Extreme Antiscaling Performance of Slippery Omniphobic Covalently Attached Liquids

Comparison of Anti-Icing, Antifouling, and Anticorrosion Performances of the Superhydrophobic and Lubricant-Infused Coatings Based on a Hollow-Structured Kapok Fiber

The superhydrophobic surface and slippery liquid-infused porous surface (SLIPS)/lubricant-infused surface (LIS) have attracted increasing attention owing to their multifunctionality. However, their practical applications face several problems such as complex and inefficient preparation technology, loss of lubricant, and fragile microstructures. Therefore, new strategies for preparing microstructures must be developed for constructing superhydrophobic and lubricant-infused coatings. Herein, a low-cost and high-efficiency method for developing superhydrophobic and lubricant-infused coatings based on in situ grown TiO2 on the surface of a hollow kapok fiber (KF) is reported. The anti-icing, antifouling, and anticorrosion performance of the superhydrophobic and lubricant-infused coatings are compared. The superhydrophobic coating reduces the formation and accumulation of ice. The lubricant-infused coating exhibits an extremely low ice adhesion strength and durable anti-icing properties. The superhydrophobic and lubricant-infused coatings show the outstanding antifouling property of diatom; the superhydrophobic surface exhibits superior stability over LIS without an external force field. The lubricant-infused coating shows excellent corrosion resistance and durability when immersed in a 3.5% NaCl solution. The superhydrophobic coating loses its protection as a result of the corrosion media permeating the metal substrate via the electrolytic cell and coating interface, and the lubricant-infused coating provides lasting corrosion resistance because of the lubricant filling into the interface. Although the superhydrophobic coating is fragile and the lubricant-infused coating will lose lubricant, this simple and convenient approach can be repeated to keep the coatings active. This study provides new inspiration for the fabrication of superhydrophobic surfaces and LIS based on natural products.

Transparent PDMS Surfaces with Covalently Attached Lubricants for Enhanced Anti-adhesion Performance

Liquid-like surfaces featuring slippery, omniphobic, covalently attached liquids (SOCALs) reduce unwanted adhesion by providing a molecularly smooth and slippery surface arising from the high mobility of the liquid chains. Such SOCALs are commonly prepared on hard substrates, such as glass, wafers, or metal oxides, despite the importance of nonpolar elastomeric substrates, such as polydimethylsiloxane (PDMS) in anti-fouling or nonstick applications. Compared to polar elastomers, hydrophobic PDMS elastomer activation and covalent functionalization are significantly more challenging, as PDMS tends to display fast hydrophobic recovery upon activation as well as superficial cracking. Through the extraction of excess PDMS oligomers and fine-tuning of plasma activation parameters, homogeneously functionalized PDMS with fluorinated polysiloxane brushes could be obtained while at the same time reducing crack formation. Polymer brush mobility was increased through the addition of a smaller molecular silane linker to exhibit enhanced dewetting properties and reduced substrate swelling compared to functionalizations featuring hydrocarbon functionalities. Linear polymer brushes were verified by thermogravimetric analysis. The optical properties of PDMS remained unaffected by the activation in high-frequency plasma but were impacted by low-frequency plasma. Drastic decreases in solid adhesion of not just complex contaminants but even ice could be shown in horizontal push tests, demonstrating the potential of SOCAL-functionalized PDMS surfaces for improved nonstick applications.

Unraveling the role of vaporization momentum in self-jumping dynamics of freezing supercooled droplets at reduced pressures

Supercooling of water complicates phase change dynamics, the understanding of which remains limited yet vital to energy-related and aerospace processes. Here, we investigate the freezing and jumping dynamics of supercooled water droplets on superhydrophobic surfaces, induced by a remarkable vaporization momentum, in a low-pressure environment. The vaporization momentum arises from the vaporization at droplet's free surface, progressed and intensified by recalescence, subsequently inducing droplet compression and finally self-jumping. By incorporating liquid-gas-solid phase changes involving vaporization, freezing recalescence, and liquid-solid interactions, we resolve the vaporization momentum and droplet dynamics, revealing a size-scaled jumping velocity and a nucleation-governed jumping direction. A droplet-size-defined regime map is established, distinguishing the vaporization-momentum-dominated self-jumping from evaporative drying and overpressure-initiated levitation, all induced by depressurization and vaporization. Our findings illuminate the role of supercooling and low-pressure mediated phase change in shaping fluid transport dynamics, with implications for passive anti-icing, advanced cooling, and climate physics.

Synergistic Benefits of Micro/Nanostructured Oil-Impregnated Surfaces in Reducing Fouling while Enhancing Heat Transfer

Liquid-liquid heat exchangers that operate in marine environments are susceptible to biofouling, which decreases the overall heat exchange between hot and cold liquids by increasing the conduction resistance. Recently, micro/nanostructured oil-impregnated surfaces have been shown to significantly reduce biofouling. However, their potential as a heat exchanger material has not been studied. Neither is it obvious since the oil used for impregnation increases the wall thickness and the associated conduction resistance. Here, by conducting extensive field and laboratory studies supported by theoretical modeling of heat transfer in oil-infused heat exchanger tubes, we report the synergistic benefits of micro/nanostructured oil-impregnated surfaces for reducing biofouling while maintaining good heat transfer. These benefits justify the use of lubricant-infused surfaces as heat exchanger materials, in particular in marine environments.

Advances and challenges in slippery covalently-attached liquid surfaces

Over the past decade, a new class of slippery, anti-adhesive surfaces known as slippery covalently-attached liquid surfaces (SCALS) has emerged, characterized by low values of contact angle hysteresis (CAH, less than 5°) with water and most solvents. Despite their nanoscale thickness (1 to 5 nm), SCALS exhibit behavior similar to lubricant-infused surfaces, including high droplet mobility and the ability to prevent icing, scaling, and fouling. To date, SCALS have primarily been obtained using grafted polydimethylsiloxane (PDMS), though there are also examples of polyethylene oxide (PEO), perfluorinated polyether (PFPE), and short-chain alkane SCALS. Importantly, the precise physico-chemical characteristics that enable ultra-low CAH are unknown, making rational design of these systems impossible. In this review, we conduct a quantitative and comparative analysis of reported values of CAH, molecular weight, grafting density, and layer thickness for a range of SCALS. We find that CAH does not scale monotonically with any reported parameter; instead, the CAH minimum is found at intermediate values. For PDMS, optimal behavior is observed at advancing contact angle of 106°, molecular weight between 2 and 10 kg mol^-1, and grafting density of around 0.5 nm^-2. CAH on SCALS is lowest for layers created from end-grafted chains and increases with the number of binding sites, and can generally be improved by increasing the chemical homogeneity of the surface through the capping of residual silanols. We review the existing literature on SCALS, including both synthetic and functional aspects of current preparative methods. The properties of reported SCALS are quantitatively analyzed, revealing trends in the existing data and highlighting areas for future experimental study.

Omniphobic liquid-like surfaces

Liquid-repellent surfaces, especially smooth solid surfaces with covalently grafted flexible polymer brushes or alkyl monolayers, are the focus of an expanding research area. Surface-tethered flexible species are highly mobile at room temperature, giving solid surfaces a unique liquid-like quality and unprecedented dynamical repellency towards various liquids regardless of their surface tension. Omniphobic liquid-like surfaces (LLSs) are a promising alternative to air-mediated superhydrophobic or superoleophobic surfaces and lubricant-mediated slippery surfaces, avoiding fabrication complexity and air/lubricant loss issues. More importantly, the liquid-like molecular layer controls many important interface properties, such as slip, friction and adhesion, which may enable novel functions and applications that are inaccessible with conventional solid coatings. In this Review, we introduce LLSs and their inherent dynamic omniphobic mechanisms. Particular emphasis is given to the fundamental principles of surface design and the consequences of the liquid-like nature for task-specific applications. We also provide an overview of the key challenges and opportunities for omniphobic LLSs.

Polysiloxane-Based Liquid-like Layers for Reducing Polymer and Wax Fouling

Surface fouling occurs when undesired matter adheres and accumulates on a surface, resulting in a decrease or loss of functionality. Polymer and wax fouling can cause costly blockages to crude oil pipelines, clog jet fuel injectors, foul chemical reaction vessels, and significantly decrease the efficiency of heat exchangers. Fouling occurs in many forms but can be segmented based on adherent size, modulus, and chemical functionality. Depending on the foulant, surface design strategies can vary greatly. Few strategies exist to prevent the buildup of wax and polymers on surfaces. In this report, we investigate the potential of highly disordered, siloxane liquid-like layers as a strategy for reducing wax and polymer deposition. In our tests, it was found that the liquid-like layers developed here were able to reduce postadsorption roughness for polymer and wax by as much as 35- and 47-fold, respectively, when compared to the control. SFG was utilized to investigate the molecular-level interfacial properties for each of the modified surfaces to help understand the antifouling mechanism. The data showed that the likely higher grafting density and a large degree of random conformational freedom at the liquid-surface interface make the developed siloxane-covered surfaces energetically unfavorable for polymer and wax accretion.

Designing Non-Textured, All-Solid, Slippery Hydrophilic Surfaces

Slippery surfaces are sought after due to their wide range of applications in self-cleaning, drag reduction, fouling-resistance, enhanced condensation, biomedical implants etc. Recently, non-textured, all-solid, slippery surfaces have gained significant attention because of their advantages over super-repellent surfaces and lubricant-infused surfaces. Currently, almost all non-textured, all-solid, slippery surfaces are hydrophobic. In this work, we elucidate the systematic design of non-textured, all-solid, slippery hydrophilic (SLIC) surfaces by covalently grafting polyethylene glycol (PEG) brushes to smooth substrates. Furthermore, we postulate a plateau in slipperiness above a critical grafting density, which occurs when the tethered brush size is equal to the inter-tether distance. Our SLIC surfaces demonstrate exceptional performance in condensation and fouling-resistance compared to non-slippery hydrophilic surfaces and slippery hydrophobic surfaces. Based on these results, SLIC surfaces constitute an emerging class of surfaces with the potential to benefit multiple technological landscapes ranging from thermofluidics to biofluidics.

Fresnel Diffraction Strategy Enables the Fabrication of Flexible Superomniphobic Surfaces

Doubly re-entrant surfaces inspired by springtails exhibit excellent repellency to low-surface-tension liquid. However, the flexible doubly re-entrant surfaces are difficult to fabricate, especially for the overhang of the structure. Herein, we demonstrate a simple Fresnel aperture diffraction modulation strategy in microscale lithography coupled with a molding process to obtain the flexible doubly re-entrant superomniphobic surfaces with nanoscale overhangs. The negative nanoscale overhang features were formed in a single-layer photoresist due to the fine-modulation of the optical intensity fluctuation of the Fresnel aperture diffraction. The as-prepared flexible non-fluorinated polydimethylsiloxane (PDMS) doubly re-entrant microstructure based on the Fresnel aperture diffraction (D-BF) surface (without any additional treatments) could repel ethanol droplets (21.8 mN m^-1) in the Cassie-Baxter state. The robust nanoscale overhangs obtained by the molding process enable the maximum breakthrough pressure for the low-surface-tension ethanol droplets on the D-BF surfaces up to about 230 Pa, allowing ethanol liquids with Weber numbers up to 8.7 to fully bounce off. The fabricated non-fluorinated D-BF superomniphobic surface maintains outstanding liquid repellency after the surface wettability modification and deformation test.

Nature-Inspired High Temperature Scale-Resistant Slippery Lubricant-Induced Porous Surfaces (HTS-SLIPS)

Scale formation is a longstanding and unresolved problem in a number of fields, including power production, petroleum exploration, thermal desalination, and construction. Herein, a high-temperature scale-resistant slippery lubricant-induced surface (HTS-SLIPS) is developed by one-step electrodeposition and lubricant infusion. The fractal cauliflower-like morphology with lubricant oil is conducive to forming an ultralow contact angle hysteresis of ≈1°. The 10-d real-world boiling trial indicates that by replacing the uncoated surface with HTS-SLIPS, the reduction in scale mass is greater than 200% because of the low surface free energy (4.3 mJ m^-2 ) and outstanding smoothness (R_a  = 41 ± 8 nm) of HTS-SLIPS. Thanks to the scale retardation, the bubble departure frequency of HTS-SLIPS is eightfold higher than that of uncoated surfaces, signifying superior heat transfer efficiency. In these demonstrations, HTS-SLIPS coated spiral tube exhibits better flowability and lower pressure drop than the uncoated one. In addition, favorable compatibility between HTS-SLIPS and mechanical vibration is experimentally verified to strengthen the descaling of SLIPS synergistically. It is anticipated that the simple and scalable coating fabrication approach will be applicable in numerous industrial high-temperature processes where scale formation is encountered.

Sustainable scale resistance on a bioinspired synergistic microspine coating with a collectible liquid barrier

Scale deposition, especially in the petroleum industry, has always been a serious issue because of its potential safety hazards and huge economic cost. However, conventional scale-resistant strategies based on mechanical descaling and chemical detergents can't feed the urgent demand for energy saving and environmental protection. Herein, we report a bioinspired long-term oil collectible mask (BLOCK)-a microspine coating with the synergistic effect of anti-adhesion and oil collection, displaying sustainable scale resistance towards oilfield-produced water. Inspired by pitcher plants, the oil layer as a liquid barrier inhibits scale deposition by changing the underwater scaling micro-environment from liquid/solid/solid to a liquid/solid/liquid triphase system. Oil droplets are collected by cacti-inspired microspines to enhance oil layer stability. Compared with stainless steel, the BLOCK coating shows ca. 98% reduction even after 35 days in artificial produced water. This strategy could be utilized to design integrated functional materials for conquering complex environments such as oil recovery and transportation.

One-Step Fabrication of Flexible Bioinspired Superomniphobic Surfaces

Flexible superomniphobic doubly re-entrant (Dual-T) microstructures inspired by springtails have attracted growing attention due to their excellent liquid-repellent properties. However, the simple and practical manufacturing processes of the flexible Dual-T microstructures are urgently needed. Here, we proposed a one-step molding process coupled with the lithography technique to fabricate the elastomeric polydimethylsiloxane (PDMS) Dual-T microstructure surfaces with high uniformity. The angle between the downward overhang and the horizontal direction could reach 90° (vertical overhang). The flexible superomniphobic Dual-T microstructure surfaces, without fluorination treatment and physical treatments, could repel liquids with a surface tension lower than 20 mN m^-1 in the Cassie-Baxter state. Owing to the excellent robustness of the one-step molding downward overhanging, the max breakthrough pressure of this surface could reach up to 164.3 Pa for ethanol droplets. Furthermore, the flexible superomniphobic Dual-T surface allowed impinging ethanol droplets to completely rebound at the Weber number up to 7.1 with an impact velocity of ∼0.32 m s^-1. The Dual-T microstructure surface maintained excellent superomniphobicity even after surface oxygen plasma treatment and exhibited excellent structural robustness and recoverability to various large mechanical deformations.

Polymer brush-based nanostructures: from surface self-assembly to surface co-assembly

Surface structures play an important role in the practical applications of materials. The synthesis of polymer brushes on a solid surface has emerged as an effective tool for tuning surface properties. The fabrication of polymer brush-based surface nanostructures has greatly facilitated the development of materials with unique surface properties. In this review article, synthetic methods used in the synthesis of polymer brushes, and self-assembly approaches applied in the fabrication of surface nanostructures including self-assembly of polymer brushes, co-assembly of polymer brushes and "free" block copolymer chains, and polymerization induced surface self-assembly, are reviewed. It is demonstrated that polymer brush-based surface nanostructures, including spherical surface micelles, wormlike surface structures, layered structures and surface vesicles, can be fabricated. Meanwhile, the challenges in the synthesis and applications of the surface nanostructures are discussed. This review is expected to be helpful for understanding the principles, methods and applications of polymer brush-based surface nanostructures.

Combination of Universal Chemical Deposition and Unique Liquid Etching for the Design of Superhydrophobic Aramid Paper with Bioinspired Multiscale Hierarchical Dendritic Structure

It is urgent and significant for the further development of superhydrophobic materials to exploit a facile, low-cost, scalable, and eco-friendly method for the manufacture of superhydrophobic materials with self-cleaning, antifouling, directional transportation, and other characteristics. Herein, an outstanding superhydrophobic material composed of a flexible microconvex aramid paper substrate, micron-scale cone-shaped copper, micro-nanoscale dendritic copper oxide, and hydrophobic copper stearate film has been successfully constructed through delicate architectural design and a convenient preparation approach. Based on the microstructure evolution and composition analysis results, it is revealed that the cone-shaped copper was etched into a dendritic copper oxide structure step by step from the top to bottom and from the outside to inside in an alkaline liquid environment. Moreover, by virtue of the compositional features and structural characteristics, the constructed superhydrophobic material showcased a high contact angle (CA), low sliding angle (SA), high porosity, low surface free energy, and adhesion work. Meanwhile, the dendritic microstructure analysis, the calculation of solid-liquid interfacial tension, and the force analysis of water droplets jointly revealed the mechanism of the bounce and merged bounce of water droplets. Finally, this superhydrophobic material has the functions of self-cleaning, antifouling, and directional transportation, especially by controlling the deformation of the material to realize the transportation of water droplets in a specified direction.

Rapid and Robust Surface Treatment for Simultaneous Solid and Liquid Repellency

A wide range of liquid and solid contaminants can adhere to everyday functional surfaces and dramatically alter their performance. Numerous surface modification strategies have been developed that can reduce the fouling of some solids or repel certain liquids but are generally limited to specific contaminants or class of foulants. This is due to the typically distinct mechanisms that are employed to repel liquids vs solids. Here, we demonstrate a rapid and facile surface modification technique that yields a thin film of linear chain siloxane molecules covalently tethered to a surface. We investigate and characterize the liquid-like morphology of these surfaces in detail as the key contributing factor to their anti-fouling performance. This surface treatment is extremely durable and readily repels a broad range of liquids with varying surface tensions and polarities, including water, oils, organic solvents, and even fluorinated solvents. Additionally, the flexible, liquid-like nature of these surfaces enables interfacial slippage, which dramatically reduces adhesion to various types of solids, including ice, wax, calcined gypsum, and cyanoacrylate adhesives, and also minimizes the nucleation of inorganic scale. The developed surfaces are durable and simple to fabricate, and they minimize fouling by both liquids and solids simultaneously.

Ultra-thin self-healing vitrimer coatings for durable hydrophobicity

Durable hydrophobic materials have attracted considerable interest in the last century. Currently, the most popular strategy to achieve hydrophobic coating durability is through the combination of a perfluoro-compound with a mechanically robust matrix to form a composite for coating protection. The matrix structure is typically large (thicker than 10 μm), difficult to scale to arbitrary materials, and incompatible with applications requiring nanoscale thickness such as heat transfer, water harvesting, and desalination. Here, we demonstrate durable hydrophobicity and superhydrophobicity with nanoscale-thick, perfluorinated compound-free polydimethylsiloxane vitrimers that are self-healing due to the exchange of network strands. The polydimethylsiloxane vitrimer thin film maintains excellent hydrophobicity and optical transparency after scratching, cutting, and indenting. We show that the polydimethylsiloxane vitrimer thin film can be deposited through scalable dip-coating on a variety of substrates. In contrast to previous work achieving thick durable hydrophobic coatings by passively stacking protective structures, this work presents a pathway to achieving ultra-thin (thinner than 100 nm) durable hydrophobic films.

Scalable Slippery Omniphobic Covalently Attached Liquid Coatings for Flow Fouling Reduction

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.

Innovative fouling-resistant materials for industrial heat exchangers: a review

Fouling of heat exchangers (HEs) has become a major concern across the industrial sector. Fouling is an omnipresent phenomenon but is particularly prevalent in the dairy, oil, and energy industries. Reduced energy performance that results from fouling represents significant operating loss in terms of both maintenance and impact on product quality and safety. In most industries, cleaning or replacing HEs are currently the only viable solutions for controlling fouling. This review examines the latest advances in the development of innovative materials and coatings for HEs that could mitigate the need for costly and frequent cleaning and potentially extend their operational life. To better understand the correlation between surface properties and fouling occurrence, we begin by providing an overview of the main mechanisms underlying fouling. We then present selected key strategies, which can differ considerably, for developing antifouling surfaces and conclude by discussing the current trends in the search for ideal materials for a range of applications. In our presentation of all these aspects, emphasis is given wherever possible to the potential transfer of these innovative surfaces from the laboratory to the three industries most concerned by HE fouling problems: food, petrochemicals, and energy production.

Design and applications of surfaces that control the accretion of matter

Surfaces that provide control over liquid, solid, or vapor accretion provide an evolutionary advantage to numerous plants, insects, and animals. Synthetic surfaces inspired by these natural surfaces can have a substantial impact on diverse commercial applications. Engineered liquid and solid repellent surfaces are often designed to impart control over a single state of matter, phase, or fouling length scale. However, surfaces used in diverse real-world applications need to effectively control the accrual of matter across multiple phases and fouling length scales. We discuss the surface design strategies aimed at controlling the accretion of different states of matter, particularly those that work across multiple length scales and different foulants. We also highlight notable applications, as well as challenges associated with these designer surfaces' scale-up and commercialization.

Dynamic Poly(dimethylsiloxane) Brush Coating Shows Even Better Antiscaling Capability than the Low-Surface-Energy Fluorocarbon Counterpart

Scale formation is a significant problem in a wide range of industries, including water treatment, food processing, power plants, and oilfield production. While surface modification provides a promising methodology to address this challenge, it has generally been believed that surface coatings with the lowest surface energy, such as fluorocarbon coatings, are most suitable for antiscaling applications. In contrast to this general knowledge, here we show that a liquid-like coating featuring highly mobile linear poly(dimethylsiloxane) (LPDMS) brush chains can bring an even better antiscaling performance than conventional perfluoroalkylsilane coatings, despite the fact that the former has much higher surface energy than the latter. We demonstrate that the LPDMS brush coating can more effectively inhibit heterogeneous nucleation of scale on a substrate compared with common perfluoroalkylsilane or alkylsilane coatings, and the dynamic liquid-like characteristic of the LPDMS brush coating is speculated to be responsible for its excellent nucleation inhibiting ability by reducing the affinity and effective interface interaction between the substrate and the scale nucleus. Our findings reveal the great prospect of using liquid-like coating to replace environmentally hazardous fluorine-containing organic ones as a green and cost-effective solution to address the scale problem with enhanced antiscaling performance.

Lubricant-Infused Surfaces for Low-Surface-Tension Fluids: The Extent of Lubricant Miscibility

Lubricant-infused surfaces (LISs) and slippery liquid-infused porous surfaces (SLIPSs) have shown remarkable success in repelling low-surface-tension fluids. The atomically smooth, defect-free slippery surface leads to reduced droplet pinning and omniphobicity. However, the presence of a lubricant introduces liquid-liquid interactions with the working fluid. The commonly utilized lubricants for LISs and SLIPSs, although immiscible with water, show various degrees of miscibility with organic polar and nonpolar working fluids. Here, we rigorously investigate the extent of miscibility by considering a wide range of liquid-vapor surface tensions (12-73 mN/m) and different categories of lubricants having a range of viscosities (5-2700 cSt). Using high-fidelity analytical chemistry techniques including X-ray photoelectron spectroscopy, nuclear magnetic resonance, thermogravimetric analysis, and two-dimensional gas chromatography, we quantify lubricant miscibility to parts per billion accuracy. Furthermore, we quantify lubricant concentrations in the collected condensate obtained from prolonged condensation experiments with ethanol and hexane to delineate mixing and shear-based lubricant drainage mechanisms and to predict the lifetime of LISs and SLIPSs. Our work not only elucidates the effect of lubricant properties on miscibility with various fluids but also develops guidelines for developing stable and robust LISs and SLIPSs.

Controlled Integration of Interconnected Pores under Polymeric Surfaces for Low Adhesion and Antiscaling Performance

Low-adhesive surfaces have been highlighted due to the potentials to mitigate fouling issues by preventing unwanted substances from adhering. Realizing superhydrophobicity with 3D surface structures/chemical modifiers or fabricating lubricant-assisted slippery surfaces has been demonstrated to realize low-adhesive surfaces. However, they still need to overcome the transition to Wenzel from Cassie states of droplets on 3D surface structures or the lubricant depletion issues of slippery surfaces for sustainable operations. Herein, we report the fabrication of low-adhesive polymeric surfaces, neither assisted by 3D surface structures/chemical modifiers nor lubricants, which is realized by embedding the interconnected pore networks underneath the top smooth surface using a water steaming method. The fabricated silicone surfaces exhibit low-adhesive properties due to the stress concentration effects generated by the subsurface-structured pores, favorable for easy detachment of the adherent from the surface. Our platform can be exploited to lower adhesion of superhydrophilic surfaces or to achieve ultralow-adhesive properties upon combination with superhydrophobicity. Finally, scale precipitation tests reveal 4.2 times lower scale accumulation of our low-adhesive polymeric surfaces than that in control samples.

Scalable Corrosion-Resistant Coatings for Thermal Applications

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.

High-Throughput Stamping of Hybrid Functional Surfaces

Hydrophobic-hydrophilic hybrid surfaces, sometimes termed biphilic surfaces, have shown potential to enhance condensation and boiling heat transfer, anti-icing, and fog harvesting performance. However, state of art techniques to develop these surfaces have limited substrate selection, poor scalability, and lengthy and costly fabrication methods. Here, we develop a simple, scalable, and rapid stamping technique for hybrid surfaces with spatially controlled wettability. To enable stamping, rationally designed and prefabricated polydimethylsiloxane (PDMS) stamps, which are reusable and independent of the substrate and functional coating, were used. To demonstrate the stamping technique, we used silicon wafer, copper, and aluminum substrates functionalized with a variety of hydrophobic chemistries including heptadecafluorodecyltrimethoxy-silane, octafluorocyclobutane, and slippery omniphobic covalently attached liquids. Condensation experiments and microgoniometric characterization demonstrated that the stamped surfaces have global hydrophobicity or superhydrophobicity with localized hydrophilicity (spots) enabled by local removal of the functional coating during stamping. Stamped surfaces with superhydrophobic backgrounds and hydrophilic spots demonstrated stable coalescence induced droplet jumping. Compared to conventional techniques, our stamping method has comparable prototyping cost with reduced manufacturing time scale and cost. Our work not only presents design guidelines for the development of scalable hybrid surfaces for the study of phase change phenomena, it develops a scalable and rapid stamping protocol for the cost-effective manufacture of next-generation hybrid wettability surfaces.