Robust Superhydrophobic Conical Pillars from Syringe Needle Shape to Straight Conical Pillar Shape for Droplet Pancake Bouncing

Song, Jinlong; Huang, Liu; Zhao, Cong; Song, Wei; Liu, Hong; Lu, Yao; Deng, Xu; Carmalt, Claire J.; Parkin, Ivan P.; Sun, Yuwen

doi:10.1021/acsami.9b16509

Cited by 59 publications

(33 citation statements)

References 40 publications

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“…Comparing with other state-of-the-art coating methods, our method uses only OTS and water to create hierarchical micro/ nanostructure template with low surface tension in a single step, and demonstrates superior wettability and anti-abrasion property (Supplementary Table 3) 6,[8][9][10]43,[46][47][48][49][50][51][52][53] . In comparison, most other strategies relied on the modification of "pre-made" rough structures with low surface tension coatings.…”

Section: Discussionmentioning

confidence: 99%

Functional and versatile superhydrophobic coatings via stoichiometric silanization

et al. 2021

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Superhydrophobic coatings have tremendous potential for applications in different fields and have been achieved commonly by increasing nanoscale roughness and lowering surface tension. Limited by the availability of either ideal nano-structural templates or simple fabrication procedures, the search of superhydrophobic coatings that are easy to manufacture and are robust in real-life applications remains challenging for both academia and industry. Herein, we report an unconventional protocol based on a single-step, stoichiometrically controlled reaction of long-chain organosilanes with water, which creates micro- to nano-scale hierarchical siloxane aggregates dispersible in industrial solvents (as the coating mixture). Excellent superhydrophobicity (ultrahigh water contact angle >170° and ultralow sliding angle <1°) has been attained on solid materials of various compositions and dimensions, by simply dipping into or spraying with the coating mixture. It has been demonstrated that these complete waterproof coatings hold excellent properties in terms of cost, scalability, robustness, and particularly the capability of encapsulating other functional materials (e.g. luminescent dyes).

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Section: Discussionmentioning

confidence: 99%

Functional and versatile superhydrophobic coatings via stoichiometric silanization

et al. 2021

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“…[ 13,29,30,32,40,41 ] The gray dashed line in Figure 5 represents the inertia–capillary limit (i.e., 2.2τ) for a spherical droplet. Studies have reported that t c values lower than the inertia–capillary limit were obtained on SHB surfaces at room temperature because of pancake bouncing [ 20,38,39 ] and axial symmetry breaking. [ 18,19 ] Other studies have also revealed that t c values lower than the limit were obtained on HP surfaces at high temperatures due to jet bouncing on a silicon nanowire surface, [ 13 ] explosive pancake bouncing on a nanoscale honeycomb copper surface, [ 30 ] and an asymmetric bubble momentum force on a SiN x surface with v‐shaped microgrooves.…”

Section: Resultsmentioning

confidence: 99%

Reducing Contact Time of Droplets Impacting Superheated Hydrophobic Surfaces

Huang

2022

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with liquid droplets. [15] However, because of liquid hydrodynamics, the contact time on an SHB surface is usually restricted by the theoretical limit of the inertia-capillary time scale. [16,17] With advances in micro/nanofabrication technology, the inertia-capillary limit is breakable; a contact time lower than this theoretical limit can be achieved on SHB surfaces through axial symmetry breaking, [18] asymmetric bouncing, [19] and pancake bouncing [20] at room temperature. Nevertheless, coating materials used to create an SHB surface may be damaged at high temperatures, [21] preventing the reduction of t c on SHB surfaces at high temperatures. Moreover, when the temperature is higher than the Leidenfrost point (LFP), a stable vapor cushion forms on SHB surfaces, insulating the liquid droplet and the solid surface. [22,23] Consequently, the t c reduction ability of SHB surfaces is lost in the Leidenfrost (LF) state. Furthermore, the vapor cushion inhibits heat and mass transfer between the solid surface and liquid droplet in the LF state and causes extensive thermal resistance that requires elaborate thermal management. [24][25][26] Generally, the LFP decreases with surface hydrophobicity. [27] Hence, SHB surfaces usually exhibit a very low LFP. [28] Although studies have achieved t c reduction at elevated temperatures on hydrophilic (HP) surfaces, [13,29,30] the range of such temperatures was limited to 200-400 °C because of the strong liquid-solid interaction on HP surfaces. [13,29,30] The strong liquid-solid interaction on HP surfaces at high temperatures also causes a fouling effect and may damage thermal devices. Therefore, a hydrophobic (HB) surface for minimizing liquid-solid interactions, suppressing the LF effect, and reducing t c at high temperatures is required. To realize such a surface, we developed a double-reentrant groove (DRG) array surface (hereafter referred to as DRG surface) with an overhanging structure composed of nanoscale vertical and horizontal overhangs situated on top of the microgrooves. This structure provided an upward surface tension force to prevent droplets from penetrating the microgrooves at room temperature. [5,31] The measured contact angle on the DRG surface was ≈141°. Despite its HB property, the DRG surface's specific topography could suppress the LF effect. The LFP of the DRG surface was 530 °C, which is the highest reported LFP for an HB surface. The smallest t c value of the surface, which was ≈13.3 ms, was obtained at 477 °C; this value is lower than the theoretical inertia-capillary limit of ≈15 ms. According to our review of the literature, the DRG surface is Reducing the contact time (t c ) of a droplet impacting a solid surface is crucial in various fields. Superhydrophobic (SHB) surfaces are used to reduce t c at room temperature. However, at high temperatures, SHB surfaces cannot achieve t c reduction because of the failure of the coating materials or the Leidenfrost (LF) effect. Therefore, a surface that can suppress the LF effect and reduce t c at high temper...

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“…The spine and barbs have micro/nano roughness. [44][45][46][47][48][49][50][51][52] Wettability can be evaluated by measuring the contact angle (CA) and sliding angle (SA) of a small liquid droplet on the target substrate. CA refers to the angle (θ) between the tangent of the air/liquid surface and the liquid/solid interface at the three-phase contact line when a droplet drops on a surface.…”

Section: Nature Creatures With Gradient Surfacesmentioning

confidence: 99%

Laser Fabrication of Bioinspired Gradient Surfaces for Wettability Applications

Yin

Xiao

et al. 2021

Adv Materials Inter

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materials with gradients inspired by biological surfaces has therefore attracted much interest. Strategies for preparing gradient surfaces include vapor-phase diffusion, gradual immersion, electrochemical oxidation, and photolithography that have broadly adopted. [20-26] However, their material constraints, tedious and time-consuming processes, and their single-pattern limit their widespread use. Developing a substrate-independent, facile and efficient, pattern-diverse method for preparing gradient surfaces would aid fundamental science and practical application. Among various techniques, laser processing has recently emerged as a powerful tool in integratedoptics and biomimetic micro-nanodevices. This technology can be used to precisely control the preparation of micro/nanoscale structures on various substrates such as metals, glass, ceramics, and polymers. [27-33] Besides, the high energy density of lasers allows the machining process to be completed quickly and efficiently. Combining laser machining with computer-aided control allows laser ablation parameters to be precisely controlled, including the processing position, scanning speed, scanning interval, and scanning track. Laser processing can therefore be used to produce flexible and diverse patterns in complex workpieces. And laser micro/nano fabrication has been applied to regulate surface wettability. [34-43] Therefore, laser processing has great potential for developing samples with different wettability and geometries on various materials. This review discusses laser fabrication of bioinspired gradient surfaces for wettability applications, whose overview is shown in Figure 1. The related backgrounds including gradient surfaces in natural creatures, the theoretical basis of wettability, and the distinct characteristics of laser processing are introduced. Gradient surfaces can be classified into wettability gradients and geometric gradients, and they are discussed in terms of various laser fabrication approaches and wettability applications. It is worth mentioning the definition of wettability gradient and geometric gradient in this review. Wettability gradient is defined as a surface with no obvious geometric change in the shape, and there is a difference of contact angles on the macro level resulting from the roughness gradient on the micro level. Geometric gradient is defined as a surface possessing significant geometric changes in the shape, but not much difference in the roughness of the entire surface at the microscopic level. Specially, a wettability gradient surface generates a water driving force as a result of its varying surface roughness. Wettability gradient surfaces can be applied in water droplet control, Inspired by nature, gradient surfaces have attracted broad research interest because of their potential in microfluidics, fog/water collection, and water electrolysis. Among the various techniques for preparing gradient surfaces, laser processing is substrate-independent, facile and efficient, patterndiverse, which can be used to prepare...

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Robust Superhydrophobic Conical Pillars from Syringe Needle Shape to Straight Conical Pillar Shape for Droplet Pancake Bouncing

Cited by 59 publications

References 40 publications

Functional and versatile superhydrophobic coatings via stoichiometric silanization

Functional and versatile superhydrophobic coatings via stoichiometric silanization

Reducing Contact Time of Droplets Impacting Superheated Hydrophobic Surfaces

Laser Fabrication of Bioinspired Gradient Surfaces for Wettability Applications

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