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arXiv 1902.02529cond-mat.soft
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竞争作用形成凝胶的流变学研究:数值研究

Rheological investigation of gels formed by competing interactions: A numerical study

José Ruiz-Franco, Nicoletta Gnan, Emanuela Zaccarelli

摘要:

当胶体凝胶长时间暴露于稳定的剪切力下时,会发生从固体状到液体状的转变。这种现象,其特征在于由屈服点,被发现是强烈依赖于包装分数。然而,目前尚不清楚有效粒子间势如何影响这种转变。为了这个目的,我们提出了一个数值研究的平衡凝胶的流变学中,一个短程耗尽是由一个远程静电相互作用的补充。我们观察到一个单一的屈服事件的应力-应变曲线,发生在一个固定的应变。的压力过冲被发现遵循幂律依赖于Péclet数,指数大于耗尽凝胶中发现的,这表明其值可能系统地依赖于底层的胶体-胶体相互作用。我们还建立了一个映射之间的平衡态和稳定状态下的剪切,这使我们能够识别的剪切的存在引起的结构修改。值得注意的是,我们发现,对应于相同的Péclet数,通过不同的组合的剪切速率和溶剂粘度得到的稳定状态,表现出相同的结构和流变性能。我们的研究结果强调了理解胶体相互作用,溶剂效应和流动之间的耦合的重要性,能够描述剪切下的胶体颗粒的微观组织。

英文摘要:

A transition from solid-like to liquid-like behavior occurs when colloidal gels are subjected to a prolonged exposure to a steady shear. This phenomenon, which is characterized by a yielding point, is found to be strongly dependent on the packing fraction. However, it is not yet known how the effective inter-particle potential affects this transition. To this aim, we present a numerical investigation of the rheology of equilibrium gels in which a short-range depletion is complemented by a long-range electrostatic interaction. We observe a single yielding event in the stress-strain curve, occurring at a fixed strain. The stress overshoot is found to follow a power-law dependence on the Péclet number, with an exponent larger than that found in depletion gels, suggesting that its value may depend systematically on the underlying colloid-colloid interactions. We also establish a mapping between equilibrium states and steady states under shear, which allows us to identify the structural modifications induced by the presence of the shear. Remarkably, we find that steady states corresponding to the same Péclet number, obtained by different combinations of shear rate and solvent viscosity, show identical structural and rheological properties. Our results highlight the importance of understanding the coupling between colloidal interactions, solvent effects, and flow to be able to describe the microscopic organization of colloidal particles under shear.

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