Using mixed solvent to synthesize temperature sensitive poly(N-isopropylacrylamide) gel with rapid dynamics properties.

A novel technique to prepare a fast response poly(N-isopropylacrylamide) (PNIPA) gel is proposed by using water/acetone as a mixed solvent during the polymerization/crosslinking reaction. Gels produced in this way can absorb a large amount of water at room temperature and exhibit rapid response rate as the external temperature gets changed. We suggest that, during the polymerization in the mixed solvent, the polymer chains get widely expanded. which leads to an expanded structure and a large swelling ratio (SR) of the gel in water at room temperature. From the standpoint of entropy, the expanded structure may decrease the total entropy of gel system (including the polymer chains and water molecules around them) at the swollen state, which makes this gel system yearn to collapse and undergo phase separation as the temperature gets increased. On the other hand, due to the macroporous matrix of the expanded gel, the water can diffuse out/in easily and quickly during the shrinking/reswelling process as the temperature cycles around the lower critical solution temperature (LCST).