Many of the highest performance approaches for electronic paper use voltage to reveal or hide dark pigments or dyes over a white pixel surface, and the reflectance of white pixels is lower than in real paper because the dark pigments or dyes can never be fully removed from the visible pixel area. Here, we introduce a re-designed approach for electronic paper that transposes coloured ink in front of or behind a white microfluidic film. Pixels can provide 490% reflective area and have demonstrated o15 ms switching for 150 pixels-per-inch resolution. This new approach is also the first of its kind for electrowetting-style displays by allowing non-aligned lamination fabrication, and is the first ever colourant-transposing pixel that eliminates the need for ink microencapsulation or pixel borders.
A detailed study is reported on the implications of scaling dielectrowetting optical shutters to higher resolutions. Reducing droplet sizes from millimeters to 100 μm in diameter increases the relevance of microfluidic physics such as pinning, film breakup, and dewetting speed as well as optical physics such as transmission and diffraction. In addition, in this work we present improved material systems, including optimized dielectric stacks which reduce electrochemical degradation, and blended lower-viscosity fluids which increase dewetting speed. A higher-resolution device of ~250 μm diameter demonstrates switching speeds of <100 ms and a clear, optically transmissive aperture of >70%. In addition to revealing science not previously discussed, this work has strong applied importance as scaling to higher resolutions is desirable for improving visual appearance in applications ranging from smart windows to electronic signage.
Dielectrowetting effects of surface wrinkling, isotropic vs anisotropic spreading, electrode geometry, and deterministic dewetting are presented both experimentally and by 3D numerical modeling. The numerical results are generated by COMSOL in conjunction with the phase-field and electrohydrodynamic methods, including comparisons to experimental data. The dynamic behavior of the two-phase system has been accurately characterized on both the macro- and microscopic level. This work provides a deeper theoretical insight into the operating physics of dielectrowetting superspreading devices.
Electrofluidic displays operate by transposing a pigment between an optically hidden or revealed state. The transposition is powered by electromechanical force, and over similar distance switches ∼100X faster than electrophoresis by moving the pigment with the fluid, not through the fluid. We report on progress with our previously reported pixel structures, and on a new electrofluidic film that is the first of its kind for all fluidic displays (electrowetting, electrophoretic, electrokinetic, electrofluidic). The new structure operates without capsules or pixel walls for fluid confinement, and requires no pixel electrode alignment.
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