THERMAL FIELD-FLOW FRACTIONATION APPLICATIONS (Thermal FFF)

Thermal FFF is suitable to separate polymers, gels and nanoparticles. Because the Thermal FFF channel has no stationary phase or any packing inside, the complete sample is eluted from the Thermal FFF channel and no loss of material due to shear forces or filtering effects of a stationary phase is caused.

Polymer Characterization

One application which shows the advantages of Thermal FFF is the separation of polystyrene polymers. It shows that In Thermal FFF smaller polymers can also be separated with comparable efficiency than in GPC. But also the high resolution of Thermal FFF for the higher molar mass polymers can be seen. The separation of the 900 kDa and 1,200 kDa PS shows this high separation power of Thermal FFF. On top of that, for molecular weights higher than 1,200 kDa, Thermal FFF shows an even higher resolution (Solvent = THF, Detection = ELSD).

Nanoparticle Characterization

Another interesting state-of-the-art and up-to-date application is the characterization of nanoparticles with Thermal FFF. Especially Carbon Nanotubes (CNTs) and Carbon Nanoonios (CNOs) are in the center of interest since a couple of years and can be easily investigated by Thermal FFF coupled with Light Scattering. Carbon Nanoonions are multi-layered, concentric large carbon fullerenes. Because of the unique physical and chemical properties arising from their structure and size, carbon nanoparticles have potential applications in devices requiring efficient field emitters, high-strength fibers, strong radiation shields, energy absorbing materials, nano-scale catalytic beds, efficient gas storage, nano-circuits, nano-scale transistors, charge storage materials and white light sources. In addition, they have potential applications as nano-sized, frictionless bearings, in the construction of nano-mechanical devices, electromechanical devices and optoelectronic devices. Electron Microscopy and Atomic Force Microscopy are usually applied to provide visual images of a selected region of the sample but they are incapable of giving detailed statistical information about the nano-material. A comprehensive characterization of carbon nanomaterial is possible if the bulk sample can be separated into narrow sized fractions prior to the subsequent analyses.

Field-Flow Fractionation in general and Thermal FFF in special has been proven to be an ideal method to separate and characterize Carbon Nanoonions and Carbon Nanotubes in aqueous and organic media [1,2]. 1996 Nobel Prize winner Richard E. Smalley already used Field-Flow Fractionation for the characterization of a novel type of polymer-wrapped SWNTs, as he stated in his last patent [3]. Shown here is the separation of Carbon Nanoonions in non-aqueous solvents using Thermal FFF. The figure shows the result of the analysis of Carbon Nanoonion clusters in acetonitrile by Thermal FFF coupled to Light Scattering. The fractionated samples eluting from Thermal FFF have been checked with scanning electron microscopy (SEM) as shown in the corresponding picture. The results show that Thermal FFF is easily capable of separating Carbon Nanoonions according to their size. Also, narrow sized fractions can be collected during the Thermal FFF separation for further investigations.

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