Thursday, December 12, 2013

Could a virtual wall build an invisible barrier for oil spills and stop the spread?

December 12, 2013
Conventional superoleophobic surfaces (a−c): Oil can be pinned on (a) mushroom-like structures, (b) sharp edges, and (c) bumplike structures without wetting the entire surface. The newly developed oil-repellent surface has (d) re-entrant curvatures oriented in the vertical direction and (e) re-entrant circular geometries oriented in the lateral direction. (Credit: Riberet Almeida and Jae Wan Kwon/Langmuir)
University of Missouri researchers have developed a technique to form a virtual wall for oily liquids that will help confine them to a certain area, aiding researchers who are studying these complex molecules. This development will have future implications in the guided delivery of oil and effective blockage of oil spreading.
“Our work is based on micro/nanoelectromechanical systems, or M/NEMS, which can be thought of as miniaturized electrical or mechanical structures that allow researchers to conduct their work on the micro/nanoscopic level,” said Jae Kwon, associate professor of electrical and computer engineering in the College of Engineering at MU. “Oil-based materials or low-surface tension liquids, which can wet any surface and spread very easily, pose challenges to researchers who need to control those tiny oil droplets on microdevices.”
Oil-based compounds are referred to as low-surface tension liquids because they tend to spread on the surface of a researcher’s microscope slides or microarrays where the liquids are placed. Additionally, as can be seen from oil spills in the Gulf of Mexico, oil can stick and easily spread out on any surface. Using specially designed oil-repellent surfaces, Kwon and his group demonstrated invisible “virtual walls” that block spreading of low-surface tension liquids at the boundary line with microscopic features already created in the device.
“Our newly developed surface helped keep oil, which is normally unmanageable, in predetermined pathways, making it controllable. We feel that oil-repellant surfaces can be widely utilized for many industrial applications. Virtual walls for low-surface tension liquids also have immense potential for many lab-on-a-chip devices.”
Kwon suggests that in the future, oil-repellent virtual walls may be used to control the transport of oil without spillage.

Abstract of Langmuir paper
Manipulating and controlling water-based aqueous solutions with the use of virtual walls is relatively simple compared to that of nonaqueous low-surface-tension liquids, which pose greater challenges to microfluidic devices. This letter reports a novel technique to form a virtual wall for various low-surface-tension liquids. A microfluidic channel with virtual walls has been made to guide low-surface-tension liquids by using a specially designed oil-repellent surface. Unlike generic superoleophobic surfaces, our oil-repellent surface exhibited strong repellency to the lateral flow of low-surface-tension liquids such as hexadecane and dodecane. A plasma-assisted surface micromachining process has been utilized to form the oil-repellent surface. The use of combined features of re-entrant geometries on the surface played an important role in promoting its repellence to the lateral flow of low-surface-tension liquids. We have successfully demonstrated how low-surface-tension liquids can be well confined by the virtual walls.

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