Water harvesting from air is desired for decentralized water supply wherever water is needed. When water vapor is condensed as droplets on a surface the unremoved droplets act as thermal barriers. A surface that can provide continual droplet-free areas for nucleation is favorable for condensation water harvesting. Here, we report a flow-separation condensation mode on a hydrophilic reentrant slippery liquid-infused porous surface (SLIPS) that rapidly removes droplets with diameters above 50 μm. The slippery reentrant channels lock the liquid columns inside and transport them to the end of each channel. We demonstrate that the liquid columns can harvest the droplets on top of the hydrophilic reentrant SLIPS at a high droplet removal frequency of 130 Hz/mm 2 . The sustainable flow separation without flooding increases the water harvesting rate by 110% compared to the state-of-the-art hydrophilic flat SLIPS. Such a flow-separation condensation approach paves a way for water harvesting.
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Slippery nanoemulsion-infused porous surfaces (SNIPS): anti-fouling coatings that can host and sustain the release of water-soluble agents
We report the design of ‘slippery’ nanoemulsion-infused porous surfaces (SNIPS). These materials are strongly anti-fouling to a broad range of substances, including microorganisms. Infusion with water-in-oil nanoemulsions also endows these slippery coatings with the ability to host and control or sustain the release of water-soluble agents, including polymers, peptides, and nucleic acids, opening the door to new applications of liquid-infused materials.
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- Award ID(s):
- 1720415
- NSF-PAR ID:
- 10315962
- Date Published:
- Journal Name:
- Chemical Communications
- Volume:
- 57
- Issue:
- 94
- ISSN:
- 1359-7345
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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We numerically study drop impact on slippery lubricated surfaces at varied impact speeds to comprehend the cloaking of the water drop by the lubricant. We employ a multi-material and multi-phase interface reconstruction method to capture the interaction between the drop and the lubricants of varying interfacial tensions. We demonstrate that cloaking occurs when lubricant water interfacial tensions are low and impact speeds are low. Our research demonstrates that the thickness of the encapsulating lubricant layer varies over time. At moderate impact speeds of 0.25 and 0.5 m/s, the drop displaces a large amount of lubricant, generating a lubricant–water jet, as we also demonstrate. At high impact speeds of 5 and 30 m/s, a secondary impingement forms, which displaces a significant amount of lubricant to reveal the underneath substrate that was not visible at lower impact speeds. Finally, we investigate the drop impact on lubricant infused micro-wells with varying spacing. We find that small spacing between the micro-well walls can limit lubricant drainage and displacement. The substrates with micro-wells exhibit far less splashing than those without. Furthermore, we demonstrate that micro-wells are better at preserving lubricants than substrates without micro-wells.
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The next-generation semiconductors and devices, such as halide perovskites and flexible electronics, are extremely sensitive to water, thus demanding highly effective protection that not only seals out water in all forms (vapor, droplet, and ice), but simultaneously provides mechanical flexibility, durability, transparency, and self-cleaning. Although various solid-state encapsulation methods have been developed, no strategy is available that can fully meet all the above requirements. Here, we report a bioinspired liquid-based encapsulation strategy that offers protection from water without sacrificing the operational properties of the encapsulated materials. Using halide perovskite as a model system, we show that damage to the perovskite from exposure to water is drastically reduced when it is coated by a polymer matrix with infused hydrophobic oil. With a combination of experimental and simulation studies, we elucidated the fundamental transport mechanisms of ultralow water transmission rate that stem from the ability of the infused liquid to fill-in and reduce defects in the coating layer, thus eliminating the low-energy diffusion pathways, and to cause water molecules to diffuse as clusters, which act together as an excellent water permeation barrier. Importantly, the presence of the liquid, as the central component in this encapsulation method provides a unique possibility of reversing the water transport direction; therefore, the lifetime of enclosed water-sensitive materials could be significantly extended via replenishing the hydrophobic oils regularly. We show that the liquid encapsulation platform presented here has high potential in providing not only water protection of the functional device but also flexibility, optical transparency, and self-healing of the coating layer, which are critical for a variety of applications, such as in perovskite solar cells and bioelectronics.more » « less
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Polymer zwitterions are generally regarded as hydrophilic and repellant or “slippery” materials. Here, a case is described in which the polymer zwitterion structure is tailored to decrease water solubility, stabilize emulsion droplets, and promote interdroplet adhesion. Harnessing the upper critical solution temperature of sulfonium‐ and ammonium‐based polymer zwitterions in water, adhesive droplets are prepared by adding organic solvent to an aqueous polymer solution at elevated temperature, followed by agitation to induce emulsification. Droplet aggregation is observed as the mixture cools. Variation of salt concentration, temperature, polymer concentration, and polymer structure modulates these interdroplet interactions, resulting in distinct changes in emulsion stability and fluidity. Under attractive conditions, emulsions encapsulating 50–75% oil undergo gelation. By contrast, emulsions prepared under conditions where droplets are nonadhesive remain fluid and, for oil fractions exceeding 0.6, coalescence is observed. The uniquely reactive nature of the selected zwitterions allows their in situ modification and affords a route to chemically trigger deaggregation and droplet dispersion. Finally, experiments performed in a microfluidic device, in which droplets are formed under conditions that either promote or suppress adhesion, confirm the salt‐responsive character of these emulsions and the persistence of adhesive interdroplet interactions under flow.
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Abstract Preventing water droplets from transitioning to ice is advantageous for numerous applications. It is demonstrated that the use of certain phase‐change materials, which are in liquid state under ambient conditions and have melting point higher than the freezing point of water, referred herein as phase‐switching liquids (PSLs), can impede condensation–frosting lasting up to 300 and 15 times longer in bulk and surface infused state, respectively, compared to conventional surfaces under identical environmental conditions. The freezing delay is primarily a consequence of the release of trapped latent heat due to condensation, but is also affected by the solidified PSL surface morphology and its miscibility in water. Regardless of surface chemistry, PSL‐infused textured surfaces exhibit low droplet adhesion when operated below the corresponding melting point of the solidified PSLs, engendering ice and frost repellency even on hydrophilic substrates. Additionally, solidified PSL surfaces display varying degrees of optical transparency, can repel a variety of liquids, and self‐heal upon physical damage.
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/d1cc04645d
