Temperature-driven volume transition in hydrogels: phase--coexistence and interface localization

TL;DR

This paper investigates the temperature-induced volume phase transition in hydrogels using thermodynamic models, analyzing phase coexistence, interface localization, and the effects of different Flory parameter models.

Contribution

It introduces an augmented Flory-Rehner model incorporating volume change gradients to determine phase interfaces and coexistence conditions in hydrogels.

Findings

Identifies temperature and traction ranges for phase coexistence.

Determines the interface position between swollen and shrunken phases.

Shows the impact of different Flory parameter models on equilibrium conclusions.

Abstract

We study volume transition phenomenon in hydrogels within the framework of Flory-Rehner thermodynamic modelling; we show that starting from different models for the Flory parameter different conclusions can be achieved, in terms of admissible coexisting equilibria of the system. In particular, with explicit reference to a one-dimensional problem we establish the ranges of both temperature and traction which allow for the coexistence of a swollen and a shrunk phase. Through consideration of an augmented Flory-Rehner free-energy, which also accounts for the gradient of volume changes, we determine the position of the interface between the coexisting phases, and capture the connection profile between them.