Mechanical effects of diblock copolymer at interfaces

Abstract

The effects of a thin layer of diblock copolymer on the adhesion between a glassy polymer and two different materials, an elastomer and a silicon wafer, have been examined. The glassy polymer was polystyrene and the elastomer was polyisoprene. A polystyrene-b-polyisoprene copolymer was employed at the polyisoprene-polystyrene interface whilst a polystyrene-b-polymethylmethacrylate copolymer was used at the polystyrene-silicon interface. The toughness of the glassy-rubbery interface depended on the length of time at room temperature the polyisoprene of the copolymer diffused into the crosslinked polyisoprene homopolymer, when the two were not crosslinked together, but reached a maximum toughness enhancement of a factor of 4. The diffusion process was very slow because the block polyisoprene was tethered to the polystyrene and the polyisoprene homopolymer was crosslinked. Much greater joint toughnesses were found when the block and homopolymer polyisoprene were crosslinked together. The toughness of an interface between polystyrene and a silicon wafer (SiO 2) was increased from about 1 J/m 2 with no diblock present to about 40 J/m 2 with an organized diblock layer at the interface. Copyright © 1992 by Marcel Dekker, Inc.