Propulsion and Interaction of Hot Brownian Swimmers

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Self-thermophoretic (hot) microswimmers are versatile and prototypical active particles driven by thermo-osmotic flows excited by heating at the particle surface and nearby substrates. Their interesting nonequilibrium Brownian fluctuations are theoretically and experimentally well under control. Our highly optimised parallel numerical code for supporting nonequilibrium molecular dynamics simulations establishes an independent platform to link experiment and theory. Based on the results of the preceding funding period, we will concert experiments, simulations, and theory to further elucidate the mutual interactions of swimmers and interactions with substrate surfaces. We will continue to employ the innovative technique of photon nudging for a force-free and torque-free manipulation and steering of hot swimmers, and extend it to allow for controlled measurements of the swim pressure and surface tension of flocks of hot swimmers experimentally. Theoretically, we will extend our recent progress in the systematic coarse-graining of interacting assemblies of so-called active-Brownian-particles (ABP), for which we could unambiguously derive formal expressions for the so-called swim pressure and the surface tension. We will extend this analysis to a (wet) microscopic model with momentum conservation, representing swimming by a velocity rather than by the classical (dry) ABP swim force. Eventually, we aim at an inclusion of the swimmer-specific interactions revealed by our simulations and experiments. In a more applied direction, it will be interesting to extend or supersede the physical interactions between our hot swimmers by specifically tailored artificial interactions. We plan to implement a feedback control via photon nudging as a mechanism for swimmers to mutually interact via an exchange of (delayed) information. These will be suitable to mimic the effect of information-triggered flocking in living systems. In the long run, this should turn our model system of hot swimmers into a versatile experimental laboratory to emulate generic active matter systems.