Viscosity detectors Mark-Houwink relations

If a concentration-selective detector, such as a DRI, is connected on-line with the viscosity detector, the ratio of the two signals yields the intrinsic viscosity distribution of the polymer sample. In polymer characterization, the intrinsic viscosity can be a property just as important as the molecular-weight distribution. Furthermore, polymer intrinsic viscosity follows the Mark-Houwink relation to the molecular weight, M, where K and a are Mark-Houwink viscosity constants ... 

For their characterization, alginates must first be purified and isolated under their sodium form. NMR spectroscopy ( H and C) is the most powerful technique to characterize the chemical composition and the microstructure of alginates [46 9]. Purified alginates, isolated under the sodium salt form, were also characterized by steric exclusion chromatography (SEC)with three detectors on line. For commercial products, molecular weights may range between 32 000 and 400 000. A further means of characterization is their intrinsic viscosity using the Mark-Houwink relation ... 

A viscometric detector together with a concentration detector can provide information on molar masses of macromolecules emerging from the FFF system [76,134,142-144] using the Mark-Houwink-Kuhn-Sakurada coefficients. If these coefficients are not available, an intrinsic viscosity distribution can still be determined without calibration. Detailed features of this distribution are unique to a given polymer sample, and are not affected by changes in experimental conditions [145]. In fact, since the intrinsic viscosity distribution is more directly related to end-use properties, its measurement is preferred in certain applications. 

A concentration (RI) detector is connected in parallel with the viscosity detector using a stream splitter, and the data from both devices enable the intrinsic viscosity to be determined. This relates to the molecular mass via the familiar Mark-Houwink equation ... 

The measurement of polymer molecular masses by dilute solution viscometry is not an absolute technique. However, the parameters used to relate solution viscosity to molecular mass are the same as those used in the universal calibration procedure (section 3.2.3). Earlier it was pointed out that one of the weaknesses associated with the universal calibration procedure was the use of literature values for these parameters. Alternatively, if some absolute molecular mass data is available, dilute solution viscometry can be used to determine these Mark-Houwink parameters. The choice is between extensive preliminary practical work and in making wide-ranging assumptions, often with quite old data on Mark-Houwink parameters. The use of a viscosity detector, whilst not removing the need for conventional calibration, does potentially widen the range of the applicability of the calibration, without the use of any assumptions. 

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