Dynamics of a self-diffusiophoretic particle in shear flow.

Area of Science:

• Colloid science
• Fluid dynamics
• Chemical physics

Background:

• Colloidal particles exhibit autonomous motion via physicochemical mechanisms like self-diffusiophoresis.
• Theoretical models typically assume quiescent fluids, neglecting the impact of ambient flow on solute concentration gradients.

Purpose of the Study:

• To investigate the influence of ambient shear flow on the self-diffusiophoresis of a model Janus particle.
• To quantify the distortion of self-generated solute gradients and resulting particle dynamics in flowing fluids.

Main Methods:

• Utilized matched asymptotic analysis to determine solute concentration gradients around a Janus particle in shear flow.
• Quantified the distortion using the Peclet number (Pe) to characterize the shear flow's influence.
• Analyzed the particle's cross-streamline drift, translational velocity, and in-plane trajectory.

Main Results:

• The ambient shear flow distorts the solute concentration gradient, with distortion quantified by the Peclet number (Pe).
• A Janus particle aligned with the flow experiences O(Pe) cross-streamline drift and an O(Pe(3/2)) reduction in translational velocity.
• The particle's in-plane trajectory forms elliptical orbits that decrease in size as the Peclet number increases.

Conclusions:

• Ambient flow critically affects self-diffusiophoresis, altering particle motion beyond predictions for quiescent fluids.
• The Peclet number effectively characterizes the impact of shear flow on solute gradients and particle dynamics.
• Understanding these flow effects is crucial for practical applications of self-propelled colloidal particles.