Droplet microemulsions at the emulsification boundary: The influence of the surfactant structure on the elastic constants of the amphiphillic film

The droplet structure of nonionic oil/water (O/W) microemulsions has been investigated by small-angle neutron scattering (SANS). The sum 2 kappa+<(kappa)over bar> of the elastic moduli that can be deduced from the experimental polydispersity compares well with the values independently deduced from interfacial tension measurements, thereby showing that our determination of the elastic constants appears to be reliable. Ln this study, nonionic surfactants of different chain length and with different head groups were investigated (polyethylene glycol monoalkylether CiEj and alkyldimethylamine oxides). The interpretation of the experiment data shows that the elasticity of the amphiphilic film increases with the thickness of the amphiphilic film. However, it does not depend significantly on the type of the head group but is primarily determined by the length of the alkyl chains of the surfactant. In mixtures of surfactants of different chain lengths, the sum 2 kappa+(k) over bar found to vary linearly with the molar composition of the mixture. (C) 1997 American Institute of Physics.