Optimization of water-in-oil nanoemulsions by mixed surfactants

The formation of water-in-oil (W/O) nanoemulsions in isohexadecane/mixed nonionic surfactant/water system has been achieved by a low-energy emulsification. Effects of polyoxyethylene 2-lauryl ether (C12E2) and polyoxyethylene 4-lauryl ether (C12E4) on the water in isohexadecane emulsions were systematically studied. Ratios of the two-surfactant mixture, surfactant concentrations, and oil fraction were evaluated by gauging droplet size with the aid of photon correlation spectroscopy. Hydrophilic–lipophilic balance temperature (THLB) and phase diagram were used to characterize the nanoemulsion system. The stability of the emulsions prepared was assessed based on the change in droplet size as a function of time. Instability mechanisms including coalescence and Ostwald ripening for the nanoemulsion system are discussed. The addition of a second surfactant could provide more stable nanoemulsions with the minimum size than only one surfactant. Finally, a nanoemulsion composition was optimized and found to be highly stable over a 200-day storage period. The optimum composition for W/O nanoemulsion is isohexadecane/C12E2/C12E4/water 70:6:4:20 wt%.