Electrospun nanoscale polyacrylonitrile artificial muscle

Ionic polymer gels have been known to change in volume due to external stimuli. Activated polyacrylonitrile (PAN) fibers are known to contract and elongate more than 100% in length when immersed in caustic and acidic solutions, respectively. Commercially available PAN fibers with diameters in the range of tens of micrometers have been used in previously reported work. Instead, here we tried to study the phenomenon in fibers with diameters of a few hundred nanometers (D_p<1νm). These nanometer sized fibers are expected to have faster response times when compared to commercially available fibers. Submicron diameter PAN fibers were made by electrospinning. The fibers were placed in a solution and the change in the shape of the fibers was observed with change in pH. The fibers contracted in acidic solution and expanded in basic solution similarly to reports in the literature. In this work, we measured the in situ variation in the diameter of the fibers using an environmental scanning electron microscope (E-SEM) and an atomic force microscope (AFM) while the change in pH was taking place. It appears that a variation of more than 100% was observed, similar to that observed with conventional fibers of diameter ranging from 10 to 50νm. Also, the differential scanning calorimetry (DSC) results clearly provide the phase transition information regarding the contraction/elongation of such PAN fibers. These results provide the potential for developing fast actuating PAN muscles and linear actuators, and muscle structures similar to sarcomere/myosin/actin assembly.