Coating of colloidal particles by controlled precipitation of polymers

A method is suggested for the coating of micron-sized particles by polymeri c films based on surface-controlled precipitation. Polymer particles were c oated 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 irre versible coagulation. Theoretical estimations appear to provide the proper particle and polymer concentration ranges in order to achieve smooth covera ge. The optimal concentration range also was determined experimentally and agrees with the theoretical calculations. The controlled precipitation meth od of assembling thin films on colloids is compared with the layer-by-layer adsorption approach. Advantages and drawbacks of both approaches are discu ssed.