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The principle, experiment setup and experimental results of a novel process of controlling the nanoparticle distribution in hydrogel by utilizing the theory of electrophoresis are discussed and demonstrated. The distributed nanoparticles in hydrogel changed the refractive index of the material, which provide the new application for organic gradient refractive index (GRIN) lens. For conducting the electrophoresis experiments, two miniaturized electrophoresis running tools have been designed and fabricated. The dimensions of vertical ruing tool is about 4 x 3 x 3.5 cm (L x W x H). In order to clearly observe the running results, the process of self-assembly are used to label the nanoparticles with fluorescent dye. The silica nanoparticles (7-9 nm in diameter) are being investigated to explore its effect on the optical improvement of hydrogel material. Polyacrylamide hydrogel is used as lens material. Various analysis equipments are employed to characterize the samples, including X-ray photoelectron spectroscopy (XPS), thin film measurement system and fluorescent microscopy. The experimental results from fluorescent microscope have shown that nanoparticles were moving toward the opposite charged electrode from particle resource and distributed according to the electrical field. For GRIN lens application, the electrophoresis phenomena have also been investigated by the testing setup with a circular electrode (3 cm in diameter). The testing results were examined by thin film measurement system and X-ray photoelectron spectroscopy. With the data of analyzed Si concentration, it has been proven again that the distribution of nanoparticles could be controlled by electrophoresis in hydrogel film which presents the radial gradient refractive index profiles. The refractive indices change range could be larger than 0.06. The simulation results with CoventorWare@ also predicted the nanoparticles movement and distribution in hydrogel under electrical filed with different values of electrophoretic mobilities.
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