Time Average Static Light Scattering

The intensity of scattered light I(Q) is measured as a function of scattering vector 

For a fairly dilute system, I(Q) is proportional to the number of particles N, the square of the individual scattering units V, and some property of the system (material constant) such as its refractive index, 

The instrument constant depends on the geometry of the apparatus (the light path length and the scattering cell constant). 

For more concentrated systems, I Q) also depends on the interference effects arising from particle-particle interactions, 

S(Q) is the so-called structure factor which takes into account the particle-particle interaction. 5(0 is related to the radial distribution function g(r) (which gives the number of particles in shells surrounding a central particle) [12], 

three scattering methods will be discussed Time-average (static) light scattering, dynamic (quasi-elastic) light scattering, referred to as photon correlation spectroscopy, and neutron scattering. 

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In static light scattering only the time average of the scattered intensity is recorded, while DLS measures the scattered intensity with a time resolution of milliseconds or even tenths of nanoseconds. These fluctuations in the scattered intensity can be related to dynamical processes within the sample. 

The static light-scattering measurements described in the previous section provide a measure of the time-averaged scattered intensity. On the contrary, dynamic light scattering follows the random motion of molecules in solution called Browiuan... 

AR is commonly known as the excess Rayleigh ratio and for static light scattering depends upon the time-averaged mean-square excess polariza-... 

Any measurement of time-averaged scattering intensity falls into a category known as static light scattering (which includes laser diffraction, discussed in detail in Chapter 3). We limit the content of this subsection to the measurements of scattering intensity in order to determine absolute particle mass (molecular weight) and/or other parameters of very small and weak scatterers such as macromolecules and surfactants in solution in non-disturbed (still) solutions or suspensions. 

The methods of analyzing data for the concentration and angular dependence of the time-average scattering light intensity and the intensity-intensity time correlation function can be found in many LLS books and related literature. In this section, we will mainly concern ourselves with how to combine static and dynamic LLS results to characterize special polymers in regard not only to the average molar mass, but also to the molar mass and composition distributions. 

Time-averaged light scattering, static or elastic scattering. 

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