Underwater Superoleophilic to Superoleophobic Wetting Control on the Nanostructured Copper Substrates

Abstract

Surfaces with controlled underwater oil wettability would offer great promise in the design and fabrication of novel materials for advanced applications. Herein, we propose a new approach based on self-assembly of mixed thiols (containing both HS(CH2)9CH3 and HS(CH2)11OH) on nanostructured copper substrates for the fabrication of surfaces with controlled underwater oil wettability. By simply changing the concentration of HS(CH2)11OH in the solution, surfaces with controlled oil wettability from the underwater superoleophilicity to superoleophobicity can be achieved. The tunable effect can be due to the synergistic effect of the surface chemistry variation and the nanostructures on the surfaces. Noticeably, the amplified effect of the nanostructures can provide better control of the underwater oil wettability between the two extremes: superoleophilicity and superoleophobicity. Moreover, we also extended the strategy to the copper mesh substrates and realized the selective oil/water separation on the as-prepared copper mesh films. This report offers a flexible approach of fabricating surfaces with controlled oil wettability, which can be further applied to other ordinary materials, and open up new perspectives in manipulation of the surface oil wettability in water.

Insights into the superhydrophobicity of metallic surfaces prepared by electrodeposition involving spontaneous adsorption of airborne hydrocarbons

“…In the above XPS analyses, we have demonstrated that the coverage of hydrophobic hydrocarbons at the micro/nanostructured metal surfaces should exceed a critical proportion to behave superhydrophobic, which depends on the surface roughness and the surface composition. That was also confirmed by modifying metal surface with mixed hydrophilic and hydrophobic organics [59]. To recover the superhydrophobic state from the superhydrophilic state after UV-O 3 treatment, the airborne hydrocarbons must replace, insert into and/or cover the already adsorbed superhydrophilic oxygencontaining organics at the surface.…”

Reversible switch between underwater superaerophilicity and superaerophobicity on the superhydrophobic nanowire-haired mesh for controlling underwater bubble wettability

“…Many experiments have also demonstrated that the microstructure of the Cu(OH) 2 nanowires can be controlled just through varying the immersion time in the solution of NaOH and (NH 4 ) 2 S 2 O 8 . 19,20 After the formation of the nanoneedles structure by a one-step chemical reaction and the subsequent fluoroalkylsilane surface modification, the resultant rough copper mesh shows excellent superhydrophobicity. As shown in Figure 3a, a small water droplet on such mesh can keep a spherical shape with the water CA of 152.8 • ± 1.8 • .…”

Oil‐Water Separation: A Gift from the Desert

“…Following this strategy, many mesh and porous materials that are underwater superoleophobic have been fabricated, and these materials have been successfully applied in oil-water separation. [18][19][20][21][22][23][24][25] For example, Jiang and co-workers coated microscale porous stainless steel mesh with a nanostructured hydrogel to give a novel underwater superoleophobic rough mesh. [ 18 ] This hydrogelcoated mesh effi ciently removed water from water-oil mixtures and did not become fouled with oil.…”

“…Problems that have not been adequately addressed are the cost of the materials, the equipment required, and the preparation processes required -all of which prevent large-scale applications. Another issue is that the most widely used materials are metal meshes and porous polymers that have rough microscale-nanoscale hierarchical structures, which are generally formed using chemical corrosion or other chemical methods, [20][21][22][23][24][25] meaning that solving one environmental problem (oil pollution) could cause another (disposing of the waste produced to create the superoleophobic material). It is therefore very important that we develop or fi nd stable materials that are underwater superoleophobic and can be used to simply, cheaply, and effi ciently separate large amounts of oil-water mixtures.…”

“…"Water-removing" superhydrophilic and superoleophobic materials have been developed to address the problems described above, and they have proved extremely effective in practical applications. [15][16][17][18][19][20][21][22][23][24][25] However, it is harder to produce a superoleophobic material (with an oil contact angle (OCA) greater than 150°) than to produce a superhydrophobic material because the surface tensions of oils are lower than the surface tension of water. [26][27][28][29][30] A surface that is superoleophobic several metal elements, as shown in Figure S1 of the Supporting Information.…”