| 摘要: | 研究期間：10108~10207;Since high-tech products are gradually made in a way to achieve the requirements of light weight, thin, short, and small size, many microscale driving systems become important. The examples include microchannel, lab-on-a-chip, electrophoretic display and electrowetting display. However, the behaviors of these micro-systems are significantly different from those of typical macro-systems. In their operating processes, the working fluid and colloidal particles in solvent often results in problems associated with electrokinetic phenomena, especially when solvents with low dielectric constant are used as media. The electronic paper, owning characteristics of energy saving and natural reading, is regarded as one of the most important technology. For such display technology, electrophoresis and electrowetting come to maturity and have better practical applications. The resemblance between electrophoresis and electrowetting is that both of them can use solvent with low dielectric constant as medium and drive working fluid or particle to move by applying external electric field. Microcapsulation, microcup and liquid powder display are currently the three major approaches for electrophoresis display technology and all of them use solvent with low dielectric constant as electrophoresis medium. In such media, it is not easy for working particles to carry charges due to strong Coulombic interaction. For aqueous solutions, the dielectric constant is high and the electrophoretic velocity is known to depend on the intensity of external electric field, surface potential of charged particle, dielectric constant and viscosity of electrolyte solution. For media with low dielectric constant, the relevant studies are scarce in literature. It is essential to understand why colloidal particles (dye) in electric paper can carry charges and thus migrate in a nearly ion-free medium with low dielectric constant. The performance of electronic paper depends on velocity of contrast switch, image resolution, image contrast, reflection ratio, electric energy consumption and cost, etc. However, in order for electronic paper to prevail over traditional self-luminous displays, the key issue is the velocity of contrast switch, so-called response time. For electrophoresis and electrowetting display technology, the reduction of the response time is the bottleneck and therefore the underlying electrokinetic phenomena play the key role. In this three years’ project, we will focus on the system with nearly ion-free solvent due to its low dielectric constant and try to establish theoretical models of electrokinetic phenomena in electrophoresis E-paper. In addition, we will study the influence of surface property of the substrate on the response time associated with an oil droplet wetting the dielectric materials in electrowetting E-paper. We shall apply our expertise of wetting phenomena to the improvement of the response time of oil medium with low dielectric constant on interfacial dielectric substrate. Our approaches include theoretical and experimental studies. The theoretical studies consist of the continuum approaches (solving the nonlinear Poisson-Boltzmann equation and Stokes equation, SPHysics, Surface Evolver) and molecular simulations (Brownian Dynamics). The experimental studies include capillary electrophoresis, dynamic light scattering & zeta-potential analysis, interfacial properties measurement, dynamic contact angle measurement, and high-speed zoom lens microscope system. The goal of this project is to establish a sound physical model of electrokinetic phenomena, which provides useful guidelines for the development and improvement of E-paper display technology. |
