Experimental Aspects of Light Scattering

The Rayleigh ratio as defined by Equation (24) has a precise meaning, yet it is a quantity somewhat difficult to visualize physically. After we have discussed the experimental aspects of light scattering, we shall see that Re is directly proportional to the turbidity of the solution when turbidity is the same as the absorbance determined spectrophotometrically. 

5 Schematic top view of a typical light scattering instrument showing the different components and the definition of 0. 

In order to determine M and B by means of Equation (27), it is clear that all the other quantities in the equation must be measured. It is convenient to group these factors into two categories, concentration and optical terms, for the purposes of our discussion. 

The actual measurement of the refractive index of the solution poses no difficulty, but the evaluation of the refractive index gradient is more troublesome. The assumptions of the derivation of Equation (23) restrict its applicability to dilute solutions. The refractive index of a dilute solution changes very gradually with concentration hence a plot of n versus c, the slope of which equals dn/dc, will be nearly horizontal. Since the intensity ratio depends on the square of dn/dc, it is clear that successful interpretation of Equation (23) depends on the accuracy with which this small quantity is evaluated. Measuring the absolute refractive indices of various solutions and determining dn/dc by difference or graphically would introduce an unacceptable error. A more precise method must be used to measure this quantity. 

The cells in which the scattering solutions are measured should have flat windows at the 

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Before looking at the experimental aspects of light scattering, it is convenient to define several more quantities. First, a quantity known as the Rayleigh ratio Re is defined as... 

In the late 1800 s it was recognized that light will be scattered in a medium which contains variations in the dielectric constant (Rayleigh (1964)). Since then, the theoretical and experimental aspects of light scattering have been comprehensively developed (see recent reviews by Fabelinskii (1968) and Kerker (1969)). 

Experimental aspects of light scattering and application to polymer solutions... 

Until now we have looked at various aspects of light scattering under several limiting conditions, specifically, C2 = 0, 0 = 0, or both. Actual measurements, however, are made at finite values of both C2 and 6. In the next section we shall consider a method of treating experimental data that consolidates all of the various extrapolations into one graphical procedure. 

In this paper certain aspects of light scattering as a technique for polymer characterization will be discussed from the theoretical point of view. This does not mean that the experimental problems are regarded as easy. On the contrary, it is the authors opinion that only very careful experimentation will lead to results accurate enough to be fully used in the rather difficult theoretical formulas. A great help in this respect is a good and reliable apparatus. 

Dynamic light scattering is a powerful tool to determine the size, the size distribution, and the shape of the particles in suspension. Theoretical and experimental aspects of this technique are available in standard monographs 129-31],... 

Abstract Flow cytometry is a technique for rapidly examining multiple characteristics of individual cells, by recording fluorescence signals emitted from cell-associated reporter molecules, and measuring cellular light scattering properties. This chapter introduces the principles and practice of flow cytometry, and reviews examples from the literature that highlight applications of this experimental tool in the neurosciences. The chapter concludes with protocols for three basic procedures that illustrate some practical aspects of analytical flow cytometry. 

The radial distribution function plays an important role in the study of liquid systems. In the first place, g(r) is a physical quantity that can be determined experimentally by a number of techniques, for instance X-ray and neutron scattering (for atomic and molecular fluids), light scattering and imaging techniques (in the case of colloidal liquids and other complex fluids). Second, g(r) can also be determined from theoretical approximations and from computer simulations if the pair interparticle potential is known. Third, from the knowledge of g(r) and of the interparticle interactions, the thermodynamic properties of the system can be obtained. These three aspects are discussed in more detail in the following sections. In addition, let us mention that the static structure is also important in determining physical quantities such as the dynamic an other transport properties. Some theoretical approaches for those quantities use as an input precisely this structural information of the system [15-17,30,31]. 

Elastic and inelastic light scattering are nowadays widely used techniques for the characterization of fluids. In particular, these techniques have been extensively and successfully used with microemulsion systems to obtain information about droplet sizes. Surface light scattering is a less common technique but has been used with microemulsion interfaces, in particular to measure the ultralow interfacial tensions found in these systems. In this chapter we discuss these aspects, first recalling the theoretical background and illustrating the potential of the techniques with experimental results. 

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