Mesoscopic simulations of active nematics

Abstract

Coarse-grained, mesoscale simulations are invaluable for studying soft condensed matter because of their ability to model systems in which a background solvent plays a substantial role but is not the primary interest. Such methods generally model passive solvents; however, far-from-equilibrium systems may also be composed of complex solutes suspended in an active fluid. Yet, few coarse-grained simulation methods exist to model an active medium. We introduce an algorithm to simulate active nematics, which builds on multiparticle collision dynamics (MPCD) for passive fluctuating nematohydrodynamics by introducing dipolar activity in the local collision operator. Active nematic MPCD (AN-MPCD) simulations not only exhibit the key characteristics of active nematic turbulence but, as a particle-based algorithm, also reproduce crucial attributes of active particle models. Thus, mesoscopic AN-MPCD is an approach that bridges microscopic and continuum descriptions, allowing simulations of composite active-passive systems.

Active turbulence and spontaneous phase separation in inhomogeneous extensile active gels

“…equilibrium transition between a quiescent suspension and a state where activity fuels continuous motion [9][10][11][12][13] . For sufficiently large activity, the flow and orientation patterns of the spontaneously flowing state are seemingly chaotic, and the associated state is known as "active turbulence" [14][15][16][17][18][19] . In active turbulence, active gels self-organise into a random arrangement of vortices.…”

“…[9][10][11][12][13] For sufficiently large activity, the flow and orientation patterns of the spontaneously flowing state are seemingly chaotic, and the associated state is known as ''active turbulence''. [14][15][16][17][18][19] In active turbulence, active gels self-organise into a random arrangement of vortices. Experiments and theories suggest that in the nematic phase these vortices have a typical length scale, arising from the competition between activity and elasticity, 14 while recent work points to important fundamental differences between active turbulence and its more widely studied passive counterpart.…”

Spontaneous motion of a passive fluid droplet in an active microchannel

“…[16][17][18][19][20] Some of the best known experimental realizations of such active materials are actomyosin solutions 21,22 and suspensions of microtubules and kinesin, 7,23 which are soft fluids comprising force dipoles exhibiting a long range orientational order typical of liquid crystals. [24][25][26] The former is an example of contractile material since the dipolar forces (exerted by the myosin) are directed towards the center of mass, whereas the latter pertains to extensile fluids. From a technological perspective, active gel droplets are gaining significant interest as model systems for studying the dynamics of micro-organisms, such as cells, [27][28][29][30][31] and for designing artificial microswimmers.…”

Hierarchical defect-induced condensation in active nematics

“…20 Systems exhibiting dense, purely nematic lanes have been thoroughly investigated by both simulations and hydrodynamic theories. 13,[21][22][23][24][25][26][27][28] As for half-integer topological defects, the common paradigm states that they are absent in dilute self-propelled active nematics, 29 but fundamental exclusion criteria for their existence have not been given. In fact, no steady-state topological defects have yet been found in this subclass of strongly phase-separated active matter.…”

“…20 Systems exhibiting dense, purely nematic lanes have been thoroughly investigated by both simulations and hydrodynamic theories. 13,21–28…”