SURFACE-PROPERTIES OF PLURONIC-COATED POLYMERIC COLLOIDS

With the help of field-flow fractionation, photon correlation spectroscopy, and electron spin resonance techniques, as well as more conventional labeling approaches, we have accomplished the analytical characterization of the adsorption complexes formed between, on the one hand, a series of selected triblock polymeric surfactants with comparable lengths of their central poly(propylene oxide) (PPO) block but with varying poly(ethylene oxide) (PEO) block lengths, and on the other a series of differently sized polystyrene colloids. For a given surfactant, it was found that both surface concentrations and adlayer thicknesses are strongly related to the particle size, such that smaller particles take up fewer polymer molecules per unit area than the larger ones. The reduced crowding around each PEO chain results in thinner adlayers and higher chain mobilities. In adsorption complexes involving 69-nm polystyrene particles, the adlayer thickness is close to the diameter calculated for the free PEO chain in aqueous solution. In addition, for particles of a given size, it is the size of the surfactant's hydrophobic center block (PPO), rather than its flanking tails (PEO), that determines 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 dynamics.