Synchronized molecular-dynamics simulation for the thermal lubrication of a polymeric liquid between parallel plates

TL;DR

This study uses synchronized molecular dynamics simulations to analyze how thermal conductivity affects polymeric liquid lubrication between plates, revealing transitions in behavior at high shear stress and the role of viscous heating.

Contribution

It applies a novel synchronized molecular dynamics method to explore the effects of thermal conductivity on polymer lubrication, including temperature rise and conformational changes under shear.

Findings

Temperature increase is inversely proportional to thermal conductivity at low shear stress.

Transition behavior occurs at high shear stress when Nahme-Griffith number exceeds unity.

Polymer chains stretch at low Na, but become disturbed at high Na.

Abstract

The Synchronized Molecular-Dynamics simulation which was recently proposed by authors [Phys. Rev. X {\bf 4}, 041011 (2014)] is applied to the analysis of polymer lubrication between parallel plates. The rheological properties, conformational change of polymer chains, and temperature rise due to the viscous heating are investigated with changing the values of thermal conductivity of the polymeric liquid. It is found that at a small applied shear stress on the plate, the temperature of polymeric liquid only slightly increases in inverse proportion to the thermal conductivity and the apparent viscosity of polymeric liquid is not much affected by changing the thermal conductivity. However, at a large shear stress, the transitional behaviors of the polymeric liquid occur due to the interplay of the shear deformation and viscous heating by changing the thermal conductivity. This transition is characterized by the Nahme-Griffith number $Na$ which is defined as the ratio of the viscous heating to the thermal conduction at a characteristic temperature. When the Nahme-Griffith number exceeds the unity, the temperature of polymeric liquid increases rapidly and the apparent viscosity also exponentially decreases as the thermal conductivity decreases. The conformation of polymer chains is stretched and aligned by the shear flow for $Na<1$, but the coherent structure becomes disturbed by the thermal motion of molecules for $Na>1$.