THE ADHESION OF PARTICLES TO POLYMER-COATED SUBSTRATES

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