Unidirectional water delivery on a superhydrophilic surface with two-dimensional asymmetrical wettability barriers

Geng, Hui; Bai, Haoyu; Fan, Yangyang; Wang, Shaoyu; Ba, Teer; Yu, Cunming; Cao, Moyuan; Jiang, Lei

doi:10.1039/c7mh01138e

Cited by 91 publications

(53 citation statements)

References 47 publications

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properties assisted in moisture absorption. [7] Inspired by nature, researchers have developed artificial water harvesters, [7][8][9][10][11][12][13][14][15][16][17][18] such as water collecting filaments and hydrophobichydrophilic patterned fog collectors. [3][4][5][6] These excellent water harvesting creatures elucidate the critical role of wettability irregularity and hierarchical structure gradient in guiding water transport.

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confidence: 99%

Novel Water Harvesting Fibrous Membranes with Directional Water Transport Capability

Zhou

Wang

et al. 2019

Adv Materials Inter

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properties assisted in moisture absorption. The Namib Desert beetles and Texas horned lizard collect dew using their bumpy body surface with alternating regions of hydrophilic and hydrophobic, and the honeycomb structures on the scale increase condensation foci. [3][4][5][6] These excellent water harvesting creatures elucidate the critical role of wettability irregularity and hierarchical structure gradient in guiding water transport. [7] Inspired by nature, researchers have developed artificial water harvesters, [7][8][9][10][11][12][13][14][15][16][17][18] such as water collecting filaments and hydrophobichydrophilic patterned fog collectors. [19][20][21][22] However, most of the water harvesters developed so far are based on either a 2D surface or a 1D filament.Recently, researchers have uncovered that porous membranes with wettability gradient or wettability contrast in thickness direction can have a "smart" directional wicking effect, which enables water to transfer automatically across the membrane just in one direction. [23][24][25][26][27][28][29][30] Our previous works have reported the preparation of hydrophobic-to-hydrophilic gradient fabrics that can guide directional water-transport from the hydrophobic to the hydrophilic side. [31,32] Such a unidirectional water penetration phenomenon was also reported by other researchers. In research literatures, the directional water transport was also termed "one-way water transport," "directional wicking," [33][34][35] or "water diode." [36][37][38][39][40] Almost all the directional water transport membranes have a hydrophobic layer on one side and a hydrophilic layer on the other, a typical feature of Janus membranes. However, not all Janus membranes have a directional wicking property because Janus membranes might have bidirectional or nonwicking properties, depending on the hydrophobic/hydrophilic combination layout. [36,38,39] Despite the reports about the preparation and applications of directional wicking porous media, limited attention has been devoted to using them for water harvesting.Herein, we report a novel finding about harvesting water from air using hydrophobic/superhydrophilic directional wicking nanofibrous membranes. A two-step electrospinning method was employed to prepare directional wicking fibrous membranes using polyacrylonitrile (PAN) as a starting material. The directional wicking membranes were found to have much larger water harvesting capacity than those with homogeneous wettability and the same fibrous structure. The porous structure and pore dimension also contributed to water harvesting.Previous studies about water harvesting from airborne moisture, which is driven by a directional water transport principle, are based on either a 2D surface or a 1D filament. Porous membranes with a directional water transport capability are seldom used for water harvesting. Herein, a novel hydrophobic/ hydrophilic directional-wicking nanofibrous membrane is reported showing enhanced water harvesting ability. In comparison to the hydrophobic or hy...

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confidence: 99%

Novel Water Harvesting Fibrous Membranes with Directional Water Transport Capability

Zhou

Wang

et al. 2019

Adv Materials Inter

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“…Wetting is one of the basic characteristics of solid surfaces. It is very important for processes like adhesion [1], selfcleaning [2], fluid drag reduction [3], heterogeneous nucleation [4], and the formation of coffee rings [5]. Therefore, it has attracted immense interest in a large diversity of research fields ranging from physical, biological, and environmental sciences.…”

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confidence: 99%

The Possibility of Changing the Wettability of Material Surface by Adjusting Gravity

Liu

Bao

et al. 2020

Research

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The contact angle, as a vital measured parameter of wettability of material surface, has long been in dispute whether it is affected by gravity. Herein, we measured the advancing and receding contact angles on extremely low contact angle hysteresis surfaces under different gravities (1-8G) and found that both of them decrease with the increase of the gravity. The underlying mechanism is revealed to be the contact angle hysteresis and the deformation of the liquid-vapor interface away from the solid surface caused by gradient distribution of the hydrostatic pressure. The real contact angle is not affected by gravity and cannot measured by an optical method. The measured apparent contact angles are angles of inclination of the liquid-vapor interface away from the solid surface. Furthermore, a new equation is proposed based on the balance of forces acting on the three-phase contact region, which quantitatively reveals the relation of the apparent contact angle with the interfacial tensions and gravity. This finding can provide new horizons for solving the debate on whether gravity affects the contact angle and may be useful for the accurate measurement of the contact angle and the development of a new contact angle measurement system.

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“…Learning from the nature, researchers found that the Namib Desert beetles and Texas horned lizard drive the one-way transmission of water droplets in foggy conditions on their typical bumpy backs with alternating hydrophilic and hydrophobic regions; the honeycomb surface of the scales increases the surface roughness and support more condensation foci to survive [8][9][10][11]. By exploring the creatures with excellent directional water transport ability, tremendous methods in attempting to prepare artificial materials with excellent directional water transport or capture capability have been proposed [12][13][14][15][16][17].…”

Section: Introductionmentioning

confidence: 99%

Novel Janus Fibrous Membranes with Enhanced Directional Water Vapor Transmission

Tang

Zhang

et al. 2019

Applied Sciences

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Novel hydrophobic/hydrophilic Janus fibrous membranes, the poly[4,4 -methylenebis (phenylisocyanate)-alt-1,4-butanediol/di(propylene glycol)/plycaprolactone] (PU) fibrous membrane as the hydrophobic layer and cellulose acetate (CA) fibrous membrane as the hydrophilic layer, were fabricated by the so-called "layer-by-layer" electrospinning technology. A series of the PU/CA Janus membranes with different electrospinning time of the CA layers by which the thickness of hydrophilic layer can be controlled were also prepared to uncover its influence on the directional water vapor transmission. The results showed that water vapor transmission capability from the hydrophobic side to the hydrophilic side of the PU/CA Janus fibrous membrane was enhanced rather than that from the reverse direction of the same membrane. The optimal water vapor transmission capacity existed when the electrospinning time of CA fibrous membrane reached 15 min. Such enhanced water vapor transmission originated because of the asymmetric wettability of the Janus membrane and the strong force to draw tiny water droplet from the hydrophobic side to the hydrophilic side. The novel understanding is useful for facile designing and fabrication of efficient moisture permeable fabrics and clothing.

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Unidirectional water delivery on a superhydrophilic surface with two-dimensional asymmetrical wettability barriers

Abstract: A superhydrophilic surface decorated with 2D hydrophobic water barriers is proven to be a potential platform for unidirectional liquid transport.

Cited by 91 publications

References 47 publications

Novel Water Harvesting Fibrous Membranes with Directional Water Transport Capability

Novel Water Harvesting Fibrous Membranes with Directional Water Transport Capability

The Possibility of Changing the Wettability of Material Surface by Adjusting Gravity

Novel Janus Fibrous Membranes with Enhanced Directional Water Vapor Transmission

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