Abstract
A rapid prototyping process was presented to fabricate a nylon honeycomb microstructure coated with parylene C. The surface structure was designed to obtain a hydrophobic surface using the volume of fluid (VOF) model. With the micro-molding technique, the contact angle of the polymer surface could be designed and fabricated by changing the different microstructure surface die-steel mold inserts. For the honeycomb (20 μm width and 60 μm depth) microcavity side wall, an average micro-molding filling percentage of 95% could be achieved by using a three-section constant-pressure molding process. The solid surface wettability is governed by both the geometrical microstructures and the surface energy. A 2 μm parylene C layer was deposited on the nylon honeycomb microsurface to reduce the surface energy. To design honeycomb structures with different microcavity densities, the contact angle of these artificial surfaces could change from 91° to 130°. From a comparison of the contact angle measurements with the different models, the honeycomb-structured microsurface could be described by the Cassie–Baxter model. The errors between the VOF simulation and the measured data were <10%. The drag reduction performance of the honeycomb microplates was investigated in a water tunnel with a high Reynolds number (from 0.5×106 to 4.6×106). As a result, the honeycomb microplates showed a maximum drag reduction rate of 36±0.6% in comparison with the bare plates in such turbulent flow. Benefiting from the replaceable mold insert, more designable microstructure polymer surfaces can be manufactured by this rapid prototyping technique.
Highlights
Wetting is a common phenomenon in daily production and life.Hydrophobicity is an important property of solid surfaces
The real solid–liquid contact area is larger than the apparent geometric contact area, and the hydrophobicity is enhanced
The honeycomb microstructure was designed to be fabricated on a hexagonal plastic plate, as shown in Figure 2, because the micro-molding technique can construct cos yw 1⁄4 r cos ye ð2Þ
Summary
Wetting is a common phenomenon in daily production and life. Hydrophobicity is an important property of solid surfaces. State-of-art micro electron discharge machining (micro-EDM) was interface and the solid surface once a liquid comes into contact with developed simultaneously to fabricate microstructures on the the solid surface. Using fast-exchange mold insertion, honeycomb microsurface structures with the desired contact angle could be fabricated and assembled. The honeycomb microstructure was designed to be fabricated on a hexagonal plastic plate, as shown, because the micro-molding technique can construct cos yw 1⁄4 r cos ye ð2Þ where r is the ratio between the actual solid–liquid contact area and the smooth solid surface of the solid–liquid contact area. Unlike the Wenzel model, the Cassie model assumes that the liquid droplet cannot enter the microgrooves on the roughened surface In this model, the derivation of the composite contact the macro and micro features simultaneously. The contact angle of surface structures with different duty-ratios was measured by an optical contact angle measuring instrument (OCA20, Dataphysics, Germany)
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