Modeling the nonlinear large deformation kinetics of volume phase transition for the neutral thermosensitive hydrogels

Abstract

By regarding the neutral thermosensitive hydrogel as a biphasic mixture media, an incompressible deformable porous solid skeleton, and an incompressible interstitial fluid phase saturating the interconnected space, a novel biphasic mixture theory for modeling the nonlinear large deformation kinetics of the volume phase transition was developed from the first law of thermodynamics and the continuum mixture theory. The governing equations consist of the saturated continuity equation, the momentum equations of the fluid, and the momentum equations of the bulk hydrogel. The explicit expressions of the constitutive relationships, which are capable of characterizing the nonlinear large deformation kinetics of the volume phase transition of the N-isopropylacrylamide thermosensitive hydrogels, were derived from the Helmholtz free energy formed by the elastic and mixing contributions. Both the governing equations and the constitutive relationships are in the Lagrangian framework, and special attention was paid to the deformable porous solid skeleton.