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Yield stress behavior of colloidal gels with embedded active particles
Journal of Rheology ( IF 3.3 ) Pub Date : 2021-02-19 , DOI: 10.1122/8.0000163
Keara T. Saud 1 , Mahesh Ganesan 2 , Michael J. Solomon 2
Affiliation  

The yield stress behavior of colloidal gels with embedded active particles is studied with three experiments: start-up of steady shear, oscillatory strain amplitude sweep, and creep testing. Activity is generated by Janus particles with a platinum hemisphere; these particles undergo self-diffusiophoretic and self-electrophoretic motion in hydrogen peroxide solutions. The free particle active motion of the Janus colloids is consistent with an active energy of 25 times thermal energy at the highest hydrogen peroxide concentration studied. Consistent with prior work, the gels with embedded active particles display enhanced microdynamics and a reduction in linear viscoelastic moduli. Furthermore, at the activity levels studied, the yield stress decreases by as much as threefold for gels with an active-to-passive particle ratio of only 1:1200. We additionally find the yield strain is independent of activity. The significant reduction in yield stress at a very low active-to-passive particle ratio is modeled by combining the theory of how activity changes the spring constant of interparticle bonds in the gel with an argument that the number of active fractal clusters in the gel—rather than the number of active particles—drives the activity-induced softening of rheological properties. We estimate that 1 in 40 fractal clusters in the gel is active due to the presence of an active particle. This approach explains how an extremely small fraction of active particles causes a substantial change in both linear and nonlinear rheological properties. The results and modeling are potentially useful for the creation of gels with multistate mechanical properties.

中文翻译:

包埋有活性颗粒的胶体凝胶的屈服应力行为

通过三个实验研究了具有嵌入的活性颗粒的胶体凝胶的屈服应力行为:稳定剪切的启动,振荡应变幅度扫描和蠕变测试。活性是由具有铂半球的Janus粒子产生的。这些颗粒在过氧化氢溶液中经历自扩散和自电泳运动。在研究的最高过氧化氢浓度下,Janus胶体的自由粒子主动运动与热能的25倍相一致。与先前的工作一致,具有嵌入的活性颗粒的凝胶显示出增强的微观动力学特性,并降低了线性粘弹性模量。此外,在所研究的活性水平下,主动与被动颗粒比仅为1:1200的凝胶的屈服应力降低了三倍之多。我们还发现屈服应变与活性无关。通过将活性如何改变凝胶中颗粒间键的弹性常数的理论与关于凝胶中活性分形团簇数目的论点结合起来,可以模拟出在极低的主动与被动颗粒比率下屈服应力的显着降低。而不是活性颗粒的数量-驱使活性引起的流变性能软化。我们估计,由于存在活性颗粒,凝胶中40个分形簇中有1个具有活性。这种方法解释了极少量的活性颗粒如何引起线性和非线性流变性质的实质性变化。结果和模型可能对创建具有多态机械性能的凝胶有用。
更新日期:2021-03-01
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