Multiparticle collision dynamics simulations of squirmers in a nematic fluid

 We study the dynamics of a squirmer in a nematic liquid crystal using the multiparticle collision

dynamics (MPCD) method. A recently developed nematic MPCD method [Phys. Rev. E 99, 063319 (2019)]

which employs a tensor order parameter to describe the spatial and temporal variations of the nematic order

is used to simulate the suspending anisotropic fluid. Considering both nematodynamic effects (anisotropic

viscosity and elasticity) and thermal fluctuations, in the present study, we couple the nematic MPCD

algorithm with a molecular dynamics (MD) scheme for the squirmer. A unique feature of the proposed

method is that the nematic order, the fluid, and the squirmer are all represented in a particle-based

framework. To test the applicability of this nematic MPCD-MD method, we simulate the dynamics of a

spherical squirmer with homeotropic surface anchoring conditions in a bulk domain. The importance of

anisotropic viscosity and elasticity on the squirmer’s speed and orientation is studied for different values

of self-propulsion strength and squirmer type (pusher, puller or neutral). In sharp contrast to Newtonian

fluids, the speed of the squirmer in a nematic fluid depends on the squirmer type. Interestingly, the speed

of a strong pusher is smaller in the nematic fluid than for the Newtonian case. The orientational dynamics

of the squirmer in the nematic fluid also shows a non-trivial dependence on the squirmer type. Our results

compare well with existing experimental and numerical data. We also discuss early results on the dynamics of multiple squirmers in anisotropic fluids.