Coarse Graining Nonisothermal Microswimmer Suspensions

TL;DR

This paper develops and verifies coarse-grained models for self-thermophoretic microswimmers, demonstrating how local temperature fields influence propulsion and Brownian motion, with implications for hydrodynamic modeling of suspensions.

Contribution

It introduces a validated coarse-grained framework linking molecular dynamics simulations to hydrodynamic descriptions of thermophoretic microswimmer suspensions.

Findings

Local temperature fields drive particle propulsion.

Effective nonequilibrium temperatures describe Brownian motion.

Models remain valid under further spatial coarse-graining.

Abstract

We investigate coarse-grained models of suspended self-thermophoretic microswimmers. Upon heating, the Janus spheres, with hemispheres made of different materials, induce a heterogeneous local solvent temperature that causes the self-phoretic particle propulsion. Starting from atomistic molecular dynamics simulations, we verify the coarse-grained description of the fluid in terms of a local molecular temperature field, and its role for the particle's thermophoretic self-propulsion and hot Brownian motion. The latter is governed by effective nonequilibrium temperatures, which are measured from simulations by confining the particle position and orientation. They are theoretically shown to remain relevant for any further spatial coarse-graining towards a hydrodynamic description of the entire suspension as a homogeneous complex fluid.