Department of Chemical Engineering, University of Michigan, 2300 Hayward Street, Ann Arbor, MI 48109, USA.
Proc Natl Acad Sci U S A. 2012 Oct 2;109(40):16029-34. doi: 10.1073/pnas.1206742109. Epub 2012 Sep 17.
We report a simple correlation between microstructure and strain-dependent elasticity in colloidal gels by visualizing the evolution of cluster structure in high strain-rate flows. We control the initial gel microstructure by inducing different levels of isotropic depletion attraction between particles suspended in refractive index matched solvents. Contrary to previous ideas from mode coupling and micromechanical treatments, our studies show that bond breakage occurs mainly due to the erosion of rigid clusters that persist far beyond the yield strain. This rigidity contributes to gel elasticity even when the sample is fully fluidized; the origin of the elasticity is the slow Brownian relaxation of rigid, hydrodynamically interacting clusters. We find a power-law scaling of the elastic modulus with the stress-bearing volume fraction that is valid over a range of volume fractions and gelation conditions. These results provide a conceptual framework to quantitatively connect the flow-induced microstructure of soft materials to their nonlinear rheology.
我们通过可视化胶体凝胶在高应变速率流动中团簇结构的演变，报告了微观结构与应变相关弹性之间的简单相关性。我们通过在折射率匹配的溶剂中悬浮的粒子之间诱导不同程度的各向同性耗尽吸引力来控制初始凝胶微观结构。与模式耦合和细观力学处理的先前观点相反，我们的研究表明，键的断裂主要是由于刚性簇的侵蚀，而刚性簇在屈服应变之后仍然存在。即使样品完全流化，这种刚性也有助于凝胶弹性；弹性的起源是刚性的、流体力学相互作用的簇的缓慢布朗松弛。我们发现弹性模量与承载体积分数呈幂律关系，该关系在一系列体积分数和凝胶化条件下有效。这些结果为定量连接软物质的流动诱导微观结构与其非线性流变学提供了一个概念框架。
