UBC Theses and Dissertations

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UBC Theses and Dissertations

Electrostatic manipulation of fluidic interfaces for optical control purposes Kwong, Vincent Hugh


Three original, different, yet complementary optical techniques are presented in this thesis. They can be employed individually or in combination, to yield new methods of optical control. The common theme linking these techniques is the application of patterned electric fields to control the bulk and/or surface properties of fluidic structures, yielding a variety of optical effects. These effects may be useful in a multitude of optical structures, including variable Bragg gratings, reflective displays, optical memory devices, and the like. The first technique, here termed the fluid interface grating, uses a spatially modulated electric field to alter the interfacial pressure between two immiscible fluidic layers having different indices of refraction. The pattern of the electric field determines the amplitude and spatial frequency of the deformation in the interface between the two layers. Since the two fluids have different indices of refraction, this patterned deformation produces a diffractive structure. The second technique, here termed the electrophoretic grating, uses electrophoresis to microscopically control the location of charged, high refractive index particles suspended in a low index perfluorinated hydrocarbon fluid. By controlling the amplitude and spatial frequency of the electric field in the suspension, a spatial periodic change in the effective index of refraction occurs in the bulk of the suspension, forming another new diffractive structure. The third technique uses an effect known as electrowetting to alter the shape, and hence the reflective properties, of tiny water drops on an air-polymer interface. As a result of electrically inducing changes in the surface energy of the drops, the shape of each drop is deformed as its contact angle is altered. This corresponds to a substantial change in the reflectance of the drop, which could, for example, form the basis for a new type of reflective display. The results presented in this thesis demonstrate the feasibility of these three new techniques to actively control optical properties of surfaces. These three methods can be used separately but there is also potential for combining these techniques. The results are encouraging and are suggestive that further research is warranted.

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