TIME-DEPENDENT ADHESION-INDUCED PHENOMENA - VISCOELASTIC CREEP OF A SUBSTRATE POLYMER OVER RIGID PARTICLES

The adhesion of micrometer-size particles to an alternating block copo lymer composed of polydimethylsiloxane and polyester was found to be a ccompanied by substantial viscoelastic how of the substrate polymer. T his how gave rise to contact radii, which were substantially larger th an those predicted by the JKR theory. Moreover, tensile-induced creep of the substrate resulted in anomalously large menisci that actually f lowed up several particle heights. The flow of the material occurred o ver a period of days and, in some instances, the observed contact radi i were greater than a critical radius for substantial engulfment of th e particles by the substrate. Craters were left behind after particle removal, suggesting plastic-rather than elastic response of the substr ate polymer to the surface-force-induced stresses. Size-exclusion chro matography has identified the presence of lower molecular weight polyd imethylsiloxane-rich copolymer species in the n-hexane soluble mobile phase responsible for the unexpected behavior exhibited by this polyme r substrate.