Adsorption of amphiphilic copolymers on hydrophobic particles in aqueous media

The adsorption properties of two rake-type polydimethylsiloxane-graft-polyether copolymers and two poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) block copolymers (Pluronic F108 and F127) on carbon black (CB) nanoparticles dispersed in water have been investigated. The adsorption on CB obeys the Langmuir isotherm at low filtrate concentrations (below CMC). At higher filtrate concentrations, a sharp increase in adsorbed amount is observed for both siloxane copolymers considered here. The adsorbed layer thickness was determined by dynamic light scattering. The adsorbed layer thickness of the copolymers is influenced by the copolymer concentration. Temperature also plays an important role in determining the adsorbed layer thickness and structure in the case of Pluronic block copolymers. Below CMC or CMT the added copolymer molecules contribute to an increase in the adsorbed layer thickness by forming a monolayer. Above CMC or CMT SANS experiments, performed under contrast matching conditions where either the copolymer or the CB particles were rendered "invisible", confirmed that the adsorbed layer has structure and dimensions similar to those of copolymer micelles present in aqueous solution in the absence of CB. This was true for both the siloxane and the PEO-PPO-PEO copolymers. Adsorption of siloxane copolymer onto talcum particle obeys the Langmuir isotherm in the studied concentration range.