Fluctuations, Light Scattering and Diffusion

Concentration fluctuations, light scattering and diffusion in solutions... 

In a two-component system, both light scattering and diffusion depend directly upon the value of dpi/dx (or an equivalent one) which, in turn, determines the thermodynamic stability of the one-phase system state and the level of concentration fluctuations (cf. formulae 1.1.2-53, 1.4- 35, and 2.4-8,-9,-43). Due to this, near the mixture critical concentration X2c at the isotherm of the state diagram there are both a maximum of the scattered light intensity and a minimum of the diffusion coefficient D xi) (see Fig-... 

The temporal evolution of P(r,t 0,0) is determined by the diffusion coefficient D. Owing to the movement of the particles the phase of the scattered light shifts and this leads to intensity fluctuations by interference of the scattered light on the detector, as illustrated in Figure 9. Depending on the size of the polymers and the viscosity of the solvent the polymer molecules diffuse more or less rapidly. From the intensity fluctuations the intensity autocorrelation function... 

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