Excellent Anti‐Icing Abilities of Optimal Micropillar Arrays with Nanohairs

Abstract

of adhesion required to remove a liquid water drop. Poulikakos and co-workers [ 7 ] investigated surfaces with nanometerscale roughness and higher wettability, which display long freezing delays, one order of magnitude longer than typical superhydrophobic surfaces with larger hierarchical roughness and low wettability. And Poulikakos also established [ 8 ] that evaporative cooling of the supercooled liquid could engender ice crystallization by homogeneous nucleation at the droplet-free surface as opposed to the expected heterogeneous nucleation at the substrate. Hirayama and co-workers [ 9 ] investigated the icephobic properties of different coatings, e.g., hydrophilic and hydrophobic coatings, sol-gel based coatings containing fl uorinated compounds and viscoelastic rubbers. Very low adhesion values were obtained in the case of coatings consisting of viscoelastic elastomers. Yarin and co-workers [ 10 ] reported a systematic study of drop impacts of polar and nonpolar liquids onto different electrospun nanofi ber membranes with an increasing degree of hydrophobicity. It is found that for any liquid/fi ber pair there exists a threshold impact velocity (≈1.5-3 m s −1 ) above which water penetrates membranes irrespective of their hydrophobicity. Yarin and co-workers [ 11 ] studied peculiarities of drop impact onto electrospun polymer (polyacrylonitrile, PAN) nanofi ber mats. It is demonstrated that drop impacts on electrospun nanofi ber mats almost instantaneously result in spread-out wetted spots over the surface. All these researches above offer the foundation at different levels. However, it still remains a challenging how to further design the surface with superhydrophobic or anti-icing properties as surface in low temperature for a long time. [12][13][14][15][16][17] Here, we present a series of surfaces combined with nanohairs and micropillar arrays, i.e., different micropillar arrays with the similar nanohairs, different nanohairs with the same micropillar arrays. Especially, we reveal that the optimal surface with excellent abilities for anti-icing or antifogging is related with cooperation between superhydrophobic nanohairs and micropillar arrays, in addition to the stability of less liquid-solid fractions at low temperature below zero. This study will provide an insight into the design of structure size on micro-nanostructured surfaces for anti-icing/fogging ability effectively, with great significance that can be extended into the applications in some surfaces of systems, e.g., microdevices worked in cold or humid environment.Anti-icing abilities are achieved on surfaces of micropillar arrays with nanohairs that are fabricated by methods of soft replication and crystal growth, i.e., different micropillar arrays with the similar nanohairs, different nanohairs with the same micropillar arrays. It is demonstrated that an optimal micropillar array with nanohairs contributes an excellent anti-icing or antifogging property at low temperature below zero. As a result, the longest icing delay time is achieved effe...

Water drop-surface interactions as the basis for the design of anti-fogging surfaces: Theory, practice, and applications trends

“…Following hydrophobization with heptadecafluorodecyltripropoxysilane (FAS-17), water drops remained in a non-freezable state at -5°C and rolled off the surface when exposed to breeze, due to the water-repellent properties of the surface (WCA ≈ 150°). Epoxy micropillars arrays covered with ZnO nanohairs fabricated by soft replication methods ("Bosch process") and crystalgrowth techniques have shown better results in terms of ice formation delay [102]. In this case, an icing delay time as high as 9839 s was noticed in the FAS-treated surfaces (an icing delay time of 7360 s at -10°C was reported in the previous study), even though the contact angle was virtually the same (WCA ≈ 152°) (Fig.…”

“…The "two-step" route (Fig. 6a), which is typically applied to ceramic substrates, is based on the deposition of "building units" followed by a treatment with a low surface energy material [99][100][101][102][103], while the "three-step" route (Fig. 6b) consists of surface microstructuring of a polymeric substrate by soft lithography (section 4.2.2), followed by coating deposition and hydrophobization [104,105].…”

Bioinspired Dynamic Wetting on Multiple Fibers

“…Compared with a traditional, textured superhydrophobic surface, water strider legs exhibit a robust water repellency that could be used on a femtoliter scale, and the legs could inspire the design of novel superhydrophobic materials for practical applications, such as antidew and anti-icing materials and dropwise condensers. [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 ).…”

Large area fabrication of high aspect ratio nano‐cylinders on micro‐pillars based on a colloidal crystal mask

“…Nanostructures on a microstructured surface (hereafter referred to simply as a micro–nanostructure) are gaining increased attention for their potential applications in the fields of anti‐icing [1, 2], superhydrophobic materials [3], drag reduction [4], oil–water separation [5], biochemical sensors [6], bionics [7], medical science [8], optics [9] and so on.…”