Hydrophilic and superhydrophilic surfaces and materials
TL;DR: The definition of superhydrophilic substrates has not been clarified yet, and unrestricted use of this term to hydrophilic surfaces has stirred controversy in the surface chemistry community.
Abstract: The term superhydrophilicity is only 11–12 years old and was introduced just after the explosion of research on superhydrophobic surfaces, in response to the demand for surfaces and coatings with exceptionally strong affinity to water. The definition of superhydrophilic substrates has not been clarified yet, and unrestricted use of this term to hydrophilic surfaces has stirred controversy in the last few years in the surface chemistry community. In this review, we take a close look into major definitions of hydrophilic surfaces used in the past, before we review the physics behind the superhydrophilic phenomenon and make recommendation on defining superhydrophilic surfaces and coatings. We also review chemical and physical methods used in the fabrication of substrates on surfaces of which water spreads completely. Several applications of superhydrophilic surfaces, including examples from the authors' own research, conclude this review.
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TL;DR: The evolution of superwettable materials is introduced, and the fundamental rules for building these superwetting materials will be discussed, followed by a summary of recent progress in the application of superWettability materials to alter the behaviors of chemical reactants and products.
Abstract: Superwettability is a special case of the wetting phenomenon among liquids, gases, and solids. The superhydrophobic/superhydrophilic effect discovered initially has undergone a century of development based on materials science and biomimetics. With the rapid development of research on anti-wetting materials, superoleophobic/superoleophilic surfaces have been fabricated to repel organic liquids besides water. Further studies of underwater superoleophobic/superoleophilic/superaerophobic/superaerophilic materials provide an alternative way to fabricate anti-wetting surfaces rather than lowering the surface energy. Owing to a series of efforts on the studying of extreme wettabilities, a mature superwettability system gradually evolved and has since become a vibrant area of active research, covering topics of superhydrophobicity/superhydrophilicity, superoleophobicity/superoleophilicity in gas or under liquid, superaerophobicity/superaerophilicity under liquid, and combinations of these states. The kinetic stu...
866 citations
TL;DR: It was found that single and successive water droplets could rebound on the superhydrophobic surface and roll off at a tilt angle larger than 30° under an extremely condensing weather condition (-10 °C and relative humidity of 85-90%).
Abstract: Four aluminum surfaces with wettability varied from superhydrophilic to superhydrophobic were prepared by combining an etching and a coating process. The surface wettability was checked in terms of water contact angle (CA) and sliding angle (SA) under different humidity at −10 °C. High-speed photography was applied to study water droplet impact dynamics on these surfaces. It was found that single and successive water droplets could rebound on the superhydrophobic surface and roll off at a tilt angle larger than 30° under an extremely condensing weather condition (−10 °C and relative humidity of 85–90%). In addition, the superhydrophobic surface showed a strong icephobic property, the ice adhesion on this surface was only 13% of that on the superhydrophilic surface, though they had a similar nano/microtopological structure. Moreover, this superhydrophobic surface displayed an excellent durability of the icephobic property. The ice adhesion only increased to 20% and 16% of that on the superhydrophobic surfa...
436 citations
TL;DR: In this article, the authors characterized pool boiling on surfaces with wettabilities varied from superhydrophobic to super-hydrophilic, and provided nucleation measurements, and developed an analytical model that describes how biphilic surfaces effectively manage the vapor and liquid transport, delaying critical heat flux and maximizing the heat transfer coefficient.
428 citations
Cites background from "Hydrophilic and superhydrophilic su..."
...In recent reviews, enhanced liquid–vapor phase change was also described as a potential application of SHPi [11] and SHPo [12] surfaces....
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TL;DR: A self-smoothing lithium–carbon anode structure based on mesoporous carbon nanofibres, coupled with a lithium nickel–manganese–cobalt oxide cathode with a high nickel content, can lead to a cell-level energy density of 350–380 Wh kg−1 and a stable cycling life up to 200 cycles.
Abstract: Despite considerable efforts to stabilize lithium metal anode structures and prevent dendrite formation, achieving long cycling life in high-energy batteries under realistic conditions remains extremely difficult due to a combination of complex failure modes that involve accelerated anode degradation and the depletion of electrolyte and lithium metal. Here we report a self-smoothing lithium–carbon anode structure based on mesoporous carbon nanofibres, which, coupled with a lithium nickel–manganese–cobalt oxide cathode with a high nickel content, can lead to a cell-level energy density of 350–380 Wh kg−1 (counting all the active and inactive components) and a stable cycling life up to 200 cycles. These performances are achieved under the realistic conditions required for practical high-energy rechargeable lithium metal batteries: cathode loading ≥4.0 mAh cm−2, negative to positive electrode capacity ratio ≤2 and electrolyte weight to cathode capacity ratio ≤3 g Ah−1. The high stability of our anode is due to the amine functionalization and the mesoporous carbon structures that favour smooth lithium deposition. Metallic lithium wets a functionalized mesoporous carbon film to create a self-smoothing anode that, in conjunction with a standard lithium nickel–manganese–cobalt cathode, delivers long cycling life, 350 Wh kg−1 high-energy cells under realistic conditions.
399 citations
TL;DR: In this article, a superhydrophilic and superoleophobic nanocomposite coating is fabricated by spray casting nanoparticle-polymer suspensions on various substrates, which can be used for the separation of oil and water.
Abstract: A novel superhydrophilic and superoleophobic nanocomposite coating is fabricated by spray casting nanoparticle–polymer suspensions on various substrates. Water droplets can spread over the coating completely; meanwhile, oil droplets can roll off the coating at low tilt angles without any penetration. Besides overcoming oil-fouling problems for the hydrophilic coating, the superhydrophilic–superoleophobic coating applied to the stainless steel mesh can be used for the separation of oil and water.
356 citations
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TL;DR: In this paper, the authors present an attempt towards a unified picture with special emphasis on certain features of "dry spreading": (a) the final state of a spreading droplet need not be a monomolecular film; (b) the spreading drop is surrounded by a precursor film, where most of the available free energy is spent; and (c) polymer melts may slip on the solid and belong to a separate dynamical class, conceptually related to the spreading of superfluids.
Abstract: The wetting of solids by liquids is connected to physical chemistry (wettability), to statistical physics (pinning of the contact line, wetting transitions, etc.), to long-range forces (van der Waals, double layers), and to fluid dynamics. The present review represents an attempt towards a unified picture with special emphasis on certain features of "dry spreading": (a) the final state of a spreading droplet need not be a monomolecular film; (b) the spreading drop is surrounded by a precursor film, where most of the available free energy is spent; and (c) polymer melts may slip on the solid and belong to a separate dynamical class, conceptually related to the spreading of superfluids.
6,042 citations
TL;DR: It is shown here for the first time that the interdependence between surface roughness, reduced particle adhesion and water repellency is the keystone in the self-cleaning mechanism of many biological surfaces.
Abstract: The microrelief of plant surfaces, mainly caused by epicuticular wax crystalloids, serves different purposes and often causes effective water repellency. Furthermore, the adhesion of contaminating particles is reduced. Based on experimental data carried out on microscopically smooth (Fagus sylvatica L., Gnetum gnemon L., Heliconia densiflora Verlot, Magnolia grandiflora L.) and rough water-repellent plants (Brassica oleracea L., Colocasia esculenta (L.) Schott., Mutisia decurrens Cav., Nelumbo nucifera Gaertn.), it is shown here for the first time that the interdependence between surface roughness, reduced particle adhesion and water repellency is the keystone in the self-cleaning mechanism of many biological surfaces. The plants were artificially contaminated with various particles and subsequently subjected to artificial rinsing by sprinkler or fog generator. In the case of water-repellent leaves, the particles were removed completely by water droplets that rolled off the surfaces independent of their chemical nature or size. The leaves of N. nucifera afford an impressive demonstration of this effect, which is, therefore, called the “Lotus-Effect” and which may be of great biological and technological importance.
5,822 citations
TL;DR: The field of photocatalysis can be traced back more than 80 years to early observations of the chalking of titania-based paints and to studies of the darkening of metal oxides in contact with organic compounds in sunlight as discussed by the authors.
5,729 citations