PHASE-SEPARATION IN AQUEOUS POLY(VINYL ALCOHOL) SOLUTION

Aqueous solutions of poly(vinyl alcohol) (PVA) were investigated by el astic and inelastic light scattering. In the initial stage of phase se paration, a plot of the logarithm of scattered intensity against time formed a straight line when measurements were made in the sol region a t less than the spinodal temperature estimated according to the method described by Cahn as being within the framework of linearized spinoda l decomposition theory. No scattering pattern under Hv polarization co nditions in the initial stage was observed for PVA gels prepared from aqueous solutions, apart from the X-type scattering pattern observed f or PVA gels prepared from a dimethylsulfoxide/water mixture. This mean s that an aqueous solution of PVA does not form assemblies of crystall ites such as rod-like and spherulitic textures in the phase-separation process. Hence the phase separation of aqueous solutions of PVA is ap parently expected to be similar to that of amorphous polymer solutions due to spinodal decomposition. However, no definite scattering peak w as observed as a function of scattering vector characterizing the latt er stage of spinodal decomposition. Furthermore, in the initial stage, in the linear part of the plot of logarithm of scattered intensity ag ainst time, the decay rate estimated by inelastic light scattering dec reased rapidly, indicating the progress of gelation. These contradicto ry phenomena indicated the possibility that the phase separation of aq ueous PVA solutions is attributed to the simultaneous progress of spin odal decomposition and gelation.