Abstract
In several phenomena in biology and industry, it is required to understand the comprehensive behavior of sedimenting micro-particles in fluids. Here, we use the numerical refocusing feature of digital holographic microscopy (DHM) to investigate the slippage effect on micro-particle sedimentation near a flat wall. DHM provides quantitative phase contrast and three-dimensional (3D) imaging in arbitrary time scales, which suggests it as an elegant approach to investigate various phenomena, including dynamic behavior of colloids. 3D information is obtained by post-processing of the recorded digital holograms. Through analysis of 3D trajectories and velocities of multiple sedimenting micro-particles, we show that proximity to flat walls of higher slip lengths causes faster sedimentation. The effect depends on the ratio of the particle size to (1) the slip length and (2) its distance to the wall. We corroborate our experimental findings by a theoretical model which considers both the proximity and the particle interaction to a wall of different hydrophobicity in the hydrodynamic forces.
Highlights
In several phenomena in biology and industry, it is required to understand the comprehensive behavior of sedimenting micro-particles in fluids
Other related works include the study of the axisymmetric sedimentation of spherical particles in a viscoelastic fluid[12], the study of the motion of a spherical particle along a rough w all[13], the study of sedimentation of a sphere near a vertical wall in an Oldroyd-B fluid[14], and numerical simulations of a shear flow past a spherical particle sitting over a rough wall[15]
To obtain the depth information of particles falling inside the fluid, we use the numerical refocusing feature of digital holographic microscopy (DHM)
Summary
In several phenomena in biology and industry, it is required to understand the comprehensive behavior of sedimenting micro-particles in fluids. Throughout the study, we consider the micro-particles to sediment near distances to the wall so that they feel the boundary presence.
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