The flow behavior of the polymer solution is highly dependent on the molecular structure of the polymer as well as on interactions of the molecules with each other in solution. As the molecular interactions decrease with decreasing concentrations, viscosity measurements are carried out with very dilute solutions. A solution free of any interactions between the polymer molecules could only be reached in the state of the “ideal dilute solution”. In this “ideal dilute solution” the concentration approaches zero meaning that the polymer molecules are isolated from each other and only interact with the solvent molecules. However, this state can never be reached in reality and therefore small polymer interactions have to be considered. Both the calculation of the reduced and the inherent viscosity require the concentration value and therefore the intrinsic viscosity is an important parameter as it is an extrapolation to a theoretical zero concentration.
Various types of glass capillary viscometers, especially Ubbelohde-type glass capillary viscometers, are used for the determination of the intrinsic viscosity and other polymer parameters. Falling-ball- and rolling-ball viscometers are suitable alternatives. The rolling-ball viscometer in particular offers several advantages in comparison to Ubbelohde viscometers . It has a smaller footprint and energy consumption as well as lower solvent and sample consumption. Furthermore, the system is closed and can be automated which makes handling much safer, efficient, and convenient for the users.
Independent of the instrument used, the determination of the intrinsic viscosity can be done in two ways as described in the following paragraphs.