CONNECTOR CHAIN AGGREGATION EFFECTS IN ELASTOMER-ELASTOMER ADHESION PROMOTION

We consider the effects of chain aggregation during pull out on the ad hesion of elastomer-elastomer surfaces fortified with interfacial conn ector chains. For the case of monodisperse end-grafted A homopolymer c hains at an A/B elastomer interface, we show that lateral aggregation of connector chains in the gap into tethered micelle-like structures o ccurs at a characteristic length zeta similar to 1/sigma set by the gr afting density sigma. This is a first-order transition, characterized by a metastable single-fibril state separated from a state of arbitrar ily large aggregates by a gap-size dependent energy barrier. As a resu lt, the threshold fracture toughness G(0) as a function of sigma is pr edicted to have a plateau reflecting a regime of spontaneous connector chain extraction induced by aggregation. Experimental access to this plateau depends on the rate of A/B elastomer separation, due to the sl ow kinetics of the aggregation instability. For the case of polydisper se connector brushes, aggregation processes are predicted to occur on many length scales, leading to a possible enhancement of adhesion prom otion compared with monodisperse brushes. We briefly highlight this ef fect with several examples of polydisperse connector brushes and pseud obrushes.