Zhuji Jin

Fabrication of Long-Term Underwater Superoleophobic Al Surfaces and Application on Underwater Lossless Manipulation of Non-Polar Organic Liquids

Underwater superoleophobic surfaces have different applications in fields from oil/water separation to underwater lossless manipulation. This kind of surfaces can be easily transformed from superhydrophilic surfaces in air, which means the stability of superhydrophilicity in air determines the stability of underwater superoleophobicity. However, superhydrophilic surfaces fabricated by some existing methods easily become hydrophobic or superhydrophobic in air with time. Here, a facile method combined with electrochemical etching and boiling water immersion is developed to fabricate long-term underwater superoleophobic surfaces. The surface morphologies and chemical compositions are investigated. The results show that the electrochemically etched and boiling-water immersed Al surfaces have excellent long-term superhydrophilicity in air for over 1 year and boehmite plays an important role in maintaining long-term stability of wettability. Based on the fabricated underwater superoleophobic surfaces, a special method and device were developed to realize the underwater lossless manipulation of immiscible organic liquid droplets with a large volume. The capture and release of liquid droplets were realized by controlling the resultant force of the applied driving pressure, gravity and buoyancy. The research has potential application in research-fields such as the transfer of valuable reagents, accurate control of miniature chemical reactions, droplet-based reactors, and eliminates contamination of manipulator components.

A Twice Electrochemical-Etching Method to Fabricate Superhydrophobic-Superhydrophilic Patterns for Biomimetic Fog Harvest

Superhydrophobic-superhydrophilic patterned surfaces have attracted more and more attention due to their great potential applications in the fog harvest process. In this work, we developed a simple and universal electrochemical-etching method to fabricate the superhydrophobic-superhydrophilic patterned surface on metal superhydrophobic substrates. The anti-electrochemical corrosion property of superhydrophobic substrates and the dependence of electrochemical etching potential on the wettability of the fabricated dimples were investigated on Al samples. Results showed that high etching potential was beneficial for efficiently producing a uniform superhydrophilic dimple. Fabrication of long-term superhydrophilic dimples on the Al superhydrophobic substrate was achieved by combining the masked electrochemical etching and boiling-water immersion methods. A long-term wedge-shaped superhydrophilic dimple array was fabricated on a superhydrophobic surface. The fog harvest test showed that the surface with a wedge-shaped pattern array had high water collection efficiency. Condensing water on the pattern was easy to converge and depart due to the internal Laplace pressure gradient of the liquid and the contact angle hysteresis contrast on the surface. The Furmidge equation was applied to explain the droplet departing mechanism and to control the departing volume. The fabrication technique and research of the fog harvest process may guide the design of new water collection devices.

Power-free water pump based on a superhydrophobic surface: generation of a mushroom-like jet and anti-gravity long-distance transport

Spontaneous anti-gravitational transportation of liquids across long distances has been widely discovered in nature, such as water transportation from the root to the crown of a tree. However, artificial liquid delivery remains a challenge. In this work, a new power-free pump composed of a superhydrophobic plate with a pore mounted on a leak-proof cylindrical container filled with water is presented for sustained anti-gravity and long distance transport. Water droplets can be spontaneously captured through the pore by the lower water column, forming a mushroom-like jet due to the energy transition from surface energy to kinetic energy. The spontaneously increased inside pressure in the container will push the water out, through another thin tube, realizing the energy transition from surface energy to gravitational potential energy. The dynamic driving and moving model of the pivotal mushroom-like jet were analyzed. The maximum transport height and transport abilities of the water pump were also discussed. The results show that Laplace pressure is the main driving pressure of the mushroom-like jet and that the developed power-free pump can effectively transport water to over 100 mm in height with an average transport speed of 4500 μL h−1, showing potential for application in microfluidic systems and medical devices where micropumps are needed.

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.