Study on Sorption Process in Ethyl Methacrylate-2-Hydroxyethyl Methacrylate Copolymer/Water System by [zeta]-Potential Methodt

The sorption process of ethyl methacrylate-2-hydroxyethyl methacrylate copolymers having three different compositions was pursued from C-potential change. The measurements were carried out at the room temperature to about 70°C, encompassing the glass transition point (Tg) of the copolymer examined. The rate constants K for the sorption obtained from C-potential (estimated from the streaming potential method) were compared to the diffusion constants obtained directly from sorption experiments. The results are as follows: (1) In the temperature range T> Tg, the rate constant, K, showed clearly the dependence of the sorption process upon the composition, that is, the activation energy 4. Ef (negative) increased with increasing HEMA content (i. e., with increasing surface density of OH-groups); (2) The lowering of Tg of the copolymers by plasticization of sorbed water was observed; and (3) The values of K and D were decreased with increasing HEMA content of copolymers at the experimental temperature.