Graphical analysis for gel morphology. III. Gel size and temperature effects on the volume phase transition of gels

Abstract

Just after poly(N-isopropylacrylamide) (PNIPA) gels are immersed into hot water over the critical temperature, they undergo a two- or three-step shrinking accompanied with the whitening. The size of gels and the destination temperature were changed and their effects on the shrinking process of PNIPA gels were studied. The following important knowledge in the volume phase transition process of PNIPA gels was obtained. The first is the fact that the fraction of first shrinking is determined by the shrinking rate in the first shrinking stage. The second is the fact that PNIPA gels are divided into small parts by the pinning of density fluctuation in the final stage of the first shrinking and that the shrinking process of each small part undergoes in the secondary shrinking stage. The volume phase transition process of PNIPA gels is briefly discussed from the viewpoint of the scaling theory.