The Adhesion of Particles to Polymer Coated Substrates

A rigid polyester substrate was overcoated with 10 μm, 25 μm, and 50 μm thick coatings of polystyrene containing varying concentrations of plasticizer between 0% and 20%. Micrometer-size glass spheres were deposited onto these substrates and the deformations of the substrates resulting from the forces of adhesion were then examined using scanning electron microscopy (SEM). For substrates which were in the glassy phase, the power law dependence of the contact radius on particle radius was 0.48. In contrast, for the case of rubbery substrates, the contact radius was found to vary as the particle radius to the 0.65 power. These results are consistent with the predictions of the adhesion models of Maugis and Pollock [D. Maugis and H. M. Pollock, Acta Metall. 32, 1323 (1984) and Johnson et al., [K. L. Johnson, K. Kendall, and A. D. Roberts, Proc. Roy. Soc. London Ser. A 324, 301 (1971)], respectively. This implies that, depending on the glass transition temperature of the substrate, either plastic or elastic deformations can occur. Also presented and discussed is the observation of critical engulfment, whereby the surface forces draw the particle substantially or totally into the substrate.