Pairwise hydrodynamic interactions of spherical colloids at a gas-liquid interface
Pairwise hydrodynamic interactions of spherical colloids at a gas-liquid interface
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DOI：
10.1017/jfm.2021.170
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发表时间：
2021-03
影响因子：
3.7
通讯作者：
Subhabrata Das;J. Koplik;P. Somasundaran;C. Maldarelli
中科院分区：
文献类型：
--
作者：
Subhabrata Das;J. Koplik;P. Somasundaran;C. Maldarelli
摘要胶体吸附并跨越流体界面形成单分子层，是二维流体景观上粒子动力学的范例。动力学通常是无惯性的（斯托克斯流），并由界面张力控制，因此界面不会因流动而变形，并且可以计算成对的阻力系数。在这里，相同的球形胶体之间的流体动力学相互作用的平面气/液界面上的计算作为一个函数的分离距离和浸没深度。阻力系数（归一化的表面上的孤立粒子的系数）的数值计算的四个典型的相互作用。前两种是沿着中心线的运动，或者是粒子相互靠近，或者是沿同一方向（一前一后）运动。后两种是垂直于中心线的运动，或者方向相反（剪切），或者方向相同（串联）。对于相互接近和剪切，由于润滑力，归一化系数随着分离的减少而增加，并且当颗粒超过一半浸没时，在接触时变得无限大。然而，当颗粒浸入不到一半时，它们在接触时保持有界，因为它们不在液体下面接触。对于串联运动，归一化系数随着分离的减小而减小;对于所有浸入深度，它们都崩溃为阻力系数对无限介质中串联运动的两个粒子的分离的依赖性。这些系数用于计算毛细管吸引力驱动的胶体的分离时间。
Abstract Colloids which adsorb to and straddle a fluid interface form monolayers that are paradigms of particle dynamics on a two dimensional fluid landscape. The dynamics is typically inertialess (Stokes flows) and dominated by interfacial tension so the interface is undeformed by the flow, and pairwise drag coefficients can be calculated. Here the hydrodynamic interaction between identical spherical colloids on a planar gas/liquid interface is calculated as a function of separation distance and immersion depth. Drag coefficients (normalized by the coefficient for an isolated particle on the surface) are computed numerically for the four canonical interactions. The first two are motions along the line of centres, either with the particles mutually approaching each other or moving in the same direction (in tandem). The second two are motions perpendicular to the line of centres, either oppositely directed (shear) or in the same direction (tandem). For mutual approach and shear, the normalized coefficients increase with a decrease in separation due to lubrication forces, and become infinite on contact when the particle is more than half immersed. However, they remain bounded at contact when the particles are less than half immersed because they do not contact underneath the liquid. For in-tandem motion, the normalized coefficients decrease with a decrease in separation; they collapse, for all immersion depths, to the dependence of the drag coefficient on separation for two particles moving in tandem in an infinite medium. The coefficients are used to compute separation against time for colloids driven together by capillary attraction.