TIME-DEPENDENT ADHESION INDUCED PHENOMENA - THE FLOW OF A COMPLIANT SLICONE-POLYESTER COPOLYMER SUBSTRATE AVER RIGID MICROMETER SIZE GOLD AND POLYSTYRENE PARTICLES

A polyester-polydimethylsiloxane block copolymer substrate (Young's mo dulus of approximately 9.2 x 10(6)N/m(2)) was observed by SEM to gradu ally creep over higher modulus gold and polystyrene micrometer sized p articles in contact with its surface. The particle/substrate and parti cle/particle interfaces were examined shortly after particle depositio n and again at various intervals up to a month later. SEM micrographs clearly showed an increase in the size of the contact menisci with tim e (for periods up to approximately two weeks) at both sets of interfac es. After only one week the gold particles appeared to be completely e ncapsulated by the substrate. These time-dependent observations confir m the plastic deformation mechanism proposed previously to explain sim ilar observations on micrometer- and submicrometer-sized glass, polyst yrene, and poly-vinylidene fluoride beads contacting the same substrat e (L.P. DeMejo, D.S. Rimai, J. Chen, and R.C. Bowen, J. Adhesion 39, 6 1 (1992)).