| 摘要: | 研究期間：10208~10307;Since the size of electronic components continuously decreases in recent years, applying a thin film to a surface (thin-film deposition) for the manufacture of optics, electronics, and packaging becomes more and more important. In general, the techniques of thin-film deposition fall into two broad categories: dry processing and wet processing. In comparison with dry processing that are focused on the manufacturing of active or protective coatings onto metals, such as chemical vapor deposition, physical vapor deposition, and plasma sputtering, the wet processing such sol-gel process and electrophoretic deposition (EPD) have a number of advantages, such as uniform coating thickness, easy control of the coating composition, and lower costs. EPD, also called electrophoretic coating or painting, is especially recognized as a powerful method for depositing thin films onto conductive substrates. EPD involves essentially two major steps. In the first step, charged colloids such as charged polymers, pigments, and ceramics migrate to the oppositely charged electrode under the influence of an electric field. In the second step, colloidal particles accumulate at one of the electrode and are deposited onto it. Aqueous EPD is the most common commercially used process, which has advantages such as better temperature control and faster kinetics but suffers bubble formation due to hydrolysis of water and corrosion of electrodes due to metal ions. In certain applications, such as the deposition of ceramic materials, higher application voltages may be desirable in order to achieve higher coating thicknesses or to increase the rate of deposition. As a result, organic solvents are used as the liquid medium. Non-aqueous EPD processes have the advantage of avoiding the electrolysis of water but suffer slow speed of electrophoresis. Applications of non-aqueous EPD are currently being explored for use in the fabrication of electronic components and the production of ceramic coatings. In this three years’ project, we shall explore the microscopic mechanism of both aqueous and non-aqueous EPD processes. The EPD systems to be investigated will involve electrically conductive substrate (graphite and metal fabricated product) and charged colloids (polyelectrolyte, SiC, Al2〇3, Ti〇2, hydroxyapatite) due to their popular and novel applications. The main topics include ⑴ the electrokinetic behavior of charged particle in the bulk solution and near the boundary, (2) charged particle adsorption and surface migration during film deposition, (3) the influence of salting out, charge reduction/neutralization during deposition, (4) the influence of the morphology of the deposited film, etc. Our approaches include both theoretical and experimental studies. The former consists of the continuum approaches (nonlinear Poisson-Boltzmann equation and Stokes equation, SPHysics) and molecular simulations (Brownian Dynamics). The latter include capillary electrophoresis, dynamic light scattering & zeta-potential analysis, interfacial properties measurement, scanning electron microscope, and high-speed zoom lens microscope system. The main goal of this project is to establish a sound physical model of electrophoretic deposition, which provides useful guidelines for the development and improvement of thin-film technology. |
