EFFECT OF THE COSURFACTANT STRUCTURE ON THE BENDING ELASTICITY IN NONIONIC OIL-IN-WATER MICROEMULSIONS

Oil-in-water microemulsions of the zwitterionic surfactant tetradecyld imethylamine oxide (TDMAO) that are formed in the presence of various alcohols as cosurfactant have been investigated by means of small-angl e neutron scattering and interfacial tension measurements. From these experiments the sum of the bending moduli 2 kappa + <(kappa)over bar> has been determined and found to be in the range of 2-5 kT. It is foun d that the admixture of the alcohol leads to relatively constant value s for longer chain alcohols whereas short chain alcohols induce a sign ificant reduction of 2 kappa + <(kappa)over bar> that is proportional to the concentration of added alcohol. This behavior of the bending el asticity corresponds to the phase behavior in the ternary systems (TDM AO/alcohol/water) where for the systems with high values for the bendi ng elasticity formation of lamellar phases is observed, whereas for sy stems of low rigidity bicontinuous isotropic phases are formed with st ructures that are characterized by a low persistence length.