Scattering Photometry

Dynamic light scattering, coupled with modern computer programs and auxiliary equipment, automatically graphs Zimm plots and computes Mw, Rg, , Cl, and flow rates. New techniques have expanded the method to the semidilute and concentrated regimes (Barth and Sun, 1991). 

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Low Angle Light Scattering Photometry Static Envelopes. We shall first consider the final scattering envelopes obtained after gelation is complete. The next subsection will be devoted to the kinetic evolution of the scattering envelopes ... 

Bulk properties associated with large deformations, such as viscosity and toughness, are most closely associated with M . The values of are most often determined by light-scattering photometry. 

However, melt elasticity is more closely related to the third moment known as the z-average molecular weight M. The values of are most often determined using either light-scattering photometry or ultracentrifugation. It is shown mathematically as ... 

For polydisperse polymer samples, measurements that lead directly to the determination of the molecular weight, such as light-scattering photometry and membrane osmometry, are referred to as absolute molecular weight methods. Techniques such as viscometry are not absolute molecular weight methods because they require calibration using an absolute molecular weight technique. 

As noted earlier, certain techniques such as colligative methods, light-scattering photometry, special mass spectrometry (MS) techniques, and ultracentrifugation allow the calculation of specific or absolute molecular weights. Under certain conditions some of these also allow the calculation of the MWD. 

SEC-MALLS and SEC-LALLS Coupled chromatography and light-scattering photometry that allows the determination of a number of important values along with chain length distribution, sedimentation equilibrium experiment Ultracentrifugation technique that allows chain length information to be determined. 

Zimm plot Type of double extrapolation used to determine the weight-average molecular weight in light-scattering photometry. 

What kind of molecular weight do you generally get from light-scattering photometry ... 

Capillary hydrodynamic chromatography Fraunhofer diffraction Light-scattering photometry Phase Doppler anemometry Ultrasonic spectroscopy... 

Light Scattering Photometry. We will limit our discussion to LALLS because it constitutes a net improvement as compared to other methods of Mw determination. It has the advantage of providing absolute values of the Rayleigh ratio by direct comparison of scattered and transmitted light. 

Low Angle Laser Light Scattering Photometry. Weight-average molecular weights were determined with a KMX-6 photometer (LDC/Milton Roy). The light source was a 2 mW vertically polarized helium-neon laser (A =... 

Molecular weights are determined by end-group analysis (Mn), membrane osmometry (Mn), viscometry (Mv), size exclusion chromatography (Mm), light scattering photometry, and sedimentation (Mw). Any molar mass computed by these methods must be evaluated critically, in view of a dependence on methodology. 

Viscometry is the most widely used method for the characterization of polymer molecular weight because it provides the easiest and most rapid means of obtaining molecular weight related data and requires a minimum amount of instrumentation. A most obvious characteristic of polymer solutions is their high viscosity, even when the amount of added polymer is small. Even so, because viscometry does not yield absolute values of M, one must calibrate the viscometry results with values obtained for the same polymer and solvent by using an absolute technique such as light scattering photometry. 

Gebhart J, Heigwer G, Heyder J, Roth C, Stahlhofen W. The use of hght scattering photometry in aerosol medicine. J Aerosol Med 1988 1 89-112... 

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