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Fabrication of High-Aspect-ratio Micro/Nano Hierarchical Structures Mimicking Gecko Foot-Hair

Author: Lv
Tutor: LiuShiYuan
School: Huazhong University of Science and Technology
Course: Mechanical and Electronic Engineering
Keywords: Gecko Adhesion Biomimic ICP Silicon Etching Process Thick Film Photolithography Micromolding Process PDMS SU-8
CLC: TB391
Type: Master's thesis
Year: 2011
Downloads: 30
Quote: 0
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Abstract


In nature, geckos have developed complex adhesion structures capable of smart adhesion, the ability to maneuver on different smooth and rough surfaces, even ceilings. The multi-scale hierarchical structure of the gecko foot-hair, especially the high-aspect-ratio structure of its micro-scale seta and nano-scale spatulae is the critical factor of the gecko’s ability to cling to any different surface with strong adhesion force. The incredible characteristics of gecko foot-hair have a very broad prospect of applications in the deployment and disassembly of MEMS devices, wall-climbing robots, etc. Accordingly, the fabrication of high-aspect-ratio micro/nano hierarchical structures mimicking gecko foot-hair has been studied in this degree thesis including the following contents:Thick film photolithography based on SU-8 photoresist was utilized to fabricate fiber arrays. The microfiber array with multiple parameters was obtained. The highest aspect ratio of SU-8 microfiber is 7. Due to high aspect ratio, the SU-8 microfibers tend to be bunched together, making it difficult to creating a mold to relicate the fibers with other polymer for batch process.Utilizing inductively coupled plasma (ICP) etching process, which is very common in the semiconductor technology, the silicon mold with deep-hole arrays with multiple parameters was fabricated. The polydimethylsiloxane (PDMS) microfiber arrays were successfully replicated from the silicon mold. As for microfiber arrays with less than 8μm in diameter, the fibers tend to be bunched together. The hydrophobic property of the synthetic PDMS microfiber arrays was observed no matter the microfibers bunched together or not. The contact angle of water droplets on PDMS microfiber arrays shows increased hydrophobic property of PDMS microfiber arrays than non-patterned PDMS surface, from 102.7°to more than 131.7°.A novel and simple method with low cost for fabricating two-level two-level hierarchical microfiber array was proposed. Utilizing the silicon mold with deep-hole arrays as a substrate, a SU-8 layer with microhole arrays was fabricated on it using thick film photolithography, and form a double layer mold. The two-level hierarchical PDMS microfiber arrays were replicated from the double layer mold. The double layer mold is reusable. Therefore this method is suitable for batch processes. The water contact angle of the two-level hierarchical PDMS microfiber array surface was observed to be 145.9°, which is a little bit higher than the one of single level PDMS microfiber array surface.

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