From Theory To Practice: Understanding de Gennes’ Scaling Laws By Measuring Polyelectrolyte Viscosity

Abstract Connecting macroscopic measurements with molecular-level interactions is central to physicochemical education and underlies the interpretation of polymer solution behavior. Although implemented in a final-year undergraduate physics course, this experiment illustrates how chemical concepts can be effectively introduced in interdisciplinary contexts. Here, we present a laboratory experiment designed to allow undergraduate students to explore the viscosity of polymer solutions across different concentration regimes. Using PDADMAC as a model polyelectrolyte, students examine how polymer concentration and ionic strength influence viscosity through electrostatic interactions. By varying salt conditions, the activity provides a clear chemical framework for interpreting the role of intermolecular forces in solution behavior. The experiment allows students to analyze experimental data in light of scaling relationships and to relate these trends to the polymer’s conformation in solution. The experimental results are consistent with the expected scaling behavior, supporting the interpretation of viscosity in terms of polymer conformation and intermolecular interactions. As ionic strength increases, a progressive transition from polyelectrolyte to neutral polymer behavior is observed, consistent with electrostatic screening effects. The activity also makes abstract physicochemical concepts accessible through direct observation and measurement, while also providing opportunities to develop practical laboratory skills and data analysis competencies. This integrated approach links theoretical concepts with experimental observation, offering a coherent framework to examine the behavior of polymer solutions within a physicochemical context.