Pulling Polymers on Energetically Disordered Surfaces: Molecular Dynamics Tests of Linear and Non-linear Response

Equilibrium and non-equilibrium molecular dynamics simulations of flexible polymer chains absorbed on heterogeneous surfaces are presented. The surfaces are flat but energetically disordered, consisting of a random mixture of weakly and more strongly absorbing sites (94 and 6%, respectively). For comparison, the two corresponding homogeneous surfaces are also simulated. This apparently weak energetic disorder can produce significant changes of the chain statistics, equilibrium dynamics, and non-equilibrium response to a horizontal pulling force. On the disordered surfaces, the polymer–surface effective friction coefficient becomes strongly force-dependent, as the dominant mode of motion changes from localized stick–slip events to smooth and continuous sliding. This is strongly reminiscent of the Schallamach model of rubber friction and the Maier–Goeritz picture of the Payne effect in filled elastomers.