Study On Anisotropic Wetting Of Tilted Nanostructures On PET Surface By Plasma Etching

Anisotropic wetting and directed flow of liquids are important in bioengineering,medical and chemical transport,mixing,and microfluidic motion.Oxygen plasma etching of polyethylene terephthalate?PET?surface by Faraday cage-assisted RF capacitive coupling mode,controlled by inrun with different angles to obtain 0°,30°,45°,60°different nanometers structure,the anisotropic wetting and directional flow behavior of nanostructures with different tilt angles under oxygen plasma etching and octafluorocyclobutane?C₄F₈?and acrylic acid?AA?polymerization modification were studied.Combined with Surface chemical composition and wettability mode.The formation mechanism of anisotropic wetting difference on nanostructures with different tilt angles and the principle of anisotropic wetting and directional flow after polymerization modification were discussed.The wettability of nanostructures with different tilt angles on PET surface was studied.Except for the super-hydrophilic spread of droplets on the tilted?vertical?structure of 0°,the droplets on the inclined structures of 30°,45°and 60°exhibits anisotropic wetting in X direction and Y direction,X direction wetting is hindered,and Y direction is easy to wet.And the larger the tilted angle,the longer the wetting length in Y direction.In the sliding of droplet on the inclined surface,the direction of the inclined structure?Y-direction?is easy to slide,and on the inclined structures of 30°,45°and 60°,the angle of the inclined structure is larger,and the droplet in Y+Y-direction is more slippery,wherein the 60°inclined structure 40?L of deionized water has a slip angle of 32.6°in Y-direction.In the case of continuously injecting water onto the surface of the inclined structure,the continuous microfluids of the 30°,45°and 60°inclined structure surfaces flow uniformly against the inclined structure?Y+direction?,while the three-phase line is pinned along the inclined structure?Y-direction?,despite increasing water injection speed of 5?L/s.And the larger the inclination angle of the structure,the faster the directional flow speed.The main reason for the directional flow is that the difference in surface tension resistance of the droplet on the Y+Y-direction.In the continuous microfluidic directional climbing behavior,the directional climbing ability is best due to the larger viscous force of the30°inclined structure and the small force of the inclined structure.The nanostructures with different tilt angles were superhydrophobic and hydrophilized on the surface under the C₄F₈ and AA plasma polymerization.Under the C₄F₈ plasma polymerization process,the contact angles of the droplets on the tilted nanostructures of 0°,30°,45°and 60°are all above 150°.With the increase of the tilt angle of the structure,the contact angle is slightly reduced and rolling angle is increased since the viscous force is enhanced.Superhydrophobization of the tilted structure reduces or even eliminates the anisotropic wetting of the droplets and the directional fluidity of the continuous microfluid.Under the plasma AA polymerization process,the hydrophilicity of the PET surface is further enhanced.The contact angle of the 30°,45°and 60°inclined structures is reduced to 30°to 40°,except for the vertical structure which is super-hydrophilic and circularly spread.And the droplets appear to be oriented along the inclined structure?Y-direction?,and the larger the tilted angle of the structure is,the larger the directed spreading speed is,and the anisotropic wetting ability is enhanced.This is mainly because the surface critical transition contact angle?r is more likely to be larger than the intrinsic contact angle?eq as the tilted angle increases,causing the structure to drive the droplets to unidirectional spreading.Continuously watering at a water injection speed of 0.1?L/s,the liquid still flows along the inclined structure,and the flow speed is twice that of the unpolymerized inclined structure oriented Y+to the flow under the same conditions,and finally by designing the microfluidic channel.The droplets are preferably linearly bidirectionally mixed.