Chemomechanical Gels for Actuator System Controlled by Electrochemical Reaction

Abstract

We aim to make an actuator that uses the osmotic pressure of chemomechanical gels and is controlled by electrochemical reaction. This paper presents the preparation of the gels and measurement of pH change and gel actuation by the electrochemical reaction. Finally, we suggest one example of application suitable for gel actuator. The gels are made by photo-polymerization with ultraviolet irradiation to vinyl-monomers which are N,N'-dimethyl aminopropyl acrolamide (DMAPAA), Methylene-bis-acrylamide (MBAAM). Poly-vinyl alcohol (PVA) is added to the monomer solution to make the gels elastic. Swelling ratio and Young's modulus of the gels were measured in electrolyte solution with deferent pH and ion concentration. It became clear that the Young 's modulus of the gels increased with increasing the swelling ratio which was proportional to the osmotic pressure. This result is suitable for the actuator which uses the swelling pressure of the gels. The oxidizing and reducing agent for the electrochemical reaction is Ethyl Viologen Dibromide. The cell with the working electrode is separated from the cell with the counter one by an ion exchange membrane. The oxidation by applied potential of + 1.0 V decreases pH from 12 to 4 within 3 minutes. In the case of reduction, the potential of -0.8 V increases pH for 4 to 12 within the same minutes. The change of pH swells or shrinks the chemomechanical gels similar to adding acid or alkaline to the solution. Without stirring, it is difficult that pH change spreads into the gel completely in the short time, which causes the hysteresis. As the application of the gel actuator, a continuous dispenser is suggested and confirmed to discharge liquid from the balloon.