Collective Thermotaxis of Thermally Active Colloids

TL;DR

This paper investigates the collective behavior of thermally active colloids under laser irradiation, revealing conditions for stable distributions and instabilities akin to gravitational collapse or supernova phenomena.

Contribution

It introduces a stochastic model for thermally active colloids and uncovers novel collective behaviors, including density depletion and laser-induced instabilities.

Findings

Positive Soret coefficient leads to stationary density profiles with depletion.

Negative Soret coefficient results in gravitational-like behavior and potential instabilities.

Critical laser intensity triggers a supernova-like collapse in colloidal solutions.

Abstract

Colloids with patchy metal coating under laser irradiation could act as local sources of heat due to the absorption of light. While for asymmetric colloids this could induce self-propulsion, it also leads to the generation of a slowly decaying temperature profile that other colloids could interact with. The collective behavior of a dilute solution of such thermally active particles is studied using a stochastic formulation. It is found that when the Soret coefficient is positive, the system could be described in stationary-state by the nonlinear Poisson-Boltzmann equation and could adopt density profiles with significant depletion in the middle region when confined. For colloids with negative Soret coefficient, the system can be described as a dissipative equivalent of a gravitational system. It is shown that in this case the thermally active colloidal solution could undergo an instability at a critical laser intensity, which has similarities to supernova explosion.