A influência do aquecimento na estrutura semicristalina da Polianilina Sal de Esmeraldina (PANI-ES)

Abstract

Polyaniline (PANI) is an Intrinsically Conducting Polymer (ICP) which is very studied in several areas due to their technological applications. The purpose of this study is to investigate the changes occurring in the structure, morphology and electrical conductivity of Polyaniline Esmeraldine Salt form (PANI-ES) when it is subjected to heat treatment at temperatures of 50, 100, 200 and 300 °C for 1h at each temperature. PANI-ES was chemically synthesized with ammonium persulfate and HCl 1M, and the samples were characterized using XRD, SAXS, FTIR and SEM techniques. By XRD a loss of crystallinity was observed after heating treatment. XRD data were also used to perform the Le Bail method in order to obtain microstructural information through FullProf program and to estimate the percentage of crystallinity using the Peak Fitting Module program. Through Le Bail method the values of average and anisotropic crystallite sizes were acquired: for PANI-ES it was found the value of 36 Å and for the heat treated samples, TT (50) TT (100), TT (200) and TT (300), these values were gradually narrowed until it reaches 16 Å at 300 °C. The percentage of crystallinity obtained for the PANI-ES and heat-treated samples ranged from 51 to 19%. Through the SAXS technique it were obtained the values of the radius of gyration (Rg), and the maximum particle size (Dmáx) from the pair distribution function p(r). The SAXS data were also used for structural reconstruction of the model for particle size, showing that the increasing of temperatures caused a significant loss of globular particle shape and their maximum particle size (Dmáx) and radius of gyration (Rg) were decreased after the heat treatment. FTIR analyzes showed a crosslinking reaction when PANI-ES was subjected to 200 °C, with no gain of crystallinity. SEM technique allowed different morphologies visualization: PANI-ES showed a nanofiber morphology formed by interconnected nanospheres, while samples heat treated lost this initial morphology having much smaller and less defined nanofibers, reflecting the loss of electrical conductivity and crystallinity. The electrical conductivity measurements have been decreasing because of the heat treatment: PANI-ES showed electrical conductivity of 0.3 x 10-4 S/cm and, after the heat treatment, the electric conductivity reached 4 x 10-6 S/cm, representing a decrease of 86%. Thus, this research allowed the structural and morphological characterization of PANI-ES, investigating the changes in its structure after heat treatment, and found that the decrease in the percentage of crystallinity influences in their electrical conductivity values. It is hoped that these results will contribute to a better understanding of the structural, morphological and electrical properties of polymeric materials