Rheological implications of embedded active matter in colloidal gels
Rheological implications of embedded active matter in colloidal gels
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胶体凝胶中嵌入活性物质的流变学意义
DOI：
10.1039/c9sm01496a
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发表时间：
2019
期刊：
影响因子：
3.4
通讯作者：
Solomon, Michael J.
中科院分区：
文献类型：
--
作者：
Szakasits, Megan E.;Saud, Keara T.;Mao, Xiaoming;Solomon, Michael J.
胶体凝胶代表了一类重要的软物质，其中由于强烈的短程相互作用而形成的网络显示出类似固体的机械性质，例如有限的低频弹性模量。在这里，我们研究嵌入的活性胶体的分形簇胶体凝胶的线性粘弹性模量的影响。我们发现，自治的，平衡动力学的活性胶体纳入胶体网络降低凝胶弹性，在肌动蛋白网络中的肌球蛋白电机观察到的硬化效应。分形簇凝胶是通过加入二价电解质聚集聚苯乙烯胶体的众所周知的机制形成的。具有铂半球的活性Janus颗粒由相同的聚苯乙烯胶体产生，并在聚集时以稀浓度均匀地嵌入凝胶中。在添加过氧化氢时-一种驱动嵌入的Janus颗粒的扩散电泳运动的燃料-微动力学和机械流变学与过氧化氢的浓度和活性胶体的数量成比例地变化。我们提出了一个理论解释这种效应，其中模量的减少是由主动运动引起的软化粒子间的吸引力介导的。此外，我们的特征在于失败的波动耗散定理在活性凝胶通过识别频率相关的宏观粘弹性模量和预测值之间的差异从测量的凝胶微观动力学的微观流变学。这些发现支持了通过调整嵌入的活性颗粒的微观动力学来设计自主功能的凝胶的努力。这种具有多状态机械特性的可重构凝胶可以应用于油漆和涂料，药物，自修复材料和软机器人等材料。
Colloidal gels represent an important class of soft matter, in which networks formed due to strong, short-range interactions display solid-like mechanical properties, such as a finite low-frequency elastic modulus. Here we examine the effect of embedded active colloids on the linear viscoelastic moduli of fractal cluster colloidal gels. We find that the autonomous, out-of-equilibrium dynamics of active colloids incorporated into the colloidal network decreases gel elasticity, in contrast to observed stiffening effects of myosin motors in actin networks. Fractal cluster gels are formed by the well-known mechanism of aggregating polystyrene colloids through addition of divalent electrolyte. Active Janus particles with a platinum hemisphere are created from the same polystyrene colloids and homogeneously embedded in the gels at dilute concentration at the time of aggregation. Upon addition of hydrogen peroxide – a fuel that drives the diffusiophoretic motion of the embedded Janus particles – the microdynamics and mechanical rheology change in proportion to the concentration of hydrogen peroxide and the number of active colloids. We propose a theoretical explanation of this effect in which the decrease in modulus is mediated by active motion-induced softening of the inter-particle attraction. Furthermore, we characterize the failure of the fluctuation–dissipation theorem in the active gels by identifying a discrepancy between the frequency-dependent macroscopic viscoelastic moduli and the values predicted by microrheology from measurement of the gel microdynamics. These findings support efforts to engineer gels for autonomous function by tuning the microscopic dynamics of embedded active particles. Such reconfigurable gels, with multi-state mechanical properties, could find application in materials such as paints and coatings, pharmaceuticals, self-healing materials, and soft robotics.