Studies on the effect of particle size and copolymer polydispersity on the adsorption of a PEO/PPO/PEO copolymer on PS latex particles

A commercial block copolymer poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) sold under the trade name of Pluronic F108 was adsorbed on polystyrene (PS) latex particles. The adsorption isotherm of the copolymer on the PS latex particles was measured using an indirect method (colorimetric depletion). Factors such as the diameter and the concentration of the PS latex particles as well as the concentration of the copolymer were investigated. The presence of a copolymer fraction with a small molecular weight in the F108 copolymer modified significantly the adsorption isotherms: a slanted linear domain appeared in the intermediate range of copolymer concentration. This change was in accordance with the predictions of previously described models. Contrary to previous findings, there was no apparent effect of particle size on F108 surface density and layer thickness. This result was confirmed by measurements performed with a direct method (sedimentation field-flow fractionation). However, the initial slope of the adsorption isotherm was increased by an increase of particle size and a decrase of particle concentration. Moreover, the maximum adsorbed amount was decreased by an increase of particle concentration. The latter observations are believed to be due to particle aggregation.