(153e) Steric-Entropic Effect on the Aspect Ratio-Based Separation of Rod-like Particles in Field-Flow Fractionation

An improved model for predicting the steric-entropic effect on the separation behaviors of rod-like particles in flow field-flow fractionation, which is a particle separation technique which utilizes a parabolic channel flow and a cross-flow field, was developed. The new model incorporates the “pole-vault” rotation of a rod-like particle near a wall under shear flow into the original model developed by Beckett and Giddings  [J. Colloid Interface Sci. 1997, 186, 53–59], which considered only Brownian rotation. I investigated the effect of the aspect ratio on the rod separation behaviors by comparing the predictions of retention ratios and cross-sectional concentration distributions from the original model with the new model under various flow conditions. My analysis, performed under non-constant cloud thickness (ratio between cross flow rate and rod diffusivity) assumption, showed that the new model can show the aspect ratio-enhanced elution trend, which was experimentally observed by Gigault et al. [Anal. Bioanal. Chem. 2013, 405, 1191–1202]. I also deducted that the flow conditions allowing for the aspect ratio-enhanced elution are related with the interplay among the axial flow rate, cloud thickness, and rod geometry.