Biomimetic fabrication and tunable wetting properties of three-dimensional hierarchical ZnO structures by combining soft lithography templated with lotus leaf and hydrothermal treatments

Abstract

Three-dimensional hierarchical ZnO films with lotus-leaf-like micro/nano structures were successfully fabricated via a biomimetic route combining sol-gel technique, soft lithography and hydrothermal treatments. PDMS mold replicated from a fresh lotus leaf was used to imprint microscale pillar structures directly into a ZnO sol film. Hierarchical ZnO micro/nano structures were subsequently fabricated by a 10 low-temperature hydrothermal growth of secondary ZnO nanorod arrays on the micro-structured ZnO film. The morphology and size of ZnO hierarchical micro/nano structures can be easily controlled by adjusting the hydrothermal reaction time. Wettability of hierarchical ZnO thin films was found to convert from superhydrophilicity to hydrophobicity after a low-surface-energy fluoroalkylsilane modification. Improved wetting properties from hydrophobic to superhydrophobic can be tuned by increasing the 15 growth of ZnO nanorods structures. 85 Notes and references

Microbumpers maintain superhydrophobicity of nanostructured surfaces upon touch

“…Hierarchical micro-nano structures, inspired by the lotus leaf, show much promise, with the larger-scale features protecting the nanoscale features. These include nanostructures coating grooves [27,28], micro-pyramids [29] or hillocks [30,31], and micro-pillars [18,[32][33][34][35][36][37][38][39][40]. (We do not include here coatings displaying multiple length scales [41][42][43][44] formed by single-step techniques such as electrodeposition or coating with composites containing multi-sized particles.)…”

“…(We do not include here coatings displaying multiple length scales [41][42][43][44] formed by single-step techniques such as electrodeposition or coating with composites containing multi-sized particles.) Such surfaces have been formed in various ways, including injection [32] or replica [27,33,34,38,40] molding, followed in some cases by nanostructure deposition; micromolding of nanoparticle-containing materials [27,45]; microfabrication (etching) [18,29,35]; microfabrication [37,39,46], sandblasting [30,44] or material deposition [36] followed by surface treatment or other material deposition; and laser microstructuring [28]. A thin hydrophobic film is often applied over these structures.…”

Superhydrophobic Hybrid Micro‐Nanocomposites with Various Applications

“…Several works were discussed the mimicking or patterning the dual hierarchical micro-nano surface roughness of lotus leaf in the synthetic materials. [17] The fabricated surface showed hierarchical micronano surface roughness with enhanced surface contact angle (CA) and stable properties. The surface wettability of a material is determined usually by the surface CA using a water droplet (surface tension of water 72.8 mN/m).…”

“…The surface wettability of a material is determined usually by the surface CA using a water droplet (surface tension of water 72.8 mN/m). [17][18][19][20] CAs are classified into various types based on the surface wettability of a coated substrate such as superhydrophilic (CA < 5 ), hydrophilic (CA < 90 ), hydrophobic (CA > 90 ), and superhydrophobic (CA > 150 ). [1,22] Among the various surface properties, superhydrophobic surfaces are emerging in various applications due to the non-adhesive property of the coated substrate to water.…”

Layer-by-layer Deposition of TiO2 Nanoparticles in the Wood Surface and its Superhydrophobic Performance

“…A superhydrophobic surface is defined as one that has a water contact angle (WCA) greater than 150° when water droplets are placed on the surface. One of the most well-known examples of superhydrophobic surfaces in nature is the lotus leaf (Wang et al 2012;Dai et al 2013). A superhydrophobic surface can be prepared by a combination of a high-surface-roughness film and a low-surface-energy thin layer (Wang et al 2011b;Wan et al 2014;Zheng et al 2015).…”