Hua Lai

pH-Controllable On-Demand Oil/Water Separation on the Switchable Superhydrophobic/Superhydrophilic and Underwater Low-Adhesive Superoleophobic Copper Mesh Film

Recently, materials with controlled oil/water separation ability became a new research focus. Herein, we report a novel copper mesh film, which is superhydrophobic and superhydrophilic for nonalkaline water and alkaline water, respectively. Meanwhile, the film shows superoleophobicity in alkaline water. Using the film as a separating membrane, the oil/water separating process can be triggered on-demand by changing the water pH, which shows a good controllability. Moreover, it is found that the nanostructure and the appropriate pore size of the substrate are important for realization of a good separation effect. This paper offers a new insight into the application of surfaces with switchable wettability, and the film reported here has such a special ability that allows it to be used in other applications, such as sewage purification, filtration, and microfluidic device.

pH-induced reversible wetting transition between the underwater superoleophilicity and superoleophobicity.

Surfaces with controlled oil wettability in water have great potential for numerous underwater applications. In this work, we report a smart surface with pH-responsive oil wettability. The surface shows superoleophilicity in acidic water and superoleophobicity in basic water. Reversible transition between the two states can be achieved through alteration of the water pH. Such smart ability of the surface is due to the cooperation between the surface chemistry variation and hierarchical structures on the surface. Furthermore, we also extended this strategy to the copper mesh substrate and realized the selective oil/water separation on the as-prepared film. This paper reports a new surface with excellently controllable underwater oil wettability, and we believe such a surface has a lot of applications, for instance, microfluidic devices, bioadhesion, and antifouling materials.

Underwater Superoleophilic to Superoleophobic Wetting Control on the Nanostructured Copper Substrates

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.

Designing heterogeneous chemical composition on hierarchical structured copper substrates for the fabrication of superhydrophobic surfaces with controlled adhesion.

Controlling water adhesion is important for superhydrophobic surfaces in many applications. Compared with numerous researches about the effect of microstructures on the surface adhesion, research relating to the influence of surface chemical composition on the surface adhesion is extremely rare. Herein, a new strategy for preparation of tunable adhesive superhydrophobic surfaces through designing heterogeneous chemical composition (hydrophobic/hydrophilic) on the rough substrate is reported, and the influence of surface chemical composition on the surface adhesion are examined. The surfaces were prepared through self-assembling of mixed thiol (containing both HS(CH2)9CH3 and HS(CH2)11OH) on the hierarchical structured copper substrates. By simply controlling the concentration of HS(CH2)11OH in the modified solution, tunable adhesive superhydrophobic surfaces can be obtained. The adhesive force of the surfaces can be increased from extreme low (about 8 μN) to very high (about 65 μN). The following two reasons can be used to explain the tunable effect: one is the number of hydrogen bond for the variation of surface chemical composition; and the other is the variation of contact area between the water droplet and surface because of the capillary effect that results from the combined effect of hydrophilic hydroxyl groups and microstructures on the surface. Noticeably, water droplets with different pH (2-12) have similar contact angles and adhesive forces on the surfaces, indicating that these surfaces are chemical resistant to acid and alkali. Moreover, the as-prepared surfaces were also used as the reaction substrates and applied in the droplet-based microreactor for the detection of vitamin C. This report provides a new method for preparation of superhydrophobic surfaces with tunable adhesion, which could not only help us further understand the principle for the fabrication of tunable adhesive superhydrophobic surfaces, but also potentially be used in many important applications, such as microfluidic devices and chemical microreactors.

Super-hydrophobic surface with switchable adhesion responsive to both temperature and pH

In this article, we report a new super-hydrophobic surface with switchable adhesion that is responsive to both temperature and pH. When the water pH is fixed (pH = 7), a water droplet (4 μL) can roll on the surface at high temperature (45 °C) and be pinned at low temperature (20 °C). Simultaneously, the surface shows strong dependence on the pH of the water droplet, an acid droplet (pH = 2, 4 μL) can roll on the surface while a basic droplet (pH = 11, 4 μL) is pinned when the temperature is constant (45 °C). Reversible transition between the low adhesive rolling state and the high adhesive pinning state can be achieved by simply changing the temperature and/or the pH alternately. The smart effect of the surface is attributed to the cooperation of chemical variation of the poly(N-isopropylacrylamide-co-acrylic acid) P(NIPAAm-co-AAc) and the hierarchical structures on the surface. Such a novel super-hydrophobic surface with dual-responsive adhesion could potentially be used in a wide range of applications with more complex environments, such as biochemical separation, lab-on-chip devices and in situ detection.

Regulating Underwater Oil Adhesion on Superoleophobic Copper Films through Assembling n-Alkanoic Acids

Controlling liquid adhesion on special wetting surface is significant in many practical applications. In this paper, an easy self-assembled monolayer technique was advanced to modify nanostructured copper substrates, and tunable adhesive underwater superoleophobic surfaces were prepared. The surface adhesion can be regulated by simply varying the chain length of the n-alkanoic acids, and the tunable adhesive properties can be ascribed to the combined action of surfaces nanostructures and related variation in surface chemistry. Meanwhile, the tunable ability is universal, and the oil-adhesion controllability is suitable to various oils including silicon oil, n-hexane, and chloroform. Finally, on the basis of the special tunable adhesive properties, some applications of our surfaces including droplet storage, transfer, mixing, and so on are also discussed. The paper offers a novel and simple method to prepare underwater superoleophobic surfaces with regulated adhesion, which can potentially be applied in numerous fields, for instance, biodetection, microreactors, and microfluidic devices.

A pH-responsive superwetting nanostructured copper mesh film for separating both water-in-oil and oil-in-water emulsions

Recently, superwetting separating materials for emulsified oil/water mixtures have become a new research focus due to their special advantages such as high efficiency and high flux. So far, although lots of superhydrophobic/superoleophilic and superhydrophilic/underwater superoleophobic films have been prepared for the separation of water-in-oil and oil-in-water emulsions, respectively, smart films that can switch between the above two wetting states and be suitable for the separation of both the two types of emulsions are still rare. Herein, we advance a simple strategy by creating a nanostructure and attaching responsive molecules onto the copper mesh substrate, and report a novel pH-responsive nanostructured copper mesh film. Results indicate that the nanostructure can not only effectively adjust the substrate pore size from the microscale to the nanoscale to meet the requirements for emulsion separation, but can also enhance the surface wettabilities. Combined with the responsive molecules, the film wettability can be switched reversibly between the superhydrophobic/superoleophilic and the superhydrophilic/underwater superoleophobic states. As a result, both water-in-oil and oil-in-water emulsions can be separated on the film with high efficiency and high flux due to the synergy effect between the nanoscale pore structure and the switchable wettability. Given the as-prepared film has such a smart ability, it is believed to be potentially useful in many practical applications, such as sewage treatment and oil recovery.

Controlled synthesis and luminescent properties of DyPO4:Eu nanostructures

In this paper, a simple hydrothermal method was designed for the selective synthesis of Eu-doped tetragonal DyPO4 and hexagonal DyPO4·1.5H2O nanocrystals. It was found that the hydrothermal conditions (temperature and pH) and organic additive are very important in determining the crystal structures and morphology of the final products. Low temperature and low pH (120 °C, pH = 2) are favorable for the formation of the hexagonal DyPO4·1.5H2O, while high temperature and high pH (200 °C, pH = 8) would be more suitable for the production of tetragonal DyPO4. When the organic additive ethylenediamine tetraacetic acid disodium salt (EDTA) was used, products with the same crystal structures (hexagonal DyPO4·1.5H2O) and different morphologies, such as nano/submicroprisms, and nanorods could be obtained. Furthermore, the luminescent properties of DyPO4:Eu with different crystal structures and morphologies were also investigated. Compared with the hexagonal DyPO4·1.5H2O, a small blue shift of the strongest excitation peak and increase in the intensity of the emission spectra can be observed for the tetragonal DyPO4. Our capability of obtaining hexagonal DyPO4·1.5H2O and tetragonal DyPO4 can not only provide some new information in the study of polymorph control and selective synthesis of inorganic materials, but also benefits the wide applications of DyPO4 due to the improved luminescent properties.

Designing Robust Underwater Superoleophobic Microstructure on Copper Substrate

Recently, surfaces with a robust underwater superoleophobicity have attracted much attention. Although it is recognized that stable microstructures are significant for such surfaces, a clear picture of how microstructural features such as morphology, size, etc. influence their own stability and related wettability is still missing. Herein, three low adhesive underwater superoleophobic copper surfaces with different microstructures (hemispheric, pinecone-like, and honeycomb) were first prepared, and then the stability of these microstructures was examined by a series of physical and chemical damage experiments (sand grain abrasion, corrosion in acid/base solutions, etc.). The results indicate that the hemispheric microstructure is more stable than the other two microstructures and the corresponding surface has a robust underwater superoleophobicity. Theoretical simulation analysis further confirms the experimental results and reveals that different stabilities are ascribed to different stress distributions on these microstructures under an external force due to distinct microstructure shapes. Furthermore, based on the same design strategy, a robust underwater superoleophobic oil/water separation copper mesh film was also prepared. This work provides an insight into the effect of microstructural features on the stability and related underwater oil-repellent properties of superoleophobic copper surfaces, and could provide us with some fresh design ideas for robust superwetting surfaces.