Zhou Yu, Jin Lihua
Department of Mechanical and Aerospace Engineering, University of California, Los Angeles, Los Angeles, California90095, United States.
Macromolecules. 2023 Jan 5;56(2):426-439. doi: 10.1021/acs.macromol.2c02356. eCollection 2023 Jan 24.
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.
本文揭示了机械约束和动态加载在触发水凝胶体积相变和相分离中的基础作用。利用在平衡自由溶胀下无法预测水凝胶相分离的弗洛里-莱纳自由能，我们表明机械约束可导致多相共存。我们系统地获得了各种机械约束下水凝胶的平衡态，并揭示了机械约束如何改变自由能的凸性和应力-应变曲线的单调性，从而导致相共存。使用相场模型，我们预测了相共存的模式演变，并表明由于共存相之间的拉伸不匹配较大，许多特征无法通过平衡均匀态来捕捉。我们进一步揭示了系统尺寸、淬火速率和加载速率可显著影响相行为，这为与水凝胶形态模式相关的实验研究提供了见解。
