Computational studies of contact time dependence of adhesive energy due to redistribution of the locations of strong specific interfacial interactions

The work required to pull a polymeric material from a solid surface with which it connects through hydrogen bonding has been studied by means of molecular dynamics simulations of a coarse-grained bead-spring model. In our simulations, the work, and hence the adhesive energy, increases with the time for which the polymeric material and the surface have been in contact. The work of adhesion G contains a reversible component due to interfacial molecular interactions, as well as an irreversible one, due to dissipative processes. Our data indicate that an increase in the irreversible and not in the reversible work causes G to increase with prolonged contact time. Hence, the phenomenon cannot be attributed to the formation of more or stronger interfacial bonds. Instead, we attribute this increase to a slow redistribution of the beads on the polymer chains that form hydrogen bonds with the surface. Two ways in which this takes effect could be specified. One is that the formation of long loops-chain sections between adjacent bonds-is suppressed after prolonged contact. Another is that over time bonds get distributed more evenly over the polymer backbone and among the polymer chains.