7.4.2.2 Intrinsic Viscosity The intrinsic viscosity [η], defined by Equation 17.14, as the limiting value of the ratio of the solution’s specific viscosity to the concentration of the solute as the concentration approaches zero, reflects the capability of a polymer in solution to increase the viscosity of the solution. Kraemer defined the intrinsic viscosity as [36] lnηr c =[η]+k1 [η]2 c (17.15) where k1 is known as the Kraemer constant. The intrinsic viscosity (or limiting viscosity number) can be obtained by measuring the relative viscosity at different concentrations and then taking the limit of the specific viscosity when the concentration is extrapolated to zero (Fig. 17.7). The behavior of the intrinsic viscosity with concentration depends on the nature of both the specific polymer molecule and the solvent. Since the intrinsic viscosity of linear polymers is related to the MW, for linear macromolecules intrinsic viscosity measurements provide a simple method for the determination of MW when the relationship between viscosity and MW is known. Additionally, Huggins described the relation ηsp/c (reduced viscosity) as [37]
ηred =
ηsp c =[η]+k2 [η]2 c