Control of polyaniline conductivity and contact angles by partial protonation

Abstract

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 σ is pH = 0.77 − 0.64 log(σ [S cm −1 ]). The wettability, i.e. water contact angles, can similarly be set by partial protonation to between 78 • for polyaniline base and 44 • 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.

Synthesis and characterization of conductive, biodegradable, elastomeric polyurethanes for biomedical applications

“…The conductivity of CPU films increased exponentially with increased amounts of CSA dopant, which was consistent with previous studies . It can be attributed to the increased concentration of carriers hopping between polymer chains available for electrical conduction .…”

Electrodynamics of the conducting polymer polyaniline on the insulating side of the metal-insulator transition

“…As such it seems that in order to observe "metallic" like conductivity, PANI would need to be protonated beyond 5M HCl. However we found a saturation and eventual decrease in dc σ (300K) for PANI prepared in high molarity acid solutions, as has been observed for PANI synthesized in other acids, 13 which was interpreted as being due to structural changes in the polymer, thus indicating that a transition to critical or metallic-like behavior cannot be achieved in HCl protonated PANI.…”

“…Beyond an upper limit of the concentration, i.e., molarity of the acid, used in the protonation process, the polyaniline chains are saturated resulting in no further increase in conductivity and in certain cases a reduction in conductivity has been observed, 3,13 phenomenologically similar to an upper limit on the level of increasing conductivity in amorphous metal semiconductor samples though for different reasons. quantum mechanical metallic and insulating systems.…”

Biocompatibility of biodegradable semiconducting melanin films for nerve tissue engineering

“…In addition to morphology and chemical composition, the electrical properties of melanin thin films were characterized. The degree of hydration is known to have a dramatic effect on the conduction of both melanin films and pellets [18]. Hence, it is imperative that the resistivity of the films should be calculated in the hydration state that most accurately resembles the environment of the final intended application.…”