ABSTRACT
The effects of an immiscible, lubricating polydimethylsiloxane fluid, referred to as silicone oil, on the static deformation and on the dynamic motion of a water drop on paper induced by electrowetting were investigated. The deformation of a drop on a hydrophobic film of amorphous fluoropolymers top-coated with less hydrophobic silicone oil was much more predictable, reversible and reproducible than on the uncoated surface. In the dynamic tribological experiment for a sliding drop along an inclined surface, a significant decrease in the friction coefficient, with an unexpected dependency of the contact area, was observed. Based on the curve fitting analysis, the shear stress and the net friction force were estimated quantitatively. Because of the tribological effect and the reduced shear friction force of the oil film, the static and the dynamic electrowetting states of the water drop were enhanced.
ABSTRACT
We present the development of a flexible bimodal sensor using a paper platform and inkjet printing method, which are suited for low-cost fabrication processes and realization of flexible devices. In this study, we employed a vertically stacked bimodal device architecture in which a temperature sensor is stacked on top of a pressure sensor and operated on different principles, allowing the minimization of interference effects. For the temperature sensor placed in the top layer, we used the thermoelectric effect and formed a closed-loop thermocouple composed of two different printable inks (conductive PEDOT:PSS and silver nanoparticles on a flexible paper platform) and obtained temperature-sensing capability over a wide range (150 °C). For the pressure sensor positioned in the bottom layer, we used microdimensional pyramid-structured poly(dimethylsiloxane) coated with multiwall carbon nanotube conducting ink. Our pressure sensor exhibits a high-pressure sensitivity over a wide range (100 Pa to 5 kPa) and high-endurance characteristics of 105. Our 5 × 5 bimodal sensor array demonstrates negligible interference, high-speed responsivity, and robust sensing characteristics. We believe that the material, process, two-terminal device, and integration scheme developed in this study have a great value that can be widely applied to electronic skin.
