Adhesion of Silica and Block Copolymer Toughened Epoxy Composites

The effect of the size and surface functionalization of silica particle additives on the bulk and adhesive mechanical properties of neat and poly(ethylene oxide)-b-poly(ethylene-alt-propylene) block copolymer (BCP)-modified epoxies was evaluated. Three types of silica particles were investigated: microscale (diameter = 500 nm–4 μm) particles with and without phenylsilane functionalization and nanoscale particles (diameter = 140 nm) with phenylsilane functionalization. Silica particles were dispersed individually or together with block copolymers in the epoxy monomers and cured. Tensile tests revealed that the incorporation of silica increased the modulus of the composites, regardless of surface functionalization and particle size. The fracture toughness, measured by compact tension, also increased substantially when BCP was added but only modestly when each of the various silica additives was dispersed in the epoxy. Together, silica and block copolymer additives enhanced the fracture toughness, without significant effects from silica size or surface functionalization. Single-lap-joint shear tests with aluminum showed anapproximately 50% increase in adhesion strength when block copolymer micelles were dispersed in the cured epoxy, but little impact was realized from any of the silica particles studied. Failure mechanisms and the observed trends are discussed.