Yanling Wan

Superhydrophobic surface prepared by micromilling and grinding on aluminium alloy

An efficient method for processing superhydrophobic surface is presented in this paper, which can realise the microstructure machining on a large area. First, the microgroove arrays were processed by high speed precision micromilling machine on the surface of the aluminium alloy. Then, the surface of the microgroove was ground by 1000 # electrostatic sand alumina water resistant abrasive belt. The machined surface topography was observed by SEM, which showed that the microgroove arrays were uniform. The contact angles of the water on the microgroove arrays were measured in different directions. In the parallel direction, the contact angle of microgroove arrays is 142±0·5°, whereas in the vertical direction, it arrives 160±0·6°. The above values of contact angle mean that a stable superhydrophobic metallic surface was prepared by the micromilling and grinding.

Experimental study of surface roughness effects on wettability

In this paper, we present a method to fabricate aluminum alloy 5083 surfaces with different surface roughness using reciprocating type high speed wire cut electrical discharge machining (HS-WEDM). Observe the processed surface by ultra-depth three-dimensional scanning system, obviously notice that craters and bumps were uniformly distributed in the surface which is machined by HS-WEDM. And the size of craters and bumps are relevant to the parameters of the pulse power supply. Then we obtain a surface with static contact angle of 136° and draw a changing trends curve of the static contact angle along with surface roughness by measuring the surface roughness and static contact angle respectively. It has provided experimental basis and theoretical foundation for fabricating aluminum alloy super-hydrophobic surface by HS-WEDM.

Effect of micro-groove size on the hydrophobicity of aluminum surface

In this paper, the micro-groove structure is designed on the surface of aluminum alloy by high speed wire cutting discharge machine (HS-WEDM). A multi-scale surface with micro structure was fabricated by this method. The paper design a series different groove spacing, groove depth and groove width and orthogonal design was using to analyze the relationship between the size of micro structure and the wettability of materials. The results show that the effect of the groove width on surface wettability is maximum, When the the groove spacing is 300μm, the groove depth is 100μm and the width of the groove is 230μm, the contact angle of the material surface is maximum, which is 155.98°. After observing the surface, it is can be known that the existence of groove structure can reduce the droplet and solid surface contact area greatly. In addition, these grooves sealed a plenty of air to increase the contact area of the droplet and the air that the solid surface are difficult to be wetted by droplets. It is feasible that realizing the change of the surface wettability by using optical combination.

HS-WEDM machining of superamphiphobic al surfaces and effect of the droplet size on wettability

In this study, superamphiphobic (SAP) aluminum (Al) alloy 5083 surfaces were produced with water/oil high contact angle (CA) greater than 150° and low sliding angle (SA). A simple and environmentally friendly technology of the high speed wire electrical discharge machining (HS-WEDM) was used to introduce submillimeter-, micro- and nano-scale structures, respectively, which resulted in a hierarchical morphology. Surface energy was reduced by coating with 1H,1H,2H,2H-perfluorodecyltriethoxysilane (PFDTES) on the structured surfaces. The CAs approaching 154.80° for water, 154.55° for glycerol, and 153.92° for ethylene glycol were obtained after building hierarchical structures by HS-WEDM. The fundamental wettability models were used to explain the experimental results. The effect of the droplet size on the wettability of surfaces was also investigated. In addition, the SAP property of the Al surfaces is still exhibited after the stability, immersion, finger pressure and ultrasonic cleaning tests. SAP Al surfaces could see many wide potential applications including self-cleaning, anti-corrosion, anti-fouling, anti-icing and oil transportation.

Cicada wing with adhesive superhydrophobicity and their biomimetic fabrication

Cicada is hymenoptera insect. It is found that cicada wing exhibit super-hydrophobicity and a high adhesive force with water, which is different from lotus leaf. The water contact angle (WCA) on cicada wing is 145.81±4.83°. The water droplet does not slide on the cicada wing surface when the surface is tilted at 90°. Observed from the SEM data, the cicada wing surface is covered by the columnar structure in regularly rule. To copy the wettability of cicada wing surfaces, we report a new approach for fabricating a super-hydrophobic surface on copper substrate using reciprocating type high speed wire cut electrical discharge machining (HS-WEDM). The resultant samples were characterized by scanning electron microscopy (SEM) and contact angle measuring instrument, It was found that water contact angle of the resulting surface was increased from 82.11° to 152.91±4.02°, realizing the transition from the hydrophilic to super-hydrophobic. When the sample is tilted at 90°, the water droplet does not roll off from the surface or even upside down, indicating the resulting surface has a high adhesive force to water. The resulting surface were covered with composite structures composed of micro-scale diamond cylinder structure and concave and protuberance, and nano-scale granular structure, which was the reason of super-hydrophobicity and high adhesive force of copper surface. Moreover, new copper oxide generated in the process of HS-WEDM is another reason of copper surface.

High speed micro-milling experiment of hydrophobic microstructure

This paper presents a method to fabricate the ordered arrays of microstructures on the metal surface using mechanical micro machining technology. With specific designed micro square pillar arrays, the wettability of a solid surface can be tuned. The samples were fabricated by high speed micromilling machine tool on the aluminum alloy surface. The apparent contact angle (CA) and microstructure of the surface were measured and the surface hydrophobic mechanism was also analysed. The results of the experiment indicate that the CA has been increased. The height-to-length ratio hr (h/a) is one of the key parameters to change the wettability of the material surface. Compared with the intrinsic CA (about 51°), the largest apparent CA is up to 102.88° when the height-to-length ratio hr (h/a) is 3/7. Furthermore, by controlling the size and layout of the micropillars, the aluminum alloy surface could be changed from hydrophilic to hydrophobic.