Atomistic simulations of long-chain polyethylene melts flowing past gold surfaces: structure and wall-slip

AP Sgouros and DN Theodorou, MOLECULAR PHYSICS, 118 (2020).

DOI: 10.1080/00268976.2019.1706775

The current article presents results from MD simulations of high molar mass polyethylene melts with the scope to investigate the structure and dynamics at the polymer/solid interphase, and to assess their dependence on strong Couette flows. The density profiles are decomposed into the contributions of specific types of segments such as tails, loops and trains in order to arrive at a detailed description of the structure under various flow conditions. The size and orientation of chain segments is quantified to assess the reorganisation of the chains at the interface leading to possible shear-thinning effects. The segmental velocity profiles and the layer- and direction-resolved mean square displacement of the chain segments are extracted from the simulations so as to compute the effective shear rate, slippage, and the emergence of possible interfacial failure mechanisms. Through representative snapshots of chain trajectories we unveil the dominant mechanisms dictating the chain reorganisation in the interfaces and the overall adsorption-desorption processes. Our findings suggest the manifestation of a hybrid boundary condition attributed mainly to interfacial failure and partly to cohesive failure.

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