Dissymmetry of scattering

Problem 4.14 Using light of wavelength 5461 A and benzene as solvent (refractive index 1.5014), what is the limiting size (root mean square end-to-end distance) of a polymer coil above which the molecule can no longer be regarded as a point source in refraction  

This represents the critical value of the diameter or length of the scattering molecule. 

The root-mean-square distance between the ends of the polymer chain is a convenient 

If the experimentally observed values of Rg and / g differ signi candy from one another, interference effects are present. These effects may be taken into accoimt by de rung a parameter P 6), called the particle scattering factor. It is simply the ratio of the scattering intensity to the intensity in the absence of interference, measured at the same angle 6  

The Rg in our previous equation (4.82) is Rg)jyo interference since in their derivation the scattering molecules have been considered as point sources. Thus Eq. (4.82) may be rearranged in terms of the observed Rg and P 9) as 

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Solutions of polystyrene and purified cyclohexane after filtration still exhibited appreciable dissymmetry of scattered intensities at high temperatures where the influence of the critical opalescence was precluded. Therefore all solutions were freed from dust by centrifugation. After a... 

Particles which are too small to show a series of maxima and minima in the angular variation of scattered light are frequently studied by measuring the dissymmetry of scattering (usually defined as the ratio of the light scattered at 45° to that scattered at 135°). The dissymmetry of scattering is a measure of the extent of the particles compared with A. If the molecular or particle size is known, it can be related to the axial ratio of rod-like particles or the coiling of flexible linear macromolecules. 

F. Reduced intensity measurements at 90° calibrated by direct turbidity measurements and corrected for angular dissymmetry of scattering. 

The dissymmetry method is useful especially if the instrument does not afford facilities for a wide angular scan of scattered intensities. For large particles the scattering envelope is not symmetrical and, as already indicated in Fig. 1, the forward scatter is larger than that in the backward direction. Hence the dissymmetry Z is greater than unity, where... 

In the determination of M , the intensity of scattered light is measured at different concentrations and at different angles 6). The incident light sends out a scattering envelope that has four equal quadrants (Figure 3.11a) for small particles. The ratio of scattering at 45° compared with that at 135° is called the dissymmetry factor or dissymmetry ratio Z. The reduced dissymmetry factor Z is the intercept of the plot of Z as a function of concentration extrapolated to zero concentration. 

Tn the critical region of mixtures of two or more components some physical properties such as light scattering, ultrasonic absorption, heat capacity, and viscosity show anomalous behavior. At the critical concentration of a binary system the sound absorption (13, 26), dissymmetry ratio of scattered light (2, 4-7, II, 12, 23), temperature coefficient of the viscosity (8,14,15,18), and the heat capacity (15) show a maximum at the critical temperature, whereas the diffusion coefficient (27, 28) tends to a minimum. Starting from the fluctuation theory and the basic considerations of Omstein and Zemike (25), Debye (3) made the assumption that near the critical point, the work which is necessary to establish a composition fluctuation depends not only on the average square of the amplitude but also on the average square of the local... 

Compared to the colligative methods light scattering can yield information on a possible dissymmetry of the aggregates. For anisotropic particles the direction of the electric field associated with the incident light may not coincide with the shift of the electron cloud. The intensity of light scattered at (usually) 90° from anisotropic aggregates is increased over the value predicted on the basis of isotropy by the Cabannes factor. 

Z collision number Z z fraction z ionic charge z coordination number z dissymmetry (light scattering) z parameter in excluded volume theory z number of nearest neighbors... 

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