475663 Application of Field-Flow Fractionation to the Shape-based Separation of Rod-like Particles: Approach by Theoretical/Numerical Models

Wednesday, November 16, 2016: 5:36 PM
Union Square 3 & 4 (Hilton San Francisco Union Square)
Joontaek Park, Chemical & Biochemical Engineering, Missouri University of Science & Technology, Rolla, MO

Field flow fractionation (FFF) has been applied to separate different size and shape of nanoparticles. Most of recent studies are focused on FFF of sphere particles while many applications are also based on separation of other particle shapes such as rod like nanoparticles. In this study various mathematical models have been derived and studied to better explain rod-like nanoparticle behavior in a field flow, also, it was assumed that rotational diffusivity is much higher than the transverse diffusion of the rod, therefore throughout this work, average local diffusivity of the particle was calculated based on a position dependent orientation average. A model was proposed to evaluate the concentration of particles along the cross-section which could be translated into a retention ratio of the nanoparticle. It was shown that the hydrodynamic interaction with wall known as “lift-hyperlayer” mode has an influence on the migration rate of the rods. Also it was demonstrated that despite previous studies, rod transvers diffusivity differs from its perpendicular diffusivity when it is not assumed to be always aligned in the axial direction. To better understanding the results, retention rate of the rod like particles was used to compare with sphere particles in several operational conditions. In another approach, the “pole-vault” behavior of rods near the wall was to taken into consideration to derive an improved prediction of the steric-entropic effect. This effect basically is a result of the inability of rod to have its own full rotation due to interactions with wall. As demonstrated in this paper, the aspect ratio of rod affects particle distribution along the cross-section, subsequently the retention ratio of the nan rods. A comparison between the new model and the original model has been done in this paper. This model is being improved by experimental study in order to come into better agreement with experimental results.

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