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 (T-HLB) 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%. (C) 2010 Elsevier B.V. All rights reserved.