Improving surface-wetting characterization Liu, Kai; Vuckovac, Maja; Latikka, Mika ...
Science (American Association for the Advancement of Science),
03/2019, Volume:
363, Issue:
6432
Journal Article
Peer reviewed
Open access
Awareness of instrument inaccuracies will boost the development of liquid-repellent coatings
Highly hydrophobic surfaces have numerous useful properties; for example, they can shed water, be ...self-cleaning, and prevent fogging (
1
,
2
). Surface hydrophobicity is generally characterized with contact angle (CA) goniometry. With a history of more than 200 years (
3
), the measurement of CAs was and still is considered the gold standard in wettability characterization, serving to benchmark surfaces across the entire wettability spectrum from superhydrophilic (CA of 0°) to superhydrophobic (CA of 150° to 180°). However, apart from a few reports e.g., (
4
–
8
), the inherent measurement inaccuracy of the CA goniometer has been largely overlooked by its users. The development of next-generation liquid-repellent coatings depends on raising awareness of the limitations of CA measurements and adopting more sensitive methods that measure forces.
Commercial membranes for membrane distillation experience severe wetting and fouling phenomena, which largely hinder their practical applications. To address these issues, a novel strategy to ...fabricate the Janus membrane is proposed via a facile layer-by-layer coating of Teflon® AF1600 and polydopamine (PDA) on an oxygen plasma treated commercial polytetrafluoroethylene/polypropylene (PTFE/PP) membrane. The resultant membrane has a unique asymmetric surface wettability. In brief, the top layer of the Janus membrane is strongly hydrophobic (145.1 ± 1.8°), while the bottom layer exhibits underwater superoleophobicity (154.2 ± 2.2°) and in-air hydrophilicity (33.5 ± 1.2°). As a result, the Janus membrane possesses a significantly enhanced wetting resistance toward common liquids including pure water, surfactant, ethanol, and crude oil, compared to the unmodified membrane. Due to the excellent anti-fouling property, the Janus membrane also shows a rather robust desalination performance (i.e., a slight decline in water flux and negligible salt passage) when treating a multi-component saline wastewater containing both humic acid and crude oil, ending up with a high water recovery ratio of 50%. Overall, the Janus membrane developed in this work is highly promising for the water reclamation from highly saline wastewater containing complex organic compounds.
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•A novel Janus membrane with asymmetrical wettability was developed.•Teflon® AF1600 for robust hydrophobicity; PDA for hydrophilicity/oleophobicity.•A rather robust desalination performance when treating multi-component wastewater.•Low energy consumption for the Janus membrane.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The increasing number of oil spill accidents have a catastrophic impact on our aquatic environment. Recently, special wettable materials used for the oil/water separation have received significant ...research attention. Due to their opposing affinities towards water and oil, i.e., hydrophobic and oleophilic, or hydrophilic and oleophobic, such materials can be used to remove only one phase from the oil/water mixture, and simultaneously repel the other phase, thus achieving selective oil/water separation. Moreover, the synergistic effect between the surface chemistry and surface architecture can further promote the superwetting behavior, resulting in the improved separation efficiency. Here, recently developed materials with special wettability for selective oil/water separation are summarized and discussed. These materials can be categorized based on their oil/water separating mechanisms, i.e., filtration and absorption. In each section, representative studies will be highlighted, with emphasis on the materials wetting properties and innovative aspects. Finally, challenges and future research directions in this emerging and promising research field will be briefly described.
Special wettable materials with opposite affinities towards water and oil have been developed for selective oil/water separation. The recent developments in this fast rising research field are summarized and discussed.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Oil spills and industrial organic pollutants have induced severe water pollution and threatened every species in the ecological system. To deal with oily water, special wettability stimulated ...materials have been developed over the past decade to separate oil-and-water mixtures. Basically, synergy between the surface chemical composition and surface topography are commonly known as the key factors to realize the opposite wettability to oils and water and dominate the selective wetting or absorption of oils/water. In this review, we mainly focus on the development of materials with either super-lyophobicity or super-lyophilicity properties in oil/water separation applications where they can be classified into four kinds as follows (in terms of the surface wettability of water and oils): (i) superhydrophobic and superoleophilic materials, (ii) superhydrophilic and under water superoleophobic materials, (iii) superhydrophilic and superoleophobic materials, and (iv) smart oil/water separation materials with switchable wettability. These materials have already been applied to the separation of oil-and-water mixtures: from simple oil/water layered mixtures to oil/water emulsions (including oil-in-water emulsions and water-in-oil emulsions), and from non-intelligent materials to intelligent materials. Moreover, they also exhibit high absorption capacity or separation efficiency and selectivity, simple and fast separation/absorption ability, excellent recyclability, economical efficiency and outstanding durability under harsh conditions. Then, related theories are proposed to understand the physical mechanisms that occur during the oil/water separation process. Finally, some challenges and promising breakthroughs in this field are also discussed. It is expected that special wettability stimulated oil/water separation materials can achieve industrial scale production and be put into use for oil spills and industrial oily wastewater treatment in the near future.
Investigations in the field of oil/water separation materials with special wettability may accelerate the settlement of industrial oily wastewater and ocean oil spill accidents.
Covalent organic frameworks (COFs) hold great potentials for addressing the challenge of highly efficient oil–water separation, but they are restricted by the poor wettability and processability as ...crystalline membranes. Here we report the design and synthesis of two‐dimensional (2D) robust COFs with controllable hydrophobicity and processability, allowing the COF layers to be directly grown on the support surfaces. Three 2D COFs with AA or ABC stacking are prepared by condensation of triamines with fluorine and/or isopropyl groups and perfluorodialdehyde. They all show excellent tolerance to water, acid, and base, with water contact angles (CA) of 111.5–145.8°. The two COFs with isopropyl and fluorine mixtures can grow as a coating on a stainless‐steel net (SSN) substrate, whereas the one with only fluorine substituents cannot. The superhydrophobic COF@SSN coating with water CA of up to 150.1° displays high water‐resistance and self‐cleaning properties, enabling high oil–water separation performances with an efficiency of over 99.5 % and a permeation flux of 2.84×105 L m−2 h−1, which are among the highest values reported for state‐of‐the‐art membranes.
Three 2D robust COFs with controllable hydrophobicity and processability were synthesized by introducing mixed hydrophobic substituents. After coating on a stainless‐steel net (SSN) substrate, the superhydrophobic COF@SSN coating exhibits an excellent oil/water separation efficiency (>99.5 %), high oil‐permeation flux (2.84±0.08)×105 L m−2 h−1, high water‐pressure resistance (>15 kPa), and a high degree of reusability (>50 cycles).
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
In recent years, controlling the salinity and composition of the injected water has become an emerging enhanced oil recovery (EOR) technique, often described as low salinity (LS) waterflooding. This ...work is done with the intention to contribute to the ongoing discussions about LS waterflooding mechanism(s). For this purpose, a series of different experiments were conducted. At first, the effect of salinity on the interfacial tension (IFT) and the contact angle was evaluated with a crude oil sample. Then to achieve more accurate results in observing oil/water interface, similar IFT experiments were also carried out on a synthetic oil containing asphaltenes. Thereafter, microscopic visualization using glass micromodel was performed on the interface of the synthetic oil sample and brines. Four brine solutions including Sea Water (SW), it's dilutions and formation water (FW) were used for various experiments. Finally, to investigate the presented mechanism by other authors, a series of Environmental Scanning Electron Microscopy (ESEM) analysis on the synthetic oil was carried out to understand better the phase behaviour after contacting both synthetic oil and water phases from the micromodel experiment. Based on the existing mechanism, there exists an optimal concentration beyond which dilution is no longer an effective process.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Abstract Condensation is commonly utilized in numerous thermal management applications and has two modes termed filmwise and dropwise, the latter providing superior heat transfer performance. However ...dropwise condensation is usually limited by its dependence on gravitational shedding of condensate. To combat this, hybrid surfaces consisting of regions of different wettability have emerged as a promising solution. Of such designs, hybrid grooved surfaces consisting of grooves with varying wettability in the groove valleys and ridge tops are of current interest. To date, most such surfaces have been silicon-based and over flat substrates. In this work, condensation experiments are performed on a copper tube with fabricated grooved hybrid surfaces. The aim is to take advantage of anisotropic wetting due to the presence of grooves and condensate drainage from higher wettability regions. The experimental results quantify the heat transfer with the degree of subcooling. At the same time, droplet dynamics were studied on the hydrophobic-hydrophilic surfaces, showing several droplet growth and departure mechanisms leading to effective heat transfer.
Heterogeneous membranes play a crucial role in osmotic energy conversion by effectively reducing concentration polarization. However, most heterogeneous membranes mitigate concentration polarization ...through an asymmetric charge distribution, resulting in compromised ion selectivity. Herein, hetero‐nanochannels with asymmetric wettability composed of 2D mesoporous carbon and graphene oxide are constructed. The asymmetric wettability of the membrane endows it with the ability to suppress the concentration polarization without degrading the ion selectivity, as well as achieving a diode‐like ion transport feature. As a result, enhanced osmotic energy harvesting is achieved with a power density of 6.41 W m−2. This represents a substantial enhancement of 102.80–137.85% when compared to homogeneous 2D membranes, surpassing the performance of the majority of reported 2D membranes. Importantly, the membrane can be further used for high‐performance ionic power harvesting by regulating ion transport, exceeding previously reported data by 89.1%.
A heterogeneous membrane used for osmotic energy harvesting is fabricated by hydrophobic 2D mesoporous carbon and hydrophilic graphene oxide. Benefiting from the asymmetric wettability structure, the membrane shows diode‐like ion transport features, suppressing the concentration polarization without degrading the ion selectivity, leading to a promoted osmotic energy conversion performance.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
499.
Switching in Metal–Organic Frameworks Bigdeli, Fahime; Lollar, Christina T.; Morsali, Ali ...
Angewandte Chemie International Edition,
March 16, 2020, Volume:
59, Issue:
12
Journal Article
Peer reviewed
Open access
In recent years, metal–organic frameworks (MOFs) have become an area of intense research interest because of their adjustable pores and nearly limitless structural diversity deriving from the design ...of different organic linkers and metal structural building units (SBUs). Among the recent great challenges for scientists include switchable MOFs and their corresponding applications. Switchable MOFs are a type of smart material that undergo distinct, reversible, chemical changes in their structure upon exposure to external stimuli, yielding interesting technological applicability. Although the process of switching shares similarities with flexibility, very limited studies have been devoted specifically to switching, while a fairly large amount of research and a number of Reviews have covered flexibility in MOFs. This Review focuses on the properties and general design of switchable MOFs. The switching activity has been delineated based on the cause of the switching: light, spin crossover (SCO), redox, temperature, and wettability.
A switch in time: Although dynamic and flexible metal–organic frameworks (MOFs) have been closely assessed in recent literature, analysis into the subcategory of switchable MOFs has been comparably lacking. By virtue of their steady rise in popularity, MOFs with intriguing, switchable responses to light, temperature, pressure, redox species and guests are surveyed.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Superhydrophobic cellulose-based products show tremendous potential applications in both industries and researches owing to their inherent biodegradability, non-toxicity, and cost-effectiveness. ...However, previous studies mainly focused on superhydrophobic cellulose bulk materials rather than universal cellulose powder. Though some methods have been proposed for preparing superhydrophobic cellulose powder, their fabricating processes involve plenty of high-toxic organic solvents. In this work, we proposed a facile one-step solvent-free method to prepare superhydrophobic cellulose powder. The modified cellulose powder shows not only superhydrophobicity but also reversible wettability. Moreover, the superhydrophobic cellulose shows immense UV resistance by enduring 60 h UV radiation. The superhydrophobic cellulose powder-coated cotton fabric could separate oil/water mixture with high efficiency and reusability. This work provides a green method to produce superhydrophobic cellulose powder which can be used as a raw material for sophisticated multifunctional material fabrication in future.
•A solvent-free method was proposed for fabricating superhydrophobic cellulose particles.•The superhydrophobic cellulose particles show reversible wettability.•The superhydrophobic cellulose particles show high stability against UV radiation.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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