Electrophoretic Hybrid Particles Synthesis by Dispersion Polymerization in Organic Media: Towards Electrophoretic Display Applications Antoine Charbonnier, Cyril Brochon, Eric Cloutet, Georges Hadziioannou* Laboratoire de chimie des polymères organiques (LCPO)-CNRS / Université bordeaux 1, UMR 5629-16 avenue Pey-Berland, 33607 Pessac, France. Abstract The effective sharing of information is a key parameter in our actual society. Electronic paper based on the controlled motion of electrophoretic particles appears thus promising since it combines the advantages of the usual paper (flexibility, reflective display) and the capacity to refresh information on the same support like the more common LCD or OLED technologies. Electrophoretic inks are composed of coloured charged particles which migrate under an electrical field between two electrodes. Depending of the position of the particles on the front plane, the colour on the screen can be tuned. The design of electrophoretic particles based on pigment or dyed polymer and their integration in electronic devices were successfully achieved during the last decade but are still limited to a two colour-electrophoretic system. Up to date the majority of these particles were synthesized in aqueous media and the electrophoretic mobility was achieved by a ionic stabilizer or by a polyelectrolyte surfactant. Moreover the final electrophoretic particles incorporated in the electronic devices have to be dispersed in an organic media (paraffin oil) in order to achieve the desired stability of the display and thus leads to a large variety of problems during the phase exchange process. In this work our goals were to rationalize and improve the ink synthesis as well as to design electrophoretic inks with the full colour panel in order to realize the next generation of electrophoretic displays. We performed the particle synthesis by using an organic dispersion technique in aliphatic hydrocarbon solvents leading to chargeable electrophoretic particles with a good size control over a large range (from 75nm to 20µm) and a good stability. In order to obtain the full color panel, the encapsulation of several inorganic pigments was achieved by using the same technique and the electrophoretic behaviour of the resulting inks was characterized in a cell specially designed for electrophoretic measurements in organic media. Author Keywords Electrophoretic ink; hybrid particle; organic medium; dispersion polymerization; electronic paper. 1. Introduction Electronic paper based on the electrophoretic ink technology is one of the challenging display of the 21th century even if the first realization was made in the 1973. Nowadays, several commercial electrophoretic particles image displays (EPID) are currently in the market but research in the field continue to be actively done 1 (more than 200 patents since 2009) . The EPID technology consists of two conductive and transparent electrodes between which a dispersion of particles in an apolar media is trapped. This dispersion of particle is also called electrophoretic ink 2 . Electrophoretic ink can be composed of one charged particle in a coloured medium ,or of two kind of particles oppositely charged in a transparent medium. In both case, particles migrate to the frontplane or backplane when an electrical field is applied between the electrodes. Finally, particles on the front plane scatter the incoming light and depending of the color of the particles different state can be obtained (white for TiO 2 , black for carbon black ,….). The contrast of the device will be fully dependent of the materials used to prepare electrophoretic particles. That’s why even if some experiment were done with dyed polymer particles, inorganic pigment are preferred for their exceptional optical qualities. Moreover lots of other parameter are important to obtain a good electrophoretic ink. Stability 3 , size, density, charge should be studied very carefully and so lots of research are made to improve electrophoretic particles behavior. Lots of papers were published on the making of electrophoretic particles using TiO 2 as a white pigment. It is well known that TiO2 and inorganic pigments in general have high density which causes really serious sedimentation and stability problems. Besides strong interactions could appear between the electrode surface and pigments causing particles to stick on electrodes and lower the good working of the device. The solution is to combine pigments with functional polymers, allowing the tuning of particle’s density and adding other properties like colloidal stability and charges. Different approaches were reported in literature. The emulsion method is often used to prepare some core-shell particle based on polystyrene 4 , polyacrylates 5 or poly(4-vinylpyridine) 6 , where the pigment is either the internal core 4 or the external shell 7 , were prepared. Another possibility is to treat pigment’s surface with surfactant 8 or charge control agent 9, 10 to both stabilize it and give electrophoretic mobility 11 . Finally the polymerization by dispersion is the last most common techniques to prepare electrophoretic material. Pigments are usually coated with poly(methyl methacrylate) (PMMA) or polystyrene (PS) 12 in low alcoholic media in a first step and often, a second layer of functional monomer is added (acrylic or methacrylic acid) 13-16 . In this work our goals were to rationalize and improve the ink synthesis as well as to design electrophoretic inks with the full colour panel in order to realize the next generation of electrophoretic displays. We performed the particle synthesis by using an organic dispersion technique in aliphatic hydrocarbon solvents leading to chargeable electrophoretic particles with a good size control over a large range of diameter (from 75nm to 20µm) and a good stability. In order to obtain the full color panel, the encapsulation of several inorganic pigments was achieved by using the aforementioned technique and the electrophoretic behavior of the resulting inks was characterized in a cell specially designed for electrophoretic measurements in organic media. P-78 / A. Charbonnier 1346 • SID 2012 DIGEST ISSN 0097-966X/12/4303-1346-$1.00 © 2012 SID