Dependence on oil chain length of the curvature elastic properties of nonionic surfactant films: Emulsification failure and phase equilibria

We compare two ternary microemulsions, stabilized by the nonionic surfactant pentaethylene-glycol-dodecyl-ether (C12E5), containing decane or hexadecane. The comparison involves phase behavior and properties of O/W droplet microemulsions investigated with SAXS, static and dynamic light scattering, and NMR. Striking differences are observed. The systems are analyzed in terms of curvature elastic properties of surfactant film. Apart from an increase of the spontaneous curvature, there also appears to be a small but significant increase in the saddle splay constant as the oil chain length is increased.