Polymer Adhesion vs Substrate Receptor Group Density

The effect of substrate receptor group density on polymer adhesion was investigated. Model substrates with varying −NH 2 density on Al 2 O 3 were prepared by a self-assembly of mixed amine-terminated silanes and methyl-terminated silanes. The model polymer was synthesized through a high-pressure carboxylation of polybutadiene. The polymer adhesion was determined by the fracture energy of the polymer−solid interfaces, G IC, from a T-peel test. The strong acid−base interactions between the polymer sticker groups (−COOH) and the substrate receptor groups (−NH 2 ) at the interface caused an interesting fracture energy variation in the range of annealing times examined. At short time, G IC increased as the density of substrate receptor groups increased. However, at long time, G IC increased up to 30% receptor group coverage and then decreased with increasing coverage. A maximum in G IC occurred because the adhesive interface strength increased between the solid surface and the adsorbed chains, and simultaneously the cohesive interface strength decreased between the adsorbed chains and the neighboring free chains with increasing density. Failure occurred at the weaker of the two interface strengths. In this paper, it was shown that the polymer adhesion was not a monotonic function of the surface energetics.