On the measurement of “tack” for adhesives

Abstract

One of the tests for determining the bond strength of adhesives involves measuring the force or the work required to pull apart two surfaces separated by a thin film of adhesive. The pull-off force is measured via the bending of a cantilever that connects one of the surfaces to a motor controlled vertical traverse. Although such tests are routinely performed, little attention has been paid to the understanding of force measurements and their relation to the dynamics of the instrument. Specifically, the measured force versus gap profile for the pull-off process is different from that measured when the same adhesive is compressed between two approaching surfaces. Through experiments on Newtonian liquids and a simple analysis involving lubrication analysis of thin liquid films, we show that the hysteresis in measurements results from a combination of an instrument-related instability and the nucleation and collapse of cavitation bubbles in the flow field.