Preparation Of A Novel Electronic Ink And Its Properties Investigation

Electronic paper technology has received a great deal of attention in recent years. Electronic paper is a paper-like display which has many properties such as high reflection, wide visual angle, portability, flexibility and bistable. Electrophoresis image displays (EPID) is the most likely candidate in search for a display which has these properties.Traditional EPIDs are thin, flexible reflective displays based on the movement of electrical charged pigment particles which are dispersed in a colored dielectric medium. Most of the reported prototype electronic papers are based on the electrophoresis of charged particles in colloidal suspension, which take the inorganic pigment titanium dioxide(TiO2) or silicon dioxide(SiO2)as particles. The dielectric medium such as tetrachloroethylene, isopar, xylene, are of high specific gravity to compatible with pigment particles. However, the pigment electrophoresis ink has a problem with suspension stability such as agglomeration, lateral migration and sedimentation because of the high density of pigment. Other materials which can substitute pigments as colored particles and the solvents which can disperse the colored particles well will be introduced later in this paper. Indeed, there are many papers referring to organic and inorganic pigment particle electrophoresis colloid, while less report is concerned about the electrophoresis of dye. In order to prepare a novel electronic ink, this study has been focused on the electrophoresis of dye in different solvent or surfactant, and the relationship between the composition and electrophoresis properties of the electronic ink of dye.3 categories, 27 kinds of dye have been tested in this paper including dispersed dyes, acid dyes, solvent dyes, metal complex dye and etc. To compatible with dye, several kinds of solvents and charge control agents also have been tested including pyridine, ethanol, xylene, Tetrachlorethylene, diethylamine, aniline, PIBI. Dyes were dissolved or dispersed in the solvents with certain surfactant and the electrophoresis performance of the solvent was observed in electrophoresis display prototype whichwas composed by 2 pieces of parallel ITO glass. The system which can perform electrophoresis are as follow: First, the colloid suspension of solvent dyes dissolved in dielectric medium with some surfactant. Second, the solvent of acid dyes dissolved in alkalescence medium. Third, the solvent of acid dyes dispersed in dielectric medium with some surfactant and metal coupling dye dissolved in polarity medium.The paper has concentrated on the system of metal coupling dye dissolved in polarity medium, for it showed advance electrophoresis display property in this paper.The conductance change of electrophoresis liquid during electrophoresis was tested by conductivity meter. It can be found that the R04 metal complex dye had the greatest stability and the lowest conductance under the applied voltage.The electrochemistry reaction of the dye, solvent and electrode was determined by electrochemistry station. It can be found that the system consisting of conductive medium is instable in electrophoresis. Electrode, electrophoresis media and dyes would be suffer electrochemical damage under the supplied voltage. Most of the dye in polarity medium would decompose during electrophoresis if the applied voltage is higher than certain value.The chemical component of dye reacted with electrode was identified by FT-IR. Take R04 in ethanol for example,the R04 dyes dissolved in ethanol would decomposed and the main outcome of this electrochemistry reaction is oxidation azobenzene, but not normal hydrogen sulfide azobenzene during electrophoresis if the applied voltage is higher than certain value.To protect electrode, electrophoresis medium and dyes against electrochemical damage, electrically inert polymers such as photosensitive polymer, PVA, PET and PI were coated to modify ITO electrode. Protection effectiveness was systematically studied by the means of atomic force microscope (AFM), electrochemistry station, IR spectral photometry, UV-Vis spectral photometry and etc. It is obvious that PI is the best material for protecting ITO electrode against the electrochemical damage. The cyclic voltametry (CV) of protected ITO in solvent shows that PI is of good insulation, easily to be coated, solvent resistant, insulated, and high transparency.Tetrafluoroethylene polymer (PTFE) was modified by making micro hole asbackground white and analyzed by scanning electron microscopy (SEM). It has been proved that Tetrafluoroethylene polymer layer (PTFE) as background white is flexible, dye resistant. Meanwhile, the dyes particles can migrate through its micro-hole.The response time and display density of this system were observed by UV-Vis spectral photometry and reflex density meter。The highest electrophoresis density of R04 in ethanol can reach to 3.0 in this experiment. The response time of electrophoresis liquid varies with the concentration of dye in medium, voltage applied on electrophoresis liquid and the thickness of electrophoresis display prototype. In the testing condition: A: the R04 in polarity medium (0.01mol/L), applied voltage(2V), thickness of electrophoresis display prototype(1mm), the response time to reach image density 2.5 is 15s; B: the R04 in polarity medium (0.01mol/L), applied voltage(10V), thickness of electrophoresis display prototype(1mm), the response time to reach image density 2.5 is 3s.(the width of display prototype is 0.8mm).In conclusion, this research about electrophoresis of dye is just in the primary stage. Much more work should be done in search for different dyes cooperating with different medium and surfactant, especially the dielectric medium system. In addition, it is necessary to develop a further investigation in how to protect electrode, medium and dye from electrochemical damage, as well as in the modification of the Tetrafluoroethylene polymer layer as background white. But all the evidences demonstrate that electrophoresis of dye are useful in e-paper.