Anisotropic wettability has recently attracted significant research attention owing to its vast areas of applications. Naturally, anisotropic superhydrophobicity has been exhibited in rice leaf due to low surface energy and anisotropic micro-/nanoscale hierarchical rough structures. This property has also been observed to provide unidirectional water adhesion in animals such as butterfly. These natural surfaces together with many more have inspired researchers to construct anisotropic patterns on poly(dimethylsiloxane) (PDMS) surface using femtosecond laser ablation to realize superhydrophobicity property. Despite fabrication of several surfaces and testing their application in water droplet manipulation, their use in the directional and no-loss movement of oil droplets in water medium have not been fully explored.
To this note Xi’an Jiaotong University researchers: Yang Cheng (PhD candidate), Professor Qing Yang, Yao Fang (PhD candidate), Professor Jiale Yong, Professor Feng Chen, and Professor Xun Hou developed a new and much simpler strategy to fabricate underwater anisotropic superoleophobic three-dimensional tracks on PDMS surface for manipulating underwater oil droplets.
They used femtosecond laser etching and oxygen plasma treatment techniques. Consequently, laser ablation was able to generate both micro- and nanoscale hierarchical rough microstructures on the PDMS surface while subsequent oxygen plasma treatment turned the textured PDMS surface from superhydrophobicity to hydrophilicity. Eventually, they investigated the influence of the laser power, scanning number, and laser scanning speed on the etching depth of the tracks. Their work is currently published in the research journal, Advanced Materials Interfaces.
According to the authors, the laser etching method provided an alternative means for fabricating underwater anisotropic superoleophobic tracks on the PDMS surface. Whereas the width of the tracks highly depended on the laser-treated area, the depth of the tracks, on the other hand, depended on the laser power, scanning number, and scanning speed. For instance, an increase in the laser power and the scanning number, as well as a decrease in the scanning speed, resulted in a corresponding increase in the depth of the tracks.
To actualize the study, the track structure was designed on the PDMS surface and it showed anisotropic oil wettability. The underwater oil droplet on the resultant PDMS surface recorded an oil contact angle of 161° that could easily roll off upon a slight tilt of 1° on the PDMS surface. The underwater oil droplets moved along the three-dimensional superoleophobic tracks due to their ultralow adhesion and anisotropic sliding property. This contributed to the realization of a microchemical reaction. No loss of reactants was observed during the whole reaction process as observed in the reaction between styrene and bromine microdroplets.
In summary, the research team successfully fabricated underwater anisotropic superoleophobic tracks and demonstrated their application in the directional movement of oil droplets and the microdroplets reaction. The anisotropic sliding property is a promising solution in advancing numerous applications including droplet manipulation, chemical engineering, microfluidic systems among others.
Cheng, Y., Yang, Q., Fang, Y., Yong, J., Chen, F., & Hou, X. (2019). Underwater Anisotropic 3D Superoleophobic Tracks Applied for the Directional Movement of Oil Droplets and the Microdroplets Reaction. Advanced Materials Interfaces, 6(10), 1900067.Go To Advanced Materials Interfaces