Surface modification by a two-liquid process deposition of A–B block copolymers

Abstract

A surface modification technique involving a two-liquid process deposition of an A–B block copolymer (where A is more hydrophilic than B) onto hydrophobic surfaces is proposed. One of the liquids is a solvent for the block copolymer as well as for the hydrophobic solid, while the second liquid is water. The solid is immersed for a short time into a solution of the block copolymer. After its withdrawal from the solution, the polymer sheet is introduced in water. This technique allows an oriented deposition of the block copolymer such that the more hydrophobic block is deeply imbedded into the substrate, while the hydrophilic block becomes exposed to water. As a result, the polar component of the solid's surface free energy is increased while the dispersion component is decreased. By controlling the amount of block copolymers deposited, it is possible to obtain a surface which will have a low interfacial free energy with a polar medium such as blood. A contact angle technique is employed to evaluate the polar and dispersion components of the surface free energy of the solid, and to confirm that the deposited block copolymers are not extracted during long exposures to the aqueous medium. Finally, a discussion is presented, suggesting that by depositing a block copolymer containing either polyethylene-oxide or polyvinylpyrrolidone as the hydrophilic block, the biocompatibility of that surface could be enhanced through the reduction of the solid—liquid interfacial free energy, and through the inhibition of protein adsorption by the steric repulsion created by the polymeric chains.