高分子交联网络中纳米棒的扩散行为模拟研究

Simulation study on the diffusion of nanorods in crosslinked polymer networks

采用分子动力学模拟研究了纳米棒在末端交联高分子网络中的扩散行为,建立了末端交联高分子网络纳米棒复合体系的粗粒化模型。模拟平衡后,通过均方位移表征了纳米棒的平动扩散行为,发现纳米棒的运动存在很强的各向异性特点,平行于纳米棒长轴方向上平动扩散的平行分量随着纳米棒长度的增加线性下降,D‖~L^(-1),其垂直分量的下降行为存在2个标度区间,纳米棒较短时,D⊥~L^(-2),纳米棒较长时,D⊥~L^(-3)。通过表征纳米棒的重取向自相关函数,获得纳米棒的转动扩散系数,发现其同平动扩散的垂直分量一样,也存在2个标度区间,分别为D R~L^(-4)和D R~L^(-5),且总体满足D R~D⊥L^(-2),表明纳米棒的垂直运动和转动扩散是相互耦合的。上述研究为高性能橡胶纳米复合材料的设计和开发奠定了坚实的科学基础。

Molecular dynamics simulations were employed to investigate the diffusion of nanorods(NRs)in end-linked polymer networks.Initially,coarse-grained models of end-linked polymer network-NR composites were constructed.After equilibrating the simulation systems,the mean square displacement of NR center-of-mass was calculated to obtain the translational diffusion coefficients.It was found that the translation of NRs is anisotropic along and normal to the rod long axis.The parallel component decreases linearly with the rod length L,following D‖~L^(-1),while the normal component follows two distinct scaling regimes with decreasing L,i.e.,D⊥~L^(-2) for short rods and D⊥~L^(-3) for long rods.The reorientation autocorrelation function of NRs was calculated to obtain the rotational diffusion coefficients.It was found that,the rod rotation scales with L in two regimes,D R~L^(-4) and D R~L^(-5) for short and long rods,respectively,similar to the normal diffusion of the rod.Additionally,D R~D⊥L^(-2) in both regimes,suggested a coupling between the rod normal diffusion and rotation.In general,this study may provide a scientific foundation for the design and development of high-performance rubber nanocomposites.