Micellar Properties of Surface Active Ionic Liquid Lauryl Isoquinolinium Bromide and Anionic Polyelectrolyte Poly(Acrylic Acid Sodium Salt) in Aqueous Solution

Abstract

AbstractThe complex formation between anionic polyelectrolyte poly(acrylic acid sodium salt) [NaPAA] and surface active ionic liquid (SAIL) lauryl isoquinolinium bromide [C12iQuin][Br] in aqueous media has been investigated by surface tension, isothermal titration calorimetry (ITC), and conductance. The self‐assembled structures have been characterized using dynamic light scattering (DLS) and turbidity measurements. A range of surface parameters have been calculated from tensiometric measurements including critical micelle concentration (CMC), surface excess concentration (Γcmc), surface pressure at the interface (Πcmc), minimum area occupied at air–solvent interface (Amin), adsorption efficiency (pC20), and surface tension at the CMC (γcmc). The thermodynamic parameters, i.e., standard enthalpy of micellization , standard free energy of micellization (), and standard entropy of micellization () have also been evaluated. Four different stages of transitions, corresponding to the progressive formation of NaPAA–[C12iQuin][Br] complex (C1), critical aggregation concentration (CAC), critical saturation concentration (C3) and CMC have been observed owing to strong electrostatic and hydrophobic interactions. The results obtained from DLS and turbidity measurements show that size of the aggregates first decreases and then increases in the presence of polyelectrolyte. The binding isotherms obtained using isothermal titration calorimetry (ITC) show the concentration dependence as well as the highly cooperative nature of interactions corresponding to formation of polyelectrolyte–SAIL complexes.