Laser Induced Decohesion Spectroscopy: A New Technique for Measuring Polymer Interfacial Adhesion

We present a new technique, laser induced decohesion spectroscopy (LIDS), which is capable of measuring the practical work of adhesion G between a transparent polymer film and an opaque substrate. In LIDS, a laser pulse directed onto the sample creates a blister at the film/substrate interface. The blister's internal pressure depends on the laser pulse energy, and at a critical pressure the sample fractures. We have derived a theoretical analysis of this experiment based on elasticity theory and fracture mechanics, and present the results. By measuring physical variables such as the thickness of the transparent polymer, the blister radius, and the blister curvature, it is possible to deduce G between the two coatings. Here we report G for a matrix of automotive finish systems consisting of four opaque basecoats of various colors (black, white, red, green) coated with a clearcoat of various thicknesses. We expect G to be a system parameter for each basecoat independent of clearcoat thickness. The values of G for the different basecoats yield the relative adhesion of the various pigmented paint formulations.