Metal-insulator transition in polyaniline doped with surfactant counter-ion

Abstract

Polyaniline (PANI) films of superior homogeneity can be prepared by using functionalized protonic acids to protonate the polymer and simultaneously induce solubility, in the conducting form, in common organic solvents. The resistivity ϱ(T), of polyaniline (PANI) complexed with camphor sulfonic acid (CSA) exhibits a positive temperature coefficient for 180K<T<300K, with ϱ(300K)∼4×10 −3 Ohmcm. Although ϱ(T) increases below 180K, indicative of disorder-induced localization, ϱ(1.2)/ϱ(300K) is only 3–12. For samples with ϱ(1.2)/ϱ(300K) > 10, ϱ(T,H=0)exp(T −1/4). For samples with ϱ(1.2K)/ϱ(300K) ∼3–5, ϱ(T,H=0) T −β where β≈0.36, consistent with transport in the critical region near the metal-insulator (M-I) boundary, whereas ϱ(T,H=8Tesla) =ϱ 0exp[(T 0/T) 1/4], indicating variable range hopping between localized states with mean localization length, L c (H=8T)∼100–140 A ̊ . Thus PANI-CSA is on the (M-I) boundary.