We simulate a colloidal particle (radius R) in a cholesteric liquid crystal (pitch p) with tangential order parameter alignment at the particle surface. The local defect structure evolves from a dipolar pair of surface defects (boojums) at small R/p to a pair of twisted disclination lines wrapping around the particle at larger values. On dragging the colloid with small velocity v through the medium along the cholesteric helix axis (an active microrheology measurement), we find a hydrodynamic drag force that scales linearly with v but superlinearly with R-in striking violation of Stokes' law, as generally used to interpret such measurements.
@article{arxiv.1101.1487,
title = {Colloids in Cholesterics: Size-Dependent Defects and Non-Stokesian Microrheology},
author = {J. S. Lintuvuori and K. Stratford and M. E. Cates and D. Marenduzzo},
journal= {arXiv preprint arXiv:1101.1487},
year = {2011}
}