Department of Mechanical Engineering, Michigan State University, East Lansing, Michigan 48824, USA.
J Chem Phys. 2012 Jun 14;136(22):224702. doi: 10.1063/1.4728106.
The results obtained from molecular dynamics simulations of the friction at an interface between polymer melts and weakly attractive crystalline surfaces are reported. We consider a coarse-grained bead-spring model of linear chains with adjustable intrinsic stiffness. The structure and relaxation dynamics of polymer chains near interfaces are quantified by the radius of gyration and decay of the time autocorrelation function of the first normal mode. We found that the friction coefficient at small slip velocities exhibits a distinct maximum which appears due to shear-induced alignment of semiflexible chain segments in contact with solid walls. At large slip velocities, the friction coefficient is independent of the chain stiffness. The data for the friction coefficient and shear viscosity are used to elucidate main trends in the nonlinear shear rate dependence of the slip length. The influence of chain stiffness on the relationship between the friction coefficient and the structure factor in the first fluid layer is discussed.
本文报道了聚合物熔体与弱吸引力晶状表面界面摩擦的分子动力学模拟结果。我们考虑了具有可调固有刚度的线性链的粗粒珠-弹簧模型。通过回转半径和第一法向模式时间自相关函数的衰减来量化聚合物链在界面附近的结构和弛豫动力学。我们发现，在小滑移速度下，摩擦系数表现出明显的最大值，这是由于与固体壁接触的半柔性链段在剪切诱导下的取向所致。在较大的滑移速度下，摩擦系数与链刚度无关。摩擦系数和剪切粘度的数据用于阐明滑移长度对非线性剪切速率的依赖性的主要趋势。讨论了链刚度对第一层流体内摩擦系数与结构因子关系的影响。
