George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, 30332 Atlanta, Georgia.
School of Physics, Georgia Institute of Technology, 30332 Atlanta, Georgia.
Proc Natl Acad Sci U S A. 2020 Nov 3;117(44):27096-27103. doi: 10.1073/pnas.2008076117. Epub 2020 Oct 19.
Suspensions of soft and highly deformable microgels can be concentrated far more than suspensions of hard colloids, leading to their unusual mechanical properties. Microgels can accommodate compression in suspensions in a variety of ways such as interpenetration, deformation, and shrinking. Previous experiments have offered insightful, but somewhat conflicting, accounts of the behavior of individual microgels in compressed suspensions. We develop a mesoscale computational model to probe the behavior of compressed suspensions consisting of microgels with different architectures at a variety of packing fractions and solvent conditions. We find that microgels predominantly change shape and mildly shrink above random close packing. Interpenetration is only appreciable above space filling, remaining small relative to the mean distance between cross-links. At even higher packing fractions, microgels solely shrink. Remarkably, irrespective of the single-microgel properties, and whether the suspension concentration is changed via changing the particle number density or the swelling state of the particles, which can even result in colloidal gelation, the mechanics of the suspension can be quantified in terms of the single-microgel bulk modulus, which thus emerges as the correct mechanical measure for these type of soft-colloidal suspensions. Our results rationalize the many and varied experimental results, providing insights into the relative importance of effects defining the mechanics of suspensions comprising soft particles.
柔软且高度可变形的微凝胶悬浮液可以比硬胶体悬浮液浓缩得多，从而导致其具有异常的机械性能。微凝胶可以通过多种方式适应悬浮液中的压缩，例如互穿、变形和收缩。以前的实验提供了有关压缩悬浮液中单个微凝胶行为的有见地但有些相互矛盾的描述。我们开发了一种介观计算模型，以研究在各种堆积分数和溶剂条件下由具有不同结构的微凝胶组成的压缩悬浮液的行为。我们发现，微凝胶主要通过改变形状和适度收缩来适应堆积。互穿只有在空间填充以上才会明显，相对于交联点之间的平均距离仍然很小。在更高的堆积分数下，微凝胶仅收缩。值得注意的是，无论单个微凝胶的性质如何，以及通过改变颗粒数密度还是颗粒的溶胀状态来改变悬浮液浓度，甚至可以导致胶体凝胶化，悬浮液的力学都可以用单个微凝胶的体模量来定量，因此体模量成为这种软胶体悬浮液的正确力学度量。我们的结果合理化了许多不同的实验结果，深入了解了定义由软颗粒组成的悬浮液力学的各种效应的相对重要性。
