Tunable polyaniline chemical actuators

Polyaniline (PANI) porous asymmetric membranes were prepared using a phase-inversion technique, and their bending-recovery behavior induced by sorption and desorption of chemical vapors was studied. It was found that the bending-recovery rates and maximum bending angles of the membranes were different in various vapors [hexane, ethyl ether, ethyl acetate, tetrahydrofuran (THF), and ethanol]. The undoped PANI membrane showed the most extensive and the fastest bending-recovery movement in THF but no bending-recovery movement in hexane. We believe that the bending-recovery movement results from the asymmetric structure of the membrane's cross section. The dense side has a larger volume expansion than the more porous side after the absorption of organic vapors, and this larger volume causes a bending toward the porous side. Desorption of organic vapor from the membrane allows it to recover to its original position. The study of the effect of the membrane structure on membrane bending-recovery behavior shows that changing the PANI emeraldine base (EB) concentration of the solution used to cast the PANI porous asymmetric membrane changes not only the mechanical properties of the membranes but also the bending-recovery rate of these membrane-based actuators. Lowering the EB concentration leads to the formation of a more porous structure, which increases the diffusion rate of the organic vapor into the membrane and thereby accelerates the bending-recovery movement induced by sorption and desorption. Reversing the hydrophobicity by doping PANI with the surfactant acid, dedecylbenzenesulfonic acid, allows the membrane to respond to less-polar organic vapors such as hexane. Simplified mechanisms between both doped and undoped PANI and organic vapors are proposed to explain the above results.