Roberts Ryan C, Poling-Skutvik Ryan, Palmer Jeremy C, Conrad Jacinta C
Department of Chemical and Biomolecular Engineering , University of Houston , Houston , Texas 77204-4004 , United States.
J Phys Chem Lett. 2018 Jun 7;9(11):3008-3013. doi: 10.1021/acs.jpclett.8b01074. Epub 2018 May 22.
Dynamic coupling of small penetrants to slow, cooperative relaxations within crowded cells, supercooled liquids, and polymer matrices has broad consequences for applications ranging from drug delivery to nanocomposite processing. Interactions between the constituents of these and other disordered media alter the cooperative relaxations, but their effect on penetrant dynamics remains incompletely understood. We use molecular dynamics simulations to show that the motions of hard-sphere tracer particles probe differences in local structure and cooperative relaxation processes in attractive and repulsive glassy liquid matrices with equal bulk packing fractions and long-time diffusivities. Coupling of the tracer dynamics to collective relaxations in each matrix affects the shape of tracer trajectories, which are fractal within the repulsive matrix and more compact in the attractive. These results reveal that the structure of relaxations controls penetrant transport and dispersion in cooperatively relaxing systems and provide insight into dynamical heterogeneity within glassy liquids.
小渗透剂与拥挤细胞、过冷液体和聚合物基质中缓慢的协同弛豫之间的动态耦合，对于从药物递送纳米复合材料加工等一系列应用具有广泛影响。这些以及其他无序介质的成分之间的相互作用会改变协同弛豫，但其对渗透剂动力学的影响仍未完全理解。我们使用分子动力学模拟表明，硬球示踪粒子的运动探测了具有相同体填充分数和长时间扩散率的吸引性和排斥性玻璃液体基质中局部结构和协同弛豫过程的差异。示踪动力学与每个基质中的集体弛豫的耦合影响示踪轨迹的形状，在排斥性基质中轨迹是分形的，而在吸引性基质中更紧凑。这些结果表明，弛豫结构控制着协同弛豫系统中渗透剂的传输和扩散，并为玻璃液体中的动力学非均匀性提供了见解。
