Graphical analysis in gels morphology I. General method

A new graphical analysis method is proposed for measurement of gels morphol ogy on volume phase transition. Poly(N-isopropylacrylamide) (PNIPA) gels sh rink and become white after jumping above the critical temperature. Whiteni ng slowly disappears and the gels become finally transparent. This final st age is regarded as the equilibrium state. The shrinking and whitening of di sk-like PNIPA gels have been monitored using a Charge-Coupled Device (CCD) video camera, and both area and whitening of the gels have been evaluated f rom time-resolved images using a new graphical analysis method. We showed t hat gels underwent a two-step shrinking in synchronism with the whitening p rocess. To fit the time-dependent shrinking process, the sum of exponential and stretched exponential functions was adequate using the "chi (2-)map me thod". The exponent characterizing the stretched exponential was found to b e greater than one. The meaning of fitting parameters is determined on the assumption that the skin layer collapses in the second shrinkage.