Quasi-elastic light scattering spectroscopy

Schematic models for the expanded structure of bile acid-phosphatidylcholine mixed micelles are shown in Fig. 2B. The original model was proposed by Small in 1967 (S36). In this model the mixed micelle consisted of a phospholipid bilayer disk surrounded on its perimeter by bile acid molecules, which were oriented with their hydrophilic surhices in contact with aqueous solvent and their hydrophobic sur ces interacting with the hydrocarbon chains of the phosphohpid molecules. This model has recently been revised, based on further studies of mixed micelles using quasi-elastic light scattering spectroscopy (M20). In a new model for the molecular structure of bile acid-phospholipid mixed micelles. Mazer et al. (M20) propose a mixed disk, in which bile acids are found not only on the perimeter of phospholipid bilayers, but also incorporated within their interior in high concentrations (Fig. 2B). The size of these mixed micelles was estimated to be as high as 200 to 400 A in radius in some solutions, and disk-shaped particles in this size range were observed by transmission electron microscopy (M20). Micellar aggregates similar in size and structure to those found in model bile solutions have been demonstrated in dog bile (M22).

The nature of polymer motion in semidilute and concentrated solutions remains a major question of macromolecular science. Extant models describe polymer dynamics very differently 3-11). Many experimental methods have been used to study polymer dynamics (12). One meAod is probe diffusion, in which inferences about polymer dynamics are made by observing the motions of dilute mesoscopic probe particles diffusing in the polymer solution of interest. Probe diffusion can be observed by several experimental techniques, for example, quasi-elastic light scattering spectroscopy (QELSS), fluorescence recovery after photobleaching (FRAP), and forced Rayleigh scattering (FRS). 

Probe diffusion was determined using quasi-elastic light scattering spectroscopy. QELSS monitors the temporal evolution of concentration fluctuations by measuring the intensity I(q,t) of the light scattered at time t, and calculating the intensity-intensity correlation function... 

The dynamics of the collective excitations can be determined conveniently by photon autocorrelation spectroscopy, which is also called self-beating, time-resolved Rayleigh or quasi-elastic light scattering spectroscopy [29]. Here the time autocorrelation function of the scattered light intensity G (t) is measured, which, in the heterodyne detection regime, is given by ... 

The literature examined here includes three major experimental approaches, namely (i) optical probe diffusion studies, largely made with quasi elastic light scattering spectroscopy (QELSS), to observe diffusion of dilute probe particles, (ii) particle tracking studies in which the detailed motions of individual particles are recorded, and (iii) true microrheology measurements of the driven motion of mesoscopic probes. 

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). 

The technique is alternatively called photon correlation spectroscopy (PCS) or quasi-elastic light scattering (QELS). 

Generally, mean size and size distribution of nanoparticles are evaluated by quasi-elastic light scattering also named photocorrelation spectroscopy. This method is based on the evaluation of the translation diffusion coefficient, D, characterizing the Brownian motion of the nanoparticles. The nanoparticle hydro-dynamic diameter, is then deduced from this parameter from the Stokes Einstein law. 

Dynamic (quasi-elastic) light scattering that is usually referred as photon correlation spectroscopy this is a rapid technique that is especially suited to measuring submicron particles (nanosize range). 

Two scattering methods, namely time-average (static) Hght scattering and dynamic (quasi-elastic) light scattering (also referred to as photon correlation spectroscopy PCS), will be discussed in the following sections. 

DLS is a method that measures the time-dependent fluctuation of scattered intensity, and is also referred to as quasi-elastic light scattering or photon correlation spectroscopy. The latter term is the most commonly used for describing the process, since most dynamic scattering techniques employ autocorrelation. 

Polymeric materials were found in the toluene-insoluble fraction [127]. The materials have no solubility in common organic solvents or so-called fullerene solvents but are partially soluble in DMSO. Evidence for the polymeric nature of the materials includes results of dynamic scattering based on photon correlation spectroscopy of quasi-elastic light scattering (PCS-QELS) [128,129] and gel permeation chromatography using DMSO as mobile phase [117]. The structural characterization of the polymers remains a challenge. 

Dynamic light scallering (DLS). also known as photon correlation spectroscopy (I CS) and quasi-elastic light scattering (OFI.S). is a powerful technique for probing solution dynamics and fur measuring particle sues.-The DLS technique can obtain size information in a few minutes for particles with diameters ranging from a few nanometers to about 5 pm. 

This is also known as photon correlation spectroscopy (PCS) or quasi-elastic light scattering (QELS). It uses scattered light to measure the rate of diffusion of protein particles in a sample. The data on molecular motion are digitally processed to yield a size distribution of particles in the sample, where the size is given by the mean Stokes radius or hydrodynamic radius of the protein particles this is the effective radius of a particle in its hydrated state. Clearly, the hydrodynamic radius depends on both mass and shape. 

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]. 

Ford NC. Theory and practice of photon correlation spectroscopy. In Dahneke BE, editor. Measurement of Suspended Particles by Quasi-elastic Light Scattering. New York WUey-Interscience 1983. p 31. 

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