Light scattering studies photon correlation spectroscopy

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. 

FIGURE 1.180 Particle size distributions in aqueous suspensions of A-300/BSA(Sigma) at CsjOj=0.45 wt% and CgsA=0.07 wt% and pH (a) 3.84 and (b) 8.53 with respect to the light-scattering intensity, particle volume and number. (Adapted from J. Colloid Interface Sci., 260, Gun ko, V.M., Mikhailova, I.V., Zarko, V.I. et al.. Study of interaction of proteins with fumed silica in aqueous suspensions by adsorption and photon correlation spectroscopy methods, 56-69, 2003c. Copyright 2003, with permission from Elsevier.)... 

In a series of papers (24-29) Eicke and co-workers reported results of thorough studies performed on inverse micellar systems involving hydrocarbons such as benzene or isooctane and surfactants such as AY or AOT aerosols. Dielectric, conductance, ultracentrifugation, NMR, light scattering, fluorescence depolarization and photon correlation spectroscopy techniques were used. The main conclusions arrived at are the following ones, as expressed in C29). For water-to-AOT molar ratios smaller than 10, water-in-isooctane systems consist of dispersions of hydrated soap aggre-... 

Measurement System Motions of polymer molecules in solution can be conveniently studied by using dynamic light scattering (DLS). It is also called quasi-elastic light scattering (QELS) and photon correlation spectroscopy... 

The scattered light was analyzed either by high resolution Fabry Perot Spectroscopy for Che propagative mode study (longitudinal and transverse) or by photon correlation spectroscopy for the nonpropagative mode study (structural relaxation process). Details of the former technique together with the high pressure optical system (0-400 MPa) have recently been described (5). 

Dynamic light scattering involves the study of time-dependent fiuctuations in the intensity of scattered light which are the result of the Brownian motion of the particles. The random movement of the particles causes the distances between the particles to fiuctuate, causing constantly varying constructive and destructive interference patterns. This time-dependent fiuctuation in the intensity can be correlated with itself to obtain the diffusion coefficient of the particles. This method is also called photon correlation spectroscopy (PCS) and quasi-elastic light scattering (QELS) [21, 22]. 

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