Simulation of nanotube separation in field-flow fractionation (FFF)

A Brownian dynamics simulation based on a prolate spheroid particle model has been developed to model the separation of nanotubes in cross flow driven, field-flow fractionation (FFF). The particle motions are governed by stochastic forms of a linear momentum balance with orientation dependent drag and diffusion coefficients, and the Jeffrey equation with rotational diffusion. The simulation shows that nanotube scale particles would be expected to elute by a normal mode mechanism up to aspect ratios of about 1000, based on a particle diameter of 1 nm. Separation of nanotubes of different length is governed by the value of the retention variable for each component in agreement with theory. Elution profiles and average velocity through the device as a function of particle size, and the flow rates in the throughput and cross-flow directions are examined. The simulation shows that clean separations between components of different size is achieved when the ratio of the retention values is greater than 2.