新穎仿生奈米材料三部曲：蛾眼結構、壁虎膠帶和玫瑰花瓣表面

Abstract

仿生科技近年來成為研究材料科學一個熱門的領域。科學家透過模仿大自然的生物研究出各種具有不同功能的人造材料，其效能甚至遠高於自然本身所具備的。在本篇論文中，我們提出三種新穎的功能性仿生奈米材料起源於蛾眼結構、壁虎腳和玫瑰花瓣。 蛾眼是由約300奈米高和間隔的突起物所組成之類最密堆積結構，可以有效地降低其反射率。因此，我們將金屬沉積在鋁和基板之中，利用陽極氧化的方式處理，這層金屬也會隨之氧化而形成奈米結構點狀陣列，有如蛾眼結構。並且我們可操控這些結構，由空心到實心，或由半球形到錐狀的陣列。利用這些次波長的奈米錐狀陣列，我們可以應用在不同的基本上形成抗反射層對於任何角度的入射光，並具有良好的機械性質。此外，這種空心的錐狀結構也被我們拿來開發成新穎的光電極結構並應用在增進染敏太陽能電池的效率。透過自主裝的二氧化鈦空心錐狀陣列和二氧化鈦奈米管壁並用陽極氧化鋁相互隔開已經被我們沉積在在導電透明基板上。此種結構應用在染敏電池上可以增加染料接觸面積、提供更直接的電子傳輸路徑並能降低電子電洞的的復合，因此可提升光電轉化之效率。 由壁虎腳所引起的乾式黏附力已引起了各界的關注，透過表面的粗糙度和指向性的改變,使其擁有強大的黏附力和微弱的脫附力且可重複使用為其迷人之處。近來，關於壁虎腳的仿生結構在理論及實驗方面的研究已被相繼提出。然而，這些研究與自然的壁虎相比之下，有著受限於材料方面的缺點；但在我們的研究中, 我們設計了一有效的方法來製作出創新的結構來更符合理想的乾式吸附力。我們首次提出，以去耦兩階段硬式陽極氧化的方式，來製作出長1.3微米、直徑380奈米的錐形陽極氧化鋁模板；經過翻模的過程後，得到了具有傾斜角度的錐狀奈米陣列。此錐狀奈米陣列在大面積的表現上具備了出色的方向性、可重複使用性及水潔淨的特性。與一般的柱狀奈米陣列相比，錐狀奈米陣列有更好的穩定性和自潔淨的特性。藉由錐狀奈米陣列在各具方向性的力上亦有出色的表現：剪力可達到每平方公分8牛頓之強, 而反方向的脫附力卻僅需要每平方公分1.4牛頓。 不同於蓮葉效應，最近幾年科學家被玫瑰花表面所深深吸引，其表面具有超疏水的特性和高水滴吸附力。此種現象是由花瓣上面微米尺度的凸起和奈米結構所產生。直至今日，許多研究者仍對如何去製造出此等複雜的結構並使其應用而感到困擾。我們發展出一種由下而上的方法：藉由簡單的酸雕刻技術來製作具有高水滴吸附力和自潔淨特性的超疏水聚二甲基矽氧烷(PDMS)。此類花瓣的聚二甲基矽氧烷其有30微米的寬度、奈米皺褶約在500奈米和小於100奈米的奈米結構。在長時間的檢測下，其也能展現大於150度的水滴接觸角。更甚者，此類花瓣展現了高水滴吸附力達到35.8 N/m2。除此之外，從酸雕刻技術得來的兩種超疏水表面讓我們得以用來製造一個新型無殘留的印章。其超疏水且對水滴具吸附力的區域可用於將染料從印章轉移至紙上。而超疏水具備自潔淨的區域可以避免染料沾附上去。

Biomimetics is a freshly explored area of materials science that deals with the science of copying or improving upon that which is found in nature. Scientists commonly produce artificial materials with properties that improved from what occurs naturally. In this thesis, we demonstrate three types of novel functional nanomaterials inspired by moth eyes, gecko feet and rose petals. Moth eyes consist of quasi-close-packed nipples having heights and spacings typically of less than 300 nm, which reduces reflection from their compound eyes. We found, a metal whose oxide form has a higher ionic conductivity than alumina was used as an underlayer preceding an Al anodization process, the underlying metal would be also oxidized and thereby form metal–oxide nanostructures as Moth-eye structures. We modulate the metal–oxide nanomaterials to form, hollow-to-solid and hemisphere-to-cone nanostructure arrays. We employ subwavelength nanocone arrays as Moth-eyes structures for high-performance antireflection coatings. These oxide nanostructures greatly suppress reflectance over a large range of wavelengths and angles of incidence and display a good mechanical stability. Also, we introduce these nanocones as a new photoelectrode architecture for improved efficiency of dye-sensitized solar cells (DSSCs).A facile synthesis of self-organized hollow TiO2 nanocones under porous anodic alumina (PAA) featuring TiO2 nanotubes (NTs) within was grown directly on a fluorine-doped tin oxide (FTO) substrate. The novel structure combines two types of TiO2 materials—0-D nanocones and 1-D NTs—to benefits from a large contact area, direct electron transport path, and slow recombination of electrons. A gecko is the largest animal that can produce high dry-adhesion to support its weight with a high factor of safety. The secret of the gecko’s adhesive properties lies in the hairy microstructure and nanostructure of gecko feet. We designed the efficient method of an innovate structure for ideal dry adhesives. A taper anodic alumina oxide mold with a length of 1.3 μm and a diameter of 380 nm was fabricated using decoupling two-step hard-anodization process which was firstly reported by us. After molding, taper-shaped nanohair array with slanted angle was presented. The approach to fabricate angled taper nanohair arrays obtained an excellent directional, reusable, and water cleanable use in large area. A remarkably directional force exhibited by angled taper nanohair arrays was showing here with strong shear attachment (8 N/cm2) in the gripping direction and easy releasing (1.4 N/cm2) in the reverse direction. Unlike “Lotus effect”, the petal’s surface which has superhydrophobicity and high water adhesion was fascinated by scientists in recent years. The phenomenon is induced by the microscale convex and nanostructures upon the petal. To mimic the petal’s surface, we developed a bottom-up method by the simple acid texture technique to fabricate the superhydrophobic PDMS surface with high water adhesion and self-cleaning ability. The resulting petal-like PDMS had convexes about 30 μm in diameter, nanowrinkles around 500 nm in width and nanostructures less than 100 nm. A high water contact angle larger than 150° was displayed. Moreover, the petal-like PDMS exhibited the high water adhesion up to 35.8 N/m2. In addition, the two superhydrophobic surfaces from the acid texture technique allowed us to fabricate a modern nonresidual stamp. The superhydrophobic and water adhesive area is applicable to transport the dye from the stamp to a paper. The superhydrophobic and self-cleaning region avoids the adhesion of dye.