Stress analysis of the swelling and deswelling process of thermo-responsive gel

Poly-N-isopropylacrylamide (PNIPA) gel is a typical thermo responsive gel which undergoes a large volume change from the low-temperature swollen phase to the high-temperature shrunken phase. In this study, the mechanical behavior of PNIPA gels was investigated by the experiment and simulation. The cylindrical shaped specimens of PNIPA gel were prepared and tensioned at various temperature. Swelling ratio at equilibrium state was calculated by diameter of swelling gels. Young modulus was obtained from stress-strain curve plotted using tensile load measured by semiconductor gauge. Also swelling and deswelling behavior of thermo sensitive gel were simulated by using finite element method. Polymer-solvent interaction parameter, X was used as a function of temperature. Calculated swelling ratio at equilibrium was compared with experimental result and theoretical swelling curve. Furthermore, change of volume fraction and stress distribution in swelling process were evaluated.