Schlieren optical method

The local position of the particles in the cell can be recorded in all cases by scanning extinction measurements. Only in the special case of chemically uniform particles can the schlieren optical method also be used. 

Experiments with Schlieren optical method, which were possible due to the differences in density, in which the whole contents of the tank could be observed (therefore M 100%), showed that, after a relatively short coarse mixing step, the mixing process took place in a material system, in which the physical properties of homogeneous mixture applied [616]. With p = /(PitPi v and v = /(vi, V2, >) the above relationship reduces to... 

The progress of the diffusion can be followed, e.g., by light absorption measurements (visible light, uv, ir) or by interference measurements. Both methods register a concentration-dependent quantity as a function of the position at a constant time (or vice versa), thus fulfilling the conditions of Equation (7-12). The concentration gradients dc / dr, however, can be found as a function of the position by means of a suitable optical method, the Schlieren optics method. To monitor experiments by Schlieren optics. Equation (7-12) has to be differentiated ... 

This shows that Schlieren optics provide a means for directly monitoring concentration gradients. The value of the diffusion coefficient which is consistent with the variation of dn/dx with x and t can be determined from the normal distribution function. Methods that avoid the difficulty associated with locating the inflection point have been developed, and it can be shown that the area under a Schlieren peak divided by its maximum height equals (47rDt). Since there are no unknown proportionality factors in this expression, D can be determined from Schlieren spectra measured at known times. 

The formation of a boundary between the dextran solution and the dextran solution containing PVP 360 (concentration 5 kg m 3) yields an apparently normal Gaussian distribution of the material detected by Schlieren optics. The various apparent diffusion coefficients obtained by an analysis of the Schlieren curves, which include diffusion coefficients obtained by the reduced height-area ratio method, the reduced second-moment and the width-at-half-height method, show the same qualitative behavior although quantitative differences do exist. This is seen in Fig. 7 where the... 

The schlieren system of optics is an analytical method that is particularly well suited to following the location of a chemical boundary with time. It is routinely employed in ultracentrifuges and also in electrophoresis experiments, as we see in Chapter 12. Schlieren optics produces an effect that depends on the way the refractive index varies with position, that is, the refractive index gradient rather than on the refractive index itself. Therefore, the schlieren effect is the same at all locations along the axis of sedimentation, except at any place where the refractive index is changing. In such a region, it will produce an optical effect that is proportional to the refractive index gradient. The boundary between two layers is thus per-... 

The method of equilibrium ultracentrifugation described by Yphantis (28) was used in these studies. A double-sector centerpiece with two 2 1/2° sectors 12 mm. in length was used with standard Schlieren optics. Apparent molecular weights, M, were determined from the equation ... 

From Rayleigh and schlieren optics, one could calculate cMwa, and hence one could calculate A (cMwa) at every r in the solution column of the ultracentrifuge cell and use the analysis used with the other methods (see Equation 76 and the discussion following it). This could also be done even if only one of the reactants had an absorption spectrum, since c = cA° + cB°. The other possibility is that the complex AnBm has a different absorption spectrum from the reactants, or that in the formation of AnBw some chromophoric groups are buried so that the absorbance of A and B represents a quantity proportional to cA and cB. In either case one could then calculate... 

Concentration changes are observed optically from time to time either by light absorption (e.g. ultraviolet absorption for protein solutions) or, more usually, by schlieren or interference methods. These optical methods for examining concentration changes in liquid columns (especially the schlieren technique in its various forms) are also employed in the ultracentrifuge and for studying movingboundary electrophoresis. The schlieren method is based on the fact that, at a boundary between two transparent liquids of different... 

In the physical methods the mixing of an additive, which differs in temperature, concentration or density (refraction index) from the vessel contents, is foUowed by measuring the temperature, the electrical conductivity, the pH-value or by Schlieren optics. Other methods worthy of mention are ... 

In connection with these studies, the thickness of the diffusion boundary layer can be directly observed by optical methods such as the Schlieren-diagonal method,7 linear laser interferometry8 and by the change in color of an indicator such as methyl red at the membrane-solution interface.9 Further, the concentration polarization at membrane-solution interfaces in electrodialysis has been experimentally and theoretically analyzed in detail.10... 

Sedimentation relies on gravity to drive the separation of macromolecules according to their size, with high rotation speeds (up to 70,(X)0 rpm) used to accelerate the process (Stuart, 2002). Ultracentrifugation (Scott et al., 2005 Laue, 1990) emerged as a versatile, powerful method with the development of new detection methods, based on Schlieren optics, UVAfIS absorption. 

The schlieren microscope is able to detect refractive index variations to six decimal places. Any small difference in optical path (index difference, film thickness, etc) is very precisely detected by the schlieren microscope, especially in the Dodd modification. It is, in effect, a darkfield method. The specimen is illuminated with light in a portion of the illuminating cone and that direct light is masked in the conjugate back focal plane of the objective (Fig. 3). The only light to pass through this plane is refracted, reflected, or diffracted by the specimen. 

J. Rienitz, Optical inhomogeneities schlieren and shadowgraphic method in the seventeenth and eighteenth centuries, Endeavour 21 (1997) 77. 

An additional need for improvement in oiu method, especially for a large-scale application, seems to be a more efficient reading proeedure. This might best be attained by using a small inexpensive computer equipped with an optical scanning device. This would not only minimize individual variation and random error in the reading of films, but could potentially provide more accurate and extensive data about the original schlieren pattern than we are able to obtain from om current manual measurements. 

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