Diffusiophoretically induced interactions between chemically active and inert particles

TL;DR

This paper investigates how chemically inert particles respond to concentration gradients created by active particles, revealing mechanisms for self-assembly and propulsion in colloidal systems through analytical and simulation methods.

Contribution

It provides a detailed analytical and simulation study of diffusiophoretic interactions between active and inert particles, highlighting self-assembly and propulsion phenomena.

Findings

Inert particles are attracted to reactive particles via diffusiophoresis.

Self-assembled dimers can propel themselves in solution.

Sphere size ratios influence flow fields and assembly behavior.

Abstract

In the presence of a chemically active particle, a nearby chemically inert particle can respond to a concentration gradient and move by diffusiophoresis. The nature of the motion is studied for two cases: first, a fixed reactive sphere and a moving inert sphere, and second, freely moving reactive and inert spheres. The continuum reaction-diffusion and Stokes equations are solved analytically for these systems and microscopic simulations of the dynamics are carried out. Although the relative velocities of the spheres are very similar in the two systems, the local and global structures of streamlines and the flow velocity fields are found to be quite different. For freely moving spheres, when the two spheres approach each other the flow generated by the inert sphere through diffu- siophoresis drags the reactive sphere towards it. This leads to a self-assembled dimer motor that is able to propel itself in solution. The fluid flow field at the moment of dimer formation changes direction. The ratio of sphere sizes in the dimer influences the characteristics of the flow fields, and this feature suggests that active self-assembly of spherical colloidal particles may be manipulated by sphere-size changes in such reactive systems.