Graphical analysis in gels morphology I. General method

A new graphical analysis method is proposed for measurement of gels morphology on volume phase transition. Poly(N-isopropylacrylamide) (PNIPA) gels shrink and become white after jumping above the critical temperature. Whitening slowly disappears and the gels become finally transparent. This final stage is regarded as the equilibrium state. The shrinking and whitening of disk-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 from time-resolved images using a new graphical analysis method. We showed that gels underwent a two-step shrinking in synchronism with the whitening process. To fit the time-dependent shrinking process, the sum of exponential and stretched exponential functions was adequate using the "chi (2-)map method". The exponent characterizing the stretched exponential was found to be greater than one. The meaning of fitting parameters is determined on the assumption that the skin layer collapses in the second shrinkage.