Authors: F.R. Phelan Jr., B.J. Bauer
Affilation: NIST, United States
Pages: 179 - 182
Keywords: Brownian dynamics, field-flow fractionation, nanotubes, separations
A Brownian dynamics simulation for modeling the separation of spheres and rodlike particles in field-flow fractionation (FFF) is developed. Modeling of particle elution for spheres from (10 to 1000) nm was examined. The simulation captures the steric transition, and results for mean elution time are in good agreement with steric inversion theory. The sphere simulations are compared with simulations for rods of equal diffusivity, as under normal mode conditions such particles should elute at the same rate. The results for rods show that nanotube size particles elute by a normal mode mechanism up to a size of about 500 nm. At larger sizes, the rods begin to deviate from normal mode theory, but less strongly and in the opposite sense as for spheres. While the steric effect for spheres causes larger spheres to elute faster than predicted by normal mode theory, an inverse steric effect occurs for rods in which larger rods move increasingly slower than predicted by theory. While this affects the calibration of such operations, it also indicates that length based separations for nanotubes are not bound by the same limitation as occurs for spheres due to steric inversion. Preferential orientation of rods has the potential to separate nanotubes by chirality by means of a steric mode mechanism.
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