Single-Chain Conformational Analysis on the Dynamic Main Chain Expansion of a Tethered Perfluoropolyether Boundary Lubricant Film

Ab initio quantum chemical computations on model perfluoropolyether (PFPE) boundary lubricant film structures are used to study the effect of main chain confinement on dynamic main chain expansion in the direction perpendicular to the underlying surface. The simulations are conducted on single-chain PFPE structures that contain a pendant branch in the middle of the main chain anchored to the underlying surface. Results indicate a substantial increase in the energy required to expand the branched chain compared to an identical but unbranched main chain. Conformational analyses as a function of main chain expansion indicate the removal of low energy torsional pathways in the branched main chain that could otherwise provide low energy pathways for conformational rearrangement to allow the main chain expansion.