平行板间聚合物液体热润滑的同步分子动力学模拟
Synchronized molecular-dynamics simulation for the thermal lubrication of a polymeric liquid between parallel plates
摘要：
作者[Phys. Rev. X { \bf 4}，041011（2014）]最近提出的同步分子动力学模拟被应用于平行板之间的聚合物润滑的分析。通过改变聚合物液体的导热系数，研究了聚合物液体的流变特性、聚合物链的构象变化以及由于粘性加热而引起的温度升高。结果表明，在较小的剪切应力作用下，聚合物液体的温度与导热系数成反比地略有升高，而导热系数的变化对聚合物液体的表观粘度影响不大。然而，在大的剪切应力下，由于剪切变形和粘性加热的相互作用，通过改变热导率，聚合物液体发生转变行为。该转变的特征在于Nahme-Griffith数$Na$，其被定义为在特征温度下粘性加热与热传导的比率。当Nahme-Griffith数超过1时，聚合物液体的温度迅速升高，表观粘度也随着热导率的降低呈指数下降。对于$Na<1$，剪切流使聚合物链的构象拉伸和排列，而对于$Na>1$，分子的热运动使聚合物链的共格结构受到干扰。
英文摘要：
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 $Na>1$.
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