FORTH/IESL and Department of Materials Science and Technology, University of Crete, 71110 Heraklion, Greece.
Soft Matter. 2017 Nov 8;13(43):7824-7833. doi: 10.1039/c7sm01655g.
A combination of experiments and Brownian Dynamics (BD) simulations is utilized to examine internal stresses in colloidal gels brought to rest from steady shear at different shear rates. A model colloidal gel with intermediate volume fraction is chosen where attractions between particles are introduced by adding non-adsorbing linear polymer chains. After flow cessation, the gel releases the stress in two distinct patterns: at high shear rates, where shear forces dominate over attractive forces, the shear-melted gel behaves as a liquid and releases stresses to zero after flow cessation. After low shear rates, though, stresses relax only partially, similar to the response of hard sphere glasses and jammed soft particles. The balance between shear and attractive forces which determines the intensity of structural distortion controls the amplitude of the residual stresses through a universal scaling. Stress decomposition to repulsive and attractive contributions in BD simulations reveals that internal stresses mainly originate from attractive forces. Moreover, analysis of particle dynamics indicates that internal stresses are associated with sub-diffusive particle displacements on average smaller than the attraction range as such short-range displacements are not sufficient to completely erase structural anisotropy caused during the course of shear.
采用实验和布朗动力学（BD）模拟的组合方法，研究了在不同剪切速率下从稳态剪切中静止的胶体凝胶中的内应力。选择具有中等体积分数的模型胶体凝胶，其中通过添加非吸附线性聚合物链来引入颗粒之间的吸引力。流动停止后，凝胶以两种不同的模式释放应力：在高剪切速率下，剪切力占主导地位，剪切熔化的凝胶表现为液体，并在流动停止后将应力释放到零。然而，在低剪切速率下，应力仅部分松弛，类似于硬球玻璃和被堵塞的软颗粒的响应。决定结构变形强度的剪切力和吸引力之间的平衡通过通用标度控制残余应力的幅度。BD 模拟中的应力分解为排斥和吸引力贡献表明，内应力主要源于吸引力。此外，颗粒动力学分析表明，内部应力与平均小于吸引力范围的亚扩散颗粒位移有关，因为这种短程位移不足以完全消除剪切过程中产生的结构各向异性。
