Self-assembly of carboxylated latex particles at charged surfaces: influences of preparation conditions on the state of order of the monolayers

A detailed study of the electrostatic adsorption of carboxylated latex particles onto positively charged substrates is presented. The particle size is 440 nm in diameter. The influence of various parameters such as pH, concentration and temperature of the dispersion on surface coverage and order formation in the monolayer is described. The adsorption was studied using scanning electron microscopy. It was found that the concentration of the dispersion had no effect on the final surface coverage C-s, but a high concentration favoured a rapid adsorption. High temperatures favoured adsorption as well as desorption so that strongly fluctuating C-s values were obtained, while at low temperature the adsorption rate was strongly diminished. In neutral dispersions the maximum C-s value was about 30% and the number average N-a of particles per aggregate was 5-6, independent of the preparation conditions. At pH values below 4, maximum C-s values up to 65% and N-a values up to 15 were found. Possible origins of the pH dependent adsorption are discussed in terms of a variation of the charge density of particle shell and substrate surface. The time dependence of the particle adsorption has also been studied. It is shown that particles are adsorbed as individual spheres, while aggregates are subsequently formed at the substrate surface. (C) 1999 Elsevier Science S.A. All rights reserved.