Looking at Rubber Adhesion

Rubber has been employed in contact with a variety of surfaces for decades, yet the adhesional mechanisms involved are not fully understood. This article describes fundamental investigations carried out over the last decade. Emphasis is placed upon the use of optical techniques for looking directly at the contact area rubber makes with another surface. The interpretation is based upon a rate-dependent surface energy approach. In this way it is possible to predict the level of peel adhesion between surfaces, for example, when a ball rolls on smooth rubber. Other examples treated in the same way are the time for detachment of a ball from a smooth rubber track under gravity, its resilience when bounced on the track, and its friction when slid over the track. The influence of surface roughness, electrostatic forces, surface bloom, and humidity are considered, together with rubber compound variables such as glass transition temperature, crosslink density, and fillers. The central theme is that the adhesional mechanisms all physically depend upon the product of surface properties and bulk viscoelasticity of the solids in contact.