论文标题

对强聚合胶体凝胶中应力传播的微机械洞察力

Micro-mechanical insights into the stress transmission in strongly aggregating colloidal gel

论文作者

Dagur, Divas Singh, Man, Yezaz Ahmed Gadi, Roy, Saikat

论文摘要

在许多领域,例如食品,药品,固体液体分离,化妆品,气凝胶和药物递送,预测软凝胶材料在外部变形下的机械响应至关重要。对凝胶材料弹性的大部分理解都是基于分形缩放的概念,而微观见解很少。以前的实验观察结果强烈表明,凝胶材料在变形和可以应用分形缩放的填料范围时失去了分形相关性,这是非常有限的。同样,正确实施分形建模需要识别弹性骨架,这是一项艰巨的任务。到目前为止,还没有清楚地了解高包装部分的凝胶弹性和控制其机械响应的正确长度尺度。在这项工作中,我们进行了广泛的数值模拟,以阐明凝胶材料中应力传播的不同方面。我们观察到两个渗透网络的存在,这些网络是靠近凝胶点的压缩和拉伸力正常力的网络。我们还发现,通过其各自的平均值标准化的压缩和拉伸部分的概率分布显示出普遍的行为,无论相互作用电位不同,热能和粒度分布不管。有趣的是,也有大量的与零法向力的接触,因此,即使在较高的压力下,也以$ f_n \ of $ f_n \大约0 $观察到正常力分布的峰值。我们还确定了关键的内部状态参数,例如平均正常力,力各向异性和平均配位数,并提出了将压力不同组成部分与内部状态参数相关的简单本构关系。我们的模型预测与模拟观察之间的一致性非常好。

Predicting the mechanical response of the soft gel materials under external deformation is of paramount importance in many areas, such as foods, pharmaceuticals, solid-liquid separations, cosmetics, aerogels and drug delivery. Most of the understanding of the elasticity of gel materials is based on the concept of fractal scaling with very little microscopic insights. Previous experimental observations strongly suggest that the gel material loses the fractal correlations upon deformation and the range of packing fraction up to which the fractal scaling can be applied is very limited. Also, correctly implementing the fractal modeling requires identifying the elastic backbone, which is a formidable task. So far, there is no clear understanding of the gel elasticity at high packing fraction and the correct length scale that governs its mechanical response. In this work, we undertake extensive numerical simulations to elucidate the different aspects of stress transmission in the gel materials. We observe the existence of two percolating networks of compressive and tensile normal forces close to the gel point. We also find that the probability distribution for the compressive and tensile part normalized by their respective mean shows universal behavior irrespective of varied interaction potential, thermal energy and particle size distribution. Interestingly, there are also large number of contacts with zero normal force, and consequently, a peak in the normal force distribution is observed at $f_n\approx0$ even at higher pressure. We also identify the critical internal state parameters such as mean normal force, force anisotropies and the average coordination number and propose simple constitutive relations that relate the different components of the stress to the internal state parameters. The agreement between our model prediction and the simulation observation is excellent.

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