No abstract

Strong charge trapping and bistable electrowetting on nanocomposite fluoropolymer:BaTiO3 dielectrics are reported. Thin nanocomposite dielectrics were spin casted from BaTiO3 nanopowder dispersed in a fluoropolymer/fluorosolvent solution. Electrowetting contact angle versus voltage and capacitance measurements confirm a severalfold increase in film dielectric constant with increasing BaTiO3 content. Bistable electrowetting was observed as droplets retained a decreased contact angle at 0V but would dewet the surface by briefly applying a reverse polarity voltage. Strong charge trapping in the nanocomposite was confirmed by charge-voltage hysteresis. These results could prove important for low-power applications such as bistable displays and electronic paper.

Corner cube and spherical retroreflectors are ubiquitous in conspicuity and range-finding applications since they reflect light back to the illumination source with unmatched efficiency. We report here a switchable electrowetting retroreflector platform that provides multiple novel features, including ͑a͒ using Ͻ0.5 J / cm 2 electrical energy to switch from a light scattering state, ͑b͒ low loss and wide spectrum as limited only by the absorption spectrum of water, ͑c͒ use of ultrasimple self-assembly of 10 3-10 5 liquid lenslets/ in. 2 on a polymer/Al corner-cube substrate, and ͑d͒ change in retroreflected irradiance of Ͼ10: 1 over a Ϯ30°field of view.

Electrowetting retroreflectors use a simple and scalable construction, and incorporate an electrically tunable liquid lenslet. By electrically modulating the lenslet geometry, the reflection is switched between retroreflection and scattering. In this paper, we report new capability and characterization, including higher index liquids and contrast ratio as a function of contact angle (theta(V)). The reflected intensity is also spatially profiled and reported as a function of view angle. A high contrast ratio of >16X is demonstrated, and methods for further improving performance are discussed. Because the electrowetting retroreflector platform is broad spectrum (VIS-IR), the electrowetting retroreflector may be useful for a large variety of naked eye applications such as safety markings, road-signage, or friend-foe-identification.

A hydrophobic fluoropolymer:BaTiO3 nanocomposite is presented for achieving lower-voltage electrowetting operation. The composite fluoropolymer film exhibits as much as a 10X increase in measured dielectric constant. Increased surface roughness with BaTiO3 content increased the sessile drop contact angle from θ∼104° to 121° with compositions ranging from 0 to 97 vol. % of BaTiO3 in the fluoropolymer. A larger change in electrowetted contact angle is observed for the 50 vol. % of BaTiO3 nanocomposite (delta theta∼60°) compared to a standard fluoropolymer film of 1 um thickness (delta theta∼30°). Furthermore, required operating voltage for electrowetting decreases by ∼30V for films with high BaTiO3 content. Strong charge storage in the nanocomposite was observed via a new bistable electrowetting effect. For samples with strong charge storage, the droplet remains wetted (>2 minutes) even after removing the applied voltage. Rapid (< 1s) droplet de-wetting could be achieved by briefly applying a reverse polarity voltage to remove the stored charge in the nanocomposite.