Jiyu Liu

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.

Unpowered oil absorption by a wettability sponge based oil skimmer

Oil spills seriously pollute the environment and cause huge economic losses. Recently, materials with extreme wettability are widely used for oil/water separation. However, the existing methods have drawbacks including complicated and costly fabrication processes for oil/water separation materials, limited oil collecting capacity and reduced oil/water separation efficiency after being polluted by oil, etc. Therefore, an efficient and low-cost method for oil spill collection is urgently needed. We proposed a one-step immersion method to fabricate an oil spill absorption material. Superhydrophobicity and superoleophilicity were obtained by a common polyurethane sponge after being immersed into a cupric stearate solution and drying process. Water droplets can be supported as a spherical shape with a contact angle above 155.5° and can easily roll off from the surface, while hexane, hexadecane, diesel oil, peanut oil and lubricating oil can spread completely on the modified sponge. The prepared sponge can maintain water repellency after continuous oil spill collection for more than 4 h. A large-scale oil skimmer was designed to collect oil spills by employing the extreme wettability sponge and was successfully used for the collection of floating diesel oil, peanut oil, and lubricating oil on water. This method is simple, low cost and mass-producable, and the obtained oil skimmer possesses a high oil collection capacity, excellent durability and recyclability. Therefore, it has application prospects for the collection of oil spills on the sea or under other harsh conditions.

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

A universal method to create surface patterns with extreme wettability on metal substrates

Extreme wettability surfaces have attracted more and more attention due to their practical applications, however, few reports have shown a universal method to create surface patterns with extreme wettability on a variety of metals. In this paper, a mask-assisted dual-chemical-processing approach without special modification is used to prepare the extreme wettability patterns on various metal substrates. Fabrication of superhydrophilic-superhydrophobic patterns on five kinds of metal substrates of Al, Ti, steel, Zn and Mg alloy proved the versatility of this method. The extreme wettability patterns prepared by this method were applied to fog harvest and we found the big differences in the collection efficiency of various metal surface patterns.

Water strider-inspired design of a water walking robot using superhydrophobic Al surface

Abstract Aquatic microrobots, which can walk freely on water mimicking water striders, have attracted considerable interest among scientists in biomimetic area. Most of previous water strider robots adopted gear pairs as their driving mechanism, which called for high assembly precision and thereby increased the processing difficulty. Here, a novel and simple method using servos as the driving module to prepare water walking robot was proposed. We fabricated this robot by using supporting and actuating legs with excellent superhydrophobicity. Our robot weighted 27.9 g, but could float and run quickly driven by mini-type servos under remote Bluetooth control in mobile terminal. The legs were obtained on Al substrates by chemical etching, boiling-water immersion and low surface energy modification. Then, surface morphology and chemical compositions were subsequently investigated by SEM, EDS and XRD. In order to better illustrate the floating and rowing mechanism of this robot on the water surface, mechanics analysis models were proposed to analyze the lifting force and resistance force, respectively. Due to its excellent floating capacity and rowing ability, the biomimetic robot has promising application potential in water quality monitoring, aquatic exploration, and other surveillance missions. Graphical Abstract

Fabrication of Extreme Wettability Patterns with Water-film Protection for Organic Liquids

ABSTRACT Selective fabrication of superhydrophilic (S-philic) region on a superhydrophobic (S-phobic) surface requires complex technology and high cost, which has limited applications of extreme wettability patterns. In this paper, a twice-chemical-etching approach without special modification is used to prepare the extreme wettability patterns. Superhydrophobicity and superhydrophilicity can be successfully achieved after twice chemical etching for 20 seconds. The obtained patterns can maintain their extreme wettability for at least 30 days. Functional platforms with single-S-philic and multi-S-philic regions are fabricated to manipulate water and various organic liquids with water-film protection in an air environment. GRAPHICAL ABSTRACT