The Translational and Rotational Dynamics of a Colloid Moving Along the Air-Liquid Interface of a Thin Film

Abstract

This study examines the translation and rotation of a spherical colloid straddling the (upper) air/liquid interface of a thin, planar, liquid film bounded from below by either a solid or a gas/liquid interface. The goal is to obtain numerical solutions for the hydrodynamic flow in order to understand the influence of the film thickness and the lower interface boundary condition. When the colloid translates on a film above a solid, the viscous resistance increases significantly as the film thickness decreases due to the fluid-solid interaction, while on a free lamella, the drag decreases due to the proximity to the free (gas/liquid) surface. When the colloid rotates, the contact line of the interface moves relative to the colloid surface. If no-slip is assumed, the stress becomes infinite and prevents the rotation. Here finite slip is used to resolve the singularity, and for small values of the slip coefficient, the rotational viscous resistance is dominated by the contact line stress and is surprisingly less dependent on the film thickness and the lower interface boundary condition. For a colloid rotating on a semi-infinite liquid layer, the rotational resistance is largest when the colloid just breaches the interface from the liquid side.

Shape Deformation in Ion Beam Irradiated Colloidal Monolayers: An AFM Investigation

“…Interfacial self-assembly has been used for the fabrication of colloidal monolayers due to its effectiveness and versatility for the assembly of very diverse materials and has been widely investigated theoretically [1,3,[45][46][47][48][49][50][51][52][53][54][55][56]. In particular, air/water interface self-assembly based on surface confinement and water discharge has been adopted [45].…”

Drag force on a particle straddling a fluid interface: Influence of interfacial deformations

“…The presence of adsorbed surfactants brings in an additional contribution to the drag, with f d up to ≃ 3, due to the viscous nature of the interface with nonvanishing shear and dilatational viscosities [8,9,15,16,17]. More recent investigations focused on the influence of contact line fluctuations on the drag force [18,19], whereas both the rotational and translational dynamics of a colloid moving at a flat air-liquid interface in a thin film were addressed in [20].…”

Dynamics of a spherical colloid at a liquid interface: A lattice Boltzmann study

“…In several experiments it has been observed that the hydrodynamic drag decreases when a larger portion of the particle is immersed in the low viscosity fluid or gas [14][15][16][17][18] . This behavior has been reproduced in theoretical studies, where the drag force is calculated using Stokes hydrodynamics with various boundary conditions, including the presence of shear and dilational surface viscosities 19 , a finite ratio of bulk viscosities 20 , or a solid or membrane boundary on the opposite surface of a thin film 22 .…”

“…Colloidal particles are spontaneously adsorbed on to the fluid-fluid interface and energetics govern the state of the system to reach a minimum energy as first observed by Ramsden 12 and Pickering 13 . The dynamics of a spherical particle trapped at an interface between two fluids or fluid and gas is a widely studied problem both experimentally [14][15][16][17][18] and theoretically [19][20][21][22][23][24][25] , due to its importance in various chemical, oil and mineral flotation industries. The hydrodynamic drag of the colloid along the interface depends crucially on the viscosity difference between the two fluids and the particle wetting.…”

“…In most previous theoretical approaches [19][20][21][22] , the particle dynamics was studied from a purely hydrodynamic perspective, with the boundary conditions implemented through an infinitely thin interface. The thermodynamics of the interface was reduced to the definition of a contact angle.…”