Polyelectrolyte Surfactant Aggregates for Stabilizing and Transporting Hydrophobic Species across Oil/Water...

The delivery of hydrophobic species dispersed in aqueous media to a nonpolar phase often involves crossing an oil/water interface. Here, we demonstrate the potential of using water-dispersible polyelectrolyte surfactant aggregates (PES) to solubilize hydrophobic moieties in an aqueous environment and deliver them to an oil phase. Central to the success of this approach is that these aggregates have the additional advantage of stabilizing fluid/fluid interfaces through interfacial elasticity, providing time for transport across the interface. The PES used is poly(cetyltrimethylammonium vinyl benzoate) (pC₁₆TVB), which forms rodlike aggregates (4 nm diameter, 120-150 nm in length) in solution that consist of a hydrophobic backbone of poly(vinyl benzoate) (pVB^-) and a stoichiometric, based on the charge, number of positively charged surfactant cetyltrimethylammonium (C₁₆TA⁺). The interfacial properties of PES aggregates adsorbed at the oil/water interfaces are compared with those at the air/water interface. These aggregates previously showed complex adsorption behavior and high dilatational elasticity at air/water interfaces. At the oil/water interface, the PES aggregates reach a higher interfacial pressure (42.2 mN/m versus 30.8 mN/m), are more persistent, and still result in a highly elastic interface (|E*| ∼ 100 mN/m). This PES system allows for the efficient transport of hydrophobic active species from aqueous solutions across an oil/water interface and stabilization of the interface by increasing the dilatational modulus and decreasing the interfacial tension.