Chemiphoretic

Chemiphoretic refers to the motion of particles induced by a chemical gradient in the surrounding medium. The phenomenon arises when a concentration difference of solutes generates an interfacial force on a colloidal particle, causing it to drift without the application of external fields. Unlike electrophoresis, which relies on electric fields, chemiphoresis is driven solely by chemical potential differences, often arising from reactions at the particle surface or from the diffusion of reactants and products.

The underlying mechanism involves the interaction of solute molecules with the particle’s surface, producing an asymmetric distribution of osmotic pressure or surface stress. This imbalance produces a slip velocity in the thin interfacial layer, which translates into bulk motion of the particle. The magnitude and direction of chemiphoretic velocity depend on factors such as the nature of the solute, surface chemistry, particle size, and the steepness of the concentration gradient.

Chemiphoretic effects are observed in a variety of systems, including catalytic Janus particles that decompose hydrogen peroxide, leading to self‑propulsion, and in biological contexts where enzymatic activity creates local concentration fields that move enzymes or substrates. The phenomenon is also relevant to microfluidic transport, where engineered chemical gradients can direct the placement and sorting of colloids without mechanical pumps.

Related concepts include diffusiophoresis, where motion is driven by gradients of non‑reactive species, and self‑diffusiophoresis, a subset of chemiphoresis in which the particle itself generates the gradient. Research continues to explore chemiphoretic propulsion for targeted drug delivery, environmental remediation, and the design of autonomous microswimmers.