Ultrasonic, Rheological and Conductivity Study of the Interaction between Polyacrylic Acid and DTAB Micelles in Aqueous Medium

The interaction between poly (acrylic acid) (PAA, MW ≈ 50,000) and dodecyl trimethyl ammonium bromide (DTAB) was investigated in aqueous solution using ultrasonic interferometry, density, viscosity, and conductivity. Experiments were performed with 0.1 M DTAB containing 0–1.0 wt/v %, PAA (at 0.2 % interval) at 298.15–313.15 K. Density and viscosity increased with PAA concentration, indicating enhanced solutesolvent interactions. Non-linear trends in reduced viscosity and relaxation time, with minima near 0.4 wt/v% PAA, suggested micelle disruption followed by cooperative polymer-micelle association. Ultrasonic velocity rose sharply (1520 → 1732 m/s) and compressibility decreased at 0.4 wt/v%, confirming compact micelle–polymer complex formation. At higher temperatures, maxima shifted to ~0.6 wt/v%, reflecting reorganization into elongated aggregates. Rheological and conductivity data supported temperature-dependent micellar hydration, counterion binding, and shape transitions. Overall, PAA significantly modulates DTAB micellization through hydrophobic and electrostatic interactions, with concentration- and temperature-dependent transitions between compact and elongated micelle–polymer assemblies. These findings provide thermodynamic and structural insight into polymer–surfactant systems with relevance to pharmaceutical, detergent, and colloidal formulations.