(382f) Simulation of Rodlike Particles in Field-Flow Fractionation (F.F.F.) | AIChE

(382f) Simulation of Rodlike Particles in Field-Flow Fractionation (F.F.F.)

Authors 

Bauer, B. J. - Presenter, National Institute of Standards and Technology


For nanotubes to achieve their full potential in applications, it is desirable to be able to separate them according to their various physical properties. One possible technique for achieving this is field-flow fractionation (FFF) [1]. Classical flow-FFF is a separation technique in which a perpendicular cross flow is imposed upon a channel flow of dilute particulates. The cross flow exits through a porous accumulation wall which is impermeable to the particulates. Competition between various flow mechanisms drives particles of different sizes to discrete equilibrium layers. Separation is achieved due to the different residence times of the particles based upon their position in the parabolic velocity profile in the throughput direction. A number of different mechanisms can be exploited to achieve separation in FFF. Normal mode separation in FFF applies to particles which are small enough to undergo significant Brownian motion. In this case, layering is achieved by a competition between advection and diffusion in the cross flow direction. Smaller particles, which are more diffusive, have an average position closer to the centerline and thus elute faster than larger particles. Steric mode separation occurs when the particle layer in FFF is strongly compressed, and thus, larger particles are more highly entrained by the throughput flow the smaller ones. In this work, we develop a Brownian dynamics simulation of prolate ellipsoidal particles to investigate the separation of rodlike particles in 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 [2,3]. 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. Elution profiles and average velocity through the device as a function of particle size, and throughput and cross flow flowrates are shown. In addition, we use the simulation to investigate whether selective orientation of metallic and semi-conducting nanotubes can be used as a basis for separating tubes according to their electronic properties by either normal or steric mode separation.

References: [1] Josef Janca, Field-Flow Fractionation (Chromatographic Science), Marcel Dekker, New York, (1987). [2] A. Satoh, Introduction to Molecular-Microsimulation of Colloidal Dispersions, Elsevier Science B.V., Amsterdam, The Netherlands, (2003). [3] Kim, S. and Karrila, S.J., Microhydrodynamics: Principles and selected applications, Butterworth-Heinemann, Stoneham, (1991).

Checkout

This paper has an Extended Abstract file available; you must purchase the conference proceedings to access it.

Checkout

Do you already own this?

Pricing

Individuals

AIChE Pro Members $150.00
AIChE Graduate Student Members Free
AIChE Undergraduate Student Members Free
AIChE Explorer Members $225.00
Non-Members $225.00