Convective Instability Driven by Diffusiophoresis of Colloids in Binary Liquid Mixtures

Abstract

In a binary fluid mixture, the concentration gradient of a heavier molecular solute leads to a diffusive flux of solvent and solute to achieve thermodynamic equilibrium. If the solute concentration decreases with height, the system is always in a condition of stable mechanical equilibrium against gravity. We show experimentally that this mechanical equilibrium becomes unstable in case colloidal particles are dispersed uniformly within the mixture, and that the resulting colloidal suspension undergoes a transient convective instability with the onset of convection patterns. By means of a numerical analysis, we clarify the microscopic mechanism from which the observed destabilisation process originates. The solute concentration gradient drives an upward diffusiophoretic migration of colloids, in turn causing the development of a mechanically unstable layer within the sample, where the density of the suspension increases with height. Convective motions arise to minimize this localized rise in gravitational potential energy.

References in corpus (8)

• Propulsion of a molecular machine by asymmetric distribution of reaction--products
• Designing phoretic micro- and nano-swimmers
• Colloidal motility and pattern formation under rectified diffusiophoresis
• Soret driven convection in a colloidal solution heated from above at very large solutal Rayleigh number
• Diffusiophoresis-Enhanced Turing Patterns
• Reversible Trapping of Colloids in Microgrooved Channels via Diffusiophoresis under Steady-State Solute Gradients
• Instabilities driven by diffusio-phoretic flow on catalytic surfaces
• Two-dimensional diffusiophoretic colloidal banding: Optimizing the spatial and temporal design of solute sinks and sources