Effect of surface roughening method on performance of IPMC artificial muscle

Abstract

Ionic Polymer Metal Composite (IPMC) is a new kind of ionic Electro-active Polymer (EAP) composed of a perfluorinated polymer membrane coated with a noble metal (usually use Pt and Au) on both sides, which behaves like biological muscle bends towards the anode (in the case of cation exchange membrane) under the influence of an applied electric field. Since it has several advantages such as large deformation, light weight, flexibility, bio-compatibility and low driving voltage compared with shape memory alloy materials and piezoelectric ceramic, IPMC, also termed “artificial muscle”, can be widely applied to the actuators, sensors, biomimetic materials and medical engineering. As a kind of composite materials composed of polymer and metal, the performance of IPMC is closely related to the construction between polymer membrane and metal electrode. Surfaces roughening treatment of the Nafion membranes is employed in order to improve the construction way of the interfaces between polymer membranes and metal electrodes, which is a significant method to improve the electromechanical properties of IPMC materials. In this paper, a controllable and directional surface treatment for IPMC was developed. A surface roughening device included friction head, membrane jig and fixed stage was demonstrated for the IPMC membranes based on linear reciprocating motion of the UMT-2 friction-abrasion testing machine. Compared with manual surfaces roughening treatment, mechanical surface roughening treatments under 20, 50 and 80 N three kinds of load was used. The same preparation process was guaranteed to prepare IPMC on the basis of Nafion membranes with different surfaces roughening methods. The surface morphology of the Nafion membranes was observed using digital microscope. The cross-sectional and metal electrodes of the IPMC were observed using scanning electron microscopy (SEM). The surface roughness of the roughened membranes were measured with surface profiler. The effect of different roughening treatments methods and loading condition on the displacement and blocking force of IPMC artificial muscle were investigated using home-built apparatus. Compared with IPMC with manual surfaces roughening treatment, the IPMC with 20 N roughening load shows the best actuation performance of displacement, and the IPMC with 50 N roughening load shows the best actuation performance of blocking force. Mechanical roughening method can exclude the human factors in the manual roughening process, and produce controllable loading strength and direction, making the polishing cracks uniform in depths and directions. Compared with manual surfaces roughening treatment, the compactness constructed of the interfaces between polymer membranes and metal electrodes can be improved by the mechanical surface roughening treatments, the adsorption capability and deposition thickness of the Pt particles were increased. Thus, the flat and dense electrode with uniform cracks was obtained, which definitely reduced the surface resistance and enhance the blocking force and displacement of IPMC. The denser and thicker electrodes can prevent water leakage and extend the effective operating time of IPMC artificial muscle in the air. This research can improve the stability of the preparation process, which lays a solid foundation for the standardization of preparation process of IPMC. Also, the actuation performance of IPMC was enhanced, guaranteeing the further development and application of IPMC artificial muscle.