Fabrication and Physical Characteristic Research on Biomimetic Micro/Nano Interfacial Structure
Date Issued
2011
Date
2011
Author(s)
Tsai, Yao-Chaun
Abstract
In this dissertation, the fabrication and the physical characteristic research on biomimetic interfacial structures has been conducted. Accompanying recently quick technology development, biomimetics has attracted many attentions of scientists and engineers. The nature’s micor-/nano- structures have been imitated and applied widely in many fields such as artificial fiber which mimicked spider silk, photonic crystal on the butterfly wings, microlen array on brittle star body surface, dry adhesive on the gecko foot, and the self-cleaning effect on the lotus leaf surface. The study of micro/nano interfacial structure is one of the important development trends for biomimetics because of its versatile applications. With the advancement of the observation and fabrication apparatus, various biomimetic mico/nano structures have been realized in this dissertation. In addition, the development of the suitable measurement has been conducted. In chapter 2, the theoretical models which provided relationships between the roughness, contact angle and contact angle hysteresis were presented and discussed. A droplet on the textured surface in practice can be categorized into air-trapped state, Wenzel state, and penetrating film state. The boundary between these three states is related to the roughness and the relative fractions of the solid phase under the droplet. Besides, the contact angle hysteresis was quantified as a function of the geometric roughness and the relative fraction area of the solid contact phase. In chapter 3, the large contact angle with high contact angle hysteresis on the hierarchical structure of the rose petal surface was introduced. Inspired from the petal effect, two types of artificial structure, fibril mesh and fibril microhills, were fabricated and compared with the rose petal surface. The fibril mesh composed of parylene nanofibrils and underneath capillary structures was fabricated using template-assisted deposition. The fibril microhills were formed by peeling the fibril mesh off. The contact angle and contact angle hysteresis on these two surfaces treated by various surface modifications for enhancing the hydrophobicity were measured. The fabricated surface showed similar wetting behavior to the rose petal which is hydrophobic and sticky to water droplet. The relation between the contact angle and the contact angle hysteresis on the various artificial surfaces and the rose petal were discussed. The qualitative estimations of the contact angle hysteresis for the various artificial surfaces were presented. In chapter 4, the effects of the curvature and stretch on the both artificial fibril surfaces fabricated in chapter 3 were discussed based on the wetting characteristics. The tunable wetting behavior on the both flexible nanofibril surface was discussed. The effect of the curvature change on tuning the wetting behavior on both two types of nanofibril surface was limited because the nanofibril surface had no obvious change after the membrane was bent to possess millimeter radius of curvature. The wetting behavior in both nanofibril surfaces can be tuned effectively by stretching. Besides the contact angle measurement in the static state on the stretch test, the contact angle measurement in the dynamic state was carried out during the stretching. Comparing with the invariable contact angle on the flat parylene film, both fibril structural surfaces had larger adhesion to the droplet. Inspired from gecko foot-hairs, the chapter 5 presented the fabrication and characterization of e-beam photoresist nano-pillar array as biomimetic self-cleaning dry adhesives. Resist pillars of different widths and pitches were designed and fabricated using e-beam lithography. An AFM plateau tip was used to measure and to characterize the adhesion force of the resist pillar array. The adhesion strengths significantly increased with the decreasing pillar width at the same pillar pitch and height. The contact angle measurement was used to evaluate the self-cleaning effect. Since the contact angle and the adhesion strength had opposite trends with the contact area ratio, the result indicated that the dry adhesive needed to decrease to nanometer scale for obtaining the self-cleaning effect. The chapter 6 presented a self-alignment fabrication of the stylus with high sphericity for micro coordinate measurement machine (μCMM), a mechanical system using micro-scale contact probes to measure the profile of high-aspect-ratio micro-structures or physical characteristics. This new process combined micro-pellets and stylus into one mechanical device. The micro-pellets were configured inside liquid environment in which the surface tension driveed the pellets into prefect spheres. Stylus arrays were patterned by the microlens-assisted self-writing of SU-8 resist waveguides. The high-aspect-ratio stylus pin consisted of a SU-8 portion and a silicon portion which was fabricated by deep reactive ion etching.
Subjects
Biomimetic
micro/nano interfacial structure
contact angle
lotus effect
petal effect
self-cleaning
self-alignment
Type
thesis
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