SURFACE-PROPERTIES OF PLURONIC-COATED POLYMERIC COLLOIDS

With the help of field-flow fractionation, photon correlation spectros copy, and electron spin resonance techniques, as well as more conventi onal labeling approaches, we have accomplished the analytical characte rization of the adsorption complexes formed between, on the one hand, a series of selected triblock polymeric surfactants with comparable le ngths of their central poly(propylene oxide) (PPO) block but with vary ing poly(ethylene oxide) (PEO) block lengths, and on the other a serie s of differently sized polystyrene colloids. For a given surfactant, i t was found that both surface concentrations and adlayer thicknesses a re strongly related to the particle size, such that smaller particles take up fewer polymer molecules per unit area than the larger ones. Th e reduced crowding around each PEO chain results in thinner adlayers a nd higher chain mobilities. In adsorption complexes involving 69-nm po lystyrene particles, the adlayer thickness is close to the diameter ca lculated for the free PEO chain in aqueous solution. In addition, for particles of a given size, it is the size of the surfactant's hydropho bic center block (PPO), rather than its flanking tails (PEO), that det ermines the surface concentration. Thus, triblocks of similar PPO size showed comparable surface concentration, while the longer PEO chains were associated with thicker adlayers as well as greater chain dynamic s.