Griffin Philip J, Bocharova Vera, Middleton L Robert, Composto Russell J, Clarke Nigel, Schweizer Kenneth S, Winey Karen I
Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104, United States.
Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, United States.
ACS Macro Lett. 2016 Oct 18;5(10):1141-1145. doi: 10.1021/acsmacrolett.6b00649. Epub 2016 Sep 23.
We measure the center-of-mass diffusion of silica nanoparticles (NPs) in entangled poly(2-vinylpyridine) (P2VP) melts using Rutherford backscattering spectrometry. While these NPs are well within the size regime where enhanced, nonhydrodynamic NP transport is theoretically predicted and has been observed experimentally (2/ ≈ 3, where 2 is the NP diameter and is the tube diameter), we find that the diffusion of these NPs in P2VP is in fact well-described by the hydrodynamic Stokes-Einstein relation. The effective NP diameter 2 is significantly larger than 2 and strongly dependent on P2VP molecular weight, consistent with the presence of a bound polymer layer on the NP surface with thickness ≈ 1.1. Our results show that the bound polymer layer significantly augments the NP hydrodynamic size in polymer melts with attractive polymer-NP interactions and effectively transitions the mechanism of NP diffusion from the nonhydrodynamic to hydrodynamic regime, particularly at high molecular weights where NP transport is expected to be notably enhanced. Furthermore, these results provide the first experimental demonstration that hydrodynamic NP transport in polymer melts requires particles of size ≳5, consistent with recent theoretical predictions.
我们使用卢瑟福背散射光谱法测量了二氧化硅纳米颗粒（NPs）在缠结的聚（2-乙烯基吡啶）（P2VP）熔体中的质心扩散。虽然这些纳米颗粒的尺寸完全处于理论预测并已通过实验观察到的增强型非流体动力学纳米颗粒传输的范围内（2/≈3，其中2是纳米颗粒直径，是管直径），但我们发现这些纳米颗粒在P2VP中的扩散实际上可以很好地用流体动力学斯托克斯-爱因斯坦关系来描述。有效纳米颗粒直径2明显大于2，并且强烈依赖于P2VP分子量，这与在纳米颗粒表面存在厚度约为1.1的结合聚合物层一致。我们的结果表明，结合聚合物层显著增加了具有吸引性聚合物-纳米颗粒相互作用的聚合物熔体中纳米颗粒的流体动力学尺寸，并有效地将纳米颗粒扩散机制从非流体动力学转变为流体动力学状态，特别是在高分子量下，预计纳米颗粒传输会显著增强。此外，这些结果首次通过实验证明，聚合物熔体中的流体动力学纳米颗粒传输需要尺寸≳5的颗粒，这与最近的理论预测一致。
