Quasielastic light scattering and diffusion

How are light scattering spectra related to the mohons of scattering centers in soluhon In a QELSS experiment, one illuminates the sample of interest with abeam of coherent monochromahc light, and uses signal analysis methods to characterize fluctuations in the hme-dependent intensity I q,r) of the scattered light. QELSS measures directly the intensity—intensity correlation function or dynamic structure factor S q,t)  

The scattering vector q is the vector difference between the propagation vectors of the incident and scattered light, with magnitude 

The directions of the incident and scattered light are conventionally taken to define the horizontal plane, the two fundamental polarizations of linearly polarized light being chosen as the vertical (V) and horizontal (H) directions. Polarized light scattering experiments study VV scattering the incident and scattered light rays 

The orientation of /I with respect to the scattering direction determines the scattered field s polarization, a is the molecular polarizability tensor for molecule i, and has a scalar (on-diagonal) component a, I being the identity tensor, that leads to VV scattering. Note that also may have a nonzero tensor component 5a = — al 

The intensity of the scattered light is related to particle orientations and positions Vi t) via 

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C. F. Schmidt, M. Baermann, G. Isenberg, and E. Sackmann. Chain dynamics, mesh size, and diffusive transport in networks of polymerized actin. A quasielastic light scattering and microfluorescence study. Macromolecules, 22 (1989), 3638-3649. 

Raj, T. and Flygare, W. H. 1974. Diffusion studies of bovine serum albumin by quasielastic light scattering. Biochemistry 13, 3336-3340. 

Phillies, G. D. J., G. B. Benedek, and N. A. Mazer, "Diffusion in Protein Solutions at High Concentrations A Study of Quasielastic Light Scattering Spectroscopy," J. Chem. Phys., 65, 1883 (1976). 

Tivant P, Turq P, Drifford M, Magdelenant H, Menez R. Effect of ionic strength on the diffusion coefficient of chondroitin sulfate and heparin measured by quasielastic light scattering. Biopolymers 1983 22 643-662. 

Phillies, G., G. Benedek, and N. Mazer, Diffusion in protein solutions at high concentrations A study by quasielastic light scattering spectroscopy. Journal of Chemical Physics, 1976, 65, 1883-1892. 

Other workers have adopted a different corpuscular model for quasielastic light scattering from a gel (122,123,124). The gel is treated as an assembly of identical, independent, harmonically bound particles, each in Brownian motion about a stationary mean position. The analysis of Garlson and co-workers (123,124) formally includes the presence of static interference scattering components resulting from spatial structuring of the polymer chains and from the consequent constraints in the diffusive motions of the chains. This formalism leads to the prediction of nonexponential scattered intensity autocorrelation functions. 

In a quasielastic light scattering study of macromolecular solutions, it is essential to establish a clear relationship between the experimental conditions and the type of relaxation phenomena manifest in the light scattering data. To accomplish this, one must perform experiments over a range of scattering angles and solution concentrations. One of our objectives is to determine the translational diffusion coefficient (D ) for xanthan, and to relate this parameter to a hydrodynamic size. 

The porosity is not a separate factor for diffusion measurements using techniques such as pulsed field gradient nuclear magnetic resonance spectroscopy and some modes of quasielastic light scattering in which the diffusivity is determined from the mean-square displacement of solutes ... 

Eq. (51) gives spectrum for the quasielastic light scattering for scatters undergoing translational diffusion, and is the equation used in obtaining difhision constants by this method. 

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