Dynamic Light Scattering Photon Correlation Spectroscopy

Dynamic Light Scattering (Photon Correlation Spectroscopy, PCS) 

In this technique one measures the intensity fluctuation of scattered light by the droplets as they undergo Brownian motion [13]. When a light beam passes through a colloidal dispersion, an oscillating dipole movement is induced in the 

The photocount correlation function gPl (t) is given by Eq. (10.30), where t is the correlation delay time. 

The correlator compares gPl (t) for many values of z. B is the background value to which gl l (t) decays at long delay times, gfll (t) is the normalised correlation function of the scattered electric field and y is a constant (- 1). 

The particle radius R can be calculated from D using the Stokes-Einstein equation, 

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Figure 17 Molar mass distributions of polystyrene in ethyl acetate obtained by dynamic light scattering (photon correlation spectroscopy, PCS) and TDFRS with short and long exposure time tp. The dashed curves represent the distribution as determined by SEC. Reproduced with permission from Rossmanith and Kohler [107]. Copyright 1996 American Chemical Society.

Methods for analysis of the particle size distribution in the aerosol cloud include techniques such as time of flight measurement (TOE), inertial impaction and laser diffraction. Dynamic light scattering (photon correlation spectroscopy) is confined to particles (in suspension) in the submicron range. In addition to the size distribution, the particle velocity distribution can be measured with the Phase Doppler technique. 

Dynamic light scattering (photon correlation spectroscopy, PCS) Laser doppler velocimetry... 

Maltose-containing washed or unwashed DRVs (33 /tmole PC) were microfluidized in the presence of water or PBS for up to 10.6 cycles, and samples were measured for vesicle size (diameter in nanometers) by dynamic light scattering (photon correlation spectroscopy). Polydispersity indexes ranging from 0.503 to 0.653 (water) and from 0.517 to 0.653 (PBS) were similar to those obtained with some of the lipid compositions of liposomes employed by others. 

Dynamic light scattering (photon correlation spectroscopy, PCS) can also be applied to obtain the hydrodynamic radius of the micelle. By measuring the intensity fluctuation of scattered light by the micelles (when these undergo Brownian diffusion), one can obtain the diffusion coefficient of the micelles D, from which the hydrodynamic radius R can be obtained using the Stokes-Einstein equation ... 

Size distribution Static and dynamic laser light scattering Photon correlation spectroscopy... 

The scattering techniques, dynamic light scattering or photon correlation spectroscopy involve measurement of the fluctuations in light intensity due to density fluctuations in the sample, in this case from the capillary wave motion. The light scattered from thermal capillary waves contains two observables. The Doppler-shifted peak propagates at a rate such that its frequency follows Eq. IV-28 and... 

Photon Correlation Spectroscopy. Photon correlation spectroscopy (pcs), also commonly referred to as quasi-elastic light scattering (qels) or dynamic light scattering (dls), is a technique in which the size of submicrometer particles dispersed in a Hquid medium is deduced from the random movement caused by Brownian diffusion motion. This technique has been used for a wide variety of materials (60—62). 

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. 

Pecora, R. (Ed.), Dynamic Light Scattering Applications of Photon Correlation Spectroscopy, Plenum, New York, 1985. 

The use of photon correlation spectroscopy to study the dynamics of concentration fluctuations in polymer solutions and gels is now well established. In bulk polymers near the glass transition there will be slowly relaxing fluctuations in density and optical anisotropy which can also be studied by this technique. In this article we review the development of the field of photon correlation spectroscopy from bulk polymers. The theory of dynamic light scattering from pure liquids is presented and applied to polymers. The important experimented considerations involved in the collection and analysis of this type of data are discussed. Most of the article focuses on the dynamics of fluctuations near the glass transition in polymers. All the published work in this area is reviewed and the results are critically discussed. The current state of the field is summarized and many suggestions for further work are presented. 

In dynamic light scattering (DLS), or photon correlation spectroscopy, temporal fluctuations of the intensity of scattered light are measured and this is related to the dynamics of the solution. In dilute micellar solutions, DLS provides the z-average of the translational diffusion coefficient. The hydrodynamic radius, Rh, of the scattering particles can then be obtained from the Stokes-Einstein equation (eqn 1.2).The intensity fraction as a function of apparent hydrodynamic radius is shown for a triblock solution in Fig. 3.4. The peak with the smaller value of apparent hydrodynamic radius, RH.aPP corresponds to molecules and that at large / Hs,Pp to micelles. 

Compared to binary mixtures of low molecular fluids, the critical behavior of polymer blends has been much less explored so far. However, a number of interesting static and dynamic critical phenomena in polymer blends attract increasing attention [4, 5], Neutron, X-ray, and static light scattering experiments belong to the major techniques for characterizing the static properties of polymer blends. Photon correlation spectroscopy (PCS) has traditionally been the method of choice for the investigation of the dynamics of critical [6-9] and noncritical [10-12] polymer blends. 

The methods described in this book are primarily concerned with the measurement of the microstructure of complex fluids subject to the application of external, orienting fields. In the case of flow, it is also of interest to measure the kinematics of the fluid motion. This chapter describes two experimental techniques that can be used for this purpose laser Doppler velocimetry for the measurement of fluid velocities, and dynamic light scattering (or photon correlation spectroscopy) for the determination of velocity gradients. 

Photon correlation spectroscopy (PCS), also referred to as dynamic light scattering, is a technique that is used to measure particles in the size range of 1 -0.001 p,m. Unlike particle sizing by laser diffraction, the sample, dispersed in a diluent, is not circulated, stirred, or sonicated during the measurement. The technique is dependent upon a stable suspension of particles that are in constant random motion due to collisions with molecules of the suspending liquid. 

Dynamic light scattering (DLS), also called photon correlation spectroscopy (PCS) or laser light scattering (LLS) is a technique based on the principle that moving objects cause a frequency shift due to the Doppler effect. If a solution of macromolecules with random Brownian motion is illuminated with monochromatic laser light, the scattered light should contain a distribution of frequencies about the incident frequency the spectral line is virtually broadened. The width of the distribution is related to the MMD. 

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