Poling-Skutvik Ryan, Slim Ali H, Narayanan Suresh, Conrad Jacinta C, Krishnamoorti Ramanan
Department of Chemical and Biomolecular Engineering, University of Houston, Houston, Texas 77204-4004, United States.
Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, United States.
ACS Macro Lett. 2019 Aug 20;8(8):917-922. doi: 10.1021/acsmacrolett.9b00294. Epub 2019 Jul 16.
We examine the dynamics of silica particles grafted with high molecular weight polystyrene suspended in semidilute solutions of chemically similar linear polymer using X-ray photon correlation spectroscopy. The particle dynamics decouple from the bulk viscosity despite their large hydrodynamic size and instead experience an effective viscosity that depends on the molecular weight of the free polymer chains. Unlike for hard-sphere nanoparticles in semidilute polymer solutions, the diffusivities of the polymer-grafted nanoparticles do not collapse onto a master curve solely as a function of normalized length scales. Instead, the diffusivities can be collapsed across two orders of magnitude in free polymer molecular weight and concentration and one order of magnitude in grafted molecular weight by incorporating the ratio of free to grafted polymer molecular weights. These results suggest that the soft interaction potential between polymer-grafted nanoparticles and free polymer allows polymer-grafted nanoparticles to diffuse faster than predicted based on bulk rheology and modifies the coupling between grafted particle dynamics and the relaxations of the surrounding free polymer.
我们使用X射线光子相关光谱法研究了接枝有高分子量聚苯乙烯的二氧化硅颗粒在化学性质相似的线性聚合物半稀溶液中的动力学。尽管颗粒具有较大的流体力学尺寸，但其动力学与本体粘度解耦，而是经历一种取决于自由聚合物链分子量的有效粘度。与半稀聚合物溶液中的硬球纳米颗粒不同，接枝聚合物的纳米颗粒的扩散系数并非仅作为归一化长度尺度的函数而汇聚到一条主曲线上。相反，通过纳入自由聚合物与接枝聚合物分子量之比，扩散系数可以在自由聚合物分子量和浓度的两个数量级以及接枝分子量的一个数量级范围内汇聚。这些结果表明，接枝聚合物的纳米颗粒与自由聚合物之间的软相互作用势使得接枝聚合物的纳米颗粒扩散得比基于本体流变学预测的速度更快，并改变了接枝颗粒动力学与周围自由聚合物弛豫之间的耦合。
