Synchronized Molecular-Dynamics Simulation via Macroscopic Heat and Momentum Transfer: An Application to Polymer Lubrication

Abstract

A synchronized molecular-dynamics simulation via macroscopic heat and momentum transfer is proposed to model the nonisothermal flow behaviors of complex fluids. In this method, the moleculardynamics simulations are assigned to small fluid elements to calculate the local stresses and temperatures and are synchronized at certain time intervals to satisfy the macroscopic heat-and momentum-transport equations. This method is applied to the lubrication of a polymeric liquid composed of short chains of ten beads between parallel plates. The rheological properties and conformation of the polymer chains coupled with local viscous heating are investigated with a nondimensional parameter, the Nahme-Griffith number, which is defined as the ratio of the viscous heating to the thermal conduction at the characteristic temperature required to sufficiently change the viscosity. The present simulation demonstrates that strong shear thinning and a transitional behavior of the conformation of the polymer chains are exhibited with a rapid temperature rise when the Nahme-Griffith number exceeds unity. The results also clarify that the reentrant transition of the linear stress-optical relation occurs for large shear stresses due to the coupling of the conformation of polymer chains with heat generation under shear flows.

Multiscale simulation for thermo-hydrodynamic lubrication of a polymeric liquid between parallel plates

“…In Ref. [25], it is also demonstrated that an interesting re-entrant transition of the linear stress-optical relation occurs for large shear stresses because of the coupling of the conformations of the polymer chains with viscous heat generation under shear flows. Figure 2 shows the apparent viscosity of the system (a), the spatial averages of the shear stress and temperature (b) and the bond orientation tensor of the polymer chains (c) as a function of the gross shear rate.…”

“…The details of SMD method can be referred in Ref. [25]. In the following, we present quantities averaged for a long time in the steady state, in which the shear stress is spatially uniform and the time derivative of the local internal energy, i.e.…”

“…[25] The rheological properties and the conformations of the polymer chains are investigated with a non-dimensional parameter, i.e. the Nahme -Griffith number.…”

“…[16 -18,21] Recently, a new multiscale simulation, termed the synchronised molecular dynamics (SMD) simulation, for the coupled heat and momentum transfer in polymer lubrication has been developed by us. [25] In this article, using this method, we investigate the rheological properties and conformation of polymer chains in thermo-hydrodynamic lubrication of a polymeric liquid composed of short chains in a gap between parallel plates, in which the width of the gap is so large that the macroscopic quantities, e.g. velocity, stress and temperature, become spatially heterogeneous.…”

Solidification of the Lennard-Jones fluid near a wall in thermohydrodynamic lubrication

“…Incidentally, the multiscale hybrid method of MD and CFD is currently a very active research field [12][13][14][15][16][17][18][19][20][21][22]. The thermohydrodynamic lubrication of polymeric fluids was also investigated by the synchronized MD method, in which a transitional behavior of the polymer conformation due to thermohydrodynamic coupling was clarified [23][24][25]. Although the multiscale approach is powerful and promising for complex fluids, to further develop the multiscale method, we require more first-principles results obtained through MD simulations.…”