期刊
NANO LETTERS
卷 16, 期 11, 页码 6767-6773出版社
AMER CHEMICAL SOC
DOI: 10.1021/acs.nanolett.6b02359
关键词
Rotational diffusivity; magnetic nanoparticles; Stokes-Einstein; dynamic magnetic susceptibility
类别
资金
- US National Science Foundation [CBET-143993]
- Directorate For Engineering
- Div Of Chem, Bioeng, Env, & Transp Sys [1439963] Funding Source: National Science Foundation
We report observations of breakdown of the Stokes-Einstein relation for the rotational diffusivity of polymer-grafted spherical nanoparticles in polymer melts. The rotational diffusivity of magnetic nanoparticles coated with poly(ethylene glycol) dispersed in poly(ethylene glycol) melts was determined through dynamic magnetic susceptibility measurements of the collective rotation of the magnetic nanoparticles due to imposed time-varying magnetic torques. These measurements clearly demonstrate the existence of a critical molecular weight for the melt polymer, below which the Stokes Einstein relation accurately describes the rotational diffusivity of the polymer-grafted nanoparticles and above which the Stokes Einstein relation ceases to apply. This critical molecular weight was found to correspond to a chain contour length that approximates the hydrodynamic diameter of the nanoparticles.
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