Reactive Adsorption of PS-PMMA Block Copolymers on Concave Alumina Surfaces

Abstract

The influence of pore size, relative block size, and solvent quality on the extent of diblock copolymer adsorption on alumina surfaces was determined. To this end, the block copolymer that was chosen was poly(styrene)-b-poly(methyl methacrylate) (PS-b-PMMA), in which the PMMA block strongly chemisorbs to the surface and the PS block weakly physisorbs. Several architectures (i.e., different ratios of M(n(PMMA)) and M(n)((PS))) of the PS-b-PMMA copolymers were adsorbed from various solvents onto porous alumina membranes with various pore sizes. It was determined that the diblock copolymer coverage decreased significantly as the pore size decreased, similar to the behavior of the PMMA homopolymer under the same conditions. However, the coverage decreased as the molecular weight of the anchoring block (PMMA) increased for all pore sizes, which is in contrast to the behavior of the PMMA homopolymer under the same conditions. The dependence of the coverage on the relative block size and solvent quality is analyzed on the basis of the anchor-buoy model and the deviation from it in a nonideal system. The results presented in this work are relevant to the study of block copolymer conformation in solutions and on surfaces, adsorption chromatography, and solvent sensors and controls.