Electrofluidic displays using Young–Laplace transposition of brilliant pigment dispersions

Conventional electrowetting displays reconfigure the contact angle of a coloured oil film on a planar hydrophobic surface. We report on electrofluidic displays, in particular a three-dimensional microfluidic display device that provides a direct view of brilliantly coloured pigment dispersions. Electromechanical pressure is used to pull the aqueous dispersion from a reservoir of small viewable area (<10%) into a surface channel of large viewable area (>90%). The hydrophobic channel and reservoir respectively impart a small or large radius of curvature on the dispersion. Therefore, with no voltage, Young– Laplace pressure forces the dispersion to retract into the reservoir. Preliminary prototypes exhibit 55% white reflectance, and future development points towards a reflectance of 85%. Uniquely, compared to electrowetting pixels, the electrofluidic pixels reduce the visible area of the coloured fluid by an additional two to three times (improving contrast), are potentially bistable, are as thin as 15 mm (giving potential for rollable displays), and can be miniaturized without increased operating voltage.