Phase-Separation Dynamics of Aqueous Hydroxypropyl Cellulose Solutions

Abstract

Time-resolved light scattering studies have been undertaken to elucidate the mechanism of thermally induced phase separation in aqueous hydroxypropyl cellulose (HPC) solutions of different molecular weight. The phase diagram was established on the basis of cloud point determination. The phase separation behavior resembles an LCST (lower critical solution temperature), but there appears a discontinuity in the cloud point curve at intermediate compositions. The phase diagram consists of three distinct regions: (1) the isotropic regime at low concentrations, (2) the anisotropic color regime at intermediate concentrations, and (3) the gel regime at high concentrations. The presence of the superstructure in the latter two regimes has complicated the phase separation dynamics; therefore, at this time we will report only the time-resolved light scattering studies on the dynamics of phase separation and phase dissolution in a 10 wt% HPC solution. The time-evolution of scattering curves were analyzed in the context of the linearized theory proposed by Cahn-Hilliard. The linearized theory describes many of the qualitative features of phase separation phenomena, but shows some deficiency in the quantitative comparison. The late stage of spinodal decomposition is dominated by non-linear behavior and the results are interpreted in comparison with recent scaling theories.