chemiphoresis

Chemiphoresis is a term used in colloid and interface science to describe the movement of particles, droplets, or interfaces in response to chemical potential or concentration gradients of dissolved species in a solvent. It is part of the broader family of phoretic phenomena, which also includes diffusion-driven and thermally driven motion. Chemiphoresis is distinct from electrophoresis, which is driven by electric fields, and from thermophoresis, which is driven by temperature gradients.

The mechanism involves the interfacial layer between a particle and its surrounding fluid. A spatially varying solute concentration creates an imbalance of molecular interactions in this layer, generating a slip flow along the particle surface that propels the particle. In the regime where advection is small compared with diffusion, the propulsion velocity is often proportional to the solute concentration gradient: v ∝ ∇C, with a mobility coefficient that depends on surface chemistry, particle size, and solvent properties. Different solutes, including neutral and ionic species, can induce diffusiophoretic motion, and ionic gradients introduce additional electrostatic contributions.

A related and highly studied case is self-diffusiophoresis, where a particle catalytically converts reagent near its surface, forming a local, self-generated chemical gradient that drives its own propulsion. This mechanism underlies many synthetic microswimmers, such as catalytic Janus particles, and is a focus in active matter research.

Applications and implications of chemiphoresis include directed transport and manipulation of colloids in microfluidic systems, assembly of colloidal structures, and insights into transport processes in biological contexts where chemical gradients influence movement. Related concepts include diffusiophoresis, chemotaxis, and self-propelled colloids.