Model for the phase separation of poly(N-isopropylacrylamide)–clay nanocomposite hydrogel based on energy-density functional

Abstract

The time-dependent Ginzburg-Landau (TDGL) mesoscopic method is utilized to simulate the phase separation of the poly(N-isopropylacrylamide)–clay nanocomposite hydrogel in the three-dimensional case, where the Cahn-Hilliard-Cook equation with a proposed free energy, which consists of the stretching and mixing energy based on Flory's mean theory, is considered. The main features of the presently proposed model include the following: (i) the proposed free energy consists of both the stretching and mixing energy; (ii) the processes of polymer chains detaching from and reattaching on crosslinks are considered in the proposed free energy; (iii) polymer chains have inhomogeneous chain lengths, which are divided into different types. A stabilized semi-implicit difference scheme is used to numerically solve the corresponding Cahn-Hilliard-Cook equation. Numerical results show the process of the phase separation and are consistent with morphology of the nanocomposite hydrogel.