Synthetic Butterfly Scale Surfaces with Compliance‐Tailored Anisotropic Drop Adhesion

Abstract

Many natural surfaces such as butterfly wings, beetles' backs, and rice leaves exhibit anisotropic liquid adhesion; this is of fundamental interest and is important to applications including selfcleaning surfaces, microfluidics, and phase change energy conversion. Researchers have sought to mimic the anisotropic adhesion of butterfly wings using rigid surface textures, though natural butterfly scales are sufficiently compliant to be deflected by capillary forces exerted by drops. Here, inspired by the flexible scales of the Morpho aega butterfly wing, we fabricate synthetic surfaces coated with flexible carbon nanotube (CNT) micro-scales with anisotropic drop adhesion properties.

Fabrication and applications of stimuli‐responsive micro/nanopillar arrays

“…CNT, carbon nanotube; CVD, chemical vapor deposition; RIE, reactive ion etching; PS, polystyrene; Si, silicon to many researchers because of their high electroconductivity and lightweight advantages. 7,[34][35][36][37][38] As shown in Figure 5(C), hexagonally arranged microhole arrays were first prepared by photolithography that patterns positive tone PR resist by developing it with solvents. 34 Then, PVD was introduced to deposit catalyst, Fe/Al 2 O 3 , on the PR master mold.…”

“…Hart et al suggested an approach to modulate the growth rate of the CNTs 7,35,36 to design a freeform morphology of microstructures with a patterned underlayer (Figure 5(E)). 35 A titanium nitride (TiN) layer was selectively deposited on a SiO 2 layer by lithography including a lift-off process.…”

“…Bio-mimetic surface designs have been actively applied by many researchers because of the hierarchical micro/ nanotextured morphologies and their unique performance in natural creatures. For example, Gecko feet, [1][2][3][4][5] snail pedal muscles, 6 butterfly wings, 7 octopus suckers [8][9][10] and springtail cuticles, [11][12][13][14][15] have been investigated to identify correlations between their surface morphology and functional performance, such as adhesion, [1][2][3][4][5][6] antireflection, [16][17][18][19] structural color, 20,21 suction, [8][9][10] and hydro/omniphobic properties, 7,[11][12][13][14][15]21 respectively. To artificially mimic the unique performance of living creatures, hierarchical micro/nanoscale architectures have been devised to have periodicity in spatial arrangement, named pillar (or cilia, wire) arrays.…”

“…For example, molecular assembly can be introduced to grow metal oxide nanopillar arrays with the assistance of a seed layer organized by sputtering 32 or spin-coating. 33 Advancing from that, carbon nanotube (CNT) micro 7,[34][35][36][37] /nanoforests 38 are rendered by bottomup assembly of C x H y molecules on a catalyst patterned by top-down lithography. Highly electroconductive and lightweight CNT micro/nanopillar arrays were obtained with high uniformity and periodicity.…”

Hierarchical 3D Patterns with Dynamic Wrinkles Produced by a Photocontrolled Diels–Alder Reaction on the Surface

“…Hierarchically patterned surfaces are widely found in natural and man‐made materials and biological skins, in which structures with a topographic hierarchy across multiple scales can impart intriguing and outstanding properties to the surface due to the synergistic effects of hierarchical structures . Inspired by these hierarchical patterns, researchers have engineered hierarchical surfaces for various applications ranging from wetting control and structural colors to tissue scaffolds using diverse patterning approaches, including typical lithography, chemical deposition, and nanoimprinting .…”