Antifogging abilities of model nanotextures

Abstract

Nanometre-scale features with special shapes impart a broad spectrum of unique properties to the surface of insects. These properties are essential for the animal's survival, and include the low light reflectance of moth eyes, the oil repellency of springtail carapaces and the ultra-adhesive nature of palmtree bugs. Antireflective mosquito eyes and cicada wings are also known to exhibit some antifogging and self-cleaning properties. In all cases, the combination of small feature size and optimal shape provides exceptional surface properties. In this work, we investigate the underlying antifogging mechanism in model materials designed to mimic natural systems, and explain the importance of the texture's feature size and shape. While exposure to fog strongly compromises the water-repellency of hydrophobic structures, this failure can be minimized by scaling the texture down to nanosize. This undesired effect even becomes non-measurable if the hydrophobic surface consists of nanocones, which generate antifogging efficiency close to unity and water departure of droplets smaller than 2 μm.

Recent Progress in Bionic Condensate Microdrop Self‐Propelling Surfaces

“…In sharp contrast to lotus-like micro-and nanostructures, closely packed nanocones with smaller tip sizes and interspaces can prevent moisture penetration while minimizing solid-liquid interface adhesion, which is the key to generating the desired CMDSP function. [51] It should be noted that the self-jumping phenomenon of condensate microdrops is not unique in nature. For example, Buller's droplet effect is essentially a typical CMDSP effect that is exploited by basidiomycete fungi to actively eject their spores into the air.…”

“…[66][67][68][69] Second, their tip size should be as small as possible to minimize the interface adhesion. [31,50,51,[66][67][68][69] Third, the building blocks must have a certain height or depth to avoid the collapse of the suspended water bridges. [68] Following these design principles and inspired by nature, our group proposed and demonstrated that efficient self-propelling of small-scale condensed microdrops can be [5] Copyright 2007, Wiley-VCH.…”

Bioinspired Dynamic Wetting on Multiple Fibers

“…[19] Recently, Quéré and co-workers compared the water condensation behaviors of nanopillars (Sample A) and nanocones (Sample C) (Figure 3a 4 ) and demonstrated that the conical shape of a nanostructure is crucial for further enhancing its antifogging ability. [20] The conical geometry provides a Laplace expulsion out of the texture, prevents the formation of durable wet patches, maintains the liquid in a full Cassie state, even for isolated microdrops (Figure 3a 5 ). As shown in Figure 3a 6 , the antifogging behavior of nanocones markedly differs from that of nanopillars under realistic dew formation conditions, and nanocones exhibit great antifogging properties.…”

“…[12] a 3 ) Droplets moved from the bottom to the top of the hairs. a 4 ) SEM images of the pillar textures in sample A and the cone textures in sample C. [20] a 5 ) Sketch showing the effect of the cone geometry: the droplets beneath a large drop can be reabsorbed. In addition, small droplets condensing in cones can reconfigure at the top of the cone.…”

“…a 4 -a 6 ) Reproduced with permission. [20] Copyright 2017, Nature Publishing Group. b 1 -b 3 ) Reproduced with permission.…”