A novel 'dual mode' actuation in chitosan/polyaniline/carbon nanotube fibers

Fibers composed of chitosan, polyaniline (PANi), and single-wall carbon nanotubes (SWNTs) have been fabricated using a wet spinning method. We investigated the structural properties, morphology, and mechanical properties of the fibers using Raman spectroscopy, environmental scanning electron microscopy (ESEM), and tensile testing, respectively. The conductivity and electroactivity of the fibers were studied using the four-point probe method and cyclic voltammetry. The actuation of the fibers during pH switching in acidic or basic electrolyte solutions with and without applied electrical potential was determined. For the first time, a dual mode actuation is reported. The pH switching showed large strains due to the protonation/deprotonation of amine groups of the chitosan. In addition, a second strain response was produced by redox reactions of the PANi. Dual mode actuation is useful in practice, as it allows independent small scale adjustment of the pH induced large strains. The carbon nanotubes improved the conductivity and mechanical strength of the fibers.