Effective thermodynamic properties of inertial active microswimmers with alignment interaction

Self propelling feature, resulting from the associated internal or external energy sources, distinguishes microswimmers or micromotors from equilibrium passive systems of similar scales. Properties of background medium and the associated scales, often, make the microswimmers a low Reynolds number system (Re ≈ 10⁻⁴ − 10⁻⁵). However, there are many instances where Re is orders of magnitude higher, where inertial effects play major role. Recently, we have demonstrated[1] that active Langevin system without explicit alignment exhibits thermodynamic equilibrium-like properties despite inherent out-of-equilibrium nature.

Alignment is an essential component of active microparticles. Their asymmetric shapes, symmetric shapes with specific propulsion mechanisms, hydrodynamic interactions, and external flows add to the alignment. We have performed large scale (of few millions agents) Langevin dynamics simulation with alignment dynamics in our model. We demonstrate that the alignment dynamics bring in important changes in the effective thermodynamic-like features. We believe that our findings may be demonstrated experimentally in inertial microscale systems, e.g., active Marangoni surfers, active complex plasmas.

[1] S. De Karmakar and R. Ganesh, Phys. Rev. E 101, 032121 (2020)