The adsorption mechanism of a series of PEO-PPO-PEO triblock copolymer has been studied at the water/hydrophobic interface and water/Au interface by Ellipsometry and Surface plasma resonance (SPR). The copolymer forms monolayer with the middle PPO block anchoring at the surface and the PEO groups either anchoring at the surface or protruding into aqueous phase. Two plateaus have been observed in the adsorption isotherms. At very low bulk concentration, the surface coverage is low and that the PEO segments of the adsorbed copolymer is believed to be fully extended. As the surface coverage increases with the increase of bulk concentration, the extended EO segments on surface become saturated and reach the first pseudo-plateau of the isotherm. By further increasing the bulk concentration the oversaturated EO segments at the interface will then be gradually forced away from the surface and extruded into the bulk solution. Since the free space released by the desorbed EO segment will allow for further adsorption of the copolymer, one observes a 2nd stage increase in the adsorption isotherm. As the coverage increases, EO is increasingly forced away from the surface and finally formed a brush structure provided the bulk concentration and the adsorption affinity of the Pluronics are both high enough. The adsorption state of PPO segment on various surfaces is mainly determined by its affinity with surfaces. The stability of the adsorbed film is also studied by series desorption tests.
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