Optothermally Induced Active and Chiral Motion of the Colloidal Structures

TL;DR

This paper demonstrates how optothermal effects can induce active and chiral motion in colloidal structures without chemical environments, advancing control over microscale manipulation and active matter systems.

Contribution

It introduces a novel method using optical illumination to generate thermal fields that drive non-reciprocal, active motion in colloids, eliminating the need for chemical interactions.

Findings

Thermal gradients induce various swimming modes in colloids.

Active propulsion and chiral motion observed and validated experimentally.

Optothermal interactions enable control over colloidal behavior in non-equilibrium systems.

Abstract

Artificial soft matter systems have appeared as important tools to harness mechanical motion for microscale manipulation. Typically, this motion is driven either by the external fields or by mutual interaction between the colloids. In the latter scenario, dynamics arise from non-reciprocal interaction among colloids within a chemical environment. In contrast, we eliminate the need for a chemical environment by utilizing a large area of optical illumination to generate thermal fields. The resulting optothermal interactions introduce non-reciprocity to the system, enabling active motion of the colloidal structure. Our approach involves two types of colloids: passive and thermally active. The thermally active colloids contain absorbing elements that capture energy from the incident optical beam, creating localized thermal fields around them. In a suspension of these colloids, the thermal gradients generated drive nearby particles through attractive thermo-osmotic forces. We investigate the resulting dynamics, which lead to various swimming modes, including active propulsion and chiral motion. We have also experimentally validated certain simulated results. By exploring the interplay between optical forces, thermal effects, and particle interactions, we aim to gain insights into controlling colloidal behavior in non-equilibrium systems. This research has significant implications for directed self-assembly, microfluidic manipulation, and the study of active matter.