Scattering static light

Light scattering has been widely nsed to characterize polymer chains in a solution. We can find the weight-average molecnlar weight (M ), the radius of gyration (R ), and the second virial coefficient (Ap. We can also learn abont the shape of the polymer molecnle—whether it is spherical, random-coiled, or rodlike. These quantities are difficnlt to obtain with other methods. Commercial instrnments are available. 

Two pinholes or two vertical slits are placed along the path of the scattered beam to restrict the photons reaching the detector to those scattered by the molecules in a small part of the solution called the scattering volume. The scattering volume is an intersection of the laser beam with the solid angle subtended by the two pinholes (Fig. 2.33). 

The above considerations are valid only for monodisperse samples of rather low molecular weight. When characterizing polydisperse samples, all components i having different molecular weights M, and concentrations c, scatter independently from each other. Thus one obtains the following equation  

This internal interference is described by the particle form factor, P. It allows the direct calculation of the radius of gyration, of the macromolecules 

Because all the above deductions are valid for infinite low polymer concentrations but practical measurements have to be carried out at finite values of c, it is necessary to include the second virial coefficient A2. Thus the equation according to which evaluation of light-scattering experiments can be done is  

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These combined HDF and GPC separations require the use of detectors such as static light scattering or viscometers to help sort out the convoluted elution profiles seen in those type of experiments. It should also be remembered in these situations that the typical refractive index or ultraviolet detector responses may not be representative of the actual mass fraction of insolubles eluting from the column because of the significant light scattering that can occur with those large particles in the detector cell. 

Size exclusion chromatography coupled to static light scattering (SEC-MALLs) Molecular weight, molecular weight distribution. Polydispersity. Radius of gyration and distribution solution conformation and flexibility. Method of choice for moleciflar weight work. [4]... 

Scattering experiments can be performed to help determine the size and shape of the vesicles without the need for the extensive sample preparation required for electron microscopy and AFM. Dynamic (DLS) and static light scattering (SLS) are widely used to determine the size and possible shape of vesicle systems [40,42,48,49,51,... 

Scattering techniques Static light scattering Mw( a) M>104 300a Moderate to high... 

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. 

Fig. 13 Schematic diagram of a static light scattering (SLS) system.

A relationship for evaluation of static light scattering (LS) data from dilute solutions is given by... 

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