Effects of Surface Modification on the Structure of Adsorbed Block Copolymer Monolayers

Abstract

ABSTRACTImproving the processing and formability of ceramic components prior to firing (as green bodies) requires an enhanced understanding of how the polymeric binder components function. We report on the role of surface energetics on the structure of the copolymeric monolayers formed via adsorption from solution. Also, results on the effects of surface energetics on the kinetics of the adsorption are reported. A silicon wafer with an oxide layer is used as the surface and adsorption takes place from toluene. Surface energetics are varied by treatment of the oxide surface with a series of silane coupling agents which contain either amine, epoxide, or vinyl functional groups. The block copolymers used consist of relatively short poly(ethylene oxide) (PEO) blocks and much longer polystyrene (PS) blocks. Ellipsometry is used to determine the grafting density, σ (chains/nm2), and Fourier Transform Infrared spectroscopy is used to investigate the copolymer on the surface. It is seen that the time required to reach equilibrium increases as the strength of the interaction between the copolymer and the surface increases. Also, the diblock copolymers appear to obey the scaling laws proposed by Marques and Joanny on all the surfaces studied. ( i.e., σ ∝ 1/NA, when the copolymer is symmetric or moderately symmetric and σ ∝ 1/β2, when the copolymers are asymmetric, where NA is the number of segments of the adsorbing block and β is the ratio of the size of the nonadsorbing block to that of the adsorbing block.)