Cross-link Clusters: reality or fiction? A review of the state of the art,enlarged with recent AFM-data

One of the intriguing questions has always been how chemical rubber-network s really look like. One possible explanation for the fundamental difference s in properties between sulphur and peroxide cured networks, is that the cr oss-links formed by either of the two tend to cluster leading to what we wi ll call network heterogeneity. The paper gives an overview of past and rece nt attempts to characterize this heterogeneity of vulcanisation networks, R ecent data generated with Atomic Force Microscopy on sulphur, peroxide and radiation cured EPDM shed new light on this fundamental question. Grainy st ructures are observed, as were seen before with TEM-microscopy, which can t entatively be interpreted in terms of heterogeneities of the pertinent cros s-linked networks.