Passive Coatings Research Articles

High purity aluminum in its bulk form has intrinsicallyhigh reflectancein the far-ultraviolet (FUV) regime and finds utility in astrophysicalinstrumentation applications. However, bulk Al oxidizes rapidly inthe atmosphere, and its native oxide strongly absorbs and severelydegrades the observed FUV properties relative to bare Al. Varioustechniques have been investigated to produce coatings that inhibitaluminum oxide formation and lead to high FUV mirror reflectance.This work examines the development and use of a uniquely modified,hybrid plasma-enhanced atomic layer deposition (PEALD) system to passivatealuminum mirrors with metal fluoride films. This system combines twoplasma sources in a commercial atomic layer deposition (ALD) reactor.The first is a conventional inductively coupled plasma (ICP) sourceoperated as a remote plasma, and the second is an electron beam (e-beam)driven plasma near the mirror surface. To establish the operatingconditions for the in situ e-beam plasma source, the effects of samplegrounding, SF6/Ar flow, and sample temperature on resultingAlF3 films were investigated. Optimal operating conditionsproduced mirrors with excellent FUV reflectivity, 92% at 121 nm and42% at 103 nm wavelengths, which is comparable to state-of-the-artAlF3-based passivation coatings and matches that of previouslyreported ex situ e-beam plasma-processed mirrors. This optimized insitu e-beam process, along with XeF2 passivation, is thenexplored to produce a clean seed layer (unoxidized Al surface) forsubsequent PEALD of AlF3. Both approaches are demonstratedas valid pretreatments before PEALD of AlF3, showing apromising pathway for the deposition of other fluoride-based layers,such as MgF2 or LiF, with ALD or PEALD.

In-flight icing presents a critical safety hazard for unmanned aerial vehicles (UAVs), resulting in ice accumulation on propeller surfaces that compromise UAV aerodynamic performance and operational integrity. While hybrid anti-/de-icing systems (i.e., combining active heating with passive superhydrophobic coatings) have been developed recently to efficiently address this challenge, conventional active heating sub-systems utilized in the hybrid anti-/de-icing systems face significant limitations when applied to curved geometries of UAV propeller blades. This necessitates the development of innovative self-heating superhydrophobic coatings that can conform perfectly to complex surface topographies. Carbon-based electrothermal coatings, particularly those incorporating graphite and carbon nanotubes, represent a promising approach for ice mitigation applications. This study presents a comprehensive experimental investigation into the development and optimization of a novel self-heating carbon nanotube (CNT)-based superhydrophobic coating specifically designed for UAV icing mitigation. The coating’s anti-/de-icing efficacy was evaluated through a comprehensive experimental campaign conducted on a rotating UAV propeller under typical glaze icing conditions within an advanced icing research tunnel facility. The durability of the coating was also examined in a rain erosion test rig under the continuous high-speed impingement of water droplets. Experimental results demonstrate the successful application of the proposed sprayable self-heating superhydrophobic coating in UAV icing mitigation, providing valuable insights into the viability of CNT-based electrothermal coatings for practical UAV icing protection. This work contributes to the advancement of icing protection technologies for un-manned aerial systems operating in adverse weather conditions.

All‐solid‐state batteries offer enhanced safety and energy density compared to conventional systems, but their performance critically depends on the microstructure of the composite cathode. Sulfide‐based solid electrolytes (SEs) are promising Li‐ion conductors, yet they degrade upon contact with cathode active materials, necessitating passivating coatings that impair electronic conductivity. Herein, an electron‐conducting matrix of SE and 4 wt% conductive additive (C65) at the percolation threshold is introduced to minimize side reactions. The effect of coated active material fraction on ionic and electronic conductivities is investigated using electrochemical impedance spectroscopy, rate tests, 2D/3D imaging, and numerical simulations. The results highlight the critical role of the electronically conductive network, which percolates at low CAM loadings, collapses at 50 wt% as C65 adheres to coated CAM surfaces—depleting the bulk network—and recovers at higher loadings via percolation of C65‐coated particles, demonstrating the essential function of C65. At 70 wt%, a robust network yields 99.8 mAh g−1 at C/10 and 84% retention at C/5; at 80 wt%, ionic conductivity diminishes despite improved electronic transport, reducing rate performance. These findings underscore the need to balance ionic and electronic pathways and provide new insights into the role of additives in composite cathodes.

Polymer ligands offer precise control over the surface properties of metal nanoparticles, such as accessibility and hydrophobicity, to enhance their catalytic efficiency. In this talk, I will discuss our recent studies on the effects of two distinct types of polymer ligands on CO2 electroreduction catalyzed by metal nanocatalysts (Au and Pd). The first group is hydrophobic polystyrene terminated with N-heterocyclic carbenes (NHCs). Compared to conventional ligands, such as thiols and amines, these hydrophobic polymer ligands significantly improve CO2 reduction selectivity over proton reduction. Acting as passive coatings on metal nanocatalyst surfaces, NHC-terminated polymers regulate substrate accessibility through enhancing CO2 concentration and clustering H2O, and therefore, Faradaic efficiency for CO2 reduction. Additionally, the stability of metal-NHC bonds under reductive potential can prevent nanocatalyst aggregation, a critical factor for practical applications. The second group includes fluorinated polymer zwitterions, which combine hydrophilic ionic phosphorylcholine with hydrophobic fluorinated moieties. These polyzwitterions form fractal structures with mixed branched cylinders on nanocatalyst surfaces. Unlike hydrophobic polystyrene, polyzwitterions allow extensive water permeation as chain structures through hydration or ion-dipole interactions. Both types of polymer ligands create a significant channeling effect for CO2, enhancing its reduction selectivity. Our findings provide valuable guidelines for improving the catalytic efficiency and stability of metal nanocatalysts for CO2 electroreduction and other cathodic electroreduction reactions.

Photothermal hydrophobic surfaces offer a promising solution for mitigating ice hazards under low-temperature, high-humidity conditions via solar-driven de-icing. However, surface contamination can compromise photothermal efficiency, while fabric-applicable coatings must also provide flexibility, breathability, durability, and safe thermal regulation (≈50°C). Current systems require further optimization to balance these demands for practical use. Here, a nanorod-embedded photothermal strategy is presented that integrates superhydrophobicity, anti-icing, and de-icing capabilities with environmental robustness in fabrics. The composite comprises a polypyrrole-loaded cellulose nanocrystal inner layer for photothermal conversion and a fluoroalkyl silane-modified silica top layer for superhydrophobicity. The synergy between hierarchical micro-nano roughness and photothermal activation enables an "external repellency, internal heating" mechanism, effectively overcoming the limitations of passive coatings. This dual-functional architecture achieves a solar absorption rate of 97.2% and reaches 53.1°C under 100mWcm⁻2 irradiation, while remaining safe for human contact and maintaining breathability (moisture permeability: 6.86 × 103g·m⁻2·d⁻¹). It delays freezing by 417s at -15°C and reduces the melting time of an ice cube by 53.2% under 1-sun illumination. The fabric exhibits appreciable chemical stability, abrasion resistance, flexibility, and robustness under extreme conditions, ensuring long-term performance. This work offers a scalable solution for outdoor and personal protective equipment in cold environments.

Studies that involve mitigating aerodynamic noise in rotating components such as rotors of wind turbines or propellers of Unmanned Aerial Vehicles have gained immense interest in the research community over the last few years. The present study explores noise mitigation potential of passive compliant coatings through Computational Aeroacoustics Analysis (CAA) and experimentation through wind tunnel testing. CAA was performed on a flat plate for a chord-based Reynolds number of Re c = 460,000 using the SST k-ω Improved Delayed Detached Eddy Simulation and the Ffowcs Williams and Hawkings acoustic analogy. Trailing edge (TE) noise was accurately predicted from 750 to 7000 Hz. Noise results were compared with cases where compliant coatings with different material properties are applied onto flat plate. It was observed that coating-1 (Dow Corning Silastic S-2) may increase TE noise by 10 – 15 dB/Hz throughout the frequency range of interest, with an increase in Overall Sound Pressure Level (OASPL) by 2.89 dB. Whereas coating-2 (Dow Corning Sylgard 184) shifted energy content in TE noise to a lower frequency range and reduced noise by 2 – 4 dB/Hz from 600 to 1575 Hz. Additionally, it resulted in a 1.85 dB reduction in OASPL, thus demonstrating that choice of coating material’s viscoelastic properties plays a crucial role in its ability to mitigate TE noise. Further, noise measurements recorded inside a closed loop wind tunnel revealed a farfield noise reduction of 2 – 4 dB/Hz from 253 to 1367 Hz, with a corresponding 3.23 dB reduction in OASPL. These results demonstrate the favorable effects of compliant coatings on TE noise.

This article shows the fabrication, electrical characterization and modeling of SiO/SiO2 layers for passivation of Indoor MOS solar cells operating in inversion mode. After the electrical characterization of Al/SiO/SiO2/p-Si structures as MOS (Metal-Oxide-Semiconductor) capacitors, the effective positive charge in the SiO layer was obtained from the Capacitance x Voltage (CV) characteristics. This positive charge will promote the formation of the depletion mode at the exposed regions SiO/SiO2/p-Si around the metal grid that is the gate of Al/SiO2/p-Si solar cells. The tunneling process through the Al/SiO2/p-Si structure was modeled as a lumped parallel conductance Gp and substrate and contact resistance as a lumped series resistance RS. On the other hand, the effective positive charge of the SiO layer, ~180-195 nm thick, was obtained from the flat band voltage (VFB) shift since the Al/SiO/SiO2/p-Si structure is not influenced by Gp and RS due the high thickness of the SiO/SiO2 dielectrics (~180-195 nm + 1.8 nm or 4.0 nm). As a result, the effective positive charge density from the Al/SiO/SiO2/p-Si structure was 1.24x1012/cm2 and the accumulation regime was modelled by an approximately constant parallel conductance Gp of ~20mS in the Al/SiO2/p-Si structure. Furthermore, an experimental improvement of the conversion yield of light to electricity was observed for SiO/SiO2 passivation layers on indoor MOS solar cells after annealing at 300 oC during 30 min in N2 + H2(10%). Current density x voltage curves (JxV), using solar simulator of 100 mW/cm2 (1 sun) or indoor light illumination of 5.0 mW/cm2 (LED) or 11.7 mW/cm2 (halogen lamp) at 25oC on the sample surface, were extracted for ~180-195 nm SiO thick and the main electrical parameters were obtained for the MOS photovoltaic cells such as the short circuit current (Jsc), the open circuit voltage (Voc) and energy conversion efficiency (η). As a result, a significant increase of the in-door energy conversion efficiency was obtained for the MOS solar cell recovered with SiO layer illuminated with 5.0 mW/cm2 (LED) or 11.7 mW/cm2 (halogen lamp), this is to say, η ≈ 1.0% and η ≈ 5.5%, respectively, which was explained by an increase of the effective positive charges in the SiO layers after annealing.

Accurate defect passivation is critical for characterizing intrinsic carrier lifetimes in semiconductor materials, as surface defects induce recombination centers that distort lifetime measurements. While conventional passivation coatings (e.g., SiO2, SiNx, Al2O3, a‐Si:H(i)) require complex high‐temperature/vacuum processes, this work proposes an innovative low‐temperature solution‐based approach utilizing organic passivation materials. The Nafion/Polystyrene sulfonic acid‐based system achieves electrochemical interaction between sulfonic groups (SO3−) and silicon dangling bonds, forming interfacial silicon oxides that effectively neutralize trap states. This versatile technique accommodates multiple deposition methods—including spin coating, blade coating, spraying, and brush coating—without vacuum requirements. Demonstrated for silicon, CuInxGa(1‐x)Se2, and perovskite thin films, the solution‐processed passivation enables rapid, large‐area characterization while maintaining exceptional stability. The combined advantages of ambient processing conditions, material compatibility, and scalability position this methodology as a cost‐effective industrial solution for high‐throughput semiconductor evaluation.

Passive anti-icing coatings are a promising solution to the dangers of ice accumulation on surfaces. We studied plain polydimethylsiloxane (PDMS) and (commercially available) NuSil R-2180 coatings alongside PDMS coatings infused with two molecular weights and percentages of silicone oil. The icephobicity of the coatings was measured via ice adhesion strength and freezing time. 100 repeated deicing cycles were performed, which showed the oil-infused coatings had consistently lower ice adhesion strengths (∼10-20 kPa) than nonoil-infused coatings (∼100 kPa). The nonoil-infused coatings also showed increasing instances of exceptionally high ice adhesion strengths (>650 kPa), reducing the reliability of their icephobicity long-term. Oil infusion did not negatively affect the freezing time of the coatings, and despite decreases in freezing time after 100 deicing cycles, the coatings maintained an improvement compared to uncoated aluminum. Analysis showed adhesion strength is more strongly affected by shear modulus than coating thickness, work of adhesion, or static water contact angle. Wear from the deicing cycles was minimal. Any wear that was present did not significantly affect icephobicity. Oil infusion of elastomer coatings reduces ice accumulation on surfaces and provides a more reliable long-term solution for anti-icing applications.

This work aims to develop multilayer coating systems to enhance the long-term corrosion performance of aluminium-based components. The systems consists of a high-performance ceramic matrix that provides physical barrier protection, and a topcoat layer containing encapsulated Ce-based inhibitors, offering active corrosion protection through controlled released mechanisms. Two types of nanoparticles were used for the encapsulation, zeolite and halloysite nanotubes, each with different release triggers and kinetics. Multifunctional coatings demonstrated a superior corrosion performance compared to the passive unmodified coatings. Inhibitor release from the nanoparticles was triggered by ionic exchange processes and changes in pH associated with corrosion activity.

Unveiling the potential of dual-extrinsic/intrinsic self-healing lignin-based coatings for anticorrosion applications

Preparation of active–passive anticorrosion antistatic epoxy nanocomposite coatings loaded with CeO2, CeO2@C, and CHS particles

The acid pollution produced from coal gangue piles is a global environmental problem. Terminal technologies, such as neutralization, precipitation, adsorption, ion exchange, membrane technology, biological treatment, and electrochemistry, have been developed for acid mine drainage (AMD) treatment. These technologies for treating pollutants with low concentrations over a long period of time in coal gangue piles appear to be costly and unsustainable. Conversely, in situ remediation appears to be more cost-effective and material-efficient, but it is a challenge that coal producing countries need to solve urgently. The primary prerequisite for preventing acidic pollutants is to clarify the oxidation mechanisms of coal gangue, which can be summarized as four aspects: pyrite oxidation, microbial action, low-temperature oxidation of coal, and free radical action. The two key factors of oxidation are pyrite and coal, and the four necessary conditions are water, oxygen, microorganisms, and free radicals. The current in situ remediation technologies mainly focus on one or more of the four necessary conditions, forming mixed co-disposal, coverage barriers, passivation coatings, bactericides, coal oxidation inhibitors, microorganisms, plants, and so on. It is necessary to scientifically and systematically carry out in situ remediation coupled with various technologies based on oxidation mechanisms when carrying out large-scale restoration and treatment of acidic coal gangue piles.

The development of scalable and passive coatings that can adapt to seasonal temperature changes while maintaining superhydrophobic self-cleaning functions is crucial for their practical applications. However, the incorporation of passive cooling and heating functions with conflicting optical properties in a superhydrophobic coating is still challenging. Herein, an all-in-one coating inspired by the hierarchical structure of a lotus leaf that combines surface wettability, optical structure, and temperature self-adaptation is obtained through a simple one-step phase separation process. This coating exhibits an asymmetrical gradient structure with surface-embedded hydrophobic SiO2 particles and subsurface thermochromic microcapsules within vertically distributed hierarchical porous structures. Moreover, the coating imparts superhydrophobicity, high infrared emission, and thermo-switchable sunlight reflectivity, enabling autonomous transitions between radiative cooling and solar warming. The all-in-one coating prevents contamination and over-cooling caused by traditional radiative cooling materials, opening up new prospects for the large-scale manufacturing of intelligent thermoregulatory coatings.

Transparent passive cooling materials can cool targets environmentally without interfering with light transmission or visual information reception. They play a prominent role in solar cells and flexible display cooling. However, achieving potent transparent cooling remains challenging, because light transmission is accompanied by thermal energy. Here we propose to realize effective passive cooling in transparent materials via a microscale phase separation hydrogel film. The poly(N-isopropylacrylamide-co-acrylamide) hydrogel presents light transmittance of >96% and infrared emissivity as high as 95%. The microphase-separated structure affords a higher enthalpy of evaporation. The film is highly adhesive. In field applications, it reduces temperatures by 9.14 °C compared to those with uncovered photovoltaic panels and 7.68 °C compared to those for bare flexible light-emitting diode screens. Simulations indicate that energy savings of 32.76-51.65 MJ m-2 year-1 can be achieved in typical tropical monsoon climates and temperate continental climates. We expect this work to contribute to energy-efficient materials and a carbon-neutral society.

Ice shedding tests for the assessment of hybrid ice protection systems

Human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs) are a promising cell source for cardiac regenerative medicine and in vitro modeling. However, hPSC-CMs exhibit immature structural and functional properties compared with adult cardiomyocytes. Various electrical, mechanical, and biochemical cues have been applied to enhance hPSC-CM maturation but with limited success. In this work, we investigated the potential application of the semiconducting polymer poly{[N,N'-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5'-(2,2'-bithiophene)} (P(NDI2OD-T2)) as a light-sensitive material to stimulate hPSC-CMs optically. Our results indicated that P(NDI2OD-T2)-mediated photostimulation caused cell damage at irradiances applied long-term above 36 μW/mm2 and did not regulate cardiac monolayer beating (after maturation) at higher intensities applied in a transient fashion. However, we discovered that the cells grown on P(NDI2OD-T2)-coated substrates showed significantly enhanced expression of cardiomyocyte maturation markers in the absence of a light exposure stimulus. A combination of techniques, such as atomic force microscopy, scanning electron microscopy, and quartz crystal microbalance with dissipation monitoring, which we applied to investigate the interface of the cell with the n-type coating, revealed that P(NDI2OD-T2) impacted the nanostructure, adsorption, and viscoelasticity of the Matrigel coating used as a cell adhesion promoter matrix. This modified cellular microenvironment promoted the expression of cardiomyocyte maturation markers related to contraction, calcium handling, metabolism, and conduction. Overall, our findings demonstrate that conjugated polymers such as P(NDI2OD-T2) can be used as passive coatings to direct stem cell fate through interfacial engineering of cell growth substrates.

Self-regulated secretory materials for long-term icephobicity

Conventional gas plasma treatments are crucial for functionalizing materials in biomedical applications, but have limitations hindering their broader use. These methods require exposure to reactive media under vacuum conditions, rendering them unsuitable for substrates that demand aqueous environments, such as proteins and hydrogels. In addition, complex geometries are difficult to treat, necessitating extensive customization for each material and shape. To address these constraints, an innovative approach employing plasma polymer nanoparticles (PPN) as a versatile functionalization tool is proposed. PPN share similarities with traditional plasma polymer coatings (PPC) but offer unique advantages: compatibility with aqueous systems, the ability to modify complex geometries, and availability as off-the-shelf products. Robust immobilization of PPN on various substrates, including synthetic polymers, proteins, and complex hydrogel structures is demonstrated in this study. This results in substantial improvements in surface hydrophilicity. Materials functionalization with arginylglycylaspartic acid (RGD)-loaded PPN significantly enhances cell attachment, spreading, and substrate coverage on inert scaffolds compared to passive RGD coatings. Improved adhesion to complex geometries and subsequent differentiation following growth factor exposure is also demonstrated. This research introduces a novel substrate functionalization approach that mimics the outcomes of plasma coating technology but vastly expands its applicability, promising advancements in biomedical materials and devices.

Direct thrombin inhibiting coating for active coagulant management in extracorporeal circulation