Fluorescent Labeling of Ultrahigh Molecular Weight Polyacrylamide Polymers in Microemulsion Systems

Fluorescent labeling of ultrahigh molecular weight polymers is crucial for understanding their behavior in complex environments yet remains challenging due to purification difficulties. Here, we present an efficient postpolymerization labeling method for industrially important polyacrylamide-based polymers up to 20 MDa, which allows simultaneous labeling and purification through manipulation of EDC/NHS coupling reagent concentrations. We demonstrate successful labeling of partially hydrolyzed polyacrylamide (HPAM) with iFluor 647 amine dye, confirmed through spectroscopic, microscopic, and single-molecule techniques with preserved polymer integrity. HPAM is vital in industrial applications, including enhanced oil recovery, water-oil separations, wastewater treatment, mining, and papermaking due to its high viscosity, water solubility, and ability to enhance process efficiency. Applying our labeling method to HPAM in water-oil-surfactant systems, we investigate the interactions between labeled HPAM and surfactant micelles in Winsor-type microemulsions, providing direct evidence for theoretical models of polymer-micelle complexation. Our visualization reveals that HPAM partially enwraps micellar structures while penetrating their headgroup domains, a key insight for optimizing surfactant-polymer formulations. These findings pave the way for optimizing the industrial applications of HPAM and deepen our understanding of polymer behavior in complex multiphase fluids.