Junfei Ou

Superhydrophobic surfaces on light alloy substrates fabricated by a versatile process and their corrosion protection.

After hydrothermally treated in H2O (for Mg alloy and Al alloy) or H2O2 (for Ti alloy), microstructured oxide or hydroxide layers were formed on light alloy substrates, which further served as the active layers to boost the self-assembling of 1H,1H,2H,2H-perfluorooctyltriethoxysilane (PFOTES) and finally endowed the substrates with unique wettability, that is, superhydrophobicity. For convenience, the so-fabricated superhyrdophobic surfaces (SHS) were abridged as HT-SHS. For comparison, SHS coded as CE-SHS were also prepared based on chemical etching in acid and succedent surface passivation with PFOTES. To reveal the corrosion protection of these SHS, potentiodynamic polarization measurements in NaCl solution (3.5 wt %) were performed. Moreover, to reflect the long-term stability of these SHS, SHS samples were immersed into NaCl solution and the surface wettability was monitored. Experimental results indicated that HT-SHS was much more stable and effective in corrosion protection as compared with CE-SHS. The enhancement was most likely due to the hydrothermally generated oxide layer by the following tow aspects: on one hand, oxide layer itself can lower the corrosion due to its barrier effect; on the other hand, stronger interfacial bonding is expected between oxide layer and PFOTES molecules.

Superoleophobic Textured Copper Surfaces Fabricated by Chemical Etching/Oxidation and Surface Fluorination

We report a convenient route to fabricate superoleophobic surfaces (abridged as SOS) on copper substrate by combining a two-step surface texturing process (first, the substrate is immersed in an aqueous solution of HNO3 and cetyltrimethyl ammonium bromide, and then in an aqueous solution of NaOH and (NH4)2S2O8) and succeeding surface fluorination with 1H,1H,2H,2H-perfluorodecanethiol (PFDT) or 1-decanethiol. The surface morphologies and compositions were characterized by field emission scanning electron microscopy and X-ray diffraction, respectively. The results showed that spherical micro-pits (SMP) with diameter of 50-100 μm were formed in the first step of surface texturing; in the second step, Cu(OH)2 or/and CuO with structures of nanorods/microflowers/microballs were formed thereon. The surface wettability was further assessed by optical contact angle meter by using water (surface tension of 72.1 mN m(-1) at 20°C), rapeseed oil (35.7 mN m(-1) at 20°C), and hexadecane (25.7 mN m(-1) at 20°C) as probe liquids. The results showed that, as the surface tension decreasing, stricter choosing of surface structures and surface chemistry are required to obtain SOS. Specifically, for hexadecane, which records the lowest surface tension, the ideal surface structures are a combination of densely distributed SMP and nanorods, and the surface chemistry should be tuned by grafted with low-surface-energy molecules of PFDT. Moreover, the stability of the so-fabricated sample was tested and the results showed that, under the testing conditions, superhydrophobicity and superoleophobicity may be deteriorated after wear/humidity resistance test. Such deterioration may be due to the loss of outermost PFDT layer or/and the destruction of the above-mentioned ideal surface structures. For UV and oxidation resistance, the sample remained stable for a period of 10 days.

One-Step Solution Immersion Process to Fabricate Superhydrophobic Surfaces on Light Alloys

A simple and universal one-step process bas been developed to render light alloys (including AZ91D Mg alloy, 5083 Al alloy, and TC4 Ti alloy) superhydrophobic by immersing the substrates in a solution containing low-surface-energy molecules of 1H,1H,2H,2H-perfluorooctyltrichlorosilane (PFOTS, 20 μL), ethanol (10 mL), and H2O (10 mL for Al and Mg alloy)/H2O2 (15%, 10 mL for Ti alloy). Field-emission scanning electron microscopy, X-ray photoelectron spectroscopy, and water contact angle measurements have been performed to characterize the morphological features, chemical composition, and wettability of the surfaces, respectively. The results indicate that the treated light alloys are rough-structured and covered by PFOTS molecules; consequently, the surfaces show static contact angles higher than 150° and sliding angles lower than 10°. This research reveals that it is feasible to fabricate superhydrophobic surfaces (SHS) easily and effectively without involving the traditional two-step processes. Moreover, this one-step process may find potential application in the field of industrial preparation of SHS because of its simplicity and universality.

Tunable Water Adhesion on Titanium Oxide Surfaces with Different Surface Structures

Tunable water adhesion with high static contact angle (SCA) on titanium oxide surfaces was achieved by a two-step process: first, titanium oxide surfaces with different structures were obtained by immersion the titanium alloy substrates into H₂O-H₂O₂-HF solution at 140 °C for different time of 30, 60, and 120 min; then, low-surface-energy molecules of 1H, 1H, 2H, 2H-perfluorooctyltrichlorosilane (PFOTS) were deposited thereon. SCA for all so-fabricated samples were higher than 150° and sliding angle (SA) for different immersion time of 30 min, 60 min, and 120 min is 180°, 31±2°, and 8±1°, respectively. To analyze the correlation between the surface structures and the dynamic wetting behaviors, we adopted, three contact modes (i.e., Wenzel, Cassie impregnating, and Cassie modes). The analyses showed that the surface adhesion was influenced greatly by water/solid interfacial interaction and could be artificially tuned between Wenzel state with high adhesion to Cassie state with low adhesion through the design of appropriate microstructures.

Mechanically durable superhydrophobic surfaces prepared by abrading

Superhydrophobic surfaces with both excellent mechanical durability and easy reparability based on polytetrafluoroethylene/room temperature vulcanized silicone rubber (PTFE/RTVSR) composites were prepared by a simple abrading method. The surface energy of RTVSR matrix decreased with the increasing volume fraction of PTFE particles, and the surface rough microstructures of the composites were created by abrading. A water droplet on the surface exhibited a contact angle of about 165° ± 3.4° and a sliding angle of about 7.3° ± 1.9°. Such superhydrophobic surfaces showed strong mechanical durability against sandpaper because the surfaces were prepared in the way of mechanical abrasion, and the fresh exposed surfaces were still superhydrophobic. In addition, the micro-structures on the elastic surface of the composite will be compressed by elastic deformation to avoid being broken during the friction cycles when cotton fabric was used as an abrasion surface. The deformation will rebound to renew the original s...

Fabrication and Tribological Investigation of a Novel Hydrophobic Polydopamine/Graphene Oxide Multilayer Film

Polydopamine (PDA)/graphene oxide (GO) multilayer was successfully constructed on the surface of silicon substrate by a layer-by-layer self assembling process. In order to further obtain hydrophobic outer surface, low energy molecules of 1H, 1H, 2H, 2H-perfluorodecyltrichlorosilane (PFDTS) were grafted thereon and the sample was coded as PDA/GO-PFDTS. The microstructures, chemical compositions, and morphologies of PDA/GO-PFDTS were characterized by the water contact angle (WCA) measurements, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). In particular, the tribological performances were investigated by AFM and ball-on-plate tribometer. Experimental results showed that PDA/GO-PFDTS could lower the stiction and friction greatly as compared with the bare substrate and control samples. It was indicated that the as-fabricated film of PDA/GO-PFDTS was a very promising candidate for solving the tribological problems in micro/nano devices.

Green Approach to the Fabrication of Superhydrophobic Mesh Surface for Oil/Water Separation

We report a simple and environment friendly method to fabricate superhydrophobic metallic mesh surfaces for oil/water separation. The obtained mesh surface exhibits superhydrophobicity and superoleophilicity after it was dried in an oven at 200 °C for 10 min. A rough silver layer is formed on the mesh surface after immersion, and the spontaneous adsorption of airborne carbon contaminants on the silver surface lower the surface free energy of the mesh. No low-surface-energy reagents and/or volatile organic solvents are used. In addition, we demonstrate that by using the mesh box, oils can be separated and collected from the surface of water repeatedly, and that high separation efficiencies of larger than 92 % are retained for various oils. Moreover, the superhydrophobic mesh also possesses excellent corrosion resistance and thermal stability. Hence, these superhydrophobic meshes might be good candidates for the practical separation of oil from the surface of water.

A superhydrophobic and superoleophilic miniature mesh box for oil spill clean up

In this paper, we have fabricated a miniature mesh box (SS-MB) with surface superhydrophobicity and superoleophilicity for possible application in the field of oil spill clean up. The superhydrophobic SS-MB was fabricated by boiling a sheet of copper mesh in CuSO4 aqueous solution for an hour. The as-prepared SS-MB rapidly and selectively contained various industrial oils, with a high separation capacity, but did not adsorb any water due to its porosity, superoleophilicity and superhydrophobicity. Additionally, the oil contained by the SS-MB could be easily sucked out using a dropper, for reuse. After washing with toluene, the SS-MB could be used in the next oil–water separation cycle without losing its high separating ability even after 20 separation cycles. Furthermore, the SS-MB is stable under ambient conditions and also shows desirable corrosion resistance under conditions that mimic marine water. Therefore, the SS-MB has the advantages of easy fabrication, excellent oil–water separation and collection properties from the surface of the water, reusability, and reasonable stability under ambient and corrosive conditions, which make it suitable for the fast cleanup of oil spills.

On the correlation between surface morphology and electron work function of indium tin oxide

The electron work function (EWF) is an important parameter of a semiconductor. The understanding of the correlation between the EWF and surface morphology is of much significance for revealing related photoelectric mechanisms. In this study, the surface of indium tin oxide (ITO) was treated by chemical corrosion or absorption of copper phthalocyanine molecules, and their changes in EWF were systematically investigated using scanning Kelvin probe. The decrease of the EWF with the increase of surface roughness was found. Based on a microcapacitor model, the correlation between the EWF and surface microstructures was built up, which was well consistent with the experimental results. These data are of help for improving the photoelectric behaviors of ITO-based devices by adjusting surface/interface structures.

Superhydrophobic fibers from cigarette filters for oil spill cleanup

Cigarette butts make up the largest contribution to solid waste worldwide. A promising way to control the environmental impacts of cigarette butts is to convert the filter wastes to desired products. Herein, by immersing cigarette filters sequentially into an aqueous solution of NaOH and an ethanolic solution of hexadecyltrimethoxysilane, the filters became converted into superhydrophobic/superoleophilic fibers, with measured water and kerosene contact angles of 156.9° ± 3.1° and approximately 0°, respectively. Due to this ability to exclude water and absorb kerosene, the so-obtained fibers were used to clean up a staged spill of kerosene on the surface of water. The cleanup efficiency of these fibers was measured to be as high as approximately 96%, and did not decrease after 10 cycles of use. The moisture content in the kerosene collected from the surface of the water was unexpectedly lower than the moisture content in the kerosene before it was poured onto the water surface.