Hydrodynamic volumes of molecules

Since the increasing salt concentrations in NaCl brines have negligible effects on polyacrylamide solution viscosities between 2 and 10% salt content, the hydrodynamic volumes of molecules are about the same in that range of salt concentration. Since the density of polymer in the adsorption layer is certainly proportional to the hydrodynamic volume of molecules in the bulk liquid, above 2% NaCl the salt concentration should have little further affect on polymer adsorption. 

Finally, SEC is merely a separation technique based on differences in hydrodynamic volumes of molecules. No direct measurement of molecular weight is made. SEC itself does not render absolute information on molecular weights and their distribution or on the structure of the polymers studied without the use of more specialized detectors (e.g., viscometry and light scattering). With these detectors, a self-calibration may be achieved for each polymer sample while it is... 

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