SEC with Viscosity Measurement

As noted above, it has been empirically demonstrated that for many polymer types, a universal calibration is obtained if the log. product of molecular weight and intrinsic viscosity is used rather than simple log. molecular weight. This is utilized by combining the response of a viscosity detector and a concentration detector to give the universal calibration directly. The viscosity monitor measures the differential pressure as polymer solution travels through a capillary; detectors have been developed which use a single capillary, a pair of capillaries or four capillaries (arranged in a manner analogous to a Wheatstone bridge).

SEC-viscosity is not theoretically an absolute approach but should give the true molecular weight distribution, providing that the polymer of interest conforms to the Universal Calibration approach. As with SEC-light scattering, SEC-viscosity is valuable for obtaining information on branching. Again, the solution concentration is an important parameter in the calculation. The differential refractive index does not appear in the calculation but could produce inaccuracies in the assumed concentration and hence is also problematic for copolymers.

M. L. Marina and M. A. Garcia, Universidad de Alcala, Alcala de Henares, Madrid, Spain

Copyright © 2000 Academic Press

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Solar Panel Basics

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