Phase separation dynamics in aqueous solutions of thermoresponsive polymers

TL;DR

This study investigates the phase separation kinetics of aqueous hydroxypropyl cellulose solutions using turbidimetric monitoring and mathematical modeling, revealing three stages of spinodal decomposition and the influence of temperature on cluster concentration.

Contribution

The paper introduces a nonlinear Cahn-Hilliard model with a concentration-dependent mobility to simulate phase separation in thermoresponsive polymers, highlighting the role of interfacial energy.

Findings

Identification of three stages of spinodal decomposition

Cluster growth follows diffusion-like kinetics with a 1/3 scaling exponent

Final cluster concentration depends on temperature and interfacial energy

Abstract

Phase transition kinetics of aqueous hydroxypropyl cellulose solution was studied by using turbidimetric monitoring and mathematical modelling techniques. Based on the nonlinear Cahn-Hilliard equation with a mobility depending on the component concentration, the phase separation has been modeled on a simple one-dimensional Flory lattice. For value set of the interfacial energy parameter, data were obtained on the changing of the average values of the cluster sizes, their mass and concentration. The simulation results allow us to distinguish three stages of the spinodal decomposition: early, intermediate and final. It was found that for the intermediate stage, the kinetics of the cluster mass growth is described by a dependence that is characteristic of the usual diffusion mass transfer; the change in the average cluster size can be represented by a scaling function with an exponent close to 1/3, typical of the systems with a conserved scalar order parameter. It is shown that the concentration of clusters at the final stage is determined by the temperature dependence of the interfacial energy.