Light scattering approximation

P. L. Frattini, and G. G. Fuller, Conservative dichroism of a sheared suspension in the Rayleigh-Gans light scattering approximation, J. Coll. Inter. Sci., 119, 335 (1987). 

Inasmuch as molecular weights obtained from light scattering approximate Mw more closely than Mn, the necessary substitutions for Ott/dc from Eq. (4.35) and Mn are made in Eq. (4.34) to give... 

The most widely used molecular weight characterization method has been GPC, which separates compounds based on hydrodynamic volume. State-of-the-art GPC instruments are equipped with a concentration detector (e.g., differential refractometer, UV, and/or IR) in combination with viscosity or light scattering. A viscosity detector provides in-line solution viscosity data at each elution volume, which in combination with a concentration measurement can be converted to specific viscosity. Since the polymer concentration at each elution volume is quite dilute, the specific viscosity is considered a reasonable approximation for the dilute solution s intrinsic viscosity. The plot of log[r]]M versus elution volume (where [) ] is the intrinsic viscosity) provides a universal calibration curve from which absolute molecular weights of a variety of polymers can be obtained. Unfortunately, many reported analyses for phenolic oligomers and resins are simply based on polystyrene standards and only provide relative molecular weights instead of absolute numbers. 

The incorporation of non-Gaussian effects in the Rouse theory can only be accomplished in an approximate way. For instance, the optimized Rouse-Zimm local dynamics approach has been applied by Guenza et al. [55] for linear and star chains. They were able to obtain correlation times and results related to dynamic light scattering experiments as the dynamic structure factor and its first cumulant [88]. A similar approach has also been applied by Ganazzoli et al. [87] for viscosity calculations. They obtained the generalized ZK results for ratio g already discussed. 

Set up the flow cytometer with fluorescence detectors turned off and the acquisition terminator set for TIME, so that a constant volume from each sample will be analyzed. A time interval (e.g., 1 min) that will be sufficient for the acquisition of approximately 10,000 events in the control samples should be used. Acquire light scatter signals (ESC and SSC) for each sample, vortexing the cell suspensions briefly but vigorously before introducing each sample into the flow cytometer. 

The average DNA helix diameter used in modeling applications such as the ones described here includes the diameter of the atomic-scale B-DNA structure and— approximately—the thickness of the hydration shell and ion layer closest to the double helix [18]. Both for the calculation of the electrostatic potential and the hydrodynamic properties of DNA (i.e., the friction coefficient of the helix for viscous drag) a helix diameter of 2.4 nm describes the chain best [19-22]. The choice of this parameter was supported by the results of chain knotting [23] or catenation [24], as well as light scattering [25] and neutron scattering [26] experiments. 

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