Novel functional brush coatings: applications to microfluidic devices

Thin polymeric coatings applied to the surface of different materials can dramatically improve the properties of lab-on-chip devices as they allow to control the interaction of the surface with its environment. Examples of interfacial phenomena that can be controlled by a polymeric coating include the electroosmotic flow and the adsorption of macromolecules in microchannels. Polymeric coatings can be obtained by “grafting-onto” or by a “grafting from” approach. The former technique that involves reacting an appropriate functional group of the polymer with the surface results in low graft densities as the steric hindrance imposed by the chains, already grafted to the surface, obstacles the diffusion of the incoming polymer chains. In contrast, the “grafting from” method leads to higher graft densities as the existing grafted polymers does not hinder the diffusion of the small-sized monomers on the surface. The work presented here was aimed at developing high density, brush coatings. The goal has been achieved by combining surface-initiated and a controlled polymerization technique, the so called Reversible Addition-Fragmentation Chain Transfer (RAFT) polymerization (Fig.1). The versatility and the simplicity of the RAFT process to control the polymerization of a wide variety of monomers were explored to prepare living polymer chains with controlled molecular weight and polydispersity. The living character of the chains allows the formation of a di-block architecture. A novel RAFT agent bearing a silanating moiety was synthesized and anchored onto the surface on which a mono-block and di-block brush architecture were obtained (Fig. 2). In this work we report on two applications of brush coatings obtained by RAFT polymerization: suppression of electroosomtic flow in capillary electrophoresis and covalent attachment of biological molecules to the active area of sensing devices.