ADHESION INDUCED FLOW OF A SOFT POLYESTER-POLYDIMETHYLSILOXANE COPOLYMER SUBSTRATE OVER MICROMETER AND SUBMICROMETER SIZE SPHERICAL-PARTICLES - OBSERVATIONS OF ANOMALOUSLY LARGE MENISCI, INTERPARTICLE BRIDGING AND PARTICLE ENCAPSULATION

Observations made with a scanning electron microscope (SEM) provided direct evidence for a soft polyester-polydimethylsiloxane block copolymer substrate undergoing extensive surface-force-induced plastic deformation upon contact with micrometer or submicrometer size spherical particles. Anomalously large menisci were detected at the particle/substrate interfaces. Moreover, the substrate material appeared to bridge or encapsulate the particles. The heights of the contact menisci between the 2.2 micrometer radius polystyrene beads and the substrate were found to be approximately 0.4 micrometers; those between 3.6 micrometer radius glass spheres and the substrate were approximately 0.5 micrometers. The heights of the observed menisci were found to be large compared with the values calculated using Tabor's analysis (D. Tabor, J. Colloid Interface Sci. 58, 2 (1977)) based on the elastic model proposed by Johnson, Kendall and Roberts (K. L. Johnson, K. Kendall, and A. D. Roberts, Proc. R. Soc. London A. 324, 301 (1971)). These results suggest that the surface-force-induced tensile stresses may have exceeded the elastic limit of the substrate or that the surface material has an unexpectedly low surface modulus.