BENDING OF IONIC POLYMER GEL CAUSED BY SWELLING UNDER SINUSOIDALLY VARYING ELECTRIC-FIELDS

Deformation of poly(vinyl alcohol)-poly(sodium acrylate) composite hydrogel (PVA-PAA gel) under sinusoidally varying electric fields was studied in electrolyte solutions. The PVA-PAA gel was prepared by repeatedly freezing and thawing a mixed solution of PVA and polyacrylic acid. A cyclic bending-straightening motion of the PVA-PAA gel rods of about 1 mm in diameter have been observed in Na2CO3 aqueous solutions under the fields. The PVA-PAA gel had a response time of less than several hundreds milliseconds. The bending has also been observed in organic solvents containing an electrolyte when the organic solvent is electrolyzed. It was found that the motion of the gel under electric fields of less than 1 Hz occurred mainly through swelling due to the change of the osmotic pressure based upon the difference of the ion concentration. However, it has not been determined whether the motion at higher frequencies is caused by the osmotic effect.