Light-induced manipulation of passive and active microparticles

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 crystalline packing, formation of dilute lattices of well-separated particles, and other states. Graphic Abstract

Motion of a self-propelled particle with rotational inertia

“…In natural systems, however, the environment may be heterogeneous and fluctuating, and the particle parameters can change over time. 1,2,52,[56][57][58][59]65,[88][89][90] To summarize, in the framework of the two-dimensional active Langevin particle model, we have presented general analytical equations that describe the mean kinetic energy, mean-square displacement (mass-transfer function) and noise-averaged trajectory of the self-propelled particle with any moment of inertia and rotational diffusivity in a medium with any dynamic viscosity. This study fills a gap in the theory of active Brownian motion in the field where rotational inertia significantly affects the random walk of active particles on all time scales.…”

“…In natural systems, however, the environment may be heterogeneous and fluctuating, and the particle parameters can change over time. 1,2,52,56–59,65,88–90…”

How to Make a Surface Act as a Micropump

“…The colloids trapped near the surface are passively dragged along the DO flow and form either a densely packed crystal or a cleaned surface. [ 38 ]…”

“…The colloids trapped near the surface are passively dragged along the DO flow and form either a densely packed crystal or a cleaned surface. [38] In this paper, the phenomenon of light-driven diffusioosmotic (DO) long-range attractive and repulsive interactions between micro-sized objects trapped near a solid wall is investigated. The range of the DO flow extends several times the size of microparticles and can be adjusted to point towards or away from the particle by varying irradiation parameters such as intensity or wavelength of light.…”

Editorial: Motile active matter

“…More information about these aspects can be found in Refs. [4,14,[18][19][20][21][22][23][24][25][26][27][28][29] of this Topical Issue.…”