Diffusion wave spectroscopy DWS

DWS addresses dynamic light scattering in the multiple scattering concentration range. Pine et. al. [326] describe the theory for the technique and it has been applied to the determination of mean size and polydispersity [327,328]. The method has also been used for on-line measurement of concentrated suspensions [329]. 

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Foam rheology has been a challenging area of research of interest for the yield behavior and stick-slip flow behavior (see the review by Kraynik [229]). Recent studies by Durian and co-workers combine simulations [230] and a dynamic light scattering technique suited to turbid systems [231], diffusing wave spectroscopy (DWS), to characterize coarsening and shear-induced rearrangements in foams. The dynamics follow stick-slip behavior similar to that found in earthquake faults and friction (see Section XU-2D). 

Slow release rates and remarkable long shelf-life (months) were obtained compared to typical multiple emulsions stabilized by two short surfactants (SMO and polyoxyethylene (20) sorbitan monolaurate). Finally, the long lifetime of the emulsions allowed study via diffusing wave spectroscopy (DWS) of the interactions between the droplets and the globule surface [37],... 

FIG. 5.1 Multiple scattering is viewed as a random walk of the photon in diffusing wave spectroscopy (DWS). 

FIGURE 5.75 Diffusion wave spectroscopy (DWS). The light reaches the detector after multiple acts of scattering from dispersed particles. The optical path of the hght in the dispersion is modeled as a result of random diffusion motion. Forward (a) or backward (b) scattered hght can be analyzed. 

Unfortunately, because of space, we have not covered important new developments in light scattering for the study of nontransparent systems such as diffusion wave spectroscopy (DWS), fiber-optic quasi-elastic light scattering (FOQELS), dual-color cross-correlation, 3D crosscorrelation DLS, and improved techniques followed from these techniques [1-4]. 

For the interpretation of DLS measurements, it is prerequisite that multiple scattering has been avoided by sufficiently high sample dilution or even suppressed by technical means. In contrast, diffusing wave spectroscopy (DWS) evaluates the light fluctuations in the presence of strong multiple scattering. The decay of the... 

We can answer the first question by direct observation of the inner droplets using confocal microscopy. The dynamics of the inner droplets can be observed by a light diffusion technique suited to turbid media, diffusing wave spectroscopy (DWS). Both observations show that attractive interactions—either depletion or van der Waals interactions—occur between the droplets and the... 

Diffusing wave spectroscopy (DWS) is a light-scattering technique that allows the measurement of the dynamics of turbid systems (Weitz and Pine, 1993 Pine et al., 1990). A thick sample of multiple emulsions is illuminated with an enlarged laser beam. This sample diffuses light, and both backscattered and... 

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