Electrophoretic image display

Recently, the theory of dielectrophoresis was applied to explain the microscopic physics of the movement of pigments in electrophoretic image displays and to prove the discrepancies between theory and measurement [9], Dielectrophoresis is induced by the interaction of the electric field and the induced dipole and is used to describe the behavior of polarizable particles in a locally nonuniform electric field. For example, the phenomenon of the delay time can be explained by the principle of dielectrophoresis. In electrophoresis, when the backplane voltage is switched, the particles on the electrode have to move instantaneously under a given electric field. However, the particles need a removal time which results in a delay time in the switching process. The time constant to obtain an induced dipole from a particle at rest is derived by Schwarz s formula [10] and used to compute the dielectrophoretic force at its steady-state value. The force and the velocity fields under a nonuniform electric field due to the presence of pigments also help to estimate realistic values for physical properties. 

Because the electrophoretic display effect that is used is multi-stable, the row drivers are only operational during an image update. This is different from the commonly used LC display effects that need to be driven continuously during use of the display. In view of bias stress effects, this makes the electrophoretic display effect ideal for integration of row drivers in organic electronics. 

Amundson K, Sjodin T (2006) Achieving graytone images in a microencapsulated electrophoretic display. SID Dig Tech Pap 37 1918-1921... 

So-called microencapsulated electronic inks have received much publicity in recent years. They consist of microencapsulated electrophoretic media that change color (eg, black to white) when an electric field is applied to thin microcapsule layers placed between thin electrodes. This color change occurs because the microcapsules contain a mixture of two color components dispersed in a dielectric fluid. The two color components can conceptually be two different colored particles (eg, white titanium dioxide and carbon black) or particles of one color (eg, titanium dioxide) dispersed in a dyed dielectric fluid. In either case, application of an external electrical field causes the color components to migrate or separate inside the microcapsules, thereby forming different colored images. Such inks make it possible to create flexible electronic paper displays that require low power and can receive and display information electronically (34-36). 

The instrument displays the zeta potential as calculated from the Smoluchowski equation. At the point where the particles image is stationary, the displayed potential is the zeta-potential of the sample. The zeta potential can then be converted to electrophoretic mobility by deviding [sic] by an appropriate constant. The concentration of the sample was 0.15% for the cotton fibers. This method allows the measurement of the entire particle cloud simultaneously yielding average mobility values. [2]... 

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