Kinetics of the Adsorption of a Polystyrene−Poly(ethylene oxide) Block Copolymer on Silica:  A Study of the Time Dependence in Surface/Segment Interactions

The kinetic aspects of polymer adsorption on surfaces are important in many practical applications. Usually, the dynamic conformational behavior of an adsorbed polymer is not measured directly but is interpreted from changes in the thickness of the layer or in the adsorbed amount. Infrared spectroscopy is now used to present direct evidence of the dynamic behavior of segment/surface interactions. The time dependent behavior of the segment/surface interactions of a PS−PEO (polystyrene−poly(ethylene oxide)) block copolymer adsorbed on silica particles is reported. Three distinct zones are identified. In the first region, the polymer adsorbs on vacant sites on the surface and does not undergo any rearrangement. The relative number of surface-anchored PEO and PS segments is dictated by the differential sticking enthalpies rather than the geometric size of each block. In the second region, the surface sites are fully covered and fresh polymer arriving at the surface is accommodated by a rearrangement of the existing adsorbed polymer layer. The more weakly attached PS segments are displaced by PEO units of the incoming chains. In a final stage, a slow rearrangement of the adsorbed polymer layer occurs. The adsorbed PS segments are sacrificed for additional adsorbed PEO segments, and the adsorbed layer tends toward the brush conformation.