Dynamic light scattering technique

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). 

Fig. 4 PIC dye nanoparticles prepared by the ion-association method. (1) Particle size distributions (determined by the dynamic light scattering technique) and the corresponding electron micrographs of the dye nanoparticles. The average diameter can be controlled by tuning the molar ratio of TPB- to PIC+ (=[TPB-]/[PIC+]. With an increase in the molar ratio, the average diameter decreased. (2) Absorption spectra of PIC nanoparticles in aqueous solution with different sizes (125 and 64 nm in diameter), exhibiting size-dependent peak shift of the 0-0 band. The spectrum of the aqueous PIC-Br monomer solution is also shown...

Particles of a size of less than 2 turn are of particular interest in Process Engineering because of their large specific surface and colloidal properties, as discussed in Section 5.2. The diffusive velocities of such particles are significant in comparison with their settling velocities. Provided that the particles scatter light, dynamic light scattering techniques, such as photon correlation spectroscopy (PCS), may be used to provide information about particle diffusion. 

Critical phenomena of gels have been studied mainly by dynamic light scattering technique, which is one of the most well-established methods to study these phenomena [18-20]. Recently, the critical phenomena of gels were also studied by friction measurement [85, 86] and by calorimetry [55, 56]. In the case of these methods, the divergence of the specific heat or dissipation of the friction coefficient could be monitored as a function of an external intensive variable, such as temperature. These phenomena might be more plausible to some readers than the divergence of the scattered intensity since they can observe the critical phenomena in terms of a macroscopic physical parameter. 

Using dynamic light-scattering techniques, Lechner was able to prove that this effect is due to the tendency of PVA to agglomerate for more details see Kulicke, Bose, Bouldin. On the other hand, a decrease in viscosity has been obtained with no detectable change in the average molecular weight. 

The size distribution of solid samples can be determined by static and dynamic light-scattering techniques the size ranges from a few nanometers to a few microns. The concept uses the idea that small particles in a suspension move in a random pattern called Brownian motion. When the moving particles are irradiated by a... 

Dynamic light scattering (DLS) techniques measure the fluctuations in the scattered light intensity caused by the random Brownian motion of the dispersed particles. The use of a theoretical model of particle Brownian motion enables us to extract particle size from DLS data. Other dynamic light scattering techniques such as electrophoretic light scattering (ELS) study collective particle motions. Theoretical interpretation of ELS data leads to other particle properties such as electrophoretic mobility fi and zeta potential f. These techniques will be discussed in more detail in subsequent sections. 

Sol-gel silica particles of four different sizes, viz. 0.2 pm, 0.5 pm, 1.0 pm and 1.5 pm were obtained from Geltech Corporation. Particle size analysis on the slurries was carried out using a Honeywell Microtrac UPA 150 particle size analyzer, which utilizes the dynamic light scattering technique. In addition. Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM) was also used for determining particle size and shape. 

To measure the droplet size distribution of the primary emulsion (W/O in W/O/W or O/W in O/W/O) that has a micron range (with an average radius of 0.5-1.0 pm), a dynamic light-scattering technique (also referred to as photon correlation spectroscopy PCS) can be apphed. Details of this method are described in Chapter 19. Basically, the intensity fluctuation of scattered light by the droplets as they undergo Brownian diffusion is measured from this, the diffusion coefficient of the droplets can be determined, and in turn the radius can be obtained by using the Stokes-Einstein equation. 

When assessing a nanoemulsion formation, the normal approach is to measure the droplet size distribution using dynamic light scattering techniques, including photon correlation spectroscopy (PCS). In this technique, the intensity fluctuation of light scattered by the droplets is measured as they undergo Brownian motion... 

Both static and dynamic light-scattering techniques will continue to find wide applications in the study of the structure of more concentrated systems. 

The practical implementation of dynamic light-scattering techniques is not a difficult task, but there are a number of choices to be made and a few pitfalls that should be avoided. The following describes the simplest configuration of a PFS instmment and provides a guide to these choices and problems. 

We would like to thank the S.E.R.C. and Unilever Research for support for one of us (DNS) Unilever Research also provided access to Si NMR and laser Raman spectrometers. We thank EKA AB, Surte, Sweden, for financial support for another of us (KRA) and for help with the ultrafiltration experiments. We are also very grateful to Mr. Kenneth Rosenquist of the Swedish Institute for Surface Chemistry, Stockholm, for his assistarce in applying the dynamic light scattering technique. Finally we are grateful to the PQ Corporation for making it possible for this paper to be presented at New York. 

The ability of DCAA to act as a dispersant for SWNTs and the effect of the addition of AMPSA on this ability was investigated using the dynamic light scattering technique. The hydrodynamic diameter distribution for DCAA-SWNT (0.0 % (w/w)) solutions containing %(w/w) AMPSA was determined (Figure 1). 

The translational diffusion coefficients of the xanthans could not be measured by a dynamic light scattering technique. Other modes of motion in addition to translational diffusion may have been detected at the 40° scattering angle as a direct result of the high pol3nmer molecular weights. 

Rotstein et al. included polystyrene (PS) as a probe polymer in poly(vinyl methyl ether) that is with a network chain concentration of 0.235 g/ml and is swollen by toluene. They measured the diffiision coefficient of PS, Dps, using the dynamic light scattering technique and obtained the results as shown in Fig. 15 [15]. The slope of this plot is —2.8. Similarly, the slope for the gel with network chain concentration of 0.200 g/ml was —2.7. These values for molecular weight dependence are larger than expected in a reptation region of —2. This was explained as due to the distribution of network size and the fact that the probe polymer localized near the entropically stable large networks. When the ratio r of... 

The difference in diffusion behavior of probe polymers has been investigated where the network formation of the host polymer is due to physical entanglement such as in a semidilute solution or covalent cross-linking as in a gel. Aven and Cohen [16] used polystyrene (PS) as a probe polymer. They studied the diffiision coefficient of PS (A/, = 4140,7620, and 14,100) in various concentrations O swollen by tetrahydrofuran (THF) and PDMS M — 26,500) solution using a dynamic light scattering technique. 

Dynamic light scattering technique, 151 Dynamic screening distance, 149 Dynamic shielding distance, 162... 

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