Anomalous Dielectric Behavior of Water in Ionic Newton Black Films

The electrostatics of two charged surfactant layers in aqueous media (surfactant/water/surfactant films) is investigated using molecular dynamics simulations. In the films studied (with a surfactant-surfactant distance from approximately 35 A to contact) we observe an anomalous dielectric response of water. The electrostatic potential phi(z) inside the aqueous core of the films (containing bulk water with rho=1 g/cm(3)) is completely different from that expected for a film containing a dielectric medium with the dielectric constant of water. In addition, our results are not consistent with a local relation between the water polarization P(z)(z) and the electric field E(z)(z). The polarization P(z)(z) is maximum at the interfaces (due to solvent molecules forming part of the structure of the surfactant layers) and decays from the interfaces inside the aqueous core with a decay length of order of approximately 10 A.