Time-averaged Light Scattering

Rayleigh ratio Ro(K), is given in the Rayleigh-Debye approximation by  

In order to allow for correlations in the positions of the particles, equation (40) is supplemented by 

In principle, then, through equation (45), light-scattering studies of concentrated colloidal dispersions yield structural information in the form of h(r). In practice, however, the usefulness of equation (45) is severely limited by the fact that it is valid only in the absence of multiple scattering. With concentrated aqueous dispersions of latex particles, this means studying very small sample volumes in which structure could be influenced by the surface properties of the container. Even so, no measurements of this sort have yet been reported due to the experimental difficulties involved. 

The multiple-scattering problem has so far restricted the study of structure to two types of dispersion (i) dilute latex dispersions at very low salt concentration (ku 1), where structure results from the repulsion between long-range double-layers,and (ii) polymer latex particles dispersed in an organic solvent of closely matched refractive index. 

Information about the form of the pair potential (r) may be derived from 

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Time-averaged light scattering, static or elastic scattering. 

As with time-average light scattering, there is a need to introduce a stracture factor when calculating the average diffusion coeflflcient For comparative purposes, the collective diffusion coefficient D can be calculated, and this can be related to its value at inflnite dilution by [14],... 

VI. Time-Averaged Light-Scattering Experiments on Liquid Films.367... 

VI. TIME-AVERAGED LIGHT-SCATTERING EXPERIMENTS ON LIQUID FILMS... 

For time-averaged light-scattering in the Rayleigh-Debye approximation, equation (18) reduces to ... 

The average floccule radius in a flocculating colloidal suspension was measured as a function of time by light-scattering methods and the data were fitted to the equation ... 

The angular differential cross-section is calculated by taking dP/dQ, where dP is the time-averaged power scattered into solid angle dQ, and dividing by the intensity of the incident light. This is equivalent to writing da/dQ = r )/ Eq so that... 

The total scattered light intensity used in LD theory (W/m ) Time-average light intensity when radiating through a bubble mixture by LDA (W/m )... 

Figure 5B. Correlation of right-angle light scatter measured by fluorometry and flow cytometry. The top panel shows flow-cytometric data of side scatter of fixed, stained cells during the time course of stimulation by 1-nM (solid line, solid circles) or 0.01-nH (dashed line, open circle) FLPEP. The bottom panel shows the corresponding right-angle light-scatter data acquired pseudo-simultaneously on live cells in the fluorometer. The flow-cytometric data have been averaged, but the fluorometry data are plotted for both duplicates from one donor. Reproduced with permission from Ref. 27. Copyright 1985 Rockefeller University Press.

In static light scattering only the time average of the scattered intensity is recorded, while DLS measures the scattered intensity with a time resolution of milliseconds or even tenths of nanoseconds. These fluctuations in the scattered intensity can be related to dynamical processes within the sample. 

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