Reversible pH-responsive Pickering emulsions stabilized by amine oxide-functionalized nanoparticles: interfacial regulation and stabilization mechanisms

This study introduces a novel pH-responsive Pickering emulsion system stabilized by lauramidopropyl amine oxide (LAO)-functionalized SiO₂ nanoparticles, demonstrating reversible stabilization controlled by LAO's protonation state. At pH 7, the protonated cationic LAO electrostatically adsorbs onto nano-SiO₂ surfaces, imparting optimal amphiphilicity (θ = 87.6°). The resulting interfacial stabilization is attributable to three synergistic mechanisms: (1) enhanced electrostatic nanoparticle adhesion, (2) hydrophobic shielding by oriented lauryl chains, and (3) mechanical reinforcement via nanoparticle aggregation at the interface. When the pH is increased to 10, LAO deprotonation induces complete demulsification due to interfacial film disintegration. Zeta potential measurements, interfacial rheology, and confocal laser scanning microscopy (CLSM) have been employed to confirm the system's fully reversible pH response (7 ↔ 10) over multiple cycles, with >80 % efficiency retention even at ultralow LAO concentrations (0.1 mM). The system's exceptional recyclability and rapid pH response, in conjunction with minimal surfactant requirements, establish it as a sustainable platform for applications such as enhanced oil recovery. Furthermore, it serves as a fundamental framework for designing smart, stimulus-responsive materials with tunable stability and reversible properties.