Light scattering measurement

The intense light scattering of nematics is due to thermally induced orientational fluctuations of the nematic director field. These orientational fluctuation modes are related to the viscous and elastic properties of the nematic (see, for example, Litster [27]). 

The de Gennes formulae [28, 29] establish a relation between the elastic coefficients and the scattering intensities. Small thermal director fluctuations can be expressed in terms of two eigenmodes, the splay-bend mode Srii and the twist-bend mode Sn2. The equipartition theorem gives the intensities 

The de Gennes equations have been reexamined by Chen et al. [31], who discussed experimental limitations as boundary influences and finite sample dimensions. Possible error sources are stray light in the detector and inaccurate adjustment of the sample cell, which may lead to systematic errors in the scattering angle. 

Antigen excess and matrix effects are limitations encountered in the use of turbidimeters and nephelometers in measurement of analytes of cfinical interest. 

Large particles, such as suspended dust, also cause significant background interference. This background interference is controlled by filtering all buffers and diluted antisera before analysis is attempted. 

Blackburn GF, Shah HP, Kenten JH, et al. Electrochemiluminescence development of immunoassays and DNA probe assays for clinical diagnostics. Clin Chem 1991 37 1534-9. 

DeLuca M, McElroy WD. Bioluminescence and Chemiluminescence, Part B. Methods in Enzymology, vol 133, San Diego Academic Press, 1986, 649pp. 

Diamandis E, Christopoulos TK. Europium chelate labels in time-resolved fluorescence immunoassays and DNA hybridization assays. Anal Chem 1990 62 1149A-57A. 

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Light-scattering measurements made over two suitably chosen angle intervals can combine with depolarized light-scattering measurements to... 

Witkowski, W.R., Miller, S.M. and Rawlings, J.B., 1990. Light scattering measurements to estimate kinetic parameters of crystallization. In Crystallization as a separation process, ACS Symposium Series, 438, 102. 

Figure 5B. Correlation of right-angle light scatter measured by fluorometry and flow cytometry. The top panel shows flow-cytometric data of side scatter of fixed, stained cells during the time course of stimulation by 1-nM (solid line, solid circles) or 0.01-nH (dashed line, open circle) FLPEP. The bottom panel shows the corresponding right-angle light-scatter data acquired pseudo-simultaneously on live cells in the fluorometer. The flow-cytometric data have been averaged, but the fluorometry data are plotted for both duplicates from one donor. Reproduced with permission from Ref. 27. Copyright 1985 Rockefeller University Press.

This stipulation of the interaction parameter to be equal to 0.5 at the theta temperature is found to hold with values of Xh and Xs equal to 0.5 - x < 2.7 x lO-s, and this value tends to decrease with increasing temperature. The values of = 308.6 K were found from the temperature dependence of the interaction parameter for gelatin B. Naturally, determination of the correct theta temperature of a chosen polymer/solvent system has a great physic-chemical importance for polymer solutions thermodynamically. It is quite well known that the second viiial coefficient can also be evaluated from osmometry and light scattering measurements which consequently exhibits temperature dependence, finally yielding the theta temperature for the system under study. However, the evaluation of second virial... 

G(S) and G(X) have been estimated by quantifying the effect on molecular size distributions inferred from sedimentation velocity, gel permeation chromatography, and dynamic light-scattering measurements [58]. 

Thus both the numerator and denominator terms in Eq. (41), or in Eq. (44), depend on the concentration. Because of this situation empirical extrapolation of D is particularly hazardous (for random coiling polymers). If F2 is known from osmotic or light-scattering measurements at a series of concentrations, extrapolation according to Eq. (44) will be facilitated. (If such measurements have been carried out, however, the molecular weight also will have been determined.)... 

Turbidity as determined by light-scattering measurements, and the same quantity corrected for dissymmetry (Chap. VII). 

The parameter c can be easily determined by using viscometric measurements, which yield a relative number, or by performing, for example, light scattering measurements, which yield absolute values of c. Viscometric measurements are most commonly used because results are obtained quickly. However, this relative method is not equivalent to the absolute value of c LS and only absolute determination methods such as light scattering result in correct values of c. ... 

Normally (T is used without considering the solvent quality. However, a master low curve can only be established using such a method. In Table 5 a comparison of the model prediction with the experimental findings, obtained by laser light scattering measurements, is given. 

C.Elastic and quasi-elastic light scattering measurements have revealed that their size scales as Ca13 at 1 ppm of A1 (or 3 10"... 

Lechna-Marczynska M., Ulatowska A., Podbielska H., Grzegorzewski B., Light scattering measurements in ormosil and PHEMA - possible new materials for contact lenses, EOS 23, 33-34, (1999). 

Light-scattering measurements are of great intrinsic value for studying the starch components, but few measurements have been carried out. Recently, the question of the absolute value of the standards used in tur-bidimetry has been discussed,133 and several new instruments have been described.133 134 It is to be hoped that more use will be made of this method in the future. 

Intermediate forms must also exist, and, indeed, structural models of the amylose molecule exhibit considerable flexibility. Evidence for aggregated helices (very stable aggregates of amylose molecules) has been provided by Paschal] and Foster142 from light-scattering measurements on amylose in solvents of varying pH. 

Temperature of measurement varies between 22.5-35°C. 6 O. P. = osmotic-pressure measurements t = light-scattering measurements C. = colorimetric measurements S. D. = sedimentation and diffusion measurements. 

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