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

ABSTRACT

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.

GRAPHICAL ABSTRACT

KEYWORDS:

• Slip
• Couette flow
• polyethylene
• interface
• molecular dynamics

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This research work was supported by the Hellenic Foundation for Research and Innovation (H.F.R.I.) under the ‘First call for H.F.R.I. Research Projects to support Faculty members and Researchers and the procurement of high-cost research equipment grant’ (Project Number: 1263). The authors are grateful for financial support, through the project ‘Multiscale Simulations of Complex Polymer Systems’ [MuSiComPS, grant agreement 10062/18], by the Limmat Foundation, Zurich, Switzerland during the initial stages of the work. Part of this work was supported by computational time granted from the Greek Research & Technology Network (GRNET) in the National HPC facility – ARIS – under project ID pr006038_thin (MUSIBIOAPP).