Temperature-responsive poly(N-isopropylacrylamide) gels containing polymeric surfactants

Poly(N-isopropylacrylamide) (PNIPA) gel containing polymer surfactant poly(2-(methacryloyloxyl)decylphosphate) (PMDP) was synthesized and was found to show rapid volume phase transition above its transition temperature. Interestingly, the phase transition temperature of the PNIPA–PMDP gel was equal to that of the PNIPA gels alone. The concentration gradient of PMDP within the PNIPA gel can be obtained by applying an electric field on the gel, similar to the gel electrophoretic technique. The PMDP-gradient PNIPA gel clearly demonstrated the prevention of skin formation and the acceleration of the phase transition rate of the PNIPA gel by PMDP. The rapid volume phase transition allows potential applications of the PNPA–PMDP gel to soft actuators and drug delivery systems. Recently we also succeeded in synthesizing cylindrical microgels (0.8 μm in diameter, 5 μm in length) by a novel strategy where template-guiding synthesis and photochemical polymerization are combined. The obtained microgels can be characterized in individual level by a laser-trapping/Raman spectroscopy. In this article we also briefly described a famous gel system containing ionic surfactant capable of electrically driven actuators although it is not PNIPA gel.