Nanostructured Surfaces Enhance Nucleation Rate of Calcium Carbonate.

Nucleation and growth of calcium carbonate on surfaces is of broad importance in nature and technology, being essential to the calcification of organisms, while negatively impacting energy conversion through crystallization fouling, also called scale formation. Previous work studied how confinements, surface energies, and functionalizations affect nucleation and polymorph formation, with surface-water interactions and ion mobility playing important roles. However, the influence of surface nanostructures with nanocurvature-through pit and bump morphologies-on scale formation is unknown, limiting the development of scalephobic surfaces.

Three-Dimensional Metallic Surface Micropatterning through Tailored Photolithography-Transfer-Plating.

Precise micropatterning on three-dimensional (3D) surfaces is desired for a variety of applications, from microelectronics to metamaterials, which can be realized by transfer printing techniques. However, a nontrivial deficiency of this approach is that the transferred microstructures are adsorbed on the target surface with weak adhesion, limiting the applications to external force-free conditions. We propose a scalable "photolithography-transfer-plating" method to pattern stable and durable microstructures on 3D metallic surfaces with precise dimension and location control of the micropatterns.

Imparting scalephobicity with rational microtexturing of soft materials.

Crystallization fouling, a process where scale forms on surfaces, is widespread in nature and technology, negatively affecting energy and water industries. Despite the effort, rationally designed surfaces that are intrinsically resistant to it remain elusive, due in part to a lack of understanding of how microfoulants deposit and adhere in dynamic aqueous environments. Here, we show that rational tuning of coating compliance and wettability works synergistically with microtexture to enhance microfoulant repellency, characterized by low adhesion and high removal efficiency of numerous individual microparticles and tenacious crystallites in a flowing water environment.

Engineering Electrode Rinse Solution Fluidics for Carbon-Based Reverse Electrodialysis Devices.

Natural salinity gradients are a promising source of so-called "blue energy", a renewable energy source that utilizes the free energy of mixing for power generation. One promising blue energy technology that converts these salinity gradients directly into electricity is reverse electrodialysis (RED). Used at its full potential, it could provide a substantial portion of the world's electricity consumption.

Freezing-induced wetting transitions on superhydrophobic surfaces.

Supercooled droplet freezing on surfaces occurs frequently in nature and industry, often adversely affecting the efficiency and reliability of technological processes. The ability of superhydrophobic surfaces to rapidly shed water and reduce ice adhesion make them promising candidates for resistance to icing. However, the effect of supercooled droplet freezing-with its inherent rapid local heating and explosive vaporization-on the evolution of droplet-substrate interactions, and the resulting implications for the design of icephobic surfaces, are little explored.

Transparent sunlight-activated antifogging metamaterials.

Counteracting surface fogging to maintain surface transparency is important for a variety of applications including eyewear, windows and displays. Energy-neutral, passive approaches predominantly rely on engineering the surface wettability, but suffer from non-uniformity, contaminant deposition and lack of robustness, all of which substantially degrade durability and performance. Here, guided by nucleation thermodynamics, we design a transparent, sunlight-activated, photothermal coating to inhibit fogging.

Ultrathin Durable Organic Hydrophobic Coatings Enhancing Dropwise Condensation Heat Transfer.

Organic hydrophobic layers targeting sustained dropwise condensation are highly desirable but suffer from poor chemical and mechanical stability, combined with low thermal conductivity. The requirement of such layers to remain ultrathin to minimize their inherent thermal resistance competes against durability considerations. Here, we investigate the long-term durability and enhanced heat-transfer performance of perfluorodecanethiol (PFDT) coatings compared to alternative organic coatings, namely, perfluorodecyltriethoxysilane (PFDTS) and perfluorodecyl acrylate (PFDA), the latter fabricated with initiated chemical vapor deposition (iCVD), in condensation heat transfer and under the challenging operating conditions of intense flow (up to 9 m s) of superheated steam (111 °C) at high pressures (1.

Bistability of Dielectrically Anisotropic Nematic Crystals and the Adaptation of Endothelial Collectives to Stress Fields.

Endothelial monolayers physiologically adapt to flow and flow-induced wall shear stress, attaining ordered configurations in which elongation, orientation, and polarization are coherently organized over many cells. Here, with the flow direction unchanged, a peculiar bi-stable (along the flow direction or perpendicular to it) cell alignment is observed, emerging as a function of the flow intensity alone, while cell polarization is purely instructed by flow directionality. Driven by the experimental findings, the parallelism between endothelia is delineated under a flow field and the transition of dual-frequency nematic liquid crystals under an external oscillatory electric field.

Microscale investigation on interfacial slippage and detachment of ice from soft materials.

Surface icing is detrimental to applications ranging from transportation to biological systems. Soft elastomeric coatings can engender remarkably low ice adhesion strength, but mechanisms at the microscale and resulting ice extraction outcomes need to be understood. Here we investigate dynamic ice-elastomer interfacial events and show that the ice adhesion strength can actually vary by orders of magnitude due to the shear velocity.

Enhanced Atmospheric Water Harvesting with Sunlight-Activated Sorption Ratcheting.

The global challenge of clean water scarcity needs to be confronted with novel sustainable, climate neutral solutions, over the entire spectrum of possible clean water availability. Atmospheric moisture represents a major untapped resource that can be harvested by sorbents, enabling water production in dry inland regions where it is needed. While benefiting from the utilization of an important renewable energy source, solar-driven, sorbent-based atmospheric water harvesting systems are inseparably based on a single water harvesting cycle per day, which severely limits the daily water productivity and the competitiveness of this very promising technology.

Exploiting radiative cooling for uninterrupted 24-hour water harvesting from the atmosphere.

Atmospheric water vapor is ubiquitous and represents a promising alternative to address global clean water scarcity. Sustainably harvesting this resource requires energy neutrality, continuous production, and facility of use. However, fully passive and uninterrupted 24-hour atmospheric water harvesting remains a challenge.

Leidenfrost droplet trampolining.

A liquid droplet dispensed over a sufficiently hot surface does not make contact but instead hovers on a cushion of its own self-generated vapor. Since its discovery in 1756, this so-called Leidenfrost effect has been intensively studied. Here we report a remarkable self-propulsion mechanism of Leidenfrost droplets against gravity, that we term Leidenfrost droplet trampolining.

Superhydrophobic surfaces for extreme environmental conditions.

Superhydrophobic surfaces for repelling impacting water droplets are typically created by designing structures with capillary (antiwetting) pressures greater than those of the incoming droplet (dynamic, water hammer). Recent work has focused on the evolution of the intervening air layer between droplet and substrate during impact, a balance of air compression and drainage within the surface texture, and its role in affecting impalement under ambient conditions through local changes in the droplet curvature. However, little consideration has been given to the influence of the intervening air-layer thermodynamic state and composition, in particular when departing from standard atmospheric conditions, on the antiwetting behavior of superhydrophobic surfaces.

Transparent Photothermal Metasurfaces Amplifying Superhydrophobicity by Absorbing Sunlight.

Imparting and maintaining surface superhydrophobicity has been receiving significant research attention over the last several years, driven by a broad range of important applications and enabled by advancements in materials and surface nanoengineering. Researchers have investigated the effect of temperature on droplet-surface interactions, which poses additional challenges when liquid nucleation manifests itself, due to ensuing condensation into the surface texture that compromises its antiwetting behavior. Maintaining surface transparency at the same time poses an additional and significant challenge.

Bitumen surface microstructure evolution in subzero environments.

Bitumen is a widely used material employed as a binder in pavement engineering and as a surface sealant in construction. Its surface microstructure and microscale properties have been shown to be temperature-dependent, with effects manifesting themselves on surface composition and texture, including the formation of the visually striking catana 'bee'-like structures. Despite the importance of a good performance of bitumen in subzero environments (<0°C), the behaviour of bitumen surface texture and composition at cold temperatures, affecting cracking, degradation and road icing, has received practically no attention.

Wetting transitions in droplet drying on soft materials.

Droplet interactions with compliant materials are familiar, but surprisingly complex processes of importance to the manufacturing, chemical, and garment industries. Despite progress-previous research indicates that mesoscopic substrate deformations can enhance droplet drying or slow down spreading dynamics-our understanding of how the intertwined effects of transient wetting phenomena and substrate deformation affect drying remains incomplete. Here we show that above a critical receding contact line speed during drying, a previously not observed wetting transition occurs.

Transparent Metasurfaces Counteracting Fogging by Harnessing Sunlight.

Surface fogging is a common phenomenon that can have significant and detrimental effects on surface transparency and visibility. It affects the performance in a wide range of applications including windows, windshields, electronic displays, cameras, mirrors, and eyewear. A host of ongoing research is aimed at combating this problem by understanding and developing stable and effective antifogging coatings that are capable of handling a wide range of environmental challenges "passively" without consumption of electrical energy.

3D-Printed Surface Architecture Enhancing Superhydrophobicity and Viscous Droplet Repellency.

Macrotextured superhydrophobic surfaces can reduce droplet-substrate contact times of impacting water droplets; however, surface designs with similar performance for significantly more viscous liquids are missing, despite their importance in nature and technology such as for chemical shielding, food-staining repellency, and supercooled (viscous) water droplet removal in anti-icing applications. Here, we introduce a deterministic, controllable, and upscalable method to fabricate superhydrophobic surfaces with a 3D-printed architecture, combining arrays of alternating surface protrusions and indentations. We show a more than threefold contact time reduction of impacting viscous droplets up to a fluid viscosity of 3.

Cascade Freezing of Supercooled Water Droplet Collectives.

Surface icing affects the safety and performance of numerous processes in technology. Previous studies mostly investigated freezing of individual droplets. The interaction among multiple droplets during freezing is investigated less, especially on nanotextured icephobic surfaces, despite its practical importance as water droplets never appear in isolation, but in groups.

Desublimation Frosting on Nanoengineered Surfaces.

Ice nucleation from vapor presents a variety of challenges across a wide range of industries and applications including refrigeration, transportation, and energy generation. However, a rational comprehensive approach to fabricating intrinsically icephobic surfaces for frost formation-both from water condensation (followed by freezing) and in particular from desublimation (direct growth of ice crystals from vapor)-remains elusive. Here, guided by nucleation physics, we investigate the effect of material composition and surface texturing (atomically smooth to nanorough) on the nucleation and growth mechanism of frost for a range of conditions within the sublimation domain (0 °C to -55 °C; partial water vapor pressures 6 to 0.

Metasurfaces Leveraging Solar Energy for Icephobicity.

Inhibiting ice accumulation on surfaces is an energy-intensive task and is of significant importance in nature and technology where it has found applications in windshields, automobiles, aviation, renewable energy generation, and infrastructure. Existing methods rely on on-site electrical heat generation, chemicals, or mechanical removal, with drawbacks ranging from financial costs to disruptive technical interventions and environmental incompatibility. Here we focus on applications where surface transparency is desirable and propose metasurfaces with embedded plasmonically enhanced light absorption heating, using ultrathin hybrid metal-dielectric coatings, as a passive, viable approach for de-icing and anti-icing, in which the sole heat source is renewable solar energy.

Spontaneous self-dislodging of freezing water droplets and the role of wettability.

Spontaneous removal of liquid, solidifying liquid and solid forms of matter from surfaces, is of significant importance in nature and technology, where it finds applications ranging from self-cleaning to icephobicity and to condensation systems. However, it is a great challenge to understand fundamentally the complex interaction of rapidly solidifying, typically supercooled, droplets with surfaces, and to harvest benefit from it for the design of intrinsically icephobic materials. Here we report and explain an ice removal mechanism that manifests itself simultaneously with freezing, driving gradual self-dislodging of droplets cooled via evaporation and sublimation (low environmental pressure) or convection (atmospheric pressure) from substrates.

Imparting Icephobicity with Substrate Flexibility.

Ice accumulation hinders the performance of, and poses safety threats for, infrastructure both on the ground and in the air. Previously, rationally designed superhydrophobic surfaces have demonstrated some potential as a passive means to mitigate ice accretion; however, further studies on material solutions that reduce impalement and the contact time for impacting supercooled droplets (high viscosity) and can also repel droplets that freeze during surface contact are urgently needed. Here we demonstrate the collaborative effect of substrate flexibility and surface micro/nanotexture on enhancing both icephobicity and the repellency of viscous droplets (typical of supercooled water).

Detergency and Its Implications for Oil Emulsion Sieving and Separation.

Separating petroleum hydrocarbons from water is an important problem to address in order to mitigate the disastrous effects of hydrocarbons on aquatic ecosystems. A rational approach to address the problem of marine oil-water separation is to disperse the oil with the aid of surfactants in order to minimize the formation of large slicks at the water surface and to maximize the oil-water interfacial area. Here we investigate the fundamental wetting and transport behavior of such surfactant-stabilized droplets and the flow conditions necessary to perform sieving and separation of these stabilized emulsions.

Contactless Transport and Mixing of Liquids on Self-Sustained Sublimating Coatings.

Controlled handling of liquids and colloidal suspensions as they interact with surfaces, targeting a broad palette of related functionalities, is of great importance in science, technology, and nature. When small liquid volumes (drops on the order of microliters or nanoliters) need to be processed in microfluidic devices, contamination on the solid/liquid interface and loss of liquid due to adhesion on the transport channels are two very common problems that can significantly alter the process outcome, for example, the chemical reaction efficiency or the purity and the final concentration of a suspension. It is, therefore, no surprise that both levitation and minimal contact transport methods-including nonwetting surfaces-have been developed to minimize the interactions between liquids and surfaces.