Lungova M, Krutyeva M, Pyckhout-Hintzen W, Wischnewski A, Monkenbusch M, Allgaier J, Ohl M, Sharp M, Richter D
Jülich Centre for Neutron Science (JCNS) & Institute for Complex Systems (ICS), Forschungszentrum Jülich GmbH, 52425 Jülich, Germany.
Institute Laue Langevin (ILL), 38000 Grenoble, France and European Spallation Source (ESS), 22363 Lund, Sweden.
Phys Rev Lett. 2016 Sep 30;117(14):147803. doi: 10.1103/PhysRevLett.117.147803. Epub 2016 Sep 28.
We have studied the motion of polyhedral oligomeric silsesquioxane (POSS) nanoparticles modified with poly(ethylene glycol) (PEG) arms immersed in PEG matrices of different molecular weight. Employing neutron spin echo spectroscopy in combination with pulsed field gradient (PFG) NMR we found the following. (i) For entangled matrices the center of mass mean square displacement (MSD) of the PEG-POSS particles is subdiffusive following a t^{0.56} power law. (ii) The diffusion coefficient as well as the crossover to Fickian diffusion is independent of the matrix molecular weight and takes place as soon as the center of mass has moved a distance corresponding to the particle radius-this holds also for unentangled hosts. (iii) For the entangled matrices Rubinstein's scaling theory is validated; however, the numbers indicate that beyond Rouse friction the entanglement constraints appear to strongly increase the effective friction even on the nanoparticle length scale imposing a caveat on the interpretation of microrheological experiments. (iv) The oligomer decorated PEG-POSS particles exhibit the dynamics of a Gaussian star with an internal viscosity that rises with an increase of the host molecular weight.
我们研究了用聚（乙二醇）（PEG）臂修饰的多面体低聚倍半硅氧烷（POSS）纳米颗粒在不同分子量的PEG基质中的运动。结合脉冲场梯度（PFG）核磁共振技术，利用中子自旋回波光谱法，我们发现了以下几点：（i）对于缠结基质，PEG-POSS颗粒的质心均方位移（MSD）遵循t^0.56幂律，呈现亚扩散状态。（ii）扩散系数以及向菲克扩散的转变与基质分子量无关，一旦质心移动了与颗粒半径相当的距离就会发生这种转变——这对于非缠结主体也成立。（iii）对于缠结基质，鲁宾斯坦标度理论得到了验证；然而，数据表明，除了劳斯摩擦之外，缠结约束似乎在纳米颗粒长度尺度上也显著增加了有效摩擦，这对微观流变学实验的解释提出了一个警示。（iv）用低聚物修饰的PEG-POSS颗粒表现出高斯星型的动力学特性，其内部粘度随着主体分子量的增加而升高。
