Ultrathin Coatings Research Articles

Brush-Like Interface on Surface-Attached Hydrogels Repels Proteins and Bacteria.

Interfacing artificial materials with biological tissues remains a challenge. The direct contact of their surface with the biological milieu results in multiscale interactions, in which biomacromolecules adsorb and act as transducers mediating the interactions with cells and tissues. So far, only antifouling polymer brushes have been able to conceal the surface of synthetic materials. However, their complex synthesis has precluded their translation to applications. Here, it is shown that ultrathin surface-attached hydrogel coatings of N-(2-hydroxypropyl) methacrylamide (HPMA) and carboxybetaine methacrylamide (CBMAA) provide the same level of protection as brushes. In spite of being readily applicable, these coatings prevent the fouling from whole blood plasma and provide a barrier to the adhesion of Gram positive and negative bacteria. The analysis of the components of the surface free energy and nanoindentation experiments reveals that the excellent antifouling properties stem from the strong surface hydrophilicity and the presence of a brush-like structure at the water interface. Moreover, these coatings can be functionalized to achieve antimicrobial activity while remaining stealth and non-cytotoxic to eukaryotic cells. Such level of performance is previously only achieved with brushes. Thus, it is anticipated that this readily applicable strategy is a promising route to enhance the biocompatibility of real biomedical devices.

Vapor deposition of ultrathin hydrophilic polymer coatings enabling candle soot composite for highly sensitive humidity sensors

Candle soot (CS) is a desirable carbon nanomaterial for sensors owing to its highly porous nanostructure and large specific surface area. CS is advantageous in its low-cost and facile preparation compared to graphene and carbon nanotubes, but its pristine nanostructure is susceptible to collapse, hampering its application in electronic devices. This article reports conformal coating of nanoscale crosslinked hydrophilic polymer on CS film using initiated chemical vapor deposition, which well preserved the CS nanostructure and obtained nanoporous CS@polymer composites. Tuning coating thickness enabled composites with different morphologies and specific surface areas. Surprisingly, the humidity sensor made from composite with the lowest filling degree, thus largest specific surface area, showed relatively low sensitivity, which is likely due to its discontinuous structure, thus insufficient conductive channels. Composite sensor with optimum filling degree shows excellent sensing response of more than 103 with the linearity of R2 = 0.9400 within a broad relative humidity range from 11% to 96%. The composite sensor also exhibits outstanding sensing performance compared to literature with low hysteresis (3.00%), a satisfactory response time (28.69 s), and a fast recovery time (0.19 s). The composite sensor is fairly stable and durable even after 24 h soaking in water. Furthermore, embedding a humidity sensor into a face mask realizes real-time monitoring of human breath and cough, suggesting promising applications in respiratory monitoring.

Al alloy protection via ultra-thin ceramic coatings and different surface pretreatments

The efficiency of ultra-thin corrosion protection coatings for susceptible to local corrosion AA2024-T3 is demonstrated. For this purpose, with atomic layer deposition (ALD) 50 nm thick TiO2, Al2O3, an Al2O3-TiO2 mixture and Al2O3/TiO2 nanolaminate coatings are grown on AA2024-T3 substrates, receiving different pretreatments prior to ALD coating. One pretreatment involves polishing and cleaning with organic solvents, and the second utilizes an additional low-potential electrochemical treatment in sulfuric acid. The samples are characterized with scanning electron microscopy, scanning transmission electron microscopy, wavelength-dispersive X-ray fluorescence spectroscopy, X-ray diffraction and reflection, and nanoindentation and are tested using linear sweep voltammetry, electrochemical impedance spectroscopy, and immersion in a salt solution. The study shows that ultrathin metal oxide coatings applied via ALD can significantly enhance the corrosion resistance of Al alloys, and the performance depends on the pretreatment of the alloy, as well as on the material/structure of the coating. The best ultrathin coating with less than 100 nm thickness withstood well 1000 h immersion test.

The deformation response of ultra-thin polymer films on steel sheet in a tensile straining test: the role of slip bands emerging at the polymer/metal interface

Abstract Forming of pre-coated sheet metal becomes of increasing importance in various fields of industrial application. In the recent years, ultra-thin plasma-polymer films have emerged as promising candidates as pre-treatments for steel sheet. Not much, however, is known about the forming behaviour of ultra-thin polymer coatings on ductile substrates, while an extensive literature exists for the reverse case, metal films on polymer, or brittle films on deformable substrates in general. For these cases, advanced models exist, mostly based on the so-called shear lag approximation. The heterogenous, highly localized strain and stress distribution, typical of ductile substrates, as well as out of plane displacements at the interface are disregarded, but cannot be neglected at the high strain levels of interest for elastic polymer films. This paper will focus on the role of slip bands on cracking of ultra-thin polymer films.

Structure and performance insights in carbon dots-functionalized MXene-epoxy ultrathin anticorrosion coatings

• A novel CD-Ti 3 C 2 T x was synthesized to efficiently protect sensitive MXene from oxidation and deterioration. • The self-aligned B-CM-EP coating with CD-Ti 3 C 2 T x was prepared through a facile flow-induction strategy. • The self-aligned parallel arrangement CD-Ti 3 C 2 T x enhanced greatly the anticorrosion performance of coating. • The CD-Ti 3 C 2 T x endowed the coating with a superior passivation property. • The highly distributed and orientated CD-Ti 3 C 2 T x completely inhibited the corrosion-promotion activity of MXene. MXene nanosheets have showed potential application in metal protection fields due to their large specific surface area and superior mechanical properties. However, MXene for anticorrosion is still underdeveloped, and some associated matters involving susceptibility to oxidation as well as corrosion-promotion activity derived from high conductivity need to be solved. Herein, we use carbon dot (CD) to functionalize Ti 3 C 2 T x MXene nanosheets via Ti-O-C bonding to obtain CD-Ti 3 C 2 T x hybrids, which significantly improves the chemical stability of MXene in water. Then a flow-induced approach is introduced to construct CD-Ti 3 C 2 T x reinforced epoxy (EP) composite coatings, in which CD-Ti 3 C 2 T x is self-aligned to form an oriented layered structure. The unique structure endows the EP coatings with outstanding anticorrosion performance, and more than 4 orders improvement in impedance modulus at an ultrathin thickness of ∼ 25 μm, and 2 orders much higher than random-dispersed composites with the same fillers content. Besides, the CD also provides additional passivation effect to efficiently suppress crack and local damage propagation. More importantly, the parallel arrangement CD-Ti 3 C 2 T x platelets can inhibit the corrosion-promotion activity by eliminating connections of MXene/MXene and MXene/metal in vertical direction, which will further improve the stability and durability of coatings. This work provides a novel strategy to realize chemically stable MXene and inhibit the corrosion-promotion activity of MXene-based coatings, which possess a combination of anticorrosion performance and passivation effect that are suitable for heavy-anticorrosion applications in harsh sea environment.

Surface tailoring of cellulose aerogel-like structures with ultrathin coatings using molecular layer-by-layer assembly

Cellulose nanofibril-based aerogels have promising applicability in various fields; however, developing an efficient technique to functionalize and tune their surface properties is challenging. In this study, physically and covalently crosslinked cellulose nanofibril-based aerogel-like structures were prepared and modified by a molecular layer-by-layer (m-LBL) deposition method. Following three m-LBL depositions, an ultrathin polyamide layer was formed throughout the aerogel and its structure and chemical composition was studied in detail. Analysis of model cellulose surfaces showed that the thickness of the deposited layer after three m-LBLs was approximately 1 nm. Although the deposited layer was extremely thin, it led to a 2.6-fold increase in the wet specific modulus, improved the acid-base resistance, and changed the aerogels from hydrophilic to hydrophobic making them suitable materials for oil absorption with the absorption capacity of 16–36 g/g. Thus, demonstrating m-LBL assembly is a powerful technique for tailoring surface properties and functionality of cellulose substrates.

Sulfobetaine-Based Ultrathin Coatings as Effective Antifouling Layers for Implantable Neuroprosthetic Devices

Sulfobetaine-Based Ultrathin Coatings as Effective Antifouling Layers for Implantable Neuroprosthetic Devices

Corrosion Resistance of Ultrathin Two-Dimensional Coatings: First-Principles Calculations towards In-Depth Mechanism Understanding and Precise Material Design

In recent years, ultrathin two-dimensional (2D) coatings, e.g., graphene (Gr) and hexagonal boron nitride (h-BN), are intriguing research foci in the field of anticorrosion because their high air stability, excellent impermeability, high optical transparency, and atomistic thickness have endowed them with attractive anticorrosion applications. The microstructure of 2D coatings, coating–substrate interactions, and properties of 2D coatings on substrates in a variety of environmental conditions (e.g., at different temperatures, stresses, and pH values) are the key factors governing the anticorrosion performance of 2D coatings and are among the central topics for all 2D-coating studies. For many conventional experimental measurements (e.g., microscopy and electrochemical methods), there exist challenges to acquire detailed information on the atomistic mechanisms for the involved subnanometer scale corrosion problems. Alternatively, as a precise and efficient quantum-mechanical simulation approach, the first-principles calculation based on density-functional theory (DFT) has become a powerful way to study the thermodynamic and kinetic properties of materials on the atomic scale, as well as to clearly reveal the underlying microscopic mechanisms. In this review, we introduce the anticorrosion performance, existing problems, and optimization ways of Gr and h-BN coatings and summarize important recent DFT results on the critical and complex roles of coating defects and coating–substrate interfaces in governing their corrosion resistance. These DFT progresses have shed much light on the optimization ways towards better anticorrosion 2D coatings and also guided us to make a prospect on the further development directions and promising design schemes for superior anticorrosion ultrathin 2D coatings in the future.

Slow light nanocoatings for ultrashort pulse compression

Transparent materials do not absorb light but have profound influence on the phase evolution of transmitted radiation. One consequence is chromatic dispersion, i.e., light of different frequencies travels at different velocities, causing ultrashort laser pulses to elongate in time while propagating. Here we experimentally demonstrate ultrathin nanostructured coatings that resolve this challenge: we tailor the dispersion of silicon nanopillar arrays such that they temporally reshape pulses upon transmission using slow light effects and act as ultrashort laser pulse compressors. The coatings induce anomalous group delay dispersion in the visible to near-infrared spectral region around 800 nm wavelength over an 80 nm bandwidth. We characterize the arrays’ performance in the spectral domain via white light interferometry and directly demonstrate the temporal compression of femtosecond laser pulses. Applying these coatings to conventional optics renders them ultrashort pulse compatible and suitable for a wide range of applications.

Limitations of Ultrathin Al2O3 Coatings on LNMO Cathodes.

This study demonstrates the application of Al2O3 coatings for the high-voltage cathode material LiNi0.5–xMn1.5+xO4−δ (LNMO) by atomic layer deposition. The ultrathin and uniform coatings (0.6–1.7 nm) were deposited on LNMO particles and characterized by scanning transmission electron microscopy, inductively coupled plasma mass spectrometry, and X-ray photoelectron spectroscopy. Galvanostatic charge discharge cycling in half cells revealed, in contrast to many published studies, that even coatings of a thickness of 1 nm were detrimental to the cycling performance of LNMO. The complete coverage of the LNMO particles by the Al2O3 coating can form a Li-ion diffusion barrier, which leads to high overpotentials and reduced reversible capacity. Several reports on Al2O3-coated LNMO using alternative coating methods, which would lead to a less homogeneous coating, revealed the superior electrochemical properties of the Al2O3-coated LNMO, suggesting that complete coverage of the particles might in fact be a disadvantage. We show that transition metal ion dissolution during prolonged cycling at 50 °C is not hindered by the coating, resulting in Ni and Mn deposits on the Li counter electrode. The Al2O3-coated LNMO particles showed severe signs of pitting dissolution, which may be attributed to HF attack caused by side reactions between the electrolyte and the Al2O3 coating, which can lead to additional HF formation. The pitting dissolution was most severe for the thickest coating (1.7 nm). The uniform coating coverage may lead to non-uniform conduction paths for Li, where the active sites are more susceptible to HF attack. Few benefits of applications of very thin, uniform, and amorphous Al2O3 coatings could thus be verified, and the coating is not offering long-term protection from HF attack.

Angstrom-Scale Transparent Overcoats: Interfacial Nitrogen-Driven Atomic Intermingling Promotes Lubricity and Surface Protection of Ultrathin Carbon.

Lubricity, a phenomenon which enables the ease of motion of objects, and wear resistance, which minimizes material damage or degradation, are important fundamental characteristics for sustainable technology developments. Ultrathin coatings that promote lubricity and wear resistance are of huge importance for a number of applications, including magnetic storage and micro-/nanoelectromechanical systems. Conventional ultrathin coatings have, however, reached their limit. Graphene-based materials that have shown promise to reduce friction and wear have many intrinsic limitations such as high temperature and substrate-specific growth. To address these concerns, a great deal of research is currently ongoing to optimize graphene-based materials. Here we discover that angstrom-thick carbon (8 Å) significantly reduces interfacial friction and wear. This lubricant shows ultrahigh optical transparency and can be directly deposited on a wide range of surfaces at room temperature. Experiments combined with molecular dynamics simulations reveal that the lubricating efficacy of 8 Å carbon is further improved via interfacial nitrogen.

Encapsulation of interdigitated electrodes by PTFE coatings via closed batch initiated chemical vapor deposition

Encapsulation of sensor electrodes is critical for stability and optimum performance of the device. Encapsulation method to be employed should be compatible with the device architecture, provide conformal coatings and be cost effective. In this study, closed batch initiated chemical vapor deposition (CB-iCVD) method is used to deposit Polytetrafluoroethylene (PTFE) encapsulation layers on interdigitated electrodes (IDE). The CB-iCVD method enables deposition of conformal, ultra thin PTFE coatings on patterned surfaces with high precursor consumption efficiencies. The electron microscopy analysis confirms the conformality of the smooth coatings on the IDEs. The encapsulation performance of the coatings in the presence of standard pH solution is demonstrated by the frequency dependent electrochemical impedance spectroscopy (EIS) analysis, which confirms that the PTFE layer can successfully isolate the electrodes from the reactive environment.

(Invited) Tailor-Made Atmospheric Plasma Solutions: From Idea to Industrial Lines

Atmospheric pressure (AP) cold plasmas have been steadily gaining importance over the last 20 years. It is often stated that AP processes reduce costs by obviating the need for expensive vacuum systems, and are much easier to implement in industrial production lines. However, every industrial process comes with its own lot of challenges that must be addressed before a viable, robust plasma solution can be put in place.Tackling these challenges is precisely the primary objective of our company, Molecular Plasma Group (MPG). Created as a spin-off from VITO (Belgium) and the Luxembourg Institute of Science and Technology (LIST) to commercialize a unique nano-coating technology using cold atmospheric plasma, MPG SA was established in 2016. Today, our ambition is to be a global Key Enabling Technology (KET) platform, providing scalable environmentally-friendly atmospheric pressure plasma solutions for industries, research and technology organizations, and academia.In this presentation, we will offer an overview of our efforts in the promotion of AP cold plasma technology to the industrial world. From an engineering point of view, we will discuss various topics such as the design of industrially-viable plasma heads, solutions for fiber and powder treatment, roll-to-roll processes, nozzle design (including modeling), dynamic process control. On the scientific side, we will cover aspects such as the benefits of precursor atomization, types of chemistries and substrates that can be processed, along with a few examples of practical applications of adhesion-promoting, release, bioactive, as well as anti-biofouling coatings.Finally, we will present our very recent “success story”, initiated in the frame of the COVID-19 pandemic. From the idea to the installation of industrial machines at customers, we have designed an AP cold plasma process to deposit ultra-thin virucidal coatings that greatly enhance safety, performance, and possibly lifetime of personal protective equipment (PPE) such as face masks. This way, PPE does not act only as a simple “mechanical barrier” to pathogen agents but can effectively prevent cross-contamination and the spread of pathogens. The additional functional layer offers active, fast disinfection properties while being harmless to the user. Figure 1

Ultrathin Coating of Metal Nitride as a Robust and Efficient Artificial Solid Electrolyte Interphase Using Atomic Layer Deposition

The lithium metal anode (LiMA) is considered promising that can achieve high specific energy > 500 Wh kg-1 for future electric vehicles. Despite attractive features, Li-metal-based anode integration still faces barriers such as lithium dendrite growth, unstable solid electrolyte interphase (SEI) formation, and continuous side reactions, limiting its use in the practical application. Here, metal nitride-based artificial SEI is designed to enhance the stability of LiMA under the synergic effect guidance provided by the SEI. During the ALD coating of MNx (where M=metal), the metal nitride reacts with Li to form Li-metal alloy and lithium nitride (Li3N). The Li-metal alloy and Li3N provide high Li-ion conductivity, lithiophilicity, and a physical barrier between the liquid electrolyte and LiMA, stabilizing the interface and suppressing the Li dendrite growth. As a result, metal nitride deposited Li, compared to bare Li, demonstrates significantly improved electrochemical cell performance with longer cycling stability and lower overpotential. This work will provide an insight on stabilizing SEI for dendrite-free Li deposition to develop long-term cycling stability and safer lithium metal batteries.

Luminescent Metal‐Phenolic Networks for Multicolor Particle Labeling

AbstractThe development of fluorescence labeling techniques has attracted widespread interest in various fields, including biomedical science as it can facilitate high‐resolution imaging and the spatiotemporal understanding of various biological processes. We report a supramolecular fluorescence labeling strategy using luminescent metal‐phenolic networks (MPNs) constructed from metal ions, phenolic ligands, and common and commercially available dyes. The rapid labeling process (<5 min) produces ultrathin coatings (≈10 nm) on diverse particles (e.g., organic, inorganic, and biological entities) with customized luminescence (e.g., red, blue, multichromatic, and white light) simply through the selection of fluorophores. The fluorescent coatings are stable at pH values from 1 to 8 and in complex biological media owing to the dominant π interactions between the dyes and MPNs. These coatings exhibit negligible cytotoxicity and their strong fluorescence is retained even when internalized into intracellular compartments. This strategy is expected to provide a versatile approach for fluorescence labeling with potential in diverse fields across the physical and life sciences.

Luminescent Metal-Phenolic Networks for Multicolor Particle Labeling.

The development of fluorescence labeling techniques has attracted widespread interest in various fields, including biomedical science as it can facilitate high-resolution imaging and the spatiotemporal understanding of various biological processes. We report a supramolecular fluorescence labeling strategy using luminescent metal-phenolic networks (MPNs) constructed from metal ions, phenolic ligands, and common and commercially available dyes. The rapid labeling process (<5 min) produces ultrathin coatings (≈10 nm) on diverse particles (e.g., organic, inorganic, and biological entities) with customized luminescence (e.g., red, blue, multichromatic, and white light) simply through the selection of fluorophores. The fluorescent coatings are stable at pH values from 1 to 8 and in complex biological media owing to the dominant π interactions between the dyes and MPNs. These coatings exhibit negligible cytotoxicity and their strong fluorescence is retained even when internalized into intracellular compartments. This strategy is expected to provide a versatile approach for fluorescence labeling with potential in diverse fields across the physical and life sciences.

Ultrathin fibre coatings on nanofibrous nonwovens by plasma enhanced chemical vapor deposition

Abstract For the generation of tailor-made polymer coatings on nanofibrous nonwovens plasma enhanced chemical vapor (PECVD) is a promising process, even for complex geometries. The plasma coatings can greatly improve their suitability for biomedical applications by optimising biocompatibility to the local needs, especially for cardiovascular disease treatments. Therein, wound healing and endothelialisation are important steps which are connected by a complex interaction. The monomers allylamine and hexamethyldisiloxane, as well as different process conditions were studied for the coating of nanofibrous thermoplastic silicone polycarbonate polyurethane (TSPCU) nonwovens. Aim of this study was to investigate the feasibility of plasma polymer coating under preservation of the nanofibrous morphological structure. Beside characterization of the nonwoven, biological evaluation with endothelial and fibroblast cells was performed. The prepared nonwoven samples support the feasibility of plasma coating under preservation of the nanofibrous structure. Also, different effects of the surfaces in contact with fibroblasts and endothelial cells could be observed.

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.

CVD growth of high-quality and large-area continuous h-BN thin films directly on stainless-steel as protective coatings

Corrosion has been one of the most challenging long-term problems for many industry sectors. It accounts for more than half of the industrial failures and costs tens of billion dollars every year. Hexagonal boron nitride (h-BN), a chemically inert layered two-dimensional electrical insulator, which is stable at high temperature under an ambient environment, has been considered as a promising candidate for ultrathin protective coatings especially for harsh environments. In this work, we develop an efficient chemical vapor deposition (CVD) method to directly grow high quality, uniform, and large-area continuous h-BN thin films on industry-relevant stainless-steel substrate. During growth, the h-BN crystalline triangles merge together to form a large-area, voids-free, and continuous thin film on both flat and curved surfaces of stainless-steel substrates. The as-grown h-BN thin films could protect the stainless-steel substrates from oxidization under ambient condition at 800 °C and from corrosion in an extremely corrosive solution at both room and elevated temperatures.

Stabilization of Plasmonic Silver Nanostructures with Ultrathin Oxide Coatings Formed Using Atomic Layer Deposition

Stabilization of Plasmonic Silver Nanostructures with Ultrathin Oxide Coatings Formed Using Atomic Layer Deposition