The influence of 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPSA) additive concentration and stretch orientation on electronic transport in AMPSA-modified polyaniline films prepared from an acid solvent mixture

We examine the effects of 2 acrylamido 2 methyl 1 propanesulfomc acid (AMPSA) additive concentration molecular weight and specimen elongation on the temperature dependent electronic transport properties of polyaniline films prepared with AMPSA in the presence of a great excess of a formic and dichloroacetic acid (DCAA) solvent mixture The AMPSA additive dependent resistivity and thermopower are reported for free standing PANI AMPSA(x) (M-w = 200 000 g mol(-1)) films (x = 01-05) in the temperature range from 2 to 325 K The low temperature data indicate that these samples are just on the insulating side of a disorder induced metal-insulator (M-I) transition (dpl dT < 0) and that thermal motion at elevated temperatures is sufficient to produce a metallic state (dp/dT > 0) at room temperature Transport occurs via variable range hopping (VRH) for temperatures below 200 K with hopping parameters that are a strong function of x increased AMPSA concentration decreases the resistivity and moves the samples towards the M-I phase boundary There is a minimum in the resistivity for all samples at a temperature To that is also doping dependent Stretch orientation of PANI AMPSA(0.5) films prepared with higher molecular weight PANI (Mw = 300 000 g mol(-1)) along the resistivity measurement direction decreases the room temperature resistivity at the expense of a more insulating low temperature state The T-m values of both stretched and unstretched PANI AMPSA(0.5) films are pushed below 200 K which reflects reduced disorder in film processed with higher molecular weight polyaniline These results reflect an evolution in the underlying inhomogeneous mesoscopic disorder present in doped conducting polymers (C) 2002 Elsevier Science B.V. All rights reserved.