hysteretic nature of the soft substrate and the strain cycle It has been shown over the last few years how the wetting (or undergone (4). Following a number of experimental studies dewetting) of a soft, elastomeric substrate can be markedly af- (9)(10) it is now well established that the wetting ridge, fected by local deformation of the solid near the triple line, due typically of the order of tens of nanometers in height, can to the component of liquid surface tension acting perpendicularly have such important consequences that viscous dissipation to the (undeformed) solid surface, i.e., the ''wetting ridge.'' Since within the liquid becomes virtually negligible.
the degree of cross-linking of an elastomer affects its mechanical
The process of ''viscoelastic braking'' described above properties, we have undertaken a study of the influence of crosshas certain parallels with the dynamic adhesion of elastolinking on (de)wetting behavior. Using a silicone rubber in four mers. When, for example, a rubber strip is peeled from a states of cross-linking, we have observed that triple-line motion of tricresyl phosphate increases in speed with degree of cross-linking. rigid substrate, the effective, or apparent, work of adhesion, Two principal factors influence this behavior, both being directly W, is usually much greater than the intrinsic, or reversible, linked to average intercross-link molecular weight, M c . A decrease energy of adhesion, W 0 , given by the Dupre ´equation:
in M c increases elastic modulus and therefore decreases the importance of the wetting ridge, whilst also lowering the dissipative
properties of the polymer. The combined effects lead, in the case studied, to a linear relationship between dewetting speed and elaswhere g 1 and g 2 represent the surface free energies of the tomeric elastic modulus to the power 10/3.