What is the surface chemistry of the particle?
The polystyrene microparticles have a negative surface charge derived from sulfate initiator end groups and adsorbed anionic surfactant. Carboxyl-modified microparticles have additional negative charge from bound carboxyl groups, and thus are much more hydrophilic. When using microparticles, note that colloidal stability will be reduced by any additive that lowers the net charge on the particle surface.
