Light scattering definition

Figure 10.11 Definition of variables required to describe interference of light scattered from points O and P.

The International Union of Pure and Applied Chemistry recommends that the definition should now be based on the ratio of the radiant power of incident radiation (Pq) to the radiant power of transmitted radiation (P). Thus, A = log(Po/P) = log T. In solution, Pq would refer to the radiant power of light transmitted through the reference sample. T is referred to as the transmittance. If natural logarithms are used, the quantity, symbolized by P, is referred to as the Napierian absorbance. Thus, B = ln(Po/P). The definition assumes that light reflection and light scattering are negligible. If not, the appropriate term for log(Po/P) is attenuance. See Beer-Lambert Law Absorption Coefficient Absorption Spectroscopy... 

Tables VI and VII give results corresponding to two series of lignin fractions obtained with a flow-through reactor (3). (The units for dn/dc and A2 are respectively ml.g-1 and mole.ml.g-2). These results show that LALLS allows the determination of low Mw values. The dn/dc values differ from sample to sample but vary only slightly for a given set of fractions. The second virial coefficient exhibits no definite trend. Negative values indicate perhaps some association effects but light scattering alone is not sufficient to ascertain this point.

We shall see that measurement of the osmotic pressure of a polydisperse system permits the experimental evaluation of M (Chapter 3), and light scattering experiments enable us to measure Mw (Chapter 5). It follows from the definition of these various averages that... 

Particle size measurement is one of the essential requirements in almost all uses of colloids. However, our discussion in Section 1.5 makes it clear that this is no easy task, especially since even the definition of particle size is difficult in many cases. A number of techniques have been developed for measuring particle size and are well documented in specialized monographs (e.g., Allen 1990). Optical and electron microscopy described in the previous section can be used when ex situ measurements are possible or can be acceptable, but we also touch on a few nonintrusive methods such as static and dynamic light scattering (Chapter 5) and field-flow fractionation (see Vignette II Chapter 2) in other chapters. 

FIG. 5.5 Schematic top view of a typical light scattering instrument showing the different components and the definition of 0. 

Fig. 11. Low-angle-laser-light-scattering results of polyacrylamides in 0.1 M Na2S04-solution at 25 °C. Note at K c/Re = 0 the molecular weight should be Mw = oo definition...

In general, the polarizability is a tensor whose invariants, trace and anisotropy, give rise to polarized and fully depolarized light scattering, respectively. Collision-induced light scattering is caused by the excess polarizability of a collisional pair (or a larger complex of atoms or molecules) that arises from the intermolecular interactions. In Section I.l, we are concerned with the definition, measurement, and computation of interaction-induced polarizabilities and their invariants. 

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