THE DOC MODEL OF MICROEMULSIONS - MICROSTRUCTURE, SCATTERING, CONDUCTIVITY AND PHASE LIMITS IMPOSED BY STERICAL CONSTRAINTS

Using a Voronoi cell, tessellation of space, a complete set of microst ructure approximations with a local morphology that evolves continuous ly from isolated spheres to disordered lamellae via connected cylinder s has been introduced by Barry Ninham and co-workers to describe micro emulsions. For 10 years, this continuous microstructural change has be en observed in a large number of microemulsion and copolymer systems. In the case of stiff interfaces, where bending energy damps local curv ature fluctuations, three constraints that govern microstructures have to be fulfilled simultaneously: the imposed volume fraction; the spec ific oil-water interface; and the minimum elastic energy, with negligi ble entropic contributions. From this model, simple analytic expressio ns are able to predict the characteristic size D and the connectivity Z of the microstructure at any composition, when the surfactant param eter p can be derived from the phase diagram shape. Once D and Z are known, the conductivity, scattering peak position as well as phase bou ndary can be predicted from the spontaneous curvature alone. The model is known as the disordered open connected model (DOC) and is still th e only model proposed for microemulsions compatible with nonmonotonic behaviour of the electric conductivity with water volume fraction. (C) 1997 Elsevier Science B.V.