8th Liquid Matter Conference September 6-10, 2011 Wien, Austria ...

P10.12Tue 611:23-14:00Simulations of microrheology experiments in activefluidsGiulia Foffano, 1 Davide Marenduzzo, 1 Juho Lintuvuori, 1 and Michael Cates 11 University of Edinburgh, Mayfield Road, EH9 3JZ, Edinburgh, United KingdomWe present numerical results concerning microrheology measures on active fluids. We use a LatticeBoltzmann method to simulate the drag of a particle in active liquid crystals (lc) -both contractileand extensile-. We find that, in general, contractile nematic lc oppose larger resistance to flow thantheir passive correspondent, and that the reverse happens when extensile active matter is considered.We pull a passive spherical colloid parallel and orthogonal to the director. We find that thehydrodynamic drag force scales linearly with the particle velocity, but superlinearly with its radius,in strong violation of Stokes law. This effect is stronger when the particle is pulled parallel to thedirector and almost absent when it is pulled orthogonally to the director for a contractile activefluid. The reverse is true in the extensile case. We explain this through a simple pictorial argument,according to which the observed effect is mainly local. This would preclude the possibilityof investigating bulk properties of active matter through microrheology experiments, that wouldnonetheless represent a direct benchmark to our numerical results. We moreover present somepreliminary intriguing results concerning the dynamics of a number of small particles embeddedin a spontaneously flowing active fluid, both in the contractile and in the extensile case.12