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.
A novel process of casting the polydimethyl-siloxane (PDMS) microstructure with hybrid photoresists mold has been developed to fabricate the 3D microstructure. This new processing includes two parts: the 3D mother mold fabrication and PDMS casting processing. The 3D mother mold, which consists of the three-dimensional partial-spherical microstructure and micro channel, was successfully fabricated and characterized. The 3D micro structure and the micro channel of the mother mold, made of two different photosensitive materials, AZ100XT and SU8 photoresist respectively, are merged very smoothly at the joint area. A mother mold of a 2200-μm-diameter chamber with a 500-μm-width channel was presented in this paper. For the best precise dimensional control, we used this mother mold to fabricate the PDMS mold for PDMS casting processing. The surface average roughness of the final 3D structure is 30 nm. This novel processing provides a new technology for achieving smooth 3D chamber surface joined with microchannel. This new technology can be applied in various lab-on-a-chip and microfluidic devices such as micropump and microvalve for which the great sealing, no dead volume and high back pressure are critical requirements. In this paper, the design, fabrication process and surface profile characterizations of this processing are presented in details.
The hard magnetic materials with a high remnant magnetic moment, Mr, have the unique advantages that can achieve bi-directional (push-pull) movement in an external magnetic field. This paper presents the results on fabrication and testing of the novel hard magnetic silicone elastomer thin films. The micro-size hard ferrite powder, NdFeB powder and different silicone elastomers have been used to fabricate the various large elongation hard magnetic thin films. The uniform thin films range from 40 μm to 216 μm and they are successfully fabricated. Three different fabrication processing have been investigated and the mechanical properties, like Young’s modulus and deflection force, have been evaluated. The simulation results with ANSYS match the experimental data. In comparison to electrostatic or piezoelectric actuation, the magnetic actuation can provide stronger forces and larger deflections. The large elongation hard magnetic thin film provides an excellent diaphragm material, which plays an important role in the micro pump or valve. This film movement has been tested in the external magnetic field, and proved to have large deflections and high performances.