Optothermally induced active and chiral motion of colloidal structures

Abstract

Artificial soft matter systems have proven to be important tools to harness mechanical motion for microscale manipulation. Typically, this motion is driven either by external fields or by mutual interactions between the colloids. In the latter scenario, dynamics arise from non-reciprocal interactions 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 simulated the dynamics of the colloidal structures by solving the coupled Langevin equations to gain insight into the emerging motion. 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.