Tailoring the Surface Properties of Silicone Elastomers to Improve Adhesion of Epoxy Topcoat

Two modification routes have been applied to control the surface properties of spin-coated and screen-printed poly(dimethylsiloxane) (PDMS) layers and to improve their adhesion to a photopatternable epoxy resin topcoat. The first route is based on the optimization of low-pressure oxygen and ammonia plasma treatments to generate acidic or basic reactive surface groups capable of forming covalent bonds with the epoxy groups of the topcoat. The main disadvantage of these fast and practicable processes is the instability of the modification effects. Therefore, the plasma-activated PDMS surfaces were used for subsequent 'grafting to' procedures with reactive polymers. The functional surface groups generated by oxygen or ammonia plasma treatments of PDMS (SiOH, OH, COOH and NH2) were used as anchors to graft epoxy group containing homopolymers and copolymers as well as maleic anhydride copolymers. All of grafted materials provided thin barrier layers that prevented the hydrophobic recovery of the modified PDMS surface. A very promising concept to tailor the surface properties of PDMS is the grafting of epoxy group containing methacrylate copolymers. Depending on the molar ratio of the monomers used the epoxy groups will act mainly as anchor groups. The surface properties of the grafted layer will, then, be controlled by the functionality of the second comonomer. In order to study the effect of the surface modifications on the surface properties of the silicone elastomer layers we used a combination of various surface-sensitive characterization techniques, namely, X-ray photoelectron spectroscopy (XPS), contact angle and electrokinetic measurements as well as roughness analysis. Additionally, pull-off tests were carried out to quantify the effect of the surface modification on the adhesion between an epoxy resin and PDMS. (C) Koninklijke Brill NV, Leiden, 2011