ELECTROSTATIC AND STERIC INTERACTIONS IN PARTICLE DEPOSITION STUDIED BY EVANESCENT-WAVE LIGHT-SCATTERING

The kinetics of deposition of bare latex particles onto bare collector surfaces and poly(ethylene oxide)- (PEO-) coated latex particles onto PEO-coated collector surfaces was studied by evanescent wave light sc attering. This allowed for the study of the effects of electrostatic a nd steric interactions affecting particle deposition. The experiments considered the effects of colloid particle surface morphology, solutio n salt concentration, and hydrodynamic layer thickness of the adsorbed polymer (PEG) on both the colloidal particles, as measured by photon correlation spectroscopy, and the collector surface, as measured by ev anescent wave spectroscopy. From the data it was found that bare and s mooth latex particles adsorb much more strongly onto collector surface s than ''hairy'' latex particles, which have long copolymer chains, su ch as itachonic acid, grafted onto their surfaces. The rate of deposit ion of uncoated latex particles onto collectors was found to be about 10 times larger than that of the analogous PEG-coated latex particles. This difference became more pronounced as the polymer molecular weigh t was increased. These results indicated that the thicker the adsorbed polymer layer, the stronger the steric force preventing deposition of the polymer-coated colloidal particles onto the collector surface. Wh en the combined ellipsometric layer thickness of the particles and the collector surface exceeded a critical value, found to be about 15 nm, no particle deposition onto the collector surface was possible. The d epth of the minimum energy required to cause deposition was calculated to be about half a kT unit. (C) 1995 Academic Press, Inc.