Confining acrylate-benzophenone copolymers into adhesive micropads by photochemical crosslinking

Abstract

The creation of micrometer adhesive pads by dewetting and subsequent crosslinking of a benzophenone-acrylatecopolymer onto a substrate that is lithographically patterned with a benzophenone-fluoropolymer, has beeninvestigated in relation to the adhesive performance of either continuous or patterned adhesive interlayers. First,the intrinsic adhesive properties of a n-butyl acrylate methacryloyl-4-oxy-benzophenone copolymer were in-vestigated as a function of composition (4, 10, 20 mol-% benzophenone), concentration (1–5 mg/ml) andphotochemical cross-linking conditions (1–120 min). Under optimized conditions, the benzophenone-acrylateprovides a good balance of adhesive strength and ductility at low concentrations of photo-reactive groups andperforms better than reference adhesives. The latter can be understood by the formation of a dense polymernetwork with different degree of crosslinking resulting in high stiffness. Second, the benzophenone-acrylate wassuccessfully confined into adhesive pads through spontaneousflow and pinning of the contact line of the liquidadhesive at the hydrophobic/hydrophilic interface of chemically patterned substrates, followed by dimensionalstabilization of the droplet shape through partial crosslinking. The adhesive strength of interfaces with discreteadhesive pads (diameter 2000 to 500μm) is significantly higher than continuous adhesive interlayers and isconfirmed by cohesive failure of the adhesive.