Phase Transition of Temperature-Sensitive Hydrogel Under Mechanical Constraint

Abstract

Temperature-sensitive hydrogel is blessed with outstanding properties which may be utilized for innovative appliance. However, this is not achievable if the phase transition property of it is not well understood. Under certain mechanical constraint or temperature stimuli, the hydrogel shows the phase transition, a very special phenomenon that has been study for decades. Those studies have cumulated many qualitative conclusions, yet the quantitative ones are still evasive. Using dynamic mechanical analysis (DMA), we have conducted experiments to quantitatively investigate this peculiar behavior. It is evident that the higher the temperature stimuli applied to hydrogel, the higher the stress which triggers phase transition. Based on the experimental results, a decision rule which predicts the stress triggering phase transition is proposed. Furthermore, theoretical study has also been carried out to study this phase transition phenomenon. With a proper fitting parameter and a transformation from referential state to free swelling state, we can compare the theoretical prediction of the stress–stretch curve with results from experiments. Besides experimental observations and theoretical analyses, another feature of this paper is to provide a numerical method to study phase transition under mechanical constraints.