Ultracentrifugation diameter

The ultracentrifuge is made up of an aluminium rotor several inches in diameter and it is rotated at high speed in an evacuated chamber. The solution to be centrifuged is kept in a small cell within the rotor near its periphery. The rotor can be driven electrically or by an oil or air turbine. 

Separation of SWNTs based on chirality and diameter with surfactants has also been evidenced by density-gradient ultracentrifugation [86]. Finally, a recent study has demonstrated the separation of semiconducting nanotubes from metallic ones by chemical interaction of the former with attached amine-terminated silane molecules assembled on a silicon wafer. In a separate experiment, metallic nanotubes were also... 

Micellar diameter and size polydispersity can be obtained directly in water or in an isotonic buffer by DLS. DLS can also provide some information on the sphericity of polymeric micelles (Kataoka et al., 1996 Nagasaki et al., 1998). Ultracentrifugation velocity studies are sometimes performed to assess the polydispersity of polymeric micelles (Yokoyama et al., 1994 Hagan et al., 1996). 

Earlier work (3) has shown that cleaned monodisperse polystyrene latexes stabilized with surface sulfate (and perhaps a few hydroxyl) groups an be used as model colloids. For example, the distribution of H ions in the electric double layer as determined by conductometric titration has been correlated with the particle diameter determined by ultracentrifugation (3). The conductometric titration gives two measures of the concentration of H+ ions the initial conductance of the latex and the amount of base required for neutralization. The number of H+ ions determined by conductance is always smaller than the number determined by titration. This difference is attributed to the distribution of the H+ ions in the electric double layer those closest to the particle surface contribute least to the overall conductance. This distribution is expressed as the apparent degree of dissociation a, which is defined as the ratio H+ ions... 

Schulman and coworkers [3-7] observed that isotropic and optically transparent dispersions of oil in water or water in oil are formed spontaneously in the presence of a surfactant and a cosurfactant such as an alkyl alcohol. Using low-angle X-rays, light scattering, ultracentrifugation, electron microscopy, and viscosity measurements, they concluded that the dispersed phase consists of almost uniform spherical droplets with diameters ranging between 8 and 80 nm. 

Sedimentation-FFF. Retention measurements give the effective particle mass m (buoyant mass). If the particle density is known, the particle mass m, particle volume Vp, and hydrodynamic diameter dH can be calculated [80,81]. Apart from the particle dimensions, the density can be determined as well [82] as the difference in the densities of the solute and the solvent, Ap, is linearly correlated to X. Fractionation can be used in regions where the solvent density is lower than the solute density (pps. The determination of particle density in a single experiment is possible by sedimentation-flotation focusing-FFF [72,73,83] analogous to density gradient ultracentrifugation. 

S-FFF has been compared with analytical ultracentrifugation (AUC) with respect to the fractionation of a 10-component latex standard mixture with narrow particle size distribution, known diameters (67-1220 nm) and concentration [ 127]. With an analytical ultracentrifuge, the particle sizes as well as their quantities could be accurately determined in a single experiment whereas in S-FFF deviations from the ideal retention behavior were found for particles >500 nm resulting in smaller particle size determination in the normal as well as in the programmed operation. It was concluded that, without a modified retention equation which accounts for hydrodynamic lift forces and steric exclusion effects, S-FFF cannot successfully be used for the size characterization of samples in that size range. 

In a round-robin test series Mueller [81] found the ultracentrifuge to be the most satisfactory size analysis method for the sub-pm range a sample containing nine monodisperse components with 10% diameter difference being resolved. 

The size distribution of particulate matter has been defined in microns (/x) as dissolved (< 0.001/x), semicolloidal (0.001-1/x), and colloidal (1-100/x). Ultracentrifugation processes can separate these size boundaries (20). A 0.45/x diameter millipore filter eluate has been defined as apparently solubility (9). This artificial cut off value is easy to attain. Most of the semicolloidal material in water therefore is included with the soluble fraction. 

By TEM of the poly-lipid liposome/lipid-heme the diameter was ca. 350 A (Fig. 9) and it did not change before and after the polymerization. The gel permeation chromatography and the ultracentrifugation of the liposome/heme showed that all of 77 was entrapped within the liposome. Solution properties of the poly-lipid liposome/ lipid-heme were almost the same as those of human blood specific gravity 1.012, viscosity 3.75-4.12 cp, and osmotic pressure 334 mOsm. The solution of the polylipid liposome/lipid-heme was stable and could be stocked for months without precipitation and change of the particle size, i.e. without aggregation and fusion of the liposome, at ambient temperature. 

Fig. 17. Mass distribution of the diameter of the PS core latex and the PS/PMMA core-shell latex studied in Refs. [46] and [47] as determined by ultracentrifugation [87]. (Taken from Ref. [46])...

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