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Principles of Colloid and Surface Chemistry, Revised and Expanded, 3rd Edition by CRC Press

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1.5c.3c Viscosity-Average Molecular Weight. The viscosity average molecular weight M¯vis is written as

M¯vis=(ΣiniMi1+aΣiniMi)1/a

(20)

The logic of this definition follows the logic used in defining average diameters based on surface area or volume discussed above and, as its name implies, M¯vis is a molecular weight average determined from viscosity measurements on polydisperse polymer samples. The exponent a in this definition is called the Mark-Houwink coefficient, generally 0.5 < a < 1.0. The exponent is characteristic of the polymer-solvent-temperature conditions of the experiment. We see how these experiments are conducted and the significance of the Mark-Houwink coefficient in Chapter 4. For now, we may take Equation (20) as merely ...

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