ELECTRO-STIMULATE RESPONSE BEHAVIOR OF PHOSPHORYLATED POLYVINYL ALCOHOL HYDROGEL

A new phosphorylated polyvinyl alcohol hydrogel was prepared by the crosslinking reaction of phosphorylated polyvinyl alcohol with glutaraldehyde, taking the urea as the catalyst in the phosphorylating reaction of polyvinyl alcohol. Swelling performance, mechanical properties and electro-stimulate response behavior of the phosphorylated polyvinyl alcohol hydrogel were studied. The experimental results show that its equilibrium swelling ratio decreased as the ionic strength of NaCl solutions increased, and the mechanical properties of phosphorylated polyvinyl alcohol hydrogel swollen in the NaCl aqueous solution of the ionic strength range of 0 similar to 0.2 were shown as follows: 0.300 similar to 0.356 MPa of Young's modulus, 91.5 similar to 137.8 kPa of tensile strength and 32.0% similar to 37.5% of elongation at break, and they all increased with the increasing of ionic strength. The phosphorylated polyvinyl alcohol hydrogel bended toward the cathode under non-contact D. C. electric field in deionized water and NaCl aqueous solution, the bending speed and strain increased with the increasing of the applied voltage, and there was an ionic strength of 0. 005 at which its bending speed and strain reached their maximum values. That could be explained as follows. When the ionic strength of NaCl solution is lower than 0. 005, the increase of ionic strength of NaCl solution induces the increase of free ions moving from the surrounding solution toward their counterelectrode or into the hydrogel, so the bending speed and strain increase. However, if the ionic strength of NaCl solution is higher than 0. 005 a shielding effect of the polyions caused by the ions in the electrolytic solution occurs, leading to the decrease of the bending speed and strain. Under a cyclically varying electric field, the hydrogel exhibited a good reversible bending behavior. The hydrogel may be applied to the fields including artificial muscle, robotic actuator and micromechanics, etc.