Zhao et al. – Dielectrowetting Optical Shutter
Large Area and Low Power Dielectrowetting Optical Shutter with Local Deterministic Fluid Film Breakup
R. Zhao,1, 2 B. Cumby,1 A. Russell,1 J. Heikenfeld,1,[a]
1Novel Devices Laboratory, Department of Electrical Engineering and Computing Systems, University of Cincinnati, Cincinnati, Ohio 45221, USA
2Center of Optofluidic Technology, College of Optoelectronic Engineering, Nanjing University of Posts and Telecommunications, Nanjing, Jiangsu 210003, China
Supplemental Material
Device Fabrication. 2"×2"aluminosilicate glass coated with indium tin oxide of resistivity 100 Ohm per square was purchased from PG & O Precision Glass & Optics. The interdigitated electrodes of width and gap spacing of 40 µm were patterned over an area of 45mm×48mm by AZ 15nXT photoresist pattering and wet etching with TIN ETCHANT TE-100 (Transene company, Inc.) for ~6 min. at 90°C. The photoresist was removed by immersion in AZ NMP Rinse for a 5 min. at 80°C. Simple epoxy resins with black dye were contact printed into circular dots of about 0.25 mm diameters. Then substrate was then dip-coated with CytonixFluoroPelTM1601Vand baked in air for 30 minutes at 120°C to form a uniform and hydrophobic fluoropolymer layer that is about 50 nm thick.
Ink Formulation. The liquid crystal used (LC, RDP-A4058, DIC Corporation, Japan) was colored with about 2.0wt. % of dye. The dyes used were Keystone Analine Corp. Liquid Oil Dyes (USA), highly purified of electrically conductive contaminants by Unichem Corp. (Taiwan), as required by and developed for our previous work in insulating colored oils for electrowetting displays29. The dye ratios used were red, yellow, and blue at a ratio of 1:1:3. Small droplets of the ink were subjected to 5 hours at 120 °C in atmosphere, and no change in droplet size was visible, indicating that ink vapor pressure is very low and the inks used could be applicable even for higher temperature environments.
Device Operation. A volume-calibrated single-channel micropipetter (0.1-2 µl) was used to dispense ink onto the device. For most experiments, AC voltage from -150V to +150V (300 Vpp) was used with frequency between 0.1Hz to 100 Hz square waveform. The voltage was provided by a dual channel Arbitrary Function Generator (AFG320, Tektronix Corporation, Japan), a phase inverter, and the inverted and non-inverted signals cumulatively providing the Vpp from a dual channel linear amplifier (Model 603, Tektronix Corporation, Japan).
Contact Angle Measurement. Contact angles were obtained with a VCA drop shape analysis system. All data sets are repeated at least 3 times at a fresh sample location and data is plotted as an average curve including error bars.
Switching Speed Measurements. Video of the device operation was taken with a DSLR camera with a 100-mm lens (Canon Rebel T2i with canon EF100m f/28 macro lens) and analyzed using Image J software. Switching time was measured by converting the video to binary mode and measuring the percentage area covered by ink versus time.
Transmission Measurements. Percent transmission measurements were performed with a LabSphereRT-060-SF integrating sphere. The test substrates wereplaced on the top source port, where white light is introduced from a tungsten lamp by a Thorlabs OSL Fiber illuminator through the sample and into the integrating sphere. Light is thencollected by an Ocean Optics P200-2-VIS-NIR optical fiberfitted with a 74-VIS collimating lens at the detector port, and then leads to an Ocean OpticsHR4000CG-UV-NIR spectrometer.
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