Priezjev Nikolai V
Department of Mechanical Engineering, Michigan State University, East Lansing, Michigan 48824, USA.
Phys Rev E Stat Nonlin Soft Matter Phys. 2009 Sep;80(3 Pt 1):031608. doi: 10.1103/PhysRevE.80.031608. Epub 2009 Sep 24.
The shear rate dependence of the slip length in thin polymer films confined between atomically flat surfaces is investigated by molecular dynamics simulations. The polymer melt is described by the bead-spring model of linear flexible chains. We found that at low shear rates the velocity profiles acquire a pronounced curvature near the wall and the absolute value of the negative slip length is approximately equal to the thickness of the viscous interfacial layer. At higher shear rates, the velocity profiles become linear and the slip length increases rapidly as a function of shear rate. The gradual transition from no-slip to steady-state slip flow is associated with faster relaxation of the polymer chains near the wall evaluated from decay of the time autocorrelation function of the first normal mode. We also show that at high melt densities the friction coefficient at the interface between the polymer melt and the solid wall follows a power-law decay as a function of the slip velocity. At large slip velocities the friction coefficient is determined by the product of the surface-induced peak in the structure factor, the temperature, and the contact density of the first fluid layer near the solid wall.
通过分子动力学模拟研究了限制在原子级平整表面之间的聚合物薄膜中滑移长度与剪切速率的关系。聚合物熔体由线性柔性链的珠簧模型描述。我们发现，在低剪切速率下，速度分布在壁面附近呈现出明显的曲率，负滑移长度的绝对值近似等于粘性界面层的厚度。在较高的剪切速率下，速度分布变为线性，滑移长度随剪切速率迅速增加。从无滑移到稳态滑移流的逐渐转变与通过第一法向模式的时间自相关函数衰减评估的壁面附近聚合物链更快的松弛有关。我们还表明，在高熔体密度下，聚合物熔体与固体壁面之间界面处的摩擦系数随滑移速度呈幂律衰减。在大滑移速度下，摩擦系数由结构因子中的表面诱导峰、温度以及固体壁面附近第一流体层的接触密度的乘积决定。
