METAL-INSULATOR-TRANSITION IN POLYANILINE DOPED WITH SURFACTANT COUNTERION

Polyaniline (PANI) films of superior homogeneity can be prepared by us ing functionalized protonic acids to protonate the polymer and simulta neously induce solubility, in the conducting form, in common organic s olvents. The resistivity rho(T), of polyaniline (PANI) complexed with camphor sulfonic acid (CSA) exhibits a positive temperature coefficien t for 180K<T<300K, with rho(300K) almost-equal-to 4x10(-3) Ohmcm. Alth ough rho(T) increases below 180K, indicative of disorder-induced local ization, rho(1.2)/rho(300K) is only 3-12. For samples with rho(1.2)/rh o(300K) > 10, rho(T,H=0) is-proportional-to exp(T-1/4). For samples wi th rho(1.2K)/rho(300K) almost-equal-to 3-5, rho(T,H=0) is-proportional -to T(-beta) where beta almost-equal-to 0.36, consistent with transpor t in the critical region near the metal-insulator (M-I) boundary, wher eas rho(T,H=8Tesla)=rho0exp[(T0/T)1/4], indicating variable range hopp ing between localized states with mean localization length, L(c)(H=8T) almost-equal-to 100-140 angstrom. Thus PANI-CSA is on the (M-I) bound ary.