Coating of colloidal particles by controlled precipitation of polymers

A method is suggested for the coating of micron-sized particles by polymeric films based on surface-controlled precipitation. Polymer particles were coated by dextran and DNA in a water/ethanol mixture containing multivalent cations. A theoretical model for depositing polymers on colloidal particles is presented using the Smoluchowski solution for diffusion-controlled irreversible coagulation. Theoretical estimations appear to provide the proper particle and polymer concentration ranges in order to achieve smooth coverage. The optimal concentration range also was determined experimentally and agrees with the theoretical calculations. The controlled precipitation method of assembling thin films on colloids is compared with the layer-by-layer adsorption approach. Advantages and drawbacks of both approaches are discussed.