Determination of the Intrinsic Viscosity - Extrapolation Methods

For precise laboratory measurements, the intrinsic viscosity is determined by the extrapolation to zero concentration of data obtained at several concentrations. This procedure will be subject to large uncertainty if the function plotted is not linear with concentration. Several methods have been proposed for carrying out the extrapolation, but those most commonly used are the Huggins plot, based on Eq. 2.112, and the Kraemer plot, based on Eq. 2.113. 

For a solution in its theta state, the Huggins constant, kf, is about 0.5, and k = 1 - 0.5). Extrapolation of either the reduced or inherent viscosity to c = 0 should give the intrinsic viscosity. Because hf is less than k the slope of a Kraemer plot is lower, which should provide better precision in the extrapolated value, but the Huggins plot is the one most commonly used. 

In making the extrapolation on a Huggins plot that is required to determine the intrinsic viscosity, the presence of concentration in the denominator of the dependent variable poses a problem in error management. Reilly et al. [65] have shown how this problem can be solved and have suggested an optimal selection of dilutions. 

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