Shen Tong, Kan Jian, Benet Eduard, Vernerey Franck J
University of Colorado Boulder, Boulder, CO 80302, USA.
Soft Matter. 2019 Jul 24;15(29):5842-5853. doi: 10.1039/c9sm00911f.
This paper explores the physical mechanisms responsible for the appearance of small blisters on the surface of temperature sensitive hydrogels as they deswell rapidly during their volume phase transition. For this, we develop a numerical model that couples the processes of hydrogel deswelling and blister growth due to the existence of a thin quasi-impermeable layer on its surface. The model points out that blister inflation originates at defects point under the gel's surface, under the effect of the increasing osmotic pressure in the gel as it undergoes its phase transition. Due to their large deformation, these blisters often experience a mechanical instability that triggers a sudden increase in their growth rate at the expense of their closest neighbors. Using a simple computational model, we then show that blisters are able to communicate via internal pressure and that these interactions are mediated by two characteristic time scales related to solvent transport within and between adjacent blisters. Our study finally indicates that these mechanisms can be controlled by temperature and the gel's cross-link density to achieve diversity of blister patterns on the gel's surface. The proposed analysis provides predictions that agree well with experimental observations of NiPAm gels which deswell in various conditions.
本文探讨了在温度敏感水凝胶体积相转变过程中快速收缩时，其表面出现小水泡的物理机制。为此，我们建立了一个数值模型，该模型将水凝胶收缩过程与由于其表面存在薄的准不透水层而导致的水泡生长过程耦合起来。该模型指出，水泡膨胀起源于凝胶表面下的缺陷点，这是由于凝胶在经历相转变时渗透压增加所致。由于这些水泡的大变形，它们经常会经历机械不稳定性，从而导致其生长速率突然增加，以牺牲其相邻水泡为代价。然后，我们使用一个简单的计算模型表明，水泡能够通过内部压力进行通信，并且这些相互作用由与相邻水泡内部和之间的溶剂传输相关的两个特征时间尺度介导。我们的研究最终表明，这些机制可以通过温度和凝胶的交联密度来控制，以在凝胶表面实现水泡图案的多样性。所提出的分析提供的预测与在各种条件下收缩的NIPAm凝胶的实验观察结果非常吻合。
