Apparatus-specific analysis of fluid adhesion measurements

Abstract

A thin film of viscous liquid between two solids acts as an adhesive due to the large force resisting separation of the solids. This effect is exploited in pressure-sensitive adhesive bonds. One method of investigating such bonds is to use a probe tack test in which a rigid probe is indented into a thin adhesive layer coating a rigid flat base. These experiments are characterized by two quantities: the total work of separation, that is, the work done in extracting the rigid punch from the adhesive film, and the peak adhesive force, otherwise known as the adhesive strength. Little effort, however, has been spent on understanding the connection between these quantities and the apparatus used to measure them. In this article we shall study the simplest case of fluid adhesion where a spherical probe and flat are bound by a high viscosity Newtonian polymer melt (polydimethylsiloxane or polybutene) and examine the role of apparatus-specific parameters in determining the measured adhesive strength and work of separation. We shall show how a dimensionless master-curve can be derived to capture the dependence of the adhesive strength on the testing regime. Specific attention is paid to the effect of system compliance on the adhesion, as introduced by the presence of a compliant load cell used to measure the adhesive force. A relationship linking the adhesive strength of a Newtonian film and the work of separation is also presented.