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Wall-induced self-diffusiophoresis of active isotropic colloids

Wall-induced self-diffusiophoresis of active isotropic colloids While chemically active homogeneous spherical particles do not undergo self-diffusiophoresis in free solution, they may do so when suspended in the vicinity of a solid boundary. We explore this possibility using a first-order kinetic model of solute absorption, where the relative magnitude of reaction to diffusion is characterized by the Damköhler number Da . When the particle is remote from the wall, it is repelled from it with a velocity that scales inversely with the square of distance. The opposite extreme, when the ratio δ of separation distance to particle size is small, results in the anomalous scaling δ 1 + 2 Da − 1 2 of the solute concentration in the narrow gap separating the particle and wall. This irrational power may only be obtained by asymptotic matching with solute transport outside the gap. For Da < 4 the self-propulsion speed possesses the same scaling, being set by the large pressures forming in the gap through a lubrication-type mechanism. For Da > 4 the particle velocity is O ( δ ) , set by the flow in the region outside the gap. Solute advection is subdominant to diffusion in both the remote and near-contact limits and accordingly affects neither the above scaling nor the resulting approximations. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Physical Review Fluids American Physical Society (APS)

Wall-induced self-diffusiophoresis of active isotropic colloids

Physical Review Fluids , Volume 1 (3): 8 – Jul 27, 2016

Wall-induced self-diffusiophoresis of active isotropic colloids

Physical Review Fluids , Volume 1 (3): 8 – Jul 27, 2016

Abstract

While chemically active homogeneous spherical particles do not undergo self-diffusiophoresis in free solution, they may do so when suspended in the vicinity of a solid boundary. We explore this possibility using a first-order kinetic model of solute absorption, where the relative magnitude of reaction to diffusion is characterized by the Damköhler number Da . When the particle is remote from the wall, it is repelled from it with a velocity that scales inversely with the square of distance. The opposite extreme, when the ratio δ of separation distance to particle size is small, results in the anomalous scaling δ 1 + 2 Da − 1 2 of the solute concentration in the narrow gap separating the particle and wall. This irrational power may only be obtained by asymptotic matching with solute transport outside the gap. For Da < 4 the self-propulsion speed possesses the same scaling, being set by the large pressures forming in the gap through a lubrication-type mechanism. For Da > 4 the particle velocity is O ( δ ) , set by the flow in the region outside the gap. Solute advection is subdominant to diffusion in both the remote and near-contact limits and accordingly affects neither the above scaling nor the resulting approximations.

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Publisher
American Physical Society (APS)
Copyright
©2016 American Physical Society
Subject
RAPID COMMUNICATIONS; Microscale and nanoscale flows
ISSN
2469-990X
eISSN
2469-990X
DOI
10.1103/PhysRevFluids.1.032101
Publisher site
See Article on Publisher Site

Abstract

While chemically active homogeneous spherical particles do not undergo self-diffusiophoresis in free solution, they may do so when suspended in the vicinity of a solid boundary. We explore this possibility using a first-order kinetic model of solute absorption, where the relative magnitude of reaction to diffusion is characterized by the Damköhler number Da . When the particle is remote from the wall, it is repelled from it with a velocity that scales inversely with the square of distance. The opposite extreme, when the ratio δ of separation distance to particle size is small, results in the anomalous scaling δ 1 + 2 Da − 1 2 of the solute concentration in the narrow gap separating the particle and wall. This irrational power may only be obtained by asymptotic matching with solute transport outside the gap. For Da < 4 the self-propulsion speed possesses the same scaling, being set by the large pressures forming in the gap through a lubrication-type mechanism. For Da > 4 the particle velocity is O ( δ ) , set by the flow in the region outside the gap. Solute advection is subdominant to diffusion in both the remote and near-contact limits and accordingly affects neither the above scaling nor the resulting approximations.

Journal

Physical Review FluidsAmerican Physical Society (APS)

Published: Jul 27, 2016

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