Local hydrodynamics of solvent near diffusing dendrimers: A test of the new Stokes–Einstein relation

Abstract

We have reported a new Stokes–Einstein relation (SER) for size determination and tested it by different nanoparticles. We assumed that the breakdown for SER results from local increases in viscosity. Here we investigate hydrodynamics of solvent near dendrimers to further test generality of our new theory. We discuss simulations of dendrimers in comparison to nanoparticles, experimental data on dendrimers from literature, and our theory. Local viscosity and local diffusivity of solvent near dendrimers are estimated by persistence times and exchange times, respectively. We find that the local dynamics of solvent near dendrimers of low density stay almost the same as that of bulk solvent. While the motions of solvent particles slow down near dendrimers of high density. This is similar with changes in local dynamics of solvent near nanoparticles. According to the causes we proposed for the deviation of SER, this is consistent with our findings that the SER works for the dendrimers of low density, while it fails for the dendrimers of high density. The new SER is then tested to predict size of the dendrimers accurately. Taking this together with the results for the nanoparticles, we believe that the new theory is general. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 1380–1392

Drag on nanoparticles in a liquid: from slip to stick boundary conditions

“…37,38 It is believed that there exists a critical particle size (roughly a few nanometers), below which Stokes' law breaks down. 39 The breakdown of Stokes' law may be attributed to the increase of fluid viscosity in the vicinity of the particles 40 or a failure of the continuum approximation. 41 Besides the stick boundary conditions, slip boundary conditions have also received extensive attention.…”