Forced reptation revealed by chain pull-out simulations

摘要

We report computation results obtained from extensive molecular dynamics simulations of tensiledisentanglement of connector chains placed at the interface between two polymer bulks. Eachpolymer chain (either belonging to the bulks or being a connector) is treated as a sequence of beadsinterconnected by springs, using a coarse-grained representation based on the Kremer–Grest model,extended to account for stiffness along the chain backbone. Forced reptation of the connectors wasobserved during their disentanglement from the bulk chains. The extracted chains are clearly seenfollowing an imaginary tubeinside the bulks as they are pulled out. The entropic and energeticresponses to the external deformation are investigated by monitoring the connector conformationtensor and the modifications of the internal parameters (bonds, bending, and torsion angles along theconnectors). The work needed to separate the two bulks is computed from the tensile force inducedduring debonding in the connector chains. The value of the work reached at total separation isconsidered as the debonding energy G. The most important parameters controlling G are the length(n) of the chains placed at the interface and their areal density. Our in silico experiments areperformed at relatively low areal density and are disregarded if chain scission occurs duringdisentanglement. As predicted by the reptation theory, for this pure pull-out regime, the powerexponent from the scaling G∝n~ais a≈2, irrespective of chain stiffness. Small variations are foundwhen the connectors form different number of stitches at the interface, or when their length israndomly distributed in between the two bulks. Our results show that the effects of the number ofstitches and of the randomness of the block lengths have to be considered together, especially whencomparing with experiments where they cannot be controlled rigorously. These results may besignificant for industrial applications, such reinforcement of polymer-polymer adhesion byconnector chains, when incorporated as constitutive laws at higher time/length scales in finiteelement calculations