOLOGY AND CHEMICAL STUCTUREP. C. Rodrigues, L. Akcelrud * . Universidade Federal do Paraná, Departamento de Química; *LACTEC (Instituto de Tecnologia para o Desenvolvimento) –– Curitiba, PR. paula@quimica.ufpr.br

Polyaniline/Polyurethane (Pani/PU) networks were prepared in such a way that the length of the PU segment was kept constant and the crosslinking density was controlled by varying the spacing between each interconnecting linkage, keeping a limiting Pani content at 30%. The mechanical properties of the networks were always better than those of the pure Pani or of the corresponding blends. UV-Vis spectra showed that the quinoid rings transitions in the Pani-EB form and the polaronic bands in Pani-ES form were shifted to lower wavelengths in the networks, indicating that the conjugation was shortened, probably due to the imposition of a certain degree of torsion near the interconnecting sites, which was confirmed by the computer generated optimized network conformation. IR absorption, electrical conductivity and DMTA lead to the proposition of a model in which Pani chains form a continuous percolating phase dispersed in a polyurethane matrix, linked together by a interphase, with a certain degree of miscibility. This interphase would be responsible for the connectivity between the two components and the good mechanical properties observed. Electrical conductivity of the networks was in the 10-4 S/cm range.

F-P18 [AL•1]3+ (1=8-OXYQUINOLINECALIX[4]ARENE) AS EMITTING AND ELECTRON-TRANSPORTING LAYER IN ORGANIC LIGHT EMISSION DEVICES (OLEDs).C. Legnani , R. Reyes, M. Cremona, DF-PUC-Rio Rua Marquês de São Vicente, 225 Rio de Janeiro Brazil; I.A. Bagatin, H.E. Toma, IQ-USP Av. Prof. Luciano Gualberto, 374 São Paulo, Brazil

RECENTLY, THERE HAS BEEN AN INCREASED INTEREST IN ORGANIC LIGHT EMITTING DIODES (OLEDS) DUE OF THEIR POTENTIAL APPLICATIONS TO COLOR FLAT PANEL DISPLAYS AND OPTOELECTRONIC COMPONENTS. THESE DEVICES ARE GENERALLY ASSEMBLED USING 3 ORGANIC MOLECULAR MATERIALS: AN ELECTRON INJECTION/TRANSPORTING LAYER, THE EMITTING ONE AND FINALLY THE HOLE INJECTION/TRANSPORTING LAYER. DUE TO THE CHEMICAL AND THERMAL STABILITY OF THE USED ORGANIC COMPOUNDS, IN MOST CASES THERE ARE DEGRADATION PROBLEMS WITH THE DEVICE PERFORMANCE. In this work, a new OLED using a calixarene thin film as emitter and electron transporting layer (ETL) is proposed. The devices were grown onto glass substrates coated with indium tin oxide (ITO) layer and aluminium thick (150 nm) cathode. A MTCD 50nm film was used as hole transporting layer. Photoluminescence (PL) spectra of the calixarene thin films were measured as a function of different parameters. Applying a dc voltage (4 V) between the device electrodes in forward bias condition, EL light emission in the active area of the device was observed. The EL emission peak varied from 446 nm to 558 nm as a function of the applied voltage bias. The peak shift can be

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associated with some energy transfer inside the calixarene compound.

F-P19 VIBRATIONAL PROPERTIES OF PPP AND PPV.R. L. de Sousa, L. C. de Carvalho, J. L. A. Alves and H. W. Leite Alves, Depto. Ciências Naturais, UFSJ, Caixa Postal 110, 36.300-000 São João del Rei, MG, Brazil Recently, the electronic and optical properties of semiconducting -conjugated polymers have attracted great interest: the improvement of the efficiency of the new polymer-based optolectronic devices was the key. Unlike in the conventional semiconductors such as Si, or in the organic crystals such as anthracene, the excitons in -conjugated polymers were in the intermediate case, subject of extense debate on the academic community because it is very hard to describe the vibronic states on the theoretical treatment of the excitations. Moreover, the experimental and theoretical data on the phonon modes available in the literature are very scarce. In this work, by using the Density Functional Theory within the Local Density Approximation, plane-wave description of the wave-functions and the pseudopotencial method, conjugated with the Unrestricted Hartree-Fock method, with the double-zeta basis set, we have calculated the electronic structure and the vibrational modes for the poly-para-phenylene(PPP) in the Pbam structure, for the poly-para-phenylene-vinylene(PPV) in the P21/c structure, and for their respective monomers. Our results agree well(within 3% of error) with the avaulable experimental data, whenever these comparison is possible. Based on our calculations, we show interesting aspects concerning their vibrational modes: the LA modes stretches the -bonds(mainly in the vynil group), while the TA ones leads only to their torsion

F-P20 INDIUM-TIN OXIDE (ITO) FILMS CHARACTERIZATION FOR USE ON POLYMER LIGHT-EMITTING DIODESR. F. Bianchi, A. J. F. Carvalho , D. T. Balogh, R. M. Faria, Instituto de Física de São Carlos, USP, 13560-970, São Carlos-SP, Brazil

Indium-tin oxide (ITO) has been traditionally used as transparent electrode in several devices of modern electronic technology, including liquid crystals and polymer light-emitting diodes (PLEDs). Work on PLEDs, ITO has been by far the common choice, not only because of its availability and lower resistivity, but mainly due to its good transparency, to the ease with which it can be patterned and also because it consists of a hole transport layer for a large class of poly(p-phenylenevinylene) and derivatives. However, recently developments in PLEDs have shown that electrical, optical and chemical properties of ITO need to be controlled in a more accurate way to improve the device performance. In this work we present studies of the influence of aquaregia treatment on the electrical, chemical and optical characterizations of patterned and non-pattern ITO thin films previously deposited on glass substrate. We report the characterization of the oxide in terms of its roughness, bulk conductivity, visible-near-ultraviolet absorption spectra, contact angle, and optics and atomic force microscopy images. The results show that the chemical treatment does not change the conductivity, but increases the roughness, decreases the thickness and shifts the

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absorption peak towards higher wavelengths, while the etching process does not change any of these properties. (This work was sponsored by Fapesp).

F-P21 MORPHOLOGICAL CHANGES IN POLY(VINYLIDENE FLUORIDE) (PVDF) INVESTIGATED WITH MICRO-RAMAN SPECTROSCOPYD. L. Chinaglia, Depto de Física/IGCE/UNESP, Rio Claro/SP, Brazil; V. Zucolotto and O. N. Oliveira Jr., IFSC/USP, São Carlos/SP, Brazil; Carlos J. L. Constantino and José A. Giacometti, DFQB/FCT/UNESP, Presidente Prudente/SP, Brazil

Pvdf Is A Semi-Crystalline Material With Mechanical And Electrical Properties Suitable For Applications In Electro-Acoustic Devices. It Is Also Being Used In Biomedical Engineering Where These Properties Are Combined With Its Biocompatibility. Key To The Applications Is The Piezoelectric Activity Of Pvdf, Which Depends On The Crystalline Phase. The Latter May Be Characterized With Micro-Raman Spectroscopy, Advantageous For Being A Non-Destructive Technique That Does Not Require Any Sample Preparation. Here We Show That Phase Changes From Pvdf- To Pvdf- Due To Stretching The Samples Can Be Monitored By The Appearance Of A New Raman Peak At 840 Cm-1, Characteristic Of Pvdf-. Furthermore, Morphological Changes Induced In The Samples By A Corona Discharge Were Detected By An Intensity Increase In The Cf2 Raman Peaks. Corona Discharge Irradiation Probably Improves The Homogeneity Of The Spherulites In Pvdf- Samples In Such A Way That The Signal-To-Noise Ratio Of The Raman Scattering Is Improved Especially For The Cf2 Groups. Acknowledgements: Fapesp, Cnpq, Immp/Mct.

F-P22 EFFECT OF PLASTIC SUBSTRATE ON THE SHEET RESISTANCE AND MORPHOLOGY IN INK JET PRINTED POLYMER CONDUCTING FILMSA.Y. Natori, A.M.Ceschin, Universidade Federal do Paraná, Departamento de Engenharia Elétrica, Caixa Postal 19011, Centro Politécnico, Jardim das Américas, CEP 81531-990, Curitiba, Paraná, Brazil; C.D. Canestraro, L.S. Roman, Universidade Federal do Paraná, Departamento de Física, Caixa Postal 19044, Centro Politécnico, Jardim das Américas, CEP 81531-990, Curitiba, Paraná, Brazil

The inkjet printing technology is a relatively novel technique in development of organic electronic devices. The technique consists of realizing depositions of organic films by a piezo-based ink jet printer. In this work, polymer conducting films have been developed by ink jet printing technique on different plastic substrates using poly(3,4-ethylenedioxythiofene)/poly(4-styrenesulfonate) [PEDOT/PSS] and PEDOT/PSS added to a small amount of glycerol, refer as G-PEDOT/PSS, like polymer conducting inks. The plastic substrates used were polyester and polyethylene terephthalate [PET]. Through a change of the substrate, combined with the kind of polymer solution used to print the films, the sheet resistance and morphology can be modified. This behavior suggests that the plastic substrate plays an important role for the modification in both the sheet resistance and morphology of the ink jet printed PEDOT/PSS films with and without glycerol.

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F- P 21

F-P23 PROCESSING PARAMETERS, STRUCTURE AND MORPHOLOGY OF XLPEJ. V. Gulmine and L. Akcelrud, Instituto de Tecnologia para o Desenvolvimento - LACTEC, Centro Politécnico da UFPR, Caixa Postal 19067, CEP 81531-990, Curitiba, Brazil

XLPE is a very important polymer for the electrical industry, as cable insulating material, and therefore the relationships between processing parameters and the resulting structure are of prime relevance, since crosslinking improves mechanical and thermal properties without interfering with the electrical performance.The level of crosslinking was set by varying processing parameters, as time, temperature and concentration of crosslinking agent. The average molecular weight between crosslinks was measured using the Flory-Rehner equation, and the morphology was studied by WAXS, making it possible to correlate processing variables , structure and morphology of XLPE.

F-P24 POLYISOBUTENE AS PASSIVATION MATERIAL FOR A SIMPLE, FAST AND EFFECTIVE ORGANIC DEVICE ENCAPSULATIONR. Toniolo, I. A. Hümmelgen, Departamento de Física, Universidade Federal do Paraná, Caixa Postal 19044, 81.531-990, Curitiba-PR, Brazil

A fast, simple, cheap, effective and non-aggressive passivation method for organic devices protection against external degrading agents (mostly water and oxygen) is demonstrated. At room temperature, polyisobutene (PIB) is a viscous polymer, which can form a device cover layer without using solvent or any aggressive deposition technique. Under N2 atmosphere a glass cover plate is placed onto a PIB amount dropped onto the device/substrate. The amount of PIB is adjusted according to the wettability of the substrate/device and cover-plate surfaces. When the PIB fills the inter-glass-sheets space the encapsulation is done. The electrical resistance of encapsulated and non-encapsulated Ca contacts exposed to the environmental conditions was investigated. After about 25 minutes of exposition, non-encapsulated Ca contacts suffer an abrupt resistance increase due to degradation, becoming fully oxidized. The encapsulated Ca contacts present negligible electrical resistance change after 6 months. PIB encapsulated polymer based devices showed a quite stable I(V) characteristic and longer operational lifetimes in contrast with non-encapsulated ones. Since the PIB layer formation does not involve any change of its chemical and physical properties, significant tensions between device and the protecting layer are not expected. The PIB viscosity allows its use in flexible substrates by substituting the glass cover plate for a flexible one, constituting another advantage.

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F-P25 SYNTHESIS AND PROPERTIES OF POLY(9,9’ DIHEXYL FLUORENE-2,7 DYIL) AND ALTERNATING COPOLYMERSA. M. Assaka, P. C. Rodrigues, A. R. M. Oliveira, L. Akcelrud* Depto de Química/UFPR, *ITD -LACTEC Caixa postal 19067, 81531-990, Curitiba-PRRecently polyfluorenes (PF’s) were introduced as a prospective emitting layer for polymer LEDs. These materials are thermally stable and display high photoluminescence efficiencies with emission wavelengths primarily in the blue spectral region. Their photostability and thermal stability are also found to be better than those of the poly(phenylene vinylene)s. Polyfluorenes contain a rigidly planarized biphenyl structure in the fluorene repeating unit, while the remote substitution at C-9 promotes solubility without steric distortions in the conjugated backbone. This work describes the synthesis of PF’s and alternating copolymers and the characterization of their opto-electronic properties aiming to correlate chemical structure and super structure with emissive properties. Poly(9,9’ dihexyl fluorene-2,7 dyil) (PF) and alternating copolymers poly(9,9’-dihexylfluorene-2,7-diil-alt-p-phenylene) (PFApF) and poly(9,9’-dihexylfluorene-2,7-diil-alt-1,4-tetrafluorobenzene) (PFAT); were prepared via Suzuki cross coupling polymerization which is based in the reaction between the boronic and dibromo derivatives of the desired chromophores, using a palladium salt as catalyst, resulting in homopolymers or perfectly alternating copolymers. The insertion of p-phenylene or 2,3,5,6 tetrafluorobenzene between each two fluorene units brought about significant effects: a hypsochromic shift in comparison with the homopolymer, a decrease in the turn on voltage of the LEDs and an improvement in emissive properties of the devices. These effects are probably related to the electronegative character of the comonomers.

F-P26 SYNTHESIS AND CHARACTERIZATION OF SOLUBLE PHOTOLUMINESCENT POLYAZOMETHYNESA. M. Machado, L. Akcelrud - Universidade Federal do Paraná (UFPR)–Depto. de Química; Instituto de Tecnologia para o Desenvolvimento (LACTEC)-Curitiba/PR-angelmac@quimica.ufpr.br; akcel@onda.com.br

Polyazomethines are conjugated polymers containing the CH=N bond which imparts better thermal and mechanical stability and interesting electro-optical properties. Their use is however restricted, due to the poor solubility. We prepared multiblock polyazomethynes by inserting non-conjugated spacers among the conjugated ones, rendering the polymer soluble in organic solvents: poly[oxyoctylenoxy-(2,6-dimetoxy-1,4-phenylene-1,2-ethenylene-6-phenyl-1,3,5-triazine-2,4-diil)] (LaPPS 09) and poly[oxyoctylenoxy-(2,6-dimetoxy-1,4-phenylene-1,2-ethenylene-phenantrene-2,4-diil)] (LaPPS 19).The chemical structure of the materials was characterized through FTIR, NMR, and Elemental Analysis, and the photophysical behavior was studied through UV-Vis absorption and fluorescence emission, in solution and in the solid state.Solutions of LaPPS 09 emitted at 348nm and 471 nm (10 -5 and 10-4 mol/L) and at 530nm (10-

3mol/L), while LaPPS 19 solutions emitted at 359nm in dilute conditions and at 496 e 533nm in concentrated conditions. This redshift was interpreted in terms of aggregate formation, which was confirmed by excitation spectra. N-protonation modified the emissive properties of LaPPS 09 but not of LaPPS 19.

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F-P27 SYNTHESIS AND CHARACTERIZATION OF POLY(9,9’-DI-HEXYLFLUORENEDIYLVINYLENE-ALT-1,4-PHENYLENEVINYLENE) (PDHFPPV) - A ELECTROLUMINESCENT POLYMERA. Glogauer, A. R. M. de Oliveira, A. M. Assaka, L. Akcelrud, Departamento de Química – Universidade Federal do Paraná, Caixa Postal 19081, 81531-990, Curitiba/PR

The main feature of electroluminescent polymers (ELP) is the presence of conjugated sequences, in various macromolecular architectures. Another important requirement is solubility, enabling processing in useful opto-electronic devices. As a result the synthesis of ELP is much more involved than of the “classical polymers”, generally the preparation of the monomers includes various steps that determine the success of the polymer synthesis. In this communication we describe the synthesis and characterization of a fully conjugated ELP, namely the poly(9,9-di-hexylfluorenediylvinylene-alt-1,4-phenylenevinylene) (PDHFPPV) which structure is similar to the extensively explored poly(phenylene vinylene) (PPV) with an additional fluorene moiety, which should impart better and optical and thermal resistance characteristics. The solubility is provided by the hexyl groups attached to the main chain. The polymer is strongly luminescent, emitting green-yellow light. The fluorescence emission spectra in solution and in the solid state are consistent, showing that emission comes from only one emitting center, excluding the possibility of aggregate formation, which is deleterious for device performance.

F-P28F-P29 LIQUID CRYSTALLINE BEHAVIOR OF A BI-SOFT SEGMENT URETHANE-UREA

ELASTOMERB. B. Postacchini and E. A. de Oliveira, Instituto de Física, USP, Brazil M. H. Godinho, Dept. Ciências dos Materiais and CENIMAT, Uni. Nova de Lisboa, Monte Caparica-Portugal

Liquid crystalline elastomers are fascinating material that combines two subsystems; a mesogenic group which will organize to give the mesomorphic properties characteristic of liquid crystals and weak density of polymeric chains reticulation which are responsible for the elasticity properties. The coupling of a mechanical stress with the liquid crystalline order can leads to a macroscopical oriented domain if the reticulation of the is weak. Therefore, the mechanico-optical properties of these materials are governed by the delicated balance between the liquid crystalline order and the reticulation of the polymer. Recently, a elastomer was prepared composed of two bi-soft segments; poli(buteno) PBDO and isocyante terminal groups (PU), and it was observed that film changes from opaque to a transparent state when submitted to a mechanical stress. Although mesogenic groups are not present in its composition, macroscopical oriented domains can be obtained by a mechanical stress. We investigate how the optical properties of this elastomer are related to the microscopical structure of the polymeric chains. Aging effects are simulated by irradiating the film with UV light and the induced structural changes are controlled by FTIR and calorimetric techniques. The correponding macroscopical changes are monitored by measuring the birefringence, of the film as a function of the exposure time. For short exposure time an increase in

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the birefringence is observed, indicating an increasing in the chains mobility. However, for long exposure times, the birefringence decreases, probably related to a higher crosslinking degree.

F-P30 CHARACTERIZATION OF A NEW ELECTROCHEMICALLY SYNTHESIZED DERIVATIVES OF POLY P-PHENYLENE VINYLENE. F.M. Nodari, L.S. Roman, I. A. Hümmelgen, Departamento de Física, Universidade Federal do Paraná, Caixa Postal 19044, 81531-990, Curitiba, Brasil; E.K.C. Yoshikawa, J. Gruber, Instituto de Química, Universidade de São Paulo, Caixa Postal 26077, 05513-970, São Paulo, Brasil

Organic optoelectronic devices have attracted much attention due to the possibility of constructing devices flexible and with large active area. The research for developing new polymeric materials are growing fast and the characterization of these materials is indeed important. In this work we have investigated the optical and electrical aspects of a derivative of poly p-phenylene vinylene synthesized electrochemically. Sandwich structured samples were fabricated using Tin Oxide doped with fluorine as the anode and Aluminum as the cathode. The current voltage curves were measured making possible to obtain the charge mobility value for positive charges. The optical properties of the polymer solution and spin coated films were investigated through photoluminescence and absorbance spectra. It was possible to obtain the energy gap.

F-P31 ORGÂNIC PHOTOVOLTAIC DEVICES BASED ON ELECTRO CHEMICALLY SYNTHESIZED POLYMERSR. Valaski, L. S. Roman, I. A. Hümmelgen, Department of Physics, University of Paraná, PO 19044, Curitiba, BRAZIL.L. Micaroni, R. M. Mello, Department of Chemistry, University of Paraná, PO 19044, Curitiba, BRAZIL

Research efforts on photovoltaic devices based on organic materials have improved the efficiencies significantly in the last years. Several materials and combinations of materials have been presented in different device configurations. In this work we present devices in which the active layer is electrochemically synthesized onto the transparent electrode. In a single active-layer photovoltaic devices with the active layer consisting of poly(3-methylthiophene), PMeT, electrochemically deposited onto indium-tin oxide substrate with aluminum as top electrode present photon to converted electron efficiencies up to 4.3%. We also report the use of sulfonated polyaniline, SPAN, as hole transporting layer in organic electronic devices, demonstrating that it can be used to significantly improve hole injection into conjugated polymers producing polymer based diodes with good rectification, even with low work function anode material such as tin oxide, TO. SPAN performance as hole-transporting layer material is compared with that of poly(3,4-ethylenedioxythiophene) : poly (styrene sulfonate), PEDOT:PSS, in current - voltage characteristics of devices constructed using poly(3-hexylthiophene), P3HT as the active layer. PEDOT:PSS is a well established material for hole injection improvement. Photovoltaic devices using SPAN as

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anode have been characterized and the efficiencies improved.

F-P32 CHARGE MOBILITIES VALUES OF ORGANIC MATERIALS IN THIN FIELD EFFECT TRANSISTORSR. Possagno, L.S. Roman, Departamento de Física, Universidade Federal do Paraná, Caixa Postal 19044, 81531-990, Curitiba, Brasil

The development of organic electronics is growing fast due to the potential advantages of using organic materials as the semiconducting layer in electronic devices. In this work we have investigated the electrical characteristics of polymers and molecules using thin field effect transistors. The FET charge mobility could be obtained measuring current-voltage characteristics of the transistor with known channel length, operating in depletion mode under different gate voltages. Current – voltage characteristics of FET devices of three organic materials will be presented and their FET mobility values compared with conventional mobility values obtained form sandwich diodes previously published. The FET-transistors were constructed using Tin Oxide doped with fluorine as the gate electrode, poly methyl-metacrilate as the insulator and gold electrodes as the source and drain electrodes. The channel length could be chosen between 50 and 100 m.

F-P33 PHOTODEGRADATION RATES OF A PPV DERIVATIVE AND ITS BLENDS WITH COMMERCIAL POLYMERSV. C. Gonçalves, D. T. Balogh, IFSC/USP, 13560-970, São Carlos/SP, Brazil; A. Marletta, LNMIS–UFU, C.P. 593, 38400-902, Uberlândia, MG

PPV derivatives are commonly used in electroluminescent devices and are known for its excellent film forming properties and its high susceptibility to photo-oxidation. Although this degradation process can be a problem to be overcome in LEDs and display devices technologies, it can be useful in certain applications, as patterning and a number of different kinds of sensors. For these applications, the knowledge of degradation rates is essential to estimate the potential lifetime of the sensor. Here we present results from the photodegradation rates of the poly[(2-methoxy-5-(2-ethyl-hexyloxy))-p-phenylenevinylene] (MEH-PPV) in solution and solid state. MEH films with different thickness were prepared and also blends of MEH and commercial polystyrene were prepared in films from chloroform solutions. FTIR and luminescence spectra showed that there is no interactions between MEH and the PS, making the latter suitable as solid solvent for MEH. The photodegradation reactions were accomplished by exposing the films or solutions (placed in closed cuvettes) to a white light (25 mW/cm2) and recording their absorption spectra. The samples temperature were kept near the ambient by a fan located close to the sample, to avoid thermal effects contributions to the photodegradation. All kinetics in solid stated are biexponentials, with rates in the order of 10-2 and 10-4 (min-1). The results showed a strong influence of the MEH thickness, indicating that the reaction is controlled by the oxygen diffusion. Acknowledgements: FAPESP, IMMP/MCT.

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F-P34 ELECTRICAL AND OPTICAL CHARACTERIZATION OF A NEW PPV DERIVATIVEA.R.V. Benvenho, I.A.Hümmelgen, Departamento de Física, Universidade Federal do Paraná, Caixa Postal 19044, 81531-990, Curitiba, Brazil, R.M.Q. de Mello, Departamento de Química, Universidade Federal do Paraná, Caixa Postal 19081, 81531-990, Curitiba, Brazil, R.W.C. Li, J. Gruber, Instituto de Química Universidade de São Paulo, Caixa Postal 26077, 05513-970, São Paulo, Brazil

In this work we perform the electrical and optical characterization of poly(2-bromo-5-hexyloxy-p-phenylenevinylene), BHPPV. We determine the positive charge carrier mobility (10 -7 cm2/V.s) using current-voltage measurements in F-TO/BHPPV/Al devices (F-TO : fluorine doped thin oxide) and applying space-charge limited current models. The optical gap was determined from the UV-visible absorption spectrum (2.55 eV). The ionization potential (4.52 eV) was obtained from the current onset in cyclic voltammetry experiments, correcting the reference potential to vacuum reference. Assuming Koopman’s theorem validity, the electroaffinity of BHPPV is estimated as 1.98 eV. The photoluminescence spectrum of BHPPV presents a maximum at wavelength of 510 nm, showing green color (CIE chromaticity coordinates x = 0.242, y=0.511).

F-P35 SUPERFICIAL ALIGNMENT OF LIQUID CRYSTALS BY PHOTOISOMERIZATION PROCESSL. T. Thieghi and E. A. Oliveira, Instituto de Física da USP, 05315-970, Cidade Universitária, São Paulo, Brazil; J. J. Bonvent, Núcleo de Pesquisas Tecnológicas, UMG, Mogi das Cruzes, Brazil; J. A. Giacometti and D. T. Balogh, IFSC/USP, São Carlos, Brazil;R. Barberi, Dipartimento di Fisica della Università della Calabria, Arcavacata di Rende (CS), Italy

The aim of this work is to study the superficial interactions of liquid crystals in an interface liquid crystal – polymer, with the use of polymer films containing azo-dye groups as side chain. In this study a photopolymer was used, where the ordering of the side group can be promoted along a preferential direction through a trans-cis-trans isomerization process. Through the irradiation of the polymeric film with polarized light it is possible to promote the formation of an optical anisotropy in the film. The intensity of this effect can be controlled through the incident energy and the concentration of azo-dye side groups presents in the polymer. In this work a systematic study of the orientation induced to the nematic liquid crystal by a polymeric film containing azo-dye groups in the side group was performed using optical techniques. The investigated aspects presented in this work are: the thermal and temporary stability of the alignment induced to the liquid crystal, and the influence of the concentration of the side groups and the irradiation energy.

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F-P36 OPTICAL AND ELECTRONIC PROPERTIES OF MEH-PPV AND BEH-PPVL. C. de Carvalho, and J. L. A. Alves Depto. Ciências Naturais, UFSJ, Caixa Postal 110, 36.300-000 São João del Rei, MG, Brazil; L. A. Cury Depto. de Física, ICEX, UFMG, Caixa Postal 702, 30.123-970 Belo Horizonte, MG, Brazil

In the last decades, the photophysics conjugated polymer properties have attracted considerable attention. Amongst these conjugated polymers, poly (para-phenylene-vinylene) (PPV) has arisen a special interest, in particular for the discovery of its electroluminescence in the region of the visible. However, the PPV presents a low solubility in organic solvents and when displayed to air it suffers to oxidation modifying its electronic and optical properties. Recent research has shown that the addition of certain side chains to the PPV contribute for its higher solubility in organic solvent and for a lower oxidation when displayed to air. Moreover, the energy gap of polymer semiconductors can be varied by the addition of side chains. In this work, we investigate theoretically and experimentally the optical and electronic properties of MEH-PPV (poly (2-metoxy-5-((2'-ethylhexyl)oxy)-1,4-phenylene-vinylene) and of BEH-PPV (poly (2,5-bis(2'-ethylhexyl)oxy)-1,4-phenylene-vinylene). In the theoretical study we use ab initio and semiempirical methods for calculations of electronic structures and in the experimental study we use the techniques of optical absorption and photoluminescence. We compare our experimental results to our theoretical results of energy band structures, density of states and optical absorption.

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