Publication Date

Summer 2013

Degree Type


Degree Name

Master of Science (MS)


Mechanical and Aerospace Engineering


Sang-Joon John Lee


electric double-layer, electronic ink, electronic paper, electrophoretic ink concentration, image contrast, steric effect

Subject Areas

Mechanical engineering


Reverse-emulsion electrophoretic display technology is based on an electro-responsive ink comprised of self-assembled nanodroplets dispersed in a non-polar liquid. The dye-containing nanodroplets are selectively driven toward or away from the viewing plane of a display by electric fields. The hypothesis of this study is that image contrast in a nanodroplet electrophoretic display is governed by concentration and steric effects that limit the intensity of the dark state. Simultaneously, steric effects as well as electrostatic screening can diminish whiteness in the light state. This hypothesis has been tested by multiphysics simulation of dilute species in electrostatic fields and experimental measurements of relative luminance in test displays. Concentration level was varied in a range of dilutions from full concentration (100%) to one-eighth (12.5%) and the highest contrast ratio was achieved at 25%. The test devices exhibited behavior that was similar to the saturation effects predicted by simulation, accounting for steric effects. Ink concentration showed little effect on switching time, reaching steady-state within approximately 2 seconds for all concentration levels. The hypothesis was further tested by experimentally observing the effect of driving voltage between 1 V to 8 V. The results showed no significant improvement of contrast even at higher voltage, further suggesting that concentration and steric effects dictate maximum contrast.

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