Post-production separation

Metallic and semiconducting SWNTs are apparently wrapped differently by DNA or more generally in the same concept by surfactant molecules, as discussed above for various approaches to exploit such differences for postproduction separation purposes. The nanotubes also have different interactions with selected functionalization or solubilization agents. Such selective interactions, sometimes considered as non-covalent functionalizations, have been found to allow relatively facile post-production separation at significant quantities. ... 

Sun and co-workers exploited the selectivity in the non-covalent functionalization of SWNTs with planar aromatic molecules, such as derivatized porphyrin or pyrene (Figure 6.3), for the post-production separation. The separation method simply splits the starting nanotube mixture by selectively solubilizing semiconducting SWNTs and leaving their metallic counterparts behind, and consequently is capable of handling significant sample quantities. Experimentally, as-produced samples of... 

Figure 6.3 The post-production separation scheme with the use of derivatized pyrene...

Figure 6.4 Upper panel the chemical structure of 1,1 -bis-pyrene butyoxyl-/ -xylene (bis-pyrene) lower panel schematic illustration of the molecular tweezers approach for the post-production separation of metallic and semiconducting SWNTs with the use of bis-pyrene.

In another study, Maeda et al fabricated transparent conductive films by air spraying enriched metallic SWNTs (from the amine-assisted post-production separation ) on to both quartz and PET substrates. The sheet resistances in the films on PET were 690 Q sq at an optical transmittance of 81% (550 nm) and 9000 Q sq at 97% (550 nm), which represented reductions by a factor of 20 in comparison with the performance in films of non-separated SWNTs. The same group also found that the effectiveness in the separation for metallic SWNTs is determined by the use of different amines at various concentrations. The proportion of metallic SWNTs against semiconducting SWNTs in the... 

Probably the biggest problem in analytical polarography is adsorption of species on to the surface of the electrode. This can be adsorption of the analyte, its electrolysis product, or any other species from the solution. The effects of adsorbed species can be very varied indeed. They can produce the splitting of polarographic waves, the distortion of their shapes, shifting of the half wave potentials, depression or even elimination of the wave heights, etc. The adsorbed forms may produce small waves of their own, known as pre-waves or post-waves, separate from the main diffusion controlled wave. On the other hand some adsorbed species have little or no effect. 

Filtration Filtration (qv) is appHed in blood cell separation to remove leukocytes from ted blood cell (RBC) and platelet concentrates. Centtifugational blood cell separators do not reduce white blood cells (WBC) in red cell and platelet products sufficiently to avoid clinical complications such as GvHD and alloimmunization. A post-apheresis filtration step is needed to further reduce the WBC load. Modem filters are capable of a 3-log reduction in white cell contamination of the blood product, eg, apheresis single-donor platelet units having a typical white cell contamination of 5 x 10 white cells in 4 x 10 platelets can be reduced to a 5 x 10 white cell contamination, a sufficiently low number to avoid severe transfusion reactions. 

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