Dynamic light scattering diffusion motion

Kops-Werkhoven, et al. measured tracer diffusion of dilute 38 nm radius silica spheres diffusing through suspensions of 33 nm silica spheres, all in cyclo-heptane(12). The experimental method was dynamic light scattering particle motions were observed over distances large compared to their radius. They found ku =-2.7 0.3. 

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 rotational diffusion coefficient Dr of a rodlike polymer in isotropic solutions can be measured by electric, flow, and magnetic birefringence, dynamic light scattering, and dielectric dispersion. However, if the polymer has some flexibility, its internal motion makes it difficult to extract Dr for the end-over-end rotation of the chain from data of these measurements. In other words, Dr can be measured only for nearly rodlike polymers. 

Evanescent wave dynamic light scattering (EWDLS) can be used to study the rapid motion of submicron particles near and on interfaces. Two situations have been studied restricted diffusion of spherical particles moving near an interface, and composition fluctuations of polymers attached to the interface. 

A method for measuring the size of aggregates in aqueous environments is dynamic light scattering (DLS). This technique uses scattered light to measure diffusion rates (Brownian motion) of particles in stable suspensions to determine a size based on the Stokes-Einstein equation ... 

Polymers in solutions incessantly change both their shape and position randomly by thermal agitation. This Brownian motion dominates various time-dependent phenomena in polymer solutions such as viscoelasticity, diffusion, birefringence, and dynamic light scattering, which are to be discussed in subsequent chapters. In this chapter, we study the basic theory of Brownian motion. Since the general aspects of the theory of Brownian motion have already been discussed in many articles, we shall limit the discussion to topics which will be useful in the application to polymer solutions and suspensions. 

I lie experimental results concerning dynamic light scattering in polymer solutions indicate the existence of two diffusion modes of a maeromolecule. The first mode is concerned with the conventional self-diffusion coefficient of the polymer. To the second one is as cribed the reptation motion of the maeromolecule in an imaginary pipe of enlanglemonl points formed from other macromolecules. 

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. 

Photon correlation spectroscopy — also dynamic light scattering (DLS) or quasi-elastic light scattering (QELS) — is a robust and rapid method for size determinations in the colloidal range (from about 5nm to 1 m ). In PCS, intensity fluctuations of the scattered light due to particle motion are measured in dependence on time. By the diffusion coefficient of the particles in the measurement fluid, the particle diameter can be calculated according the Stokes-Einstein Eq. (9.1) under the assumption of a spherical particle shape ... 

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]. 

When particles are small enough to undergo Brownian motion, there is a continuous variation in the distance between the particles. As a consequence of this motion, constructive and destructive interference of the light scattered by neighboring particles yields intensity fluctuations. Following the intensity fluctuations as a function of time, the diffusion coefficient of the particles can be measured, and consequently, via the Stokes-Einstein equation, if the viscosity of the medium is known, the hydrodynamic radius or diameter of the particles can be calculated. Dynamic light scattering is therefore a very efficient method to determine the... 

Y. Tsunashima, N. Nemoto, and M. Kurata. Dynamic light scattering studies of polymer solutions. 2. Translational diffusion and intramolecular motions of polystyrene in dilute solutions at the temperature. Macromolecules, 16 (1983), 1184-1188. 

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