Corrosion of metallic substrates is a problem for a variety of applications. Corrosion can be mitigated with the use of an electrically insulating coating protecting the substrate. Thick millimetric coatings, such as paints, are generally more corrosion-resistant when compared to nanoscale coatings. However, for thermal systems, thick coatings are undesirable due to the resulting decrease in the overall heat transfer stemming from the added coating thermal resistance. Hence, the development of ultrathin (<10 μm) coatings is of great interest. Ultrathin inorganic silicon dioxide (SiO2) coatings applied by sol–gel chemistries or chemical vapor deposition, as well as organic coatings such as Parylene C, have great anticorrosion performance due to their high dielectric breakdown and low moisture permeability. However, their application to arbitrarily shaped metals is difficult or expensive. Here, we develop a sol–gel solution capable of facile and controllable dip coating on arbitrary metals, resulting in a very smooth (<5 nm roughness), thin (∼3 μm), and conformal coating of dense SiO2. To benchmark our material, we compared the corrosion performance with in-house synthesized superhydrophobic aluminum and copper samples, Parylene C-coated substrates, and smooth hydrophobic surfaces functionalized with a hydrophobic self-assembled monolayer. For comparison with state-of-the-art commercial coatings, copper substrates were coated with an organo-ceramic SiO2 layer created by an elevated temperature and atmospheric pressure metal organic chemical vapor deposition process. To characterize corrosion performance, we electrochemically investigated the corrosion resistance of all samples through potentiodynamic polarization studies and electrochemical impedance spectroscopy. To benchmark the coating durability and to demonstrate scalability, we tested internally coated copper tubes in a custom-built corrosion flow loop to simulate realistic working conditions with shear and particulate saltwater flow. The sol–gel and Parylene C coatings demonstrated a 95% decrease in corrosion rate during electrochemical tests. Copper tube weight loss was reduced by 75% for the sol–gel SiO2-coated tubes when seawater was used as the corrosive fluid in the test loop. This work not only demonstrates scalable coating methodologies for applying ultrathin anticorrosion coatings but also develops mechanistic understanding of corrosion mechanisms on a variety of functional surfaces and substrates.

Fouling and accretion have negative impacts on a plethora of processes. To mitigate heterogeneous nucleation of a foulant, lowering the surface energy and reducing surface roughness are desired. Here, we develop a multilayer coating to mitigate solution-based heterogeneous fouling for internal flows. The first layer is a sol–gel silicon dioxide (SiO2) coating, which acts as a corrosion barrier, creates the surface chemistry needed for covalent bonding of the slippery omniphobic covalently attached liquid (SOCAL), and ensures an atomically smooth (<1 nm) interface. The second layer bonded to SiO2 is SOCAL, which further reduces the nucleation rate due to its low surface energy (<12 mJ/m2). The presence of a consistent sol–gel SiO2 base coating to bind to the SOCAL enables application to various metallic substrates. The coating is solid, making it more durable when compared to alternative slippery liquid-infused surfaces (LIS) that suffer from lubricant loss. To demonstrate performance and scalability, we apply our coating to the internal walls of aluminum (Al) tubing and test its fouling performance in a flow-fouling setup with single-phase flow of synthetic seawater. The seawater consists of saturated calcium sulfide (CaSO4), and fouling is characterized in both laminar and turbulent flow regimes (Reynolds numbers 1030 to 9300). Our coating demonstrated a reduction in salt scale fouling by 95% when compared to uncoated Al tubes. Furthermore, we show our coating to withstand turbulent flow conditions, mechanical abrasion loading, and corrosive environments for durations much longer than LIS. Our work demonstrates a coating methodology applicable to a variety of metal substrates and internal passages to achieve antifouling in single-phase flows.

Recent advancements in surface nanoengineering have spurred intense interests in their implementation for enhancing condensation heat transfer. When appropriately designed, nanoengineered surfaces not only lead to highly efficient transport mechanisms not achievable with conventional dropwise condensation, they also demonstrate the possibility of augmenting condensation of low surface tension fluids widely used in industry. These advantages are further enhanced by the development of highly scalable nanofabrication methods, which enable the potential transition from laboratory-scale prototypes to real-world industrial applications. In this review, we discuss the progress, opportunities, and challenges of enhancing condensation heat and mass transfer with nanoengineered surfaces. This article provides an overview of the recent developments in micro/nanoscale coating and structure fabrication techniques and performs a thorough comparison of their condensation performance, elucidating the complex interfacial transport mechanism involved. Surface structuring methods that are durable, scalable and low-cost are essential attributes for large-scale industrial implementation. Here, the methods used to improve surface durability and demonstrations of nanostructure-enhanced meter-scale condensers are presented. Limitations are discussed and the potential techniques to overcome these challenges are summarized. Given the recent development of metal additive manufacturing technology and its growing relevance in manufacturing processes, we end this review by providing our perspectives on the opportunities in enabling surface nanostructuring of metal additive manufactured materials and the potential of nanometric-millimetric co-design optimization for the development of next-generation additively manufactured condensers.

Dropwise condensation represents the upper limit of thermal transport efficiency for liquid-to-vapor phase transition. A century of research has focused on promoting dropwise condensation by attempting to overcome limitations associated with thermal resistance and poor surface-modifier durability. Here, we show that condensation in a microscale gap formed by surfaces having a wetting contrast can overcome these limitations. Spontaneous out-of-plane condensate transfer between the contrasting parallel surfaces decouples the nanoscale nucleation behavior, droplet growth dynamics, and shedding processes to enable minimization of thermal resistance and elimination of surface modification. Experiments on pure steam combined with theoretical analysis and numerical simulation confirm the breaking of intrinsic limits to classical condensation and demonstrate a gap-dependent heat-transfer coefficient with up to 240% enhancement compared to dropwise condensation. Our study presents a promising mechanism and technology for compact energy and water applications where high, tunable, gravityindependent, and durable phase-change heat transfer is required.

The rapid anthropomorphic emission of greenhouse gases is contributing to global climate change, resulting in the increased frequency of extreme weather events, including unexpected snow, frost, and ice accretion in warmer regions that typically do not encounter these conditions. Adverse weather events create challenges for energy systems such as wind turbines and photovoltaics. To maintain energy efficiently and operational fidelity, snow, frost, and ice need to be removed efficiently and rapidly. State‐of‐the‐art removal methods are energy‐intensive (energy density > 30 J cm−2) and slow (>1 min). Here, pulsed Joule heating is developed on transparent self‐cleaning interfaces, demonstrating interfacial desnowing, defrosting, and deicing with energy efficiency (energy density < 10 J cm−2) and rapidity (≈1 s) beyond what is currently available. The transparency and self‐cleaning are tailored to remove both snow and dust while ensuring minimal interference with optical light absorption. It is experimentally demonstrated a multi‐functional coating material on a commercial photovoltaic cell, demonstrating efficient energy generation recovery and rapid ice/snow removal with minimal energy consumption. Through the elimination of accretion, this technology can potentially widen the applicability of photovoltaics and wind technologies to globally promising locations, potentially further reducing greenhouse gas emissions and global climate change.

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Metal additive manufacturing (AM) enables unparalleled design freedom for the development of optimized devices in a plethora of applications. The requirement for the use of nonconventional aluminum alloys such as AlSi10Mg has made the rational micro/nanostructuring of metal AM challenging. Here, the techniques are developed and the fundamental mechanisms governing the micro/nanostructuring of AlSi10Mg, the most common metal AM material, are investigated. A surface structuring technique is rationally devised to form previously unexplored two-tier nanoscale architectures that enable remarkably low adhesion, excellent resilience to condensation flooding, and enhanced liquid-vapor phase transition. Using condensation as a demonstration framework, it is shown that the two-tier nanostructures achieve 6× higher heat transfer coefficient when compared to the best filmwise condensation. The study demonstrates that AM-enabled nanostructuring is optimal for confining droplets while reducing adhesion to facilitate droplet detachment. Extensive benchmarking with past reported data shows that the demonstrated heat transfer enhancement has not been achieved previously under high supersaturation conditions using conventional aluminum, further motivating the need for AM nanostructures. Finally, it has been demonstrated that the synergistic combination of wide AM design freedom and optimal AM nanostructuring method can provide an ultracompact condenser having excellent thermal performance and power density.

Novel processing phenomena coupled with various alloying materials used in metal additive manufacturing (AM) have opened opportunities for the development of previously unexplored micro-/nanostructures. A rationally devised structure nanofabrication strategy of AM surfaces that can tailor the interface morphology and chemistry has the potential for many applications. Here, through an understanding of grain formation mechanisms during AM, we develop a facile method for tuning micro-/nanostructures of one of the most used AM alloys and rationally optimize the morphology for applications requiring low surface adhesion. We demonstrate that optimized AM structures reduce the adhesion of impaling water droplets and significantly delay icing time. The structure can also be altered and optimized for antiflooding jumping-droplet condensation that exhibits significant enhancement in heat transfer performance in comparison to nanostructures formed on conventional Al alloys. In addition to demonstrating the potential of functionalized AM surfaces, this work also provides guidelines for surface-structuring optimization applicable to other AM metals.