ADHESION-INDUCED DEFORMATIONS OF POLYURETHANE SUBSTRATES IN CONTACT WITH SPHERICAL GLASS PARTICLES - THE EFFECT OF PARTICLE-SIZE ON THE RADIUS OF CONTACT

Spherical glass particles having radii between approximately 0.5 and 100-mu-m were deposited onto a polyurethane substrate and the radii of contact, resulting from the adhesion forces between the particles and the substrate, were determined using SEM. For particles having radii less than approximately 5-mu-m, it was found that the contact radius varied as the particle radius to the 0.75 power. In addition, large menisci, presumably resulting from tensile interactions, were observed. For particles having radii between 5 and 60-mu-m, the contact radius varied as the particle raidus to the 2/3 power. Stretching of the substrate was also observed for particles having radii of approximately 100-mu-m. This is probably a harbinger of the impending separation of the particle from the substrate, due to gravitational forces. The thermodynamic work of adhesion was calculated from the data and the results were compared with the predictions of several theories of particle adhesion.