Ordered structures in homogeneous magnetic fluid thin films and method

Abstract

Methods for preparing homogeneous magnetic fluid compositions capable of forming ordered one dimensional structures or two dimensional lattices in response to externally applied magnetic fields are disclosed. The compositions are prepared using improved co-precipitation methods in which the steps of the procedure have been tuned to reduce sample heterogeneity. Fe.sub.3 O.sub.4 or MnFe.sub.2 O.sub.4 particles are coated with a surfactant and dispersed in a continuous carrier phase to form these homogeneous magnetic fluid compositions. The ability of these compositions to generate ordered structures can be tested by holding a magnet near a thin film of the compositions and observing the formation of colors in the region near the magnet. Methods for controlling the characteristic spacing of the ordered structures formed by the composition also are disclosed. Relevant parameters include the thickness of the film, the strength and orientation of the externally applied magnetic field, the rate of change of field strength, the volume fraction of the magnetic particles dispersed in the continuous phase, and the temperature of the homogeneous magnetic fluid. The homogeneous magnetic fluid composition is useful for the manufacture of liquid crystal devices. The devices take advantage of the serendipitous fact that the spacings in the material are on the order of the wavelength of visible light. A variety of magnetic-optical devices can be constructed that use the ordered structures to diffract, reflect, and polarize light in a controlled and predictable manner. These devices include color displays, monochromatic light switches, and tunable wavelength filters.