Classic Ubbelöhde Intrinsic Viscosity Laboratory Exercise Made Simple and Fast

Abstract

Intrinsic viscosity is a foundational concept in a student’s understanding of macromolecular structures and solution behavior. Its measurement through simple laboratory techniques can teach undergraduate students the importance of accuracy and precision while learning concepts in polymer science such as hydrodynamic volume and the dependence of viscosity on concentration, density, and mass as well as mathematical principles such as the Taylor series and l’Hopital’s rule. Only simple and inexpensive equipment is required, but the measurements consume much time and can frustrate both students and instructors. We propose a faster method for conducting intrinsic viscosity measurements for polystyrene in toluene without forfeiting any of the valuable lessons provided in a traditional intrinsic viscosity experiment. Splitting students into teams where each use their own viscometer to measure flow times of a single solution concentration allows for the measurement of multiple concentrations at once. This practice also eliminates the need for long-term and precise temperature control and diluting (or cleaning and purging) of viscometers between different concentrations. Results from each team can be combined, allowing students to analyze one another’s data and make decisions on exclusion of erroneous measurements, data fitting, and uncertainty analyses. Choosing a polymer in pellet form reduces congestion at the analytical balance and provides valuable lessons in refractive index matching and the torpid diffusion/dissolution of entangled macromolecules. In this method, students can learn the same fundamental concepts in polymer science and critical data analysis in a much faster and less frustrating manner.