A method for reversible control over nano-roughness of colloidal particles

Colloidal particles often display a surface topography that is smooth down to the nanometer scale. Introducing roughness at this length scale can drastically change the colloidal interactions, adsorption at interfaces and bulk flow behavior. We report on a novel, simple method to induce and control nano-scale roughness on (water based) polymer latex colloids. Reducing the amount of dissolved gases in the aqueous phase from the electrolyte solution surrounding the particles, generates self-structured surface asperities with an amplitude that can be tuned via temperature and repetition of the treatment. Due to the viscoelastic nature of the polymeric asperities, a mild thermal treatment below the glass transition temperature can be used for nanostructure relaxation, so that the particles can recover their original topography, making this method fully reversible. Roughness can thus be controlled without affecting the chemical composition of the colloidal surface. Experiments for varying particle size, polymer type and surface chemistry suggest a broad applicability of our method.