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

• Synchronized Molecular-Dynamics simulation is applied to the polymer lubrication.
• We examine variations in the thermal conductivity.
• A transition is found due to the interplay of viscous heating and thermal conduction.
• We found this transition is characterized by the Nahme–Griffith number.

The Synchronized Molecular-Dynamics simulation, which was recently proposed by authors (Yasuda and Yamamoto, 2014), is applied to the analysis of polymer lubrication between parallel plates. The changes in rheological properties, conformational change of polymer chains, and temperature rise due to the viscous heating are investigated with varying values of thermal conductivity of the polymeric liquid. It is found that with a small applied shear stress on the plate, the temperature of the polymeric liquid only slightly increases in inverse proportion to the thermal conductivity; the apparent viscosity of the polymeric liquid is little affected by changing the thermal conductivity. However, at a large shear stress the transitional behaviors of the polymeric liquid are observed 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 unity, the temperature of the 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 when Na < 1, but the coherent structure becomes disturbed by the thermal motion of molecules when Na > 1.