Adhesion-induced deformations of a polyurethane substrate in contact with cross-linked polystyrene spheres, having diameters ranging from less than 2 μm to approximately 12.5 μm were observed using scanning electron microscopy. The diameters of the contact areas were measured from the micrographs. It was found that the contact radius varied as the particle radius raised to the 0.75±0.05 power. Experimental results are compared to the predictions of various adhesion models. The results are also discussed in terms of the Dupré work of adhesion.

The time dependence of the surfaceforceinduced contact radius between glass particles and polyurethane substrates: Effects of substrate viscoelasticity on particle adhesion Conduction of heat from a planar wall with uniform surface temperature to a monodispersed suspension of spheresThe contact radii between polystyrene spheres, having diameters between approximately 1.5 and 12 pm. and polished silicon wafers, arising from adhesion forces, were determined using scanning electron microscopy. It was found that the contact radius varied approximately as the square root of the particle radius. This dependence is consistent with nonelastic response models of adhesion, such as those proposed by Krupp [H. Krupp, Adv. Colloid Interface Sci. 1. III (1967) J and by H. M. Pollock, Acta Metal!. 32, 1323 ( 1984) J. but is inconsistent with various elastic response models which assume Hertzian deformations. The experimentally determined contact radii are also compared to those obtained for polystyrene spheres on a polyurethane substrate [D. S. Rimai, L. P. DeMejo, and R. C. Bowen, J. App!. Phys. 66, 3574 (1989)].

The adhesion-induced contact radius and meniscus height between soda-lime glass particles and three highly compliant polyurethane substrates (Young's modulus between 4 kPa and 0.7 MPa) were measured using scanning electron microscopy as a function of particle radius. Two distinct power-law exponents were found. A value of about 2/3, which is in good agreement with the predictions of the JKR theory (Johnson, K. L.; Kendall, K.; Roberts, A. D. Proc. R. Soc., London Ser. A 1971, 324, 301), was found for larger particles. However, the experimentally obtained exponent for smaller particles was found to be approximately 3/4. The present results are compared with the predictions of the large-scale deformation model of Maugis (Maugis, D. Langmuir 1995, 11, 679) as well as a self-consistent surface-energy model. Although both models contain some interesting features, neither theory can fully account for the observed behavior.

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