Mark-Houwink relation, viscosity measurements, dilute polymer solutions

The intrinsic viscosities are obtained by making viscosity measurements at different polymer concentrations and by plotting the above expression against the concentration. The limit that this quantity assumes as the infinite dilution is approached is the value desired. Polymer solutions exhibit a Newtonian behavior at low shear rates, changing to a non-Newtonian flow at higher shear rates (6). The intrinsic viscosities should be determined at the low shear rate range. The most commonly used equation that relates the intrinsic viscosity and the molecular weight of a macromolecule is the 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. 

Solution Characteristics of Poiymers. The molar mass characterization techniques often provide additional information on the nature of the polymer species in solution. In most cases, the solutions used are sufficiently dilute so that the properties being measured are those of the isolated molecule. At infinite dilution the size of the polymer coil is dictated by both inter- and intramolecular interactions, the nature of the solvent used, and the temperature. In a viscosity or GPC/SEC experiment the properties being observed can be related to the hydro-dynamic volume of the poljmier coil. This hydrodynamic volume is the effective volume which the poljmier occupies in solution. The hydrodynamic volume is implicit in the Mark-Houwink relationship, which describes the value of the limiting infinitely dilute increment to the viscosity—the intrinsic viscosity [ j] to the molar... 

Viscosity and Rheoiogy. Viscosity yields important information as to the disposition of the pol5uner chains in solution and is routinely used to evaluate polymers for particular applications. Dilute solution measurements can 3rield intrinsic viscosity [ j], which is a direct indication of the hydrod5mamic voliune of an isolated polymer chain. This fundamental parameter is related to molecular weight M through the Mark-Houwink-Sakiu-ada (MHS) relationship (eq. 1) ... 

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