PHYSICAL ADHESION OF RUBBER TO GLASS - CROSS-LINK DENSITY EFFECTS NEAR EQUILIBRIUM

Pre-cross-linked rubber adheres to glass mainly by physical interactions (van der Waals' bonds). Nevertheless, the measured adhesion is often greater than expected even at low separation rates. By adopting the Johnson, Kendall and Roberts (JKR) technique for assessing adhesion between a rubber hemisphere and a glass slide, it is shown that the apparently stable equilibrium state depends on the manner in which initial contact is obtained. Although the work of adhesion due to osculating contact is close to the Dupre value, that obtained following the application of direct pressure to the system increases with the average inter-cross-link molecular weight, M(c), of the elastomer. The kinetics of evolution towards equilibrium are considered using a simple dynamic energy balance argument.