| The Janus interface material has the characteristics of asymmetric wettability on both sides.Janus membranes(JM)have a porous structure and allow the opposite wettability of the membrane to work together to cause a unique unidirectional transport behavior of droplets in the membrane.The current method of preparing Janus membrane is mainly to modify the surface of the material to have the opposite wettability.However,the porous structure of the material itself will also make the manufacturing process more complicated and difficult to control,due to capillary force.It is likely to cause the modifiers to diffuse between the two layers,so more attention needs to be paid to their novel manufacturing methods and multifunctional applications.A novel and facile "plug-and-go" strategy for the fabrication of Janus membranes(JM)is proposed in the present work,which is using different combinational substrates with opposite wettability,some suitable substrates are tightly integrated through a certain pressure is also considered.The excellent compactness and controllability of the JM using foam Ni and superhydrophilic Cu mesh are demonstrated in multifunctional applications,including unidirectional liquid transportation in air-water systems,ondemand immiscible oil-water separation,droplet collection in liquid-liquid systems,and on-off switch control.In previous studies,only JM with a thin hydrophobic layer can transport water in one direction and has the characteristics of a "water diode",while JM used as a oneway oil for "oil diode" must have a thin hydrophilic layer.Herein,by controlling the front and back layers with similar thicknesses and suitable pore sizes in an oppositepolarity bulk membrane,both water and oil unidirectional transportation have been realized in liquid-liquid systems,which avoids fine adjustment of the thickness of each layer.The dual function of the resulting JMs as "water and oil diodes" is attributed to the interpenetrating structure and similar thicknesses of the formed hydrophobic and hydrophilic layers,which minimizes the penetration distance of the Janus membrane in both directions.Moreover,the proposed strategy provides a common route for the fabrication of novel composite materials with greater diversity and composability regarding membrane pore size and thickness.The hydrophobic nickel foam and super-hydrophilic copper mesh used in this experiment have certain pores.Due to the compressibility of the foam nickel,the foam nickel is partially pressed into the pores of the copper mesh with given pressure,which minimized the penetration distance of droplets from both sides of Janus membranes.In addition,the morphology of both sides of the membrane before and after the modification was observed by SEM,and the chemical composition and relative content of the surface of the material were analyzed by EDS,XRD and XPS.It found that many burr-like shapes copper hydroxide nanoneedles were formed on the surface of the modified superhydrophilic copper mesh,the nanoneedles partially pierce the pores of the foam nickel,which also reduces the distance between the two sides of the membrane to a certain extent,and this piercing structure is more conducive to the transportation of liquid across the membrane.This pressure integration strategy provides a general way to manufacture new composite materials.In addition,smart films such as pH response and ultraviolet light response also have very broad application prospects.Previous studies on pH-responsive smart membranes have adopted the gold spray method,that is after spraying gold on the surface of hydrophilic materials,the gold atoms are combined with 11mercaptoundecanoic acid and 1-decyl mercaptol to make them pH responsive.This method is expensive and requires high equipment.In this experiment,an easy-tooperate electroplating method is used to electroplate a layer of cheap silver on the surface of the material,and then let the silver atom combined with undecanoic acid and 1-decanethiol,and it provides a simple and economical method for preparing pHresponsive smart membranes. |
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