Inverse water-in-oil microemulsions are suspensions of spherical droplets of water coated by a monolayer of surfactant molecules, immersed in oil. We have studied WAD (water/AOT/decane, where AOT denotes sodium-bis-di-ethyl-sulfosuccinate) microemulsions far from critical points and near the percolative transition from electrically insulating to electrically conducting. The AOT molecules have a bulky tail and a small head so that the coating film has a spontaneous curvature toward water. Owing to this reason, water droplets are quite stable and, from 10 to 50°C, a large one- phase region, called L2 phase extends in the ternary phase triangle from the decane corner into the middle of the phase diagram. A percolation line is found in this region. We have observed optical nonlinearity near the percolation line and far from the one-phase two- phase boundary line. In this point, the material turbidity is very low and the material appears to be suitable for several nonlinear optical devices.
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