Effect of electrostatic interaction between particle and substrate on the colloidal layer structure prepared by convective self-assembly

Abstract

By soap-free emulsion polymerization using an anionic or a cationic initiator, the poly(methyl methacrylate) (PMMA) particles of a sub-micron size with negative or positive charge were prepared and then employed for the colloidal layer fabrication through the convective self-assembly (CSA) using a glass substrate to investigate the effect of the electrostatic interactions between the particle and the substrate on the resulting layer structures. In the case of the negatively charged PMMA particle, the electrostatic repulsions between the particle and the substrate as well as between the particles led to the formation of the ordered close-packed colloidal layers. When the CSA with the positively charged PMMA particles were carried out at low particle volume fraction, the colloidal layers with disordered structure were formed due to the electrostatic attraction between the particle and the substrate. With an increase in the particle volume fraction, the surface structure of the colloidal layers of the positively charged PMMA particles changed from disordered to ordered while the internal structure remained disordered. This is probably because the electrostatic repulsion that the undeposited particles receive from the particles already deposited on the substrate becomes dominant over the electrostatic attraction from the substrate.