Control of polyaniline conductivity and contact angles by partial protonation

Many studies require a specific value of conductivity when investigating conducting polymers. The conductivity of polyaniline can efficiently be controlled by partial protonation of the polyaniline base. Although this is a simple task in principle, practical guidelines are missing. In the present study, the changes in the conductivity of polyaniline base after immersion in aqueous solutions of various acids are reported. Polyaniline base has been reprotonated in aqueous solutions of picric, camphorsulfonic and phosphoric acids. The conductivity of partially reprotonated polyaniline varied between 10(-9) and 10(0) S cm(-1). The relation between the pH of a phosphoric acid solution, which was in equilibrium with polyaniline, and the conductivity a is pH = 0.77 - 0.64 log(sigma [S cm(-1)]). The wettability, i.e. water contact angles, can similarly be set by partial protonation to between 78 degrees for polyaniline base and 44 degrees for polyaniline reprotonated in 1 mol L-1 phosphoric acid. In solutions of picric acid, the transition from the non-conducting to the conducting state occurs over a narrow range of acid concentrations, and the tuning of conductivity is consequently difficult. Phosphoric acid is well suited for the control of conductivity of polyaniline because of the moderate dependence of the conductivity on the acid concentration or pH. (c) 2007 Society of Chemical Industry.