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Thin films of polymers containing azobenzene chromophores

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Author(s):
Josmary Rodrigues Silva
Total Authors: 1
Document type: Doctoral Thesis
Press: São Carlos.
Institution: Universidade de São Paulo (USP). Instituto de Física de São Carlos
Defense date:
Examining board members:
José Alberto Giacometti; Teresa Dib Zambon Atvars; Tito Jose Bonagamba; Cleber Renato Mendonça; Paulo Barbeitas Miranda
Advisor: José Alberto Giacometti
Abstract

The formation of Langmuir films and the optical and electrical properties of mixed Langmuir-Blodgett (LB) films were studied. Films were prepared using cadmium stearate (CdSt) and the polymers HPDR13, MMA-DR13 and IPDI-DR19CI. These polymers were characterized with differential scanning calorimetry, visible-ultraviolet spectroscopy (UVVis) and X-ray- diffraction. Surface pressure and surface potential isotherms of the Langmuir films indicated the presence of molecular aggregation due to dipolar interactions. UV-Vis spectroscopy suggested J-type aggregation of dipoles. Measurements on mixed LB film showed that the photoinduced birefringence depends on the number of LB layers, the power of excitation light and on the temper-re. A double exponential function and the Kohlrausch-Williams-Watts function were used for analyzing the experimental curves of growth and decay of the birefringence signal. The dependence of time constants of such functions on the temperature was also analyzed. Mixed LB films of IPDI-DR19CI/CdSt presented the most reproducible results of photoinduced birefringence, which was attributed to the better homogeneity of this type film probably due to the low dipolar aggregation. Experiments carried out with the polymer MMA-DRI3 at low temperatures revealed that the maximum of birefringence increases up to 120 K and then decreases for higher temperatures. Results under 120 K were analyzed using the free local volume theory and included photoisomerization and thermal rotational diffusion processes. Electrical measurements of LB films showed that all LB films present an ohmic conduction regime at low electric fields and a non-ohmic regime attributed to charge carrier injection into the film bulk. It is concluded that CdSt determines the conduction properties of mixed LB films (AU)