Colloids in cholesteric

I'll present a serie of Lattice Boltzmann simulations studies of colloidal particles immersed into cholesteric liquid crystal. I show that the defect structure around the particle depends crucially on the ratio between particle size and cholesteric pitch i.e. the diameter to pitch ratio D/P . Both, tangential and homeotropic, surface anchoring conditions will be discussed. I then model an ideal active microrheology experiment, in which the colloid is pulled through the liquid crystal medium and its force-velocity relation is analyzed. This is done both perpendicular and along the helical axis. The main result is that, surprisingly, the effective viscosity along the helical axis, in the small (but not infinitesimal) Ericksen number regime, depends on the size of the probe. This is tantamount to an effective drag which, along the cholesteric helix, is approximately proportional to the square of the particle size, thereby providing a striking example of giant violation of the Stokes formula.