Light Rayleigh ratio

Hence, the value of I/Iq is dependent on relative molar mass of the molecules involved in the light scattering. The Rayleigh ratio, Rg, may be defined as ... 

Values of are obtained partly by previous calibration using a series of standard light scatterers whose Rayleigh ratios have been precisely determined. Typical standards used in practice are poly(methyl methacrylate) blocks, colloidal silica suspensions, or tungsto-silicic acid, H4SiW 2O40-... 

The expressions for scattered light intensity (and Rayleigh ratio) must be corrected by dividing by the appropriate Cabannes factor. Effectively this is equivalent to replacing the optical constant K as defined in Eq. (24) by Kf and by 2 Kfj for unpolarised and vertically polarised incident light respectively. 

R(0) is the excess Rayleigh ratio, n and are the refractive index of the solvent and the wavelength of the light source. 

Light Scattering Photometry. We will limit our discussion to LALLS because it constitutes a net improvement as compared to other methods of Mw determination. It has the advantage of providing absolute values of the Rayleigh ratio by direct comparison of scattered and transmitted light. 

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... 

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. 

The formal similarity between Equations (27) and (39) helps us understand somewhat better the physical significance of the Rayleigh ratio Re. It is directly proportional to the attenuation of the light per unit optical path, measured as absorbance, when the attenuation is due to scattering alone. In this case absorbance is more properly called turbidity. 

The actual intensity of scattered light measured at a point C, denoted by ic, equals the product is times P(6). Therefore the experimental Rayleigh ratio obeys Equation (27) modified as follows ... 

What is the Rayleigh ratio How is it related to the intensity of the scattered light ... 

How does the interference of scattered light affect the Rayleigh ratio ... 

Light Scattering Experiments. This discussion is concerned only with elastic light scattering (24). In these experiments one measures the reduced scattering intensity (sometimes called the Rayleigh ratio) R(0), where... 

The quantity Re (1+cos2 0) is called the Rayleigh ratio. The unity term in (1+cos20) refers to the vertically polarised component of the scattered light, and the cos2 0 term to the horizontally polarised component. 

It is instructive to make a quantitative comparison between the experimental and theoretical curves. The light scattering intensity, expressed as the Rayleigh ratio, is a function of the size and number of particles. If all three reactions shown in Figure 7 polymerize at the same rate, Rp, then at a given time, say 10 seconds, the total volume of polymer formed, VT, will be the same in all three. Under these conditions, the scattering intensity becomes a direct measure of the relative number of particles ... 

Figure 7. Particle nucleation and growth kinetics determined by laser light scattering Rayleigh ratio vs. time. Exp. 1 no surfactant present Exp. 2 (SDS) = 6 X 10 4 mol dm 3. Theor Calculated from Curve 4, Figure 5, considering particle growth by polymerization.

---