Multilayer Barrier Research Articles

Reply to short communication ‘Comment on “Numerical approach to define a thermodynamically equivalent material for the conjugate heat transfer simulation of very thin coating layers” by P. Olmeda, X. Margot, P. Quintero, J. Escalona, International Journal of Heat and Mass Transfer, Vol. 162(2020) 120377 ” by Jaal Ghandhi and Georgios Koutsakis

In the recent paper “Surface temperature of a multi-layer thermal barrier coated wall subject to an unsteady heat flux” by G. Koutsakis, G. F. Nellis, J. B. Ghandhi, Int. J. Heat Mass Transfer 155(2020), 119645 the authors have proposed an analytical solution to determine wall temperature of surfaces coated with multi-layer coatings. The solutions are obtained based on the assumptions of one-dimensional heat flux using the matrix method in conjunction with the 1-D Laplace transformed heat diffusion equation. The authors suggest that using this analytical approach a thicker pseudo-material could be found in order to address the 3D conjugate heat transfer problem. This approach is compared with another published methodology that employs a DoE (Design of experiments) in combination with a multiple regression analysis to define a thicker equivalent coating layer.

Complete Atomic Oxygen and UV Protection for Polymer and Composite Materials in a Low Earth Orbit

With the realization of larger and more complex space installations, an increase in the surface area exposed to atomic oxygen (AO) and ultraviolet (UV) effects is expected, making structural integrity of space structures essential for future development. In a low Earth orbit (LEO), the effects of AO and UV degradation can have devastating consequences for polymer and composite structures in satellites and space installations. Composite materials such as carbon fiber-reinforced polymer (CFRP) or polymer materials such as polyetherimide and polystyrene are widely used in satellite construction for various applications including structural components, thermal insulation, and importantly radio frequency (RF) assemblies. In this paper, we present a multilayered material protection solution, a multilayered protection barrier, that mitigates the effects of AO and UV without disrupting the functional performance of tested assemblies. This multilayered protection barrier deposited via a custom-built plasma-enhanced chemical vapor deposition (PECVD) system is designed so as to deposit all necessary layers without breaking vacuum to maximize the adhesion to the surface of the substrate and to ensure no pinhole erosion is present. In the multilayer solution, a moisture and outgassing barrier (MOB) is coupled with an AO and UV capping layer to provide complete protection.

P‐6.4: Enhanced Moisture Barrier Properties by the Use of Clay Nanoparticle‐embedded Nanocomposite

Organic electronic devices, such as organic light‐emitting diodes (OLEDs), are very sensitive to air environment, so it is necessary to encapsulate these devices to increase the service life[1−2]. In this study, we report a high transparent inorganic /organic multilayer barrier film, in which the inorganic layer is a high‐quality SiNx layer and the organic layer is clay nanoparticle‐embedded organic—inorganic hybrid (C—H) nanocomposite.

A Comparison Study on Multilayered Barrier Oxide Structure in Charge Trap Flash for Synaptic Operation

A synaptic device that contains weight information between two neurons is one of the essential components in a neuromorphic system, which needs highly linear and symmetric characteristics of weight update. In this study, a charge trap flash (CTF) memory device with a multilayered high-κ barrier oxide structure on the MoS2 channel is proposed. The fabricated device was oxide-engineered on the barrier oxide layers to achieve improved synaptic functions. A comparison study between two fabricated devices with different barrier oxide materials (Al2O3 and SiO2) suggests that a high-κ barrier oxide structure improves the synaptic operations by demonstrating the increased on/off ratio and symmetry of synaptic weight updates due to a better coupling ratio. Lastly, the fabricated device has demonstrated reliable potentiation and depression behaviors and spike-timing-dependent plasticity (STDP) for use in a spiking neural network (SNN) neuromorphic system.

Study on the Multilayer Barrier Coating Using Cellulose Nanofibrils and Internal Sizing Agent

In this study, we tried to develop techniques to increase coat weight and improve water resistance at a lower number of multilayer barrier coatings with anionic and cationic cellulose nanofibrils (CNFs), which has been reported in previous research. The concentration of CNF slurry was adjusted to increase the coat weight, while alkyl ketene dimer (AKD) was added as an internal sizing agent to the anionic CNF slurry to impart hydrophobicity to the CNFs. After the preparation of CNF slurries, the multilayer barrier coating was applied on never-size base paper. The coat weight, air permeability, and Cobb size degree of the barrier-coated paper were subsequently measured, and the surface of the paper was analyzed via SEM. The coat weight and air permeability of the paper coated four times with CNF slurry at 1.4% concentration were similar to those of the paper coated six times with CNF slurry at 1.0% concentration. In addition, the Cobb size degree of the barrier-coated paper decreased as the AKD addition to anionic CNF at a concentration of 1.4% increased linearly. However, when the addition level of AKD increased more than 5.0%, the Cobb size degree of the barrier-coated paper increased due to the uneven distribution of AKD. Therefore, multilayer barrier coating can be carried out effectively with cationic and anionic CNFs at high concentrations, and AKD improves the water resistance of barrier-coated paper.

The influence of temperature on the intrinsic transport properties of water in inorganic and polymeric coatings

Barrier layers are often used to protect sensitive organic devices from the detrimental effects of oxygen and water vapor. We investigated the effect of temperature on the time-dependent behavior of water vapor permeation in multilayer barrier films, focusing on the water vapor solubility, diffusion and permeability coefficients of individual layers and layer sequences. Activation energy measurements helped to explain the permeation mechanisms and showed the possible interactions between water and silicon oxide (SiOx). The activation energy for permeation (EP) through a two-layer film of polyethylene terephthalate (PET) coated with SiOx was 5.7 kJmol−1, about twice the EP value of the uncoated PET substrate. An intermediate ORMOCER® layer, providing a smooth surface for a second SiOx layer in an alternating structure, had only a negligible effect on the EP. Temperature dependent quasi-stationary approximations were derived for permeation through films with at least one inorganic/polymer/inorganic triplet, and were validated according to experimentally determined values. These equations showed the temperature and pressure dependencies of steady-state permeation and lag time in multilayered structures. Accordingly, the temperature dependency of steady-state permeation is determined by the EP of SiOx, whereas the lag time was mainly influenced by the heat of sorption of the intermediate polymeric layer. Furthermore, the increase in water vapor transmission rate was dominated by the partial pressure change with increasing temperature. Using these equations and experimentally determined parameters, we can predict the influence of temperature and humidity on the barrier performance of multilayered barrier structures.

Pulsed terahertz spectroscopy combined with hybrid machine learning approaches for structural health monitoring of multilayer thermal barrier coatings.

Structural health monitoring of multilayer thermal barrier coatings (TBCs) is very vital to ensure the structural integrity and service performance of the hot-section components of the aero-engine. In this paper, we theoretically and numerically demonstrated that the terahertz time domain spectrum and the terahertz reflectance spectrum could be adopted to estimate the structure parameters, based on the finite difference time domain (FDTD) algorithm, 64 samples which were imported with three kinds of 64 sets structure parameters had been calculated to obtain the time domain and terahertz reflectance signals. To mimic the actual test signals, the original FDTD simulation signals were processed by adding the Gaussian white noise and wavelet noise reduction. To reduce the data dimension and improve the calculation efficiency during modeling, the principal component analysis (PCA) algorithm was adopted to reduce the dimensions of time-domain data and reflectance data. Finally, these data after multiple signal processing and PCA feature extraction were used to train the extreme learning machine (ELM), combining the genetic algorithm (GA) could optimize the PCA-ELM model and further improve the prediction performance of the hybrid model. Our proposed novel and efficient terahertz nondestructive technology combined with the hybrid machine learning approaches provides great potential applications on the multilayer TBCs structural integrity evaluation.

“Are They Saying It How I'm Saying It?” A Qualitative Study of Language Barriers and Disparities in Hospice Enrollment

ContextLanguage barriers contribute significantly to disparities in end-of-life (EOL) care. However, the mechanisms by which these barriers impact hospice care remains underexamined. ObjectivesTo gain a nuanced understanding of how language barriers and interpretation contribute to disparities in hospice enrollment and hospice care for patients with limited English proficiency. MethodsQualitative, individual interviews were conducted with a variety of stakeholders regarding barriers to quality EOL care in diverse patient populations. Interviews were audiorecorded and transcribed verbatim. Data were coded using NVivo 11 (QSR International Pty Ltd., Melbourne, Australia). Three researchers analyzed all data related to language barriers, first individually, then in group meetings, using a grounded theory approach, until they reached consensus regarding themes. Institutional review board approval was obtained. ResultsTwenty-two participants included six nurses/certified nursing assistants, five physicians, three administrators, three social workers, three patient caregivers, and two chaplains, self-identifying from a variety of racial/ethnic backgrounds. Three themes emerged regarding language barriers: 1) structural barriers inhibit access to interpreters; 2) variability in accuracy of translation of EOL concepts exacerbates language barriers; and 3) interpreters' style and manner influence communication efficacy during complex conversations about prognosis, goals of care, and hospice. Our theoretical model derived from the data suggests that Theme 1 is foundational and common to other medical settings. However, Theme 2 and particularly Theme 3 appear especially critical for hospice enrollment and care. ConclusionLanguage barriers present unique challenges in hospice care because of the nuance and compassion required for delicate goals of care and EOL conversations. Reducing disparities requires addressing each level of this multilayered barrier.

Flux-Weakening Capability Enhancement Design and Optimization of a Controllable Leakage Flux Multilayer Barrier PM Motor

In this article, a new controllable leakage flux multilayer barrier permanent magnet (PM) motor is proposed by adopting a new design concept of controllable leakage flux, where the PMs are uniquely placed in the d-axis magnetic circuit of the synchronous reluctance motor (SynRM). Compared to the conventional q-axis PM placement SynRM, the higher PM utilization and better flux-weakening capability can be obtained. For further comparison and verification, both of the controllable leakage flux multilayer barrier PM motor and the motor with traditional q-axis PM setting are designed. In addition, a multiobjective optimization method based on the correlation analysis method is proposed to obtain the optimized output torque and flux-weakening performances. Then, the performances of the two optimal motors are analyzed and compared in detail. Finally, two prototype motors are manufactured and tested. Both the theoretical and experimental analyses verify the effectiveness of the flux-weakening enhancement design and the proposed motor.

Reprint of: Surface temperature of a multi-layer thermal barrier coated wall subject to an unsteady heat flux

A one-dimensional analytical method of determining the surface temperature of a thermal barrier coated plane wall subjected to an arbitrarily time-varying heat flux was developed. The method allows fast computation, enabling it to be embedded in combustion simulation software to correctly calculate wall heat transfer, which is important for reciprocating engine applications with thin, low thermal inertia coatings that have large temperature swings. The method relies on superposition of the response to successive step changes in heat flux, obtained by discretizing the heat flux history, to compile the solution. The embedded problem of a step-change in heat flux is addressed using the one-dimensional heat diffusion equation in conjunction with the matrix method in the Laplace domain, assuming the lateral conduction is neglected. For a two-layer wall (one coating layer on top of the metal wall) in the limit where kρc of the coating is small relative to that for the wall material, an analytical inversion to the time domain can be derived. For modest values of this parameter or for more than one coating layer, the residue theorem is invoked to invert to the time domain, with the poles and residues found numerically. The analytical inversion, however, provided the impetus for defining a set of non-dimensional parameters that uniquely characterize the surface temperature swing for arbitrary periodic heat flux to the wall. Non-dimensional results are given for a sinusoidially varying surface heat flux.

Invasion of the Nervous System.

In vertebrates, the nervous system (NS) is composed of a peripheral collection of neurons (the peripheral nervous system, PNS), a central set found in the brain and spinal cord (the central nervous system, CNS). The NS is protected by rather complicated multi-layer barriers that allow access to nutrients and facilitate contact with the peripheral tissues, but block entry of pathogens and toxins. Virus infections usually begin in peripheral tissues and if these barriers are weakened, they can spread into the PNS and more rarely into the CNS. Most viral infections of the NS are opportunistic or accidental pathogens that gain access via the bloodstream (e.g., HIV and various arboviruses). But a few have evolved to enter the NS efficiently by invading neurons directly and by exploiting neuronal cell biology (e.g., rhabdoviruses and alphaherpesviruses). Most NS infections are devastating and difficult to manage. Remarkably, the alphaherpesviruses establish life-long quiescent infections in the PNS, with rare but often serious CNS pathology. In this review, we will focus on how alphaherpesviruses gain access to and spread in the NS, with particular emphasis on bidirectional transport and spread within and between neurons and neural circuits, which is regulated by complex viral-host protein interactions. Finally, we will describe the wide use of alphaherpesviruses as tools to study nerve connectivity and function in animal models.

Corrosion protection of steel pipelines with metal-polymer composite barrier liners

Pipelines are efficient in transporting natural gas over large distances. Wet carbon dioxide present in pipelines can create an environment that is corrosive to steel. Polymer liners made from either polyethylene or polyamide (nylon) are presently used to mitigate internal corrosion in natural gas pipelines. Gas diffuses through all polymers over time, and polymer-only liners lower the steel corrosion rate by reducing the reactive gas flux to the internal surface of a pipeline. Composite liners, which incorporate one or more metallic layers that are impermeable to corrosive gases, offer better protection than polymer-only liners. We measured the methane, water vapor, and carbon dioxide permeability of a multi-layer barrier film and found it to be more effective in resisting gas permeation than polyethylene and nylon-11 films. The composite barrier film was more effective in protecting steel coupons immersed in a mixture of gaseous methane and wet carbon dioxide at 1 and 24 atm compared with polyethylene and polyamide films.

Outermost AlGaOx native oxide as a protection layer for GaAs/AlGaAs core-multishell nanowires

We propose native oxide AlGaOx outer protective layer for GaAs/AlGaAs core-multishell nanowires to provide yearly stable stronger optical and electrical confinement within the nanowire core. We prepared core-multishell NWs consisting of GaAs core, Al0.2Ga0.8As multi-layered barrier layer, and amorphous Al0.9Ga0.1Ox outer shell, which was obtained simply by growing Al-rich AlGaAs and exposing the NWs to the ambient air. Photoluminescence from the NWs reveals that the Al0.9Ga0.1Ox outer shell provides efficient optical confinement and creates a compressive strain in the interior of the NW that enhances and blueshifts the photoluminescence of the GaAs core.

High-performance multilayer thin-film encapsulation for organic micro-displays by inserting in situ plasma oxidized Al layers between SiOx layers

Multilayer thin-film encapsulation plays an important role in Si-based organic micro-displays. In this letter, we demonstrate an efficient and low-process-temperature approach to fabricate high-performance barrier films by inserting in situ plasma oxidized Al layers between SiOx encapsulation layers. Calcium degradation tests show that the water vapor transmission rate of the SiOx/AlOx multilayer barrier film is 2.23 × 10−5 g m−2 day−1 under the conditions of 25 °C and 70% relative humidity after in situ plasma oxidation treatment for 20 min, which is a reduction of two orders of magnitude compared with single-layer SiOx barrier films.

Surface temperature of a multi-layer thermal barrier coated wall subject to an unsteady heat flux

A one-dimensional analytical method of determining the surface temperature of a thermal barrier coated plane wall subjected to an arbitrarily time-varying heat flux was developed. The method allows fast computation, enabling it to be embedded in combustion simulation software to correctly calculate wall heat transfer, which is important for reciprocating engine applications with thin, low thermal inertia coatings that have large temperature swings. The method relies on superposition of the response to successive step changes in heat flux, obtained by discretizing the heat flux history, to compile the solution. The embedded problem of a step-change in heat flux is addressed using the one-dimensional heat diffusion equation in conjunction with the matrix method in the Laplace domain, assuming the lateral conduction is neglected. For a two-layer wall (one coating layer on top of the metal wall) in the limit where kρc of the coating is small relative to that for the wall material, an analytical inversion to the time domain can be derived. For modest values of this parameter or for more than one coating layer, the residue theorem is invoked to invert to the time domain, with the poles and residues found numerically. The analytical inversion, however, provided the impetus for defining a set of non-dimensional parameters that uniquely characterize the surface temperature swing for arbitrary periodic heat flux to the wall. Non-dimensional results are given for a sinusoidially varying surface heat flux.

Key influencing factors for the thermal shock resistance of La2Zr2O7-based multilayer TBCs

In this study, different multilayer thermal barrier coatings (TBCs) made from La2Zr2O7 (LZ), ZrO2-7 wt% Y2O3 (YSZ) and a freestanding LZ-YSZ coat were designed and produced by plasma spraying to determine the key influencing factors on the thermal shock resistance of LZ-based multilayer TBCs. The coatings were characterized in terms of their microstructure, phase composition and thermal expansion coefficient. The thermal shock behavior of the TBCs was evaluated using thermal cyclic tests at T = 1300 °C as well as at T = 1150 °C. The results show that the compressive stresses in the LZ top coat decreased with an increasing coating thickness of the YSZ interlayer. The LZ top coat failed in the interface areas to the YSZ interlayer for an YSZ interlayer that was not thick enough. Sintering ceramic coats significantly influenced the thermal shock resistance.

Open-Air Plasma-Deposited Multilayer Thin-Film Moisture Barriers.

Emerging moisture sensitive devices require robust encapsulation strategies to inhibit water ingress and prevent premature failure. A scalable, open-air plasma process has been developed to deposit alternating layers of conformal organosilicate and dense SiO2 thin-film barriers to prevent moisture ingress. The in situ low-temperature process is suitable for direct deposition on thermally sensitive devices and is compatible with flexible polymeric substrates. Using optical calcium testing, low water vapor transmission rates on the order of 10-3 g/m2/day at an accelerated aging condition of 38 °C and 90% relative humidity (RH) are achieved. Using moisture-sensitive perovskite devices as a representative moisture-susceptible device, devices retain over 80% of their initial performance for over 660 h in a 50 °C 50% RH accelerated aging environment. The ability of the multilayer barrier to enable device resistance to humid environments is crucial toward realizing longer operating lifetimes.

Recycling of a Healing Agent by a Water‐Vapor Treatment to Enhance the Self‐Repair Ability of Ytterbium Silicate‐Based Nanocomposite in Multiple Crack‐Healing Test

Yb2Si2O7/Yb2SiO5 composites dispersed with silicon carbide (SiC) possess a self‐crack‐healing ability that makes them promising top‐coat materials for multilayered environmental barrier coatings (EBCs) of SiC/SiC gas turbine blades. Stress‐induced surface cracks can be fully healed at high temperatures by the volume expansion of SiO2 glass and the newly formed Yb2Si2O7 in the composite. The reaction between SiO2 and Yb2SiO5 to form Yb2Si2O7 is considered a critical step that determines the high healing efficiency of this composite, therefore, Yb2SiO5 is considered as the secondary healing agent apart from the primary one, SiC. However, once all the healing agents have reacted, the composite can no longer promote its crack‐healing ability. To retain this property, in this work, Yb2SiO5 is regenerated by a heat treatment in water‐vapor atmosphere at 1073 K. X‐ray diffraction (XRD) and energy‐dispersive X‐ray spectroscopy (EDS) analyses show that the healing agent can be partially recycled after the treatment. In addition, the composite treated in water vapor demonstrates a greater crack‐healing ability compared with the untreated composite. These results open a new path for the development of gas turbine blades and high‐temperature components possessing permanent crack‐healing ability.

Design of ultrathin OLEDs having oxide-based transparent electrodes and encapsulation with sub-mm bending radius

Abstract Highly flexible ultrathin organic light emitting diodes (OLEDs) hold vast potential as light sources particularly for wearable and imperceptible electronics. Most of the work demonstrated to date for highly flexible OLEDs, however, has relied on non-conventional transparent conductors such as conjugated polymers and has had no proper encapsulation or, if any, simple polymer-based encapsulation. We here demonstrate OLEDs that can be bent at a sub-mm radius even with conventional transparent conductive oxides (TCOs) and full encapsulation based on a multilayer gas barrier containing aluminum oxides, both of which are prone to strain-induced fracture. We realize such a small bending radis not only by adopting ultrathin substrates but also by exploiting the beneficial neutral plane shift toward the top of substrates identified in a system consisting of a ultrathin substrate and a multilayer device structure on its top. The proposed OLEDs exhibit stable performance after 1,000 bending iterations even at a bending radius far smaller than 1 mm and show similar reliability to that of glass-based reference devices even after two weeks in the acceleration test chamber.

Establishment of an in vitro placental barrier model cultured under physiologically relevant oxygen levels.

The human placental barrier facilitates many key functions during pregnancy, most notably the exchange of all substances between the mother and fetus. However, preclinical models of the placental barrier often lacked the multiple cell layers, syncytialization of the trophoblast cells and the low oxygen levels that are present within the body. Therefore, we aimed to design and develop an in vitro model of the placental barrier that would reinstate these factors and enable improved investigations of barrier function. BeWo placental trophoblastic cells and human umbilical vein endothelial cells were co-cultured on contralateral sides of an extracellular matrix-coated transwell insert to establish a multilayered barrier. Epidermal growth factor and forskolin led to significantly increased multi-nucleation of the BeWo cell layer and increased biochemical markers of syncytial fusion, for example syncytin-1 and hCGβ. Our in vitro placental barrier possessed size-specific permeability, with 4000-Da molecules experiencing greater transport and a lower apparent permeability coefficient than 70 000-Da molecules. We further demonstrated that the BeWo layer had greater resistance to smaller molecules compared to the endothelial layer. Chronic, physiologically low oxygen exposure (3-8%) increased the expression of hypoxia-inducible factor 1α and syncytin-1, further increased multi-nucleation of the BeWo cell layer and decreased barrier permeability only against smaller molecules (457Da/4000Da). In conclusion, we built a novel in vitro co-culture model of the placental barrier that possessed size-specific permeability and could function under physiologically low oxygen levels. Importantly, this will enable future researchers to better study the maternal-fetal transport of nutrients and drugs during pregnancy.