Thermoplastic elastomer/polyaniline blends: Evaluation of mechanical and electromechanical properties

Abstract

Conducting polymer blends whose undiluted components have different properties are promising materials for several technological applications such as electromagnetic shielding, electrostatic charge dissipation, optoelectronic displays, chemical sensors, biosensors and electromechanical sensors. The aim of this study was to obtain and evaluate the electrical conductivity and electromechanical properties of a polystyrene- block-poly(ethylene- ran-butylene)- block-polystyrene copolymer (SEBS)/polyaniline doped with dodecylbenzenesulfonic acid (PAni.DBSA) blends. Electrically conductive elastomeric blends based on SEBS/PAni.DBSA were prepared through a solution casting method, at room temperature, after dissolving both components in toluene as a common solvent. SEBS/PAni.DBSA blends were also prepared through polymerization of aniline in the presence of SEBS solution, using a one-step in situ emulsion polymerization method. The protonation degree of the PAni.DBSA used in this study was determined from X-ray photoelectron spectroscopy (XPS) analysis by calculating the amount of different neutral and positive nitrogen species of the polyaniline chain from the properly curve-fitted N-1s core-level spectrum. The PAni.DBSA used to prepare solution casting blends had a 46% protonation degree, with almost all imine groups protonated and only a small amount of residual DBSA, as expected for an emeraldine salt. This protonation degree is responsible for the high conductivity (2.4 S cm −1) and good solubility of this conducting polymer in toluene. The protonation degree of PAni.DBSA in the blends analyzed was higher than that of undiluted PAni.DBSA, due to an additional protonation during the casting or in situ processes. The insulator–conductor transition was not as sharp as those found in carbon black conducting systems and the percolation threshold was lower than 20 wt.% of PAni.DBSA. Above 20 wt.% PAni.DBSA content, the emulsion-polymerized systems had higher volume conductivity values than the corresponding solution casting blends. The mechanical properties such as tensile strength, elastic modulus and elongation at break of SEBS/PAni.DBSA blends were dependent on the blend preparation method. Blends were also characterized by electromechanical properties and optical microscopy.