Huanxi Zheng

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.

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.

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

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