Abstract: A composition comprising a lyotropic ferromagnetic liquid crystal. The lyotropic ferromagnetic liquid crystal contains 1 to 90% by weight of a surfactant, 1 to 90% by weight of a co-surfactant, 1 to 97% by weight of oil and 1 to 97% by weight of a polar liquid, the ratio of the co-surfactant mass to the surfactant mass is below 2. The four constituents form elongated aggregates with the surfactant and co-surfactant serving as an interface between the polar liquid and the oil and forming with the polar liquid the elongated aggregates. The aggregates contain ferromagnetic particles.

Abstract: There is provided a process for the production of a composition and, in particular, of a ferromagnetic liquid crystal. The process comprises (1) forming a micro-emulsion by dispersing an aqueous solution containing ferrous cations and ferric cations in an oil in the presence of a surfactant and a co-surfactant such that the aqueous solution becomes a liquid phase dispersed in ther oil as a discontinuous liquid phase, and (2) reacting the ferrous cations and ferric cations with a chemical compound to form ferromagnetic particles in situ in the aqueous solution. According to the invention, this process is useful in forming magnetite particles (Fe.sub.3 O.sub.4) from 1 to 100 mm. in size.

Abstract: Thermally, electrically or magnetically controllable lyotropic liquid crystal optical devices.The optical device comprises two insulating walls (6, 8) joined together by their edges by means of a sealing joint (9) and a lyotropic liquid crystal film (10) placed between the walls and whose light transmission varies as a function of the temperature, said liquid crystal being formed from 5 to 20% by weight of alcohol, 0 to 20% by weight of a quaternary ammonium halide, 0 to 94% by weight of oil and 1 to 95% by weight of water, the ratio of the mass of ammonium halide to the mass of alcohol being below 2.