Qiao Yiming, Liu Zhengyang, Ma Xiaolei, Keim Nathan C, Cheng Xiang
Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota 55455, United States.
Department of Physics, Pennsylvania State University, University Park, Pennsylvania 16802, United States.
Langmuir. 2023 Aug 29;39(34):12032-12040. doi: 10.1021/acs.langmuir.3c01085. Epub 2023 Aug 17.
The formation of particle clusters can substantially modify the dynamics and mechanical properties of suspensions in both two and three dimensions. While it has been well established that large network-spanning clusters increase the rigidity of particle systems, it is still unclear how the presence of localized nonpercolating clusters affects the dynamics and mechanical properties of particle suspensions. Here, we introduce self-assembled localized particle clusters at a fluid-fluid interface by mixing a fraction of Janus particles in a monolayer of homogeneous colloids. Each Janus particle binds to a few nearby homogeneous colloids, resulting in numerous small clusters uniformly distributed across the interface. Using a custom magnetic rod interfacial stress rheometer, we apply linear oscillatory shear to the particle-laden fluid interface. By analyzing the local affine deformation of particles from optical microscopy, we show that particles in localized clusters experience substantially lower shear-induced stretching than their neighbors outside clusters. We hypothesize that such heterogeneous dynamics induced by particle clusters increase the effective surface coverage of particles, which in turn enhances the shear moduli of the interface, as confirmed by direct interfacial rheological measurements. Our study illustrates the microscopic dynamics of small clusters in a shear flow and reveals their profound effects on the macroscopic rheology of particle-laden fluid interfaces. Our findings open an avenue for designing interfacial materials with improved mechanical properties via the control of formation of localized particle clusters.
颗粒团簇的形成能够显著改变二维和三维悬浮液的动力学及力学性质。虽然已有充分的研究表明，大型的跨越网络的团簇会增加颗粒系统的刚性，但局部非渗流团簇的存在如何影响颗粒悬浮液的动力学和力学性质仍不明确。在此，我们通过在单层均匀胶体中混合一部分Janus颗粒，在流体 - 流体界面处引入自组装的局部颗粒团簇。每个Janus颗粒与几个附近的均匀胶体结合，从而在界面上均匀分布形成大量小团簇。我们使用定制的磁棒界面应力流变仪，对负载颗粒的流体界面施加线性振荡剪切力。通过光学显微镜分析颗粒的局部仿射变形，我们发现局部团簇中的颗粒比团簇外的相邻颗粒经历的剪切诱导拉伸要小得多。我们推测，由颗粒团簇引起的这种非均匀动力学增加了颗粒的有效表面覆盖率，进而提高了界面的剪切模量，这一点通过直接的界面流变测量得到了证实。我们的研究阐明了剪切流中小团簇的微观动力学，并揭示了它们对负载颗粒的流体界面宏观流变学的深远影响。我们的发现为通过控制局部颗粒团簇的形成来设计具有改进力学性能的界面材料开辟了一条途径。
