Anisotropic Diffusion in Polymer Nanocomposites with Polymer-Grafted Chained Nanoparticles

We measure the tracer diffusion coefficient (D) in polymer nanocomposites having chained Fe3O4 nanoparticles (cNP, aspect ratio 5) grafted with PS brushes. When the deuterated PS tracer molecular weight is large (1866 kg/mol), D decreases monotonically with increasing nanoparticle concentration. In contrast, when the dPS molecular weight is smaller (49, 168, or 532 kg/mol), D exhibits a minimum at 0.25 vol% cNP. In all cases, the tracer molecule is larger relative to the nanotube diameter (2Rg/d > 1), but the minimum in the tracer diffusion is found only when the tracer molecule is also small relative to the cNP length (2Rg/L < 1.5, where L is the mean length of the impenetrable core of the chained NPs). The diffusion minimum is attributed to anisotropic diffusion in the vicinity of the chained NPs and requires that the long dimension of the cNP be comparable to or longer than the tracer molecule. The importance of tracer size relative to nanoparticle size (d and L) is established as well as the propensity of anisotropic nanoparticles to impose anisotropic diffusion coefficients near the nanoparticles.


C.-C. Lin, K. Ohno, N. Clarke, K. I. Winey*, R. J. Composto*, Macromolecules 47 (15), 5357-5364, 2014.
"Macromolecular Diffusion through a Polymer Matrix with Polymer-Grafted Chained Nanoparticles"