Why Does Intrinsic Viscosity Matter?

When a high molecular weight polymer is dissolved in a solvent, it forms a higher viscosity “blob” in the solution. As more and more polymers are added, the higher the viscosity of the solution becomes. Intrinsic viscosity is a measure of the viscosity increase that each added polymer molecule contributes. The higher the molecular weight, the more viscosity increases with each added molecule.

Thus, the intrinsic viscosity is defined by the equation:

Here, η is the viscosity of the solution, η₀ is the solvent viscosity, and C is the polymer concentration.

To measure the intrinsic viscosity, the viscosity of a solution is measured at different concentrations, for which the minimum and maximum concentrations have to be selected carefully. When a faster test is needed, viscosity measurement of a solution at a single concentration is often used as described in ASTM D4603-18.

Traditional Measurements & Drawbacks

Glass capillary viscometers, like Ubbelohde tubes, have traditionally been utilized in intrinsic viscosity measurements due to the high precision of these instruments. However, this style of viscometer requires extensive cleaning between samples and must be completely dry before continuing. This extensive cleaning and drying is tedious and time consuming, reducing the overall efficiency and throughput of testing. Glass capillary viscometers also require manual timing of each measurement, which can be erroneous and operator dependent.

microVISC PRO eliminates these drawbacks. Even a small sample volume can clear the full volume of the VROC chip, enabling continual measurements. The viscosity of multiple dilutions can be measured sample-after-sample without cleaning and all measurements are completely operator independent.

Learn more about measuring intrinsic viscosity in our application notes or on our blog!