Light-Induced Manipulation of Passive and Active Microparticles

TL;DR

This paper demonstrates how light can be used to manipulate and assemble both passive and active microparticles at a solid wall through a light-induced diffusio-osmotic flow driven by photosensitive surfactants, enabling dynamic pattern formation.

Contribution

It introduces a novel method of controlling colloidal particles using light-induced diffusio-osmosis, especially highlighting the active participation of porous colloids in flow generation.

Findings

Light can create and split particle regions with tunable size and shape.

Controlled flow forces can induce particle crystallization and lattice formation.

Porous colloids actively participate in flow generation, affecting their interactions.

Abstract

We consider sedimented at a solid wall particles that are immersed in water containing small additives of photosensitive ionic surfactants. It is shown that illumination with an appropriate wavelength, a beam intensity profile, shape and size could lead to a variety of dynamic, both unsteady and steady-state, configurations of particles. These dynamic, well-controlled and switchable particle patterns at the wall are due to an emerging diffusio-osmotic flow that takes its origin in the adjacent to the wall electrostatic diffuse layer, where the concentration gradients of surfactant are induced by light. The conventional nonporous particles are passive and can move only with already generated flow. However, porous colloids actively participate themselves in the flow generation mechanism at the wall, which also sets their interactions that can be very long ranged. This light-induced diffusio-osmosis opens novel avenues to manipulate colloidal particles and assemble them to various patterns. We show in particular how to create and split optically the confined regions of particles of tunable size and shape, where well controlled flow-induced forces on the colloids could result in their cristalline packing, formation of dilute lattices of well-separated particles, and other states.