Polyelectrolyte Solution Rheology

Chemists who synthesize ion-containing polymers must grapple with a severe hindrance - that of accurately measuring the molecular weight of their products. The lack of generally effective methods for determining this fundamental quantity retards research on ionic polymers, which find uses in water purification, energy conversion and storage, massive industrial scale electrolysis and other molecular separations. We are developing four methods that utilize easily measured dynamic properties of semidilute unentangled solutions of ionic polymers to obtain the number-average molecular weight M_n. Each method relies on specific combinations of calibrated measurements so that each method directly determines the number density of chains in solution and thus M_n. These four methods are insensitive to salt concentration and have the potential to enable routine molecular weight determination for ionic polymers, while using very little sample. We anticipate quick adoption of these methods, allowing rapid acceleration of the development and understanding of polyelectrolytes and ionomers to suit myriad applications.