Mechanics Underpinning Phase Separation of Hydrogels

This paper reveals the underpinning role of mechanical constraints and dynamic loading in triggering volume phase transitions and phase separation of hydrogels. Using the Flory-Rehner free energy that does not predict phase separation of hydrogels under equilibrium free swelling, we show that mechanical constraints can lead to coexistence of multiple phases. We systematically obtain the states of equilibrium for hydrogels under various mechanical constraints and unravel how mechanical constraints change the convexity of the free energy and monotonicity of the stress-stretch curves, leading to phase coexistence. Using a phase-field model, we predict the pattern evolution of phase coexistence and show that many features cannot be captured by the homogeneous states of equilibrium due to large mismatch stretch between the coexisting phases. We further reveal that the system size, quenching rate, and loading rate can significantly influence the phase behavior, which provides insights for experimental studies related to morphological patterns of hydrogels.

Automated summary

This study reveals the fundamental role of mechanical constraints and dynamic loading in triggering volume phase transitions and phase separation of hydrogels. By using the Flory-Rehner free energy, it is shown that mechanical constraints can lead to the coexistence of multiple phases. The study systematically investigates the equilibrium states of hydrogels under different mechanical constraints and explores the influence of mechanical constraints on the free energy and stress-stretch curves, resulting in phase coexistence. A phase-field model is employed to predict the pattern evolution of phase coexistence, highlighting the limitations of homogeneous equilibrium states due to the mismatch stretch between coexisting phases. Furthermore, the study uncovers that system size, quenching rate, and loading rate significantly affect the phase behavior, providing valuable insights for experimental studies on the morphological patterns of hydrogels.