Field-flow fractionation in the determination of rates of surfactant adsorption to colloidal substrates

The biomedically interesting process of coating surfaces with poly(ethylene oxide)-containing surfactants has prompted a study of the kinetics of adsorbing Pluronic(R) F108 on model substrates consisting of polystyrene nanospheres. The sedimentation field-flow fractionation method (sdFFF) is found to offer an accurate and precise way to quantify the mass uptake without the need for potentially perturbing labeling reactions. The pseudo-irreversible adsorption from a 4% solution of the polymeric surfactant is found to be 80% complete within the first hour, with the remaining surface population proceeding to completion during an additional nine hour period. These findings are verified by a more conventional method based on chemical analysis. The potential problems of basing the rate analysis on measured levels of depletion, as opposed to the direct assessment of uptake provided by sdFFF, are discussed.