Faze Chen

Creating superhydrophobic mild steel surfaces for water proofing and oil-water separation

A simple and inexpensive two-step immersion method is reported to make mild steel superhydrophobic. Micro–nano-scale roughness and surface chemistry modifications were created via immersing mild steel into a salt solution followed by treatment with a low surface-energy polymer. The fabricated mild steel has water contact angles greater than 150° and remarkable water bouncing properties. This method was also used to treat a mild steel mesh for oil–water separation. In this paper, a new, facile and reusable gravity-induced separation system is proposed to collect floating oil, the oil collection rate can reach >96%.

Creating robust superamphiphobic coatings for both hard and soft materials

Most superhydrophobic surfaces lose their water-repellency when either contaminated by oily liquids or by being mechanically damaged. Superamphiphobic surfaces are ones that repel both oil and water. However, to date such surfaces are hampered by being mechanically weak. Robust superamphiphobic surfaces with highly water and oil repellent properties are desired for a wide range of environments. Reported herein is a superamphiphobic coatings fabricated by a facile deposition method and followed by a low surface energy materials modification. These coatings can be applied on both hard and soft materials to repel water, glycerol, peanut-oil droplets and some organic solvents. Falling sand abrasion, UV irradiation and aqueous media immersion were used to test the mechanical robustness and durability of the superamphiphobic coatings. A multi-cycle stretch/release test was developed to characterize the robustness of the self-cleaning soft materials. A coated rubber-bond retained both water and oil repellency even after 50 stretch/release cycles. These tests show that the superamphiphobic coatings have remarkable mechanical robustness and UV/aqueous media resistance and can be readily applied to a wide variety of materials to form self-cleaning surfaces that are extremely robust and durable even under intense strains.

Underwater Spontaneous Pumpless Transportation of Nonpolar Organic Liquids on Extreme Wettability Patterns.

Spontaneous pumpless transportation (SPT) of liquids has generated tremendous demands in microfluidic systems and advanced devices. However, the transportation of nonpolar organic liquids on open platforms underwater remains a challenge because most existing SPT systems are only designed for use in air. Here, we report a surface-tension-driven SPT system to transport various nonpolar organic liquids using underwater extreme wettability patterns. The patterns were fabricated with a wedge-shaped superoleophilic track on a superoleophobic background by combining CuCl2 etching, stearic acid modification, and mask-based nitrogen cold plasma treatment. Three types of underwater SPT processes-horizontal transport, tilted transport, and directional transport-were studied experimentally and theoretically. For horizontal SPT and tilted SPT, the capillary force was the main driving force, which depended on the wedge angle of the superoleophilic track. The excellent transportation ability of horizontal SPT of underwater liquid droplets was obtained at a wedge angle of 3-5°. The maximum moving height of organic liquids on the tilted SPT transport was obtained at an angle of 8°. For directional SPT, organic liquids did not drop off in the moving process because of the constraint imposed by surface tension, resulting in the sustained directional transport with long distances and complex trajectories.

Stability of plasma treated superhydrophobic surfaces under different ambient conditions.

Plasma hydrophilizing of superhydrophobic substrates has become an important area of research, for example, superhydrophobic-(super)hydrophilic patterned surfaces have significant practical applications such as lab-on-chip systems, cell adhesion, and control of liquid transport. However, the stability of plasma-induced hydrophilicity is always considered as a key issue since the wettability tends to revert back to the untreated state (i.e. aging behavior). This paper focuses on the stability of plasma treated superhydrophobic surface under different ambient conditions (e.g. temperature and relative humidity). Water contact angle measurement and X-ray photoelectron spectroscopy are used to monitor the aging process. Results show that low temperature and low relative humidity are favorable to retard the aging process and that pre-storage at low temperature (-10°C) disables the treated surface to recover superhydrophobicity. When the aging is performed in water, a long-lasting hydropholicity is obtained. As the stability of plasma-induced hydrophilcity over a desired period of time is a very important issue, this work will contribute to the optimization of storage conditions of plasma treated superhydrophobic surfaces.

Characteristic and Application Study of Cold Atmospheric-Pressure Nitrogen Plasma Jet

Atmospheric-pressure discharge plasma is a promising tool for many applications due to its enhanced plasma chemistry. In this paper, a low-temperature atmospheric-pressure nitrogen plasma jet generated by bare metal electrodes discharge is reported. The typical electrical and optical characteristics of the atmospheric-pressure plasma jet (APPJ) are studied. Optical emission spectrum shows that excited OH, NO, N2(C-B), N2+ (B-X), N2(B-A), and O emissions are produced by the plasma jet. When the applied voltage is 2.5 kV, the vibrational and rotational temperatures of the APPJ are, respectively, 2275 and 325 ± 5 K. Hydrophilic treatment of the superhydrophobic aluminum surface is also presented, and the results show that the wettability of the APPJ-treated areas is obviously improved, which was mainly due to the slight morphological changes and the incorporation of oxygen-containing functional groups. A pumpless antigravity water transport on APPJ-induced wettability contrast patterning surface is also presented to show the potential applications of the APPJ hydrophilic treatment of metals. These results demonstrate the application prospects of bare electrodes discharge plasma jet, especially in metal-based smart surface fabrications.

New synthesis method to improve the properties of PbTiO3/NiTi composite film

Abstract In this article, a new synthesis process to fabricate PbTiO 3 /NiTi composite film is reported. A transitional PbTiO 3 film, prepared on NiTi substrate by a hydrothermal reaction, was introduced to improve the adhesion strength of the composite. Then an outer PbTiO 3 film was fabricated on the transitional layer by a sol-gel method. No cracks or obvious defects were observed on the outer ceramic film. Scratch tests showed that the adhesion strength of composite film was improved greatly by using this new synthesis process.

Robust platform for water harvesting and directional transport

Water harvesting is used for transforming moisture into available water resources in regions that suffer water scarcity. However, it remains a considerable challenge to design a system that functions to both collect water from the air and transport it to a certain region over a long distance. In this work, a new water harvesting platform for dropwise condensation and dropwise transportation is developed to realize both water collection and spontaneously directional transport over long-distance at low temperatures. The water harvesting platform was developed based on a biomimetic slippery liquid-infused porous surface (SLIPS) with micron-size steps and nano-sized holes through electrochemical etching, electrochemical anodizing, low surface energy modification and lubricant infusion. The anti-wetting, chemical resistance, condensation and anti-icing properties of the water harvesting platform at different pHs and temperatures were tested to show the stability of the system. The water harvesting platform exhibited excellent dropwise condensation capacity, and can directly and continuously capture moisture from the air in a low-temperature environment. Spontaneously directional transport of droplets was achieved on a choreographed wedged-platform driven by Laplace pressure, and the transport distance was unlimited due to the energy conversion from surface energy to kinetic energy induced by droplets coalescing in a repeated motion of droplet merging and chasing. This water harvesting platform shows great potential in applications for advanced transportation devices, multifunctional sensors, actuators, and is a promising potential solution to water scarcity.

Simultaneous and long-lasting hydrophilization of inner and outer wall surfaces of polytetrafluoroethylene tubes by transferring atmospheric pressure plasmas

Plasma hydrophilization is a general method to increase the surface free energy of materials. However, only a few works about plasma modification focus on the hydrophilization of tube inner and outer walls. In this paper, we realize simultaneous and long-lasting plasma hydrophilization on the inner and outer walls of polytetrafluoroethylene (PTFE) tubes by atmospheric pressure plasmas (APPs). Specifically, an Ar atmospheric pressure plasma jet (APPJ) is used to modify the PTFE tubes outer wall and meanwhile to induce transferred He APP inside the PTFE tube to modify its inner wall surface. The optical emission spectrum (OES) shows that the plasmas contain many chemically active species, which are known as enablers for various applications. Water contact angle (WCA) measurements, x-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) are used to characterize the plasma hydrophilization. Results demonstrate that the wettability of the tube walls are well improved due to the replacement of the surface fluorine by oxygen and the change of surface roughness. The obtained hydrophilicity decreases slowly during more than 180 d aging, indicating a long-lasting hydrophilization. The results presented here clearly demonstrate the great potential of transferring APPs for surface modification of the tubes inner and outer walls simultaneously.

Adjusting the stability of plasma treated superhydrophobic surfaces by different modifications or microstructures

Plasma induced hydrophilization of superhydrophobic surfaces is highly-efficient, reversible and less destructive, and has therefore been applied into fields like fabrication of wettability patterns; however, plasma treated surfaces tend to recover back to their original wettability during storage, and different time stabilities are required for diverse applications. This paper focuses on regulating the time stability of plasma treated superhydrophobic surfaces by different surface modification methods or microstructures, and the recovery time could be adjusted as either 10 hours or more than 100 days under normal ambient conditions. These differences in recovery could also be observed in wettability patterns prepared by dissimilar methods. The adjustment methods developed should facilitate applications of plasma induced hydrophilization, especially for those that require rapid recovery or long-time stability.

Wettability-gradient Surface Fabricated by Combining Electrochemical Etching and Lithography

ABSTRACT This paper proposes a simple, precise, and controllable method to fabricate wettability-gradient surfaces. Combining electrochemical etching and lithography, different micro/nanostructures can be obtained by adjusting the etching time. After being modified by low energy substances, low adhesive superhydrophobic and sticky hydrophobic regions can be obtained on one surface. Based on the obtained adhesion gradient, droplets of different volumes can be controlled to roll off at dissimilar tilted angles via designing sticky hydrophobic tracks with different widths. Directional transportation of water droplets on curve tracks is also realized based on the anisotropic sliding angles parallel and perpendicular to the tracks. GRAPHICAL ABSTRACT