(390d) Rotational Diffusivity of Polymer Grafted Particles in Polymer Melts

ROTATIONAL DIFFUSIVITY OF POLYMER GRAFTED PARTICLES IN POLYMER MELTS

Lorena Maldonado-Camargo¹ and Carlos Rinaldi, ^1,2

¹Department of Chemical Engineering, University of Florida, P.O. Box 116005, Gainesville, FL 32603

²J. Crayton Pruitt Family Department of Biomedical Engineering, P.O. Box 116131, Gainesville, FL 32611

ABSTRACT

Understanding the mobility of nanoparticles in complex environments such as polymer melts and biological fluids have been to be found critical in optimizing their transport properties. Although, it is typically assumed that a particle behaves as in a continuum with no discernible intrinsic length scales, the dynamics of particles at smaller length scales could differ from these macro-scale expectations, impacting the performance of such materials. By taking advantage of the dynamic response of magnetic nanoparticles in oscillating magnetic field, dynamics of particles with Brownian relaxation mechanism in polymers can be analyzed.

In this work, we have used cobalt ferrite nanoparticles with characteristic Brownian relaxation mechanism and calculated the rotational diffusion coefficient (D_R) of the nanoparticles in polyethylene glycol (PEG) polymer melts.  D_R values calculated were compared with those predicted by the Stokes-Einstein (SE) relation based on the knowledge of the macroscopic viscosity of the neat polymer and particle size. We demonstrate that there is a critical molecular weight where particles diffuse faster than predicted by the SE relation. Interestingly, our results suggest that the molecular weight of the grafted polymer and its graft density significantly affect not only the dispersion but also the diffusivity of nanoparticles in polymer melts.