  We show that topological defects in an ion-doped nematic liquid crystal can
be used to manipulate the surface charge distribution on chemically
homogeneous, charge-regulating external surfaces, using a minimal theoretical
model. In particular, the location and type of the defect encodes the precise
distribution of surface charges and the effect is enhanced when the liquid
crystal is flexoelectric. We demonstrate the principle for patterned surfaces
and charged colloidal spheres. More generally, our results indicate an
interesting approach to control surface charges on external surfaces without
changing the surface chemistry.
