dc.description.abstract | The commercially dominant e-paper technologies today are E Ink and SiPix. In an electrophoretic technology, charged particles are suspended in a low dielectric fluid. When an electric field is applied, the ink particles will move towards the electrode with the opposite charge to display words and photos. In general, the dissociation of counterion from charged particle is difficult in a medium with low dielectric constant due to strong Coulomb attraction.
In this work, the electrophoretic mobility and the origin of counterion dissociation from charged particle are investigated by using capillary electrophoresis system through electro-osmosis in high and low dielectric constant salt-free medium, and addition of salt.
We consider DI water and organic solvents including, tetrahydrofuran, n-methylformamide and dioxane and their mixtures with water in fused silica capillary of different sizes to measure the electro-osmotic flow (EOF). The EOF mobility of high dielectric constant solvents are essentially independent of the microchannel size. However, in low-permittivity solvents, the mobility is found to grow with the capillary radius. With ions add to the salt-free medium, the screening effect is present and the mobility is inversely proportional to salt concentration, and decays exponentially with high free ionic concentration. In low-permittivity solvents, the mobility also is found to grow with the capillary radius until the solution is an saturated solution.
In conclusion, using nonaqueous solutions, especially low dielectric constant, not only can reduce joule heat effect but also lessen the reduction of EOF mobility by the addition of salt. Consequently, in order to increase the response time in e-paper applications, the electrophoretic mobility can be increased by tuning the surface charge density or particle size.
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