Characteristics of charged networks under an electric stimulus

The electrokinetic phenomena of poly(2‐acrylamido‐2‐methyl‐1‐propane sulfonic acid‐co‐n‐butylmethacrylate) were examined to investigate physical changes of the gel under an applied electric current. When an electrical stimulus was applied to a piece of the gel, without being in contact with an electrode, reversible gel bending was observed. The bending degree was directly proportional to the intensity of the applied electric stimulus. This was explained by ‘depletion polarization’ of ionic species under the stimulus. The swelling of the gel surface facing the anode increased, due to the decreased ionic strength of the boundary layer upon electric stimulation, while gel shrinking occurred at the cathode. When the gel is in direct contact with electrodes, deswelling of the gel was observed at the anode side, while water seepage occurred at the cathode side. This observation was attributed to the electro‐osmosis inside the gel, combined with local pH changes around the electrodes resulting from electrochemical reactions, particularly water electrolysis. © 1994 John Wiley & Sons, Inc.