Preparation of functional fluid dispersing ultrafine particles and its optical property

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We have successfully prepard dielectric fluids in which barium titanate fine particles are stably dispersed in kerosene. The fluids show Electrorheological phenomena such as an increase of viscosity under an electric field. Furthermore, a thin fluid film that uses only a dielectric fluid under an electric field has been reported as a potential light shutter. The shutter action is caused by Rayleigh scattering of visible light due to the formation of barium titanate clusters under the electric field. The response time for the formation of the clusters after switching on the electric field is in the order of 10ms for kerosene-based fluids ; however, the decay time for the disappearance of barium titanate clusters after switching off the field is larger, several seconds. In addition, kerosene-based magnetic fluids with magnetite fine particles stably dispersed have been also prepared. Light scattering in a thin film of a mixture of dielectric and magnetic fluids has been studied under both electric and magnetic fields. The film can transmit visible light in no electric field. When an electric field is applied across the film, the transmittance decreased rapidly.The phenomenon is explained by Rayleigh scattering due to the dielectric clusters formed under the field. The decay time to return to the transmittance at no electric field after switching off the field is much larger than the response time after switching on the field ; however, the usage of a magnetic as well as an electric field allows the decay time to be shortened.