Lattice Boltzmann simulations of self-propelling chiral active droplets

Abstract

Active matter describes materials whose constituents are driven out of equilibrium by continuous energy consumption, for instance from ATP. Due to the orientable character of the constituents, active suspensions can attain liquid crystalline order and can be theoretically described as active liquid crystals. Their inherently nonequilibrium dynamics causes a range of new striking effects, that in most cases have been characterized with numerical simulations, using lattice Boltzmann models (LB). In many active biological systems chirality plays an important role. Biomolecules such as DNA, actin, or microtubules form helical structures which, at sufficiently high density and in the absence of active forces, tend to self-assemble into twisted cholesteric phases. Understanding the outcome of the interplay between chirality and activity is therefore an important and timely question. Studying a droplet of chiral matter in 3D, we have found evidence of a new motility mode, where the rotational motion of surface topological defects, that arrange in a fan-like pattern. The resulting regular propulsive motion due to the underlying chirality is a striking phenomenon that can be also used in practical applications. The use of a parallel (MPI) implementation of lattice Boltzmann models, and available HPC resources, have been of fundamental importance in conducting the study. We have used different HPC clusters and among these RECAS. This allowed us to conduct a scaling test performed on different computational infrastructures.