Conformal Coatings Research Articles

Neutron activation analysis of novel space shielding for terrestrial applications

Appropriate disposition of nuclear waste is a high priority in the production of nuclear energy and its minimization is of great interest to the public. Employing the use of metal oxide infused conformal coatings as a shielding material in a terrestrial reactor should ideally produce nuclear wastes no higher than class B while also reducing the neutron activations (and thus waste classification) of any materials behind the shield. This allows for the increased likelihood of the ability to use on-site sequestration or minimal near-surface disposal, in lieu of geological repositories, and thus the potential for considerable cost savings.

Near-Field Shielding Analysis of Conformal Coating Materials for Integrated Circuits

This article analyzes a near-field shielding performance of conformal shielding materials for integrated-circuits (ICs) by experiments. Two test boards with loop-type and patch-type patterns are designed to generate magnetic-field and electric-field, respectively. These sources mimic typical electromagnetic radiations from actual ICs. For shielding analysis, single-layered conductive materials, multilayered conductive and magnetic materials, hybrid materials with a mixture of conductive and magnetic pastes are considered as conformal shielding materials, which are coated on the test boards for measurements. Magnetic-field and electric-field shielding effectiveness (SE) of the materials evaluate by measurements using loop-probe, strip-line, and gigahertz transverse electromagnetic cell at the frequency range from 300 kHz to 3 GHz. Near-field SEs measured by three methods correspond generally well with each other at the frequency range up to a few hundred MHz. At the higher frequency, the ambient EM environment can affect the accuracy of the near-field measurements by the loop-probe and strip-line. For validation, numerical simulation is fulfilled and compared with measured results. Theoretical interpretation based on the Schelkunoff's SE decomposition is also addressed.

Conformal PEDOT Coating Enables Ultra-High-Voltage and High-Temperature Operation for Single-Crystal Ni-Rich Cathodes.

Single-crystal Ni-rich Li[NixMnyCo1-x-y]O2 (SC-NMC) cathodes represent a promising approach to mitigate the cracking issue of conventional polycrystalline cathodes. However, many reported SC-NMC cathodes still suffer from unsatisfactory cycling stability, particularly under high charge cutoff voltage and/or elevated temperature. Herein, we report an ultraconformal and durable poly(3,4-ethylenedioxythiophene) (PEDOT) coating for SC-NMC cathodes using an oxidative chemical vapor deposition (oCVD) technique, which significantly improves their high-voltage (4.6 V) and high-temperature operation resiliency. The PEDOT coated SC LiNi0.83Mn0.1Co0.07O2 (SC-NMC83) delivers an impressive capacity retention rate of 96.7% and 89.5% after 100 and 200 cycles, respectively. Significantly, even after calendar aging at 45 °C and 4.6 V, the coated cathode can still retain 85.3% (in comparison with 59.6% for the bare one) of the initial capacity after 100 cycles at a 0.5 C rate. Synchrotron X-ray experiments and interface characterization collectively reveal that the conformal PEDOT coating not only effectively stabilizes the crystallographic structure and maintains the integrity of the particles but also significantly suppresses the electrolyte's corrosion, resulting in improved electrochemical/thermal stability. Our findings highlight the promise of an oCVD PEDOT coating for single-crystal Ni-rich cathodes to meet the grand challenge of high-energy batteries under extreme conditions.

Porous but Mechanically Robust All-Inorganic Antireflective Coatings Synthesized using Polymers of Intrinsic Microporosity.

Here, we introduce polymer of intrinsic microporosity 1 (PIM-1) to design single-layer and multilayered all-inorganic antireflective coatings (ARCs) with excellent mechanical properties. Using PIM-1 as a template in sequential infiltration synthesis (SIS), we can fabricate highly uniform, mechanically stable conformal coatings of AlOx with porosities of ∼50% and a refractive index of 1.41 compared to 1.76 for nonporous AlOx that is perfectly suited for substrates commonly used in high-end optical systems or touch screens (e.g., sapphire, conductive glass, bendable glass, etc.). We show that such films can be used as a single-layer ARC capable of reduction of the Fresnel reflections of sapphire to as low as 0.1% at 500 nm being deposited only on one side of the substrate. We also demonstrate that deposition of the second layer with higher porosity using block copolymers enables the design of graded-index double-layered coatings. AlOx structures with just two layers and a total thickness of less than 200 nm are capable of reduction of Fresnel reflections under normal illumination to below 0.5% in a broad spectral range with 0.1% reflection at 700 nm. Additionally, and most importantly, we show that highly porous single-layer and graded-index double-layered ARCs are characterized by high hardness and scratch resistivity. The hardness and the maximum reached load were 7.5 GPa and 13 mN with a scratch depth of about 130 nm, respectively, that is very promising for the structures consisting of two porous AlOx layers with 50% and 85% porosities, correspondingly. Such mechanical properties of coatings can also allow their application as protective layers for other optical coatings.

Electrically Controlled Click-Chemistry for Assembly of Bioactive Hydrogels on Diverse Micro- and Flexible Electrodes.

The seamless integration of electronics with living matter requires advanced materials with programmable biological and engineering properties. Here electrochemical methods to assemble semi-synthetic hydrogels directly on electronically conductive surfaces are explored. Hydrogels consisting of poly (ethylene glycol) (PEG) and heparin building blocks are polymerized by spatially controlling the click reaction between their thiol and maleimide moieties. The gels are grown as conformal coatings or 2D patterns on ITO, gold, and PtIr. This study demonstrates that such coatings significantly influence the electrochemical properties of the metal-electrolyte interface, likely due to space charge effects in the gels. Further a promising route toward engineering and electrically addressable extracellular matrices by printing arrays of gels with binary cell adhesiveness on flexible conductive surfaces is highlighted.

(Invited) Stabilizing and Enhancing Lithium-Ion Batteries with Chemically Inert 2D Materials

Efficient energy storage systems represent a critical technology across many sectors including consumer electronics, electrified transportation, and a smart grid accommodating intermittent renewable energy sources. Arguably, the most important advance in energy storage over the past three decades is the lithium-ion battery, which was recently recognized with the Nobel Prize in Chemistry. However, despite its many successes, issues related to safety, energy density, charging time, and operating temperature range have hindered the realization of the full potential of lithium-ion battery technology, particularly in large-scale applications such as grid-level storage and full electrification of transportation networks. Nanostructured materials were once thought to present compelling opportunities for next-generation lithium-ion batteries, but inherent problems related to high surface area to volume ratios at the nanometer-scale (e.g., undesirable surface chemical interactions between electrodes and electrolytes) have impeded their adoption for commercial applications. This talk will explore how the chemical inertness of select two-dimensional (2D) materials are driving a resurgence in nanostructured lithium-ion battery materials [1]. For example, conformal graphene coatings on lithium-ion battery cathode powders mitigate surface degradation and minimize the formation of the solid electrolyte interphase, thus improving cycling stability [2]. In addition, the high electrical conductivity of graphene reduces cell impedance, resulting in enhanced kinetics that enable high-rate capability and low-temperature performance down to –20 °C [3]. On the other hand, ionogel electrolytes based on ionic liquids and hexagonal boron nitride (hBN) nanoplatelets provide safe, high-rate operation at high temperatures up to 175 °C, which represents the highest operating temperature to date for solid-state lithium-ion batteries [4,5]. The strong interfacial interactions between hBN and ionic liquids further enable novel electrolyte architectures based on layered heterostructure ionogels that result in unprecedently high energy densities and rate performance for solid-state batteries [6].[1] H. Bergeron, et al., Chemical Reviews, 121, 2713 (2021).[2] K.-Y. Park, et al., Advanced Energy Materials, 10, 2001216 (2020).[3] K.-Y. Park, et al., Advanced Materials, DOI: 10.1002/adma.202106402 (2021).[4] W. J. Hyun, et al., ACS Nano, 13, 9664 (2019).[5] W. J. Hyun, et al., Advanced Energy Materials, 10, 2002135 (2020).[6] W. J. Hyun, et al., Advanced Materials, 33, 2007864 (2021).

Atomic Layer Deposition of Highly Stable Manganese-Iron Oxide Bifunctional Catalysts for Zinc-Air Batteries

Incorporating intermittent renewable energy sources into the power grid will require large amounts of grid-scale energy storage. Electrochemical batteries are a versatile and scalable energy storage option and, hence, Li-ion batteries have been widely adopted to store excess wind and solar energy [1]. Li-ion batteries, however, have a relatively low energy density and serious safety concerns. An alternative electrochemical battery option lies with zinc-air batteries. This technology uses lower cost materials and is overall much safer. Furthermore, zinc-air batteries have a much larger theoretical energy density than Li-ion batteries [2]. The major impediment to wide-scale adoption of zinc-air batteries is the low energy efficiency because of the poor reaction kinetics at the air electrode. Both the charge and discharge reactions at the air electrode are sluggish and require the use of catalysts to obtain practicable performance. However, many catalysts active towards the charge reaction are not active towards the discharge reaction, and vice versa. The development of a catalyst active towards both the charge and discharge reactions, known as a bifunctional catalyst, is therefore a high priority [3]. Furthermore, catalysts employed in zinc-air batteries often show instability, with performance degradation evident after a few cycles. Ultimately, a highly stable bifunctional zinc-air battery catalyst is of the utmost importance.The aim of this work is to develop highly stable bifunctional catalysts for zinc-air batteries using atomic layer deposition (ALD). With ALD, extremely conformal catalyst coatings can be deposited directly on the air electrode of a zinc-air battery. The self-limiting surface reactions of ALD ensure that electrode porosity is maintained while maximizing the total coating surface area [4]. Since ALD operates in the gas phase, catalytic coatings can be deposited deep within the pores of the air electrode. This will help maintain the three-phase boundary necessary for the discharge reaction and ultimately improve the stability of a zinc-air battery [5]. To create a bifunctional catalyst, two ALD processes, one for manganese oxide and another for iron oxide, is combined into one ALD supercycle, depositing a mixed manganese-iron oxide. Since manganese oxide is a well-established discharge catalyst [6], and iron oxide demonstrates activity towards the charge reaction [7], this mixed manganese-iron oxide exhibits bifunctional activity in a zinc-air battery. An optimized supercycle process will be discussed and full-cell battery test results showcased. Specifically, the bifunctional efficiency of a zinc-air battery can be improved by more than 10% by using the mixed manganese-iron oxide catalyst. In addition, the high stability of the manganese-iron oxide catalyst is demonstrated, where bifunctional efficiency can be maintained at over 95% of the initial value over 200 cycles. Materials characterization of the mixed manganese-iron oxide, deposited through ALD, is also included.[1] L. Trahey, F. R. Brushett, N. P. Balsara, G. Ceder, L. Cheng, Y. M. Chiang, N. T. Hahn, B. J. Ingram, S. D. Minteer, J. S. Moore, K. T. Mueller, L. F. Nazar, K. A. Persson, D. J. Siegel, K. Xu, K. R. Zavadil, V. Srinivasan, and G. W. Crabtree, “Energy Storage Emerging: A Perspective from the Joint Center for Energy Storage Research,” Proc. Natl. Acad. Sci. U. S. A., vol. 117, no. 23, pp. 12550–12557, 2020.[2] J. Fu, R. Liang, G. Liu, A. Yu, Z. Bai, L. Yang, and Z. Chen, “Recent Progress in Electrically Rechargeable Zinc – Air Batteries,” Adv. Mater., vol. 31, no. 31, p. 1805230, 2019.[3] E. Davari and D. G. Ivey, “Bifunctional electrocatalysts for Zn – air batteries,” Sustain. Energy Fuels, vol. 2, no. 1, pp. 39–67, 2018.[4] C. Detavernier, J. Dendooven, S. Pulinthanathu Sree, K. F. Ludwig, and J. A. Martens, “Tailoring nanoporous materials by atomic layer deposition,” Chem. Soc. Rev., vol. 40, no. 11, pp. 5242–5253, 2011.[5] M. P. Clark, M. Xiong, K. Cadien, and D. G. Ivey, “High Performance Oxygen Reduction/Evolution Electrodes for Zinc − Air Batteries Prepared by Atomic Layer Deposition of MnOx,” ACS Appl. Energy Mater., vol. 3, no. 1, pp. 603–313, 2020.[6] M. P. Clark, T. Muneshwar, M. Xiong, K. Cadien, and D. G. Ivey, “Saturation Behavior of Atomic Layer Deposition MnOx from Bis(Ethylcyclopentadienyl) Manganese and Water: Saturation Effect on Coverage of Porous Oxygen Reduction Electrodes for Metal-Air Batteries,” ACS Appl. Nano Mater., vol. 2, no. 1, pp. 267–277, 2019.[7] M. Labbe, M. P. Clark, Z. Abedi, A. He, K. Cadien, and D. G. Ivey, “Atomic layer deposition of iron oxide on a porous carbon substrate via ethylferrocene and an oxygen plasma,” Surf. Coatings Technol., vol. 421, p. 127390, 2021.

(Invited) Electrochemically Induced Deposition of Thin-Film Oxides and Electronic Insulators

Electrodeposition is typically associated with the electroreduction of metal ions for the deposition of metals, alloys or semiconductors. Compounds can be electrodeposited when the metal ions form an insoluble compound upon change of its valence state at the electrode surface. A well-known example is the anodic deposition of MnO2, where aqueous solvated Mn2+ ions are oxidized to the insoluble Mn(IV) in acid sulfate solutions. Alternatively, the precipitation of a compound or oxide can be triggered by changing the local pH at the electrode by a suitable electrochemical reaction. The use of electrochemical formed base from so-called probase molecules has found applications in formation of oxides, phosphates but also organic materials such metal organic frameworks (MOFs). Nitrate was one of the first pro-bases suggested for the electrochemical precipitation of ZnO. An alternate electrochemical approach for depositing compounds and oxides is the electrochemical initiation of a sol-gel reaction first developed for the silica sol-gel process by Shacham et al. [1] During deposition, an electrode is submerged into a precursor solution followed by the application of a cathodic current. The chemical reaction is triggered by electro-generating the OH- catalyst that is required for the polycondensation of the silica precursor. Since this occurs near the surface, the method results in silica thin films deposited only on the electrode surface. Finally, also electro-polymerization can lead to thin insulating films. In this paper, several of these reaction paths will be explored. The initial stages of MnO2 electrodeposition are strongly dependent on the starting surface and determines the adhesion and attainable film thickness [2]. The relationship between (intentionally) introduced meso-porosity, growth rate and film thickness will be discussed. The poor electronic conductivity of oxides makes that the reaction is maintained by ionic conduction through the films, similar as for oxide formation by anodization. For the formation of micron thick oxide films, also good control of hydrodynamic conditions is essential. [3] The resistive nature of the layers typically allows also for good conformality over high aspect ratio substrates. Conformal deposition of oxide thin-film coatings on high aspect ratio structures is typically claimed by Atomic Layer Deposition. Inorganic-organic hybrid films such as metal cones can be similarly deposited by Molecular Layer Deposition (MLD). [4] The nature of the surface limited reactions of these vapor-phase methods allows for the formation of continuous sub-nanometer to a few tens of nanometer thin films with uniform thickness over the most complex architectures. The accuracy of the technique goes at the cost of long deposition cycles especially when very large surface areas with extreme aspect ratios (>100) are involved. The intrinsic resistive nature of the electrodeposited oxide and insulator films allows for excellent conformal coatings with growth rates much more suited for thicker films without loss in conformality or uniformity. In this paper, we will show examples where electrochemical induced deposition process are used also to coat nano-architectures such as our nanomesh with very large surface area (100 cm2 per planar cm2) and aspect ratio (100x). [1] Shacham, B. R., Avnir, D. & Mandler, D. Electrodeposition of Methylated Sol-Gel Films on Conducting Surfaces. Adv. Mater. 384–388 (1999).[2] "Electrodeposition of Adherent Submicron to Micron Thick Manganese Dioxide Films with Optimized Current Collector Interface for 3D Li-Ion Electrodes" Marina Timmermans, Nouha Labyedh, Felix Mattelaer, Stanislaw Zankowski, Stella Deheryan, Christophe Detavernier, and Philippe M. Vereecken, J. Electrochem. Soc. 164, 14, D954-D963 (2017).[3] Aggregate-Free Micrometer-Thick Mesoporous Silica Thin Films on Planar and Three-Dimensional Structured Electrodes by Hydrodynamic Diffusion Layer Control during Electrochemically Assisted Self-Assembly”, G Vanheusden, H Philipsen, SJF Herregods, PM Vereecken, Chemistry of Materials (2021).[4] “Molecular Layer Deposition of "Magnesicone", a Magnesium-based Hybrid Material" Jeroen Kint, Felix Mattelaer, Sofie S. T. Vandenbroucke, Arbresha Muriqi, Matthias M. Minjauw, Mikko Nisula, Philippe M. Vereecken, Michael Nolan, Jolien Dendooven, and Christophe Detavernier, Chem. Mater. 32, 11, 4451–4466, (2020).

Performance of islets of Langerhans conformally coated via an emulsion cross-linking method in diabetic rodents and nonhuman primates.

Polyethylene glycol (PEG)–based conformal coating (CC) encapsulation of transplanted islets is a promising β cell replacement therapy for the treatment of type 1 diabetes without chronic immunosuppression because it minimizes capsule thickness, graft volume, and insulin secretion delay. However, we show here that our original CC method, the direct method, requiring exposure of islets to low pH levels and inclusion of viscosity enhancers during coating, severely affected the viability, scalability, and biocompatibility of CC islets in nonhuman primate preclinical models of type 1 diabetes. We therefore developed and validated in vitro and in vivo, in several small- and large-animal models of type 1 diabetes, an augmented CC method—emulsion method—that achieves hydrogel CCs around islets at physiological pH for improved cytocompatibility, with PEG hydrogels for increased biocompatibility and with fivefold increase in encapsulation throughput for enhanced scalability.

Conformal Buffer Layer Coating on Ni-Rich Cathode Powder via Particle Atomic Layer Deposition for All-Solid-State Batteries

Conformal Buffer Layer Coating on Ni-Rich Cathode Powder via Particle Atomic Layer Deposition for All-Solid-State Batteries

Core shell coatings for nuclear thermal propulsion cermets

Magnetron sputtering has been employed to provide conformal tungsten coatings from approximately 70 to 540 nm thicknesses over yttria stabilized zirconia (YSZ) powders. Through a rotating vessel, the powder was continually cascaded exposing its surface enabling the line-of-sight cathode tungsten target to deposit over the entire surface. With increasing coating thickness, a particulate surface morphology developed. These tungsten particulates were plate-like in morphology and faceted in some cases. The formation of these features is contributed to the continual low energy impacts between the hard YSZ powders during deposition as well as the adhesion and de-adhesion of the coatings connecting particle clusters. The results of this work demonstrate the ability of sputter deposition to create refractory coatings for cermet fuels utilized in nuclear thermal propulsion, as well as broader applications where core-shell powder fabrication is needed.

Controlled release of low-molecular weight, polymer-free corticosteroid coatings suppresses fibrotic encapsulation of implanted medical devices

Inflammation-driven foreign body reactions, and the frequently associated encapsulation by fibrogenic fibroblasts, reduce the functionality and longevity of implanted medical devices and materials. Anti-inflammatory drugs, such as dexamethasone, can suppress the foreign body reaction for a few days post-surgery, but lasting drug delivery strategies for long-term implanted materials remain an unmet need. We here establish a thin-coating strategy with novel low molecular weight corticosteroid dimers to suppress foreign body reactions and fibrotic encapsulation of subcutaneous silicone implants. The dimer coatings are >75% dexamethasone by mass and directly processable into conformal coatings using conventional solvent-based techniques, such as casting or spray coating without added polymers or binding agents. In vitro, surface erosion of the coating, and subsequent hydrolysis, provide controlled release of free dexamethasone. In a rat subcutaneous implantation model, the resulting slow and sustained release profile of dexamethasone is effective at reducing the number and activation of pro-fibrotic macrophages both acutely and at chronic time points. Consequently, fibroblast activation, collagen deposition and fibrotic encapsulation are suppressed at least 45 days post-implantation. Thus, our approach to protect implants from host rejection is advantageous over polymeric drug delivery systems, which typically have low drug loading capacity (<30%), initial burst release profiles, and unpredictable release kinetics.

Parallel Evaluation of Polyethylene Glycol Conformal Coating and Alginate Microencapsulation as Immunoisolation Strategies for Pancreatic Islet Transplantation.

Pancreatic islet transplantation improves metabolic control and prevents complications in patients with brittle type 1 diabetes (T1D). However, chronic immunosuppression is required to prevent allograft rejection and recurrence of autoimmunity. Islet encapsulation may eliminate the need for immunosuppression. Here, we analyzed in parallel two microencapsulation platforms that provided long-term diabetes reversal in preclinical T1D models, alginate single and double capsules versus polyethylene glycol conformal coating, to identify benefits and weaknesses that could inform the design of future clinical trials with microencapsulated islets. We performed in vitro and in vivo functionality assays with human islets and analyzed the explanted grafts by immunofluorescence. We quantified the size of islets and capsules, measured capsule permeability, and used these data for in silico simulations of islet functionality in COMSOL Multiphysics. We demonstrated that insulin response to glucose stimulation is dependent on capsule size, and the presence of permselective materials augments delays in insulin secretion. Non-coated and conformally coated islets could be transplanted into the fat pad of diabetic mice, resulting in comparable functionality and metabolic control. Mac-2+ cells were found in conformally coated grafts, indicating possible host reactivity. Due to their larger volume, alginate capsules were transplanted in the peritoneal cavity. Despite achieving diabetes reversal, changes in islet composition were found in retrieved capsules, and recipient mice experienced hypoglycemia indicative of hyperinsulinemia induced by glucose retention in large capsules as the in silico model predicted. We concluded that minimal capsule size is critical for physiological insulin secretion, and anti-inflammatory modulation may be beneficial for small conformal capsules.

Atomically-thin Schottky-like photo-electrocatalytic cross-flow membrane reactors for ultrafast remediation of persistent organic pollutants

The remediation of persistent organic pollutants in surface and ground water represents a major environmental challenge worldwide. Conventional physico-chemical techniques do not efficiently remove such persistent organic pollutants and new remediation techniques are therefore required. Photo-electro catalytic membranes represent an emerging solution that can combine photocatalytic and electrocatalytic degradation of contaminants along with molecular sieving. Herein, macro-porous photo-electro catalytic membranes were prepared using conductive and porous stainless steel metal membranes decorated with nano coatings of semiconductor photocatalytic metal oxides (TiO2 and ZnO) via atomic layer deposition, producing highly conformal and stable coatings. The metal - semiconductor junction between the stainless steel membranes and photocatalysts provides Schottky - like characteristics to the coated membranes. The PEC membranes showed induced hydrophilicity from the nano-coatings and enhanced electro-chemical properties due to the Schottky junction. A high electron transfer rate was also induced in the coated membranes as the photocurrent efficiency increased by 4 times. The photo-electrocatalytic efficiency of the TiO2 and ZnO coated membranes were demonstrated in batch and cross flow filtration reactors for the degradation of persistent organic pollutant solution, offering increased degradation kinetic factors by 2.9 and 2.3 compared to photocatalysis and electrocatalysis, respectively. The recombination of photo-induced electron and hole pairs is mitigated during the photo-electrocatalytic process, resulting in an enhanced catalytic performance. The strategy offers outstanding perspectives to design stimuli-responsive membrane materials able to sieve and degrade simultaneously toxic contaminants towards greater process integration and self-cleaning operations.

Atomic layer deposition of conformal anti-reflective coatings on complex 3D printed micro-optical systems

3D printing of micro-optics has recently become a very powerful fabrication method for sub-millimeter sized optics. Miniature optical systems and entire optical instruments such as endoscopes have become possible with this technique. 3D printed complex micro-optical systems are printed in one single process, rather than being assembled. This precludes anti-reflection coating of the individual lenses before assembly by conventional coating methods such as sputtering or directed plasma etching, as voids between the individual lenses cannot be reached by a directed coating beam. We solve this issue by conformal low-temperature thermal atomic layer deposition (ALD) which is compatible with the low glass transition temperature of the utilized 3D printed polymer materials. Utilizing 4-layer designs, we decrease the broadband reflectivity of coated flat substrates in the visible to below 1%. We characterize and investigate the properties of the coatings based on transmission measurements through coated and uncoated 3D printed test samples as well as through a double-lens imaging system. We find that the reflectivity is significantly reduced and conversely the transmission is enhanced, which is of particular interest for low-light applications. Furthermore, the physical durability and resistance against humidity uptake should also be improved.

Enhanced fireproof performance of construction coatings by adding hexagonal boron nitride nanosheets

Hexagonal boron nitride (h-BN), commonly called “white graphene”, has received considerable attention thanks to its unique properties such as superior mechanical stability, high thermal conductivity, and exceptional chemical durability. Significant prior works have been dedicated for functionalizing the h-BN nanosheets for improving their optical, electrochemical, and biochemical properties. However, the application of h-BN sheets for the fire retardancy and thermal management of construction coatings has yet to be explored. In this work, we have investigated the thermal resistance and fire retardancy of the composite thin films composed of functionalized h-BN nanosheets deposited on stainless steel foils and fabrics. An efficient three-dimensional ball milling method is employed to synthesize the h-BN nanosheets with oxygen functionalities. We have shown that the h-BN-nanosheet-filled conformal coatings (including gypsum and sodium metasilicate) significantly enhance the fire retardancy of construction buildings. Uniform and homogeneous dispersity of the functionalized h-BN nanoparticles within the construction coatings has been verified by the scanning electron microscopy. Thermogravimetric analysis confirmed that the thermal resistance of the h-BN-filled coating is significantly enhanced with ultra-high thermal resistivity at 700 °C. Indeed, the addition of h-BN nanosheets improves the thermal shielding as well as the fire retardancy of the construction coatings, while serving as an efficient thermal insulating barrier. The robust design of h-BN-filled coatings demonstrated in this work paves the way for preparing green (i.e., environmentally friendly) construction materials.

The Effect of Acrylic Conformal Coating in the Reliability of Solder Joints

During the product life, electronic components are subjected to environmental conditions, such as humidity or temperature fluctuations. Solder joints, which allow the electrical and mechanical connection, are one of the most critical spots to have failures due to environmental conditions. Conformal coating, a thin layer that encapsulates all components and consequently solder joints, is one of the techniques that allows the protection of the component against these detrimental effects. Nevertheless, the application of conformal coating has not been recommended in some components, namely in ball grid arrays (BGAs) and quad-flat-no-leads (QFN), since it can compromise the reliability of their solder joints when exposed to temperature fluctuations. Herein, by using an accelerative test, the reliability of BGA- and QFN-coated solder joints with an acrylic conformal coating was studied. A thermal cycle test of temperature ranging from −40 °C to +125 °C comprising 837 cycles demonstrated no failures (confidence level of 0.99; <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$R = 4$ </tex-math></inline-formula> ppm/year; <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\beta = 3$ </tex-math></inline-formula> ) to occur due to acrylic conformal-coating application. However, the solder joints analysis indicated that conformal coating causes an excess of deformations on solder joints, compromising their reliability. Therefore, this study suggests that this acrylic conformal coating is not suitable for these electronic components.

Percolative Anodization: Tailoring TiO2 Nanotube Arrays Inside Ultrafine Ti Microchannels

Porous metals have generated increasing interest for biomedical, catalysis, energy and environmental applications, because of the high specific strength and large surface area. To make full use of the porous feature, it is of essential importance to tailor the surface morphology and wettability of the microchannels inside the metals. However, it remains a great challenge to uniformly and conformally coat the microchannels of <30 μm in view of the spatial limitation. In this work, a percolative anodization is developed to decorate the ultrafine microchannels of porous titanium with TiO2 nanotube arrays. Uniform and conformal nanotube coatings are produced throughout the channels of 0.5–10 μm with superwetting characters by optimizing the solvent viscosity. The mechanism of percolative anodization is established by investigating the nanotube growth in both torturous and straight channels. A key parameter of K value is thus introduced to elucidate the percolative anodization controlled either by electric field or concentration field. The anodization requires an electrolyte solution of low viscosity with K < 0.4, and may employ that of high viscosity with K > 0.4 to sufficiently coat the microchannels. The major findings reported herein can be extended to other porous metals for surface modification and functionalization.

Mesoporous Silk-Bioactive Glass Nanocomposites as Drug Eluting Multifunctional Conformal Coatings for Improving Osseointegration and Bactericidal Properties of Metal Implants.

Endowing metal implants with multifunctional traits to prevent implant-associated infections and improve osseointegration has become a pivotal facet in orthopedics and dental fixation. Herein, we report the synthesis of mesoporous 70S bioactive glass-silk fibroin nanocomposites inspired by the biomimetic organo-apatites of mineralized collagen. The mesoporous, biomimetic nanocomposites enabled loading of antibiotics (gentamicin and doxycycline) and favored their release in a rapid manner while preserving their bioactivity. Ease in modification of the mesoporous nanocomposites enabled tailoring of 3-(aminopropyl)-triethoxysilane to the silanol network of bioactive glass, which improved the loading capacity of the hydrophobic drug (dexamethasone). The modification favored the slow and sustained release of dexamethasone from the modified mesoporous nanocomposites, which is desired for mediating osteogenesis and immunomodulation. Conformal coatings of these drug-loaded nanocomposites were materialized on stainless-steel implants through a facile electrophoretic deposition (EPD) technique, wherein the deposition yield can be controlled by applied parameters. Antibiotic coatings exhibited antibacterial efficacy with bioactivity retained up to 28 days, while dexamethasone-loaded coatings favored mesenchymal stem cell adhesion and osteoinduction. The immunomodulatory roles were also ascertained, wherein M2 macrophage biasness was favored in dexamethasone-loaded coatings. The versatility of these mesoporous biomimetic nanocomposites guarantee the loading of scenario-specific drugs to aid their local delivery through the conformal EPD coatings developed over metal implants toward improving implant patency.

Additive Manufacturing in Atomic Layer Processing Mode.

Additive manufacturing (3D printing) has not been applicable to micro- and nanoscale engineering due to the limited resolution. Atomic layer deposition (ALD) is a technique for coating large areas with atomic thickness resolution based on tailored surface chemical reactions. Thus, combining the principles of additive manufacturing with ALD could open up a completely new field of manufacturing. Indeed, it is shown that a spatially localized delivery of ALD precursors can generate materials patterns. In this "atomic-layer additive manufacturing" (ALAM), the vertical resolution of the solid structure deposited is about 0.1 nm, whereas the lateral resolution is defined by the microfluidic gas delivery. The ALAM principle is demonstrated by generating lines and patterns of pure, crystalline TiO2 and Pt on planar substrates and conformal coatings of 3D nanostructures. The functional quality of ALAM patterns is exemplified with temperature sensors, which achieve a performance similar to the industry standard. This general method of multimaterial direct patterning is much simpler than standard multistep lithographic microfabrication. It offers process flexibility, saves processing time, investment, materials, waste, and energy. It is envisioned that together with etching, doping, and cleaning performed in a similar local manner, ALAM will create the "atomic-layer advanced manufacturing" family of techniques.