Saturated Humidity Conditions Research Articles

The Effects of Humidity on the Velocity-Dependence and Frictional Ageing of Nanoscale Silica Contacts

This work examines the effect of environmental humidity on rate-and-state friction behavior of nanoscale silica-silica nanoscale contacts in an atomic force microscope, particularly, its effect on frictional ageing and velocity-weakening vs. strengthening friction from 10 nm/s to 100 μm/s sliding velocities. At extremely low humidities (≪1%RH\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\ll 1\\% RH$$\\end{document}), ageing is nearly absent for up to 100 s of nominally stationary contact, and friction is strongly velocity-strengthening. This is consistent with dry interfacial friction, where thermal excitations help overcome static friction at low sliding velocities. At higher humidity levels (10–40% RH), ageing becomes pronounced and is accompanied by much higher kinetic friction and velocity-weakening behavior. This is attributed to water-catalyzed interfacial Si–O-Si bond formation. At the highest humidities examined (> 40% RH), ageing subsides, kinetic friction drops to low levels, and friction is velocity-strengthening again. These responses are attributed to intercalated water separating the interfaces, which precludes interfacial bonding. The trends in velocity-dependent friction are reproduced and explained using a computational multi-bond model. Our model explicitly simulates bond formation and bond-breaking, and the passivation and reactivation of reaction sites across the interface during sliding, where the activation energies for interfacial chemical reactions are dependent on humidity. These results provide potential insights into nanoscale mechanisms that may contribute to the humidity dependence observed in prior macroscale rock friction studies. They also provide a possible microphysical foundation to understand the role of water in interfacial systems with water-catalyzed bonding reactions, and demonstrate a profound change in the interfacial physics near and above saturated humidity conditions.

Insight into the crack evolution and mechanism of catalyst-coated membrane undergoing freeze–thaw cycling in fuel cells

The evolution of catalyst-coated membrane (CCM) under saturated humidity conditions during freeze–thaw cycling was investigated, with a particular focus on the evolution of initial cracks within the catalyst layer (CL) and their impact on the proton exchange membrane (PEM). A quasi in-situ fuel cell fixture was designed to enable direct observation of the CCM via scanning electron microscopy (SEM). As the number of freeze–thaw cycles increases, the initial cracks in the CL gradually propagated, with new cracks appearing around them. These CL cracks tend to extend along the larger pores, which essentially represent gaps between agglomerates. The overall trajectory of formed cracks appears to be influenced by the flow channel direction. Additionally, under freeze–thaw cycling, cracks in the CL led to the formation of cracks in the PEM. A strong correlation is found between the direction of membrane cracks and CL cracks, suggesting a direct impact of the CL defects on the structural integrity of the PEM. Furthermore, some cracks at the tips of CL cracks even penetrate through the entire membrane. This study provides valuable insights into the degradation mechanisms of CCMs under low-temperature environmental conditions and could inform future design improvements for enhanced durability.

Changes in the Chemical Composition of Polyethylene Terephthalate under UV Radiation in Various Environmental Conditions.

Polyethylene terephthalate has been widely used in the packaging industry. Degraded PET micro(nano)plastics could pose public health concerns following release into various environments. This study focuses on PET degradation under ultraviolet radiation using the NIST SPHERE facility at the National Institute of Standards and Technology in saturated humidity (i.e., ≥95% relative humidity) and dry conditions (i.e., ≤5% relative humidity) with varying temperatures (30 °C, 40 °C, and 50 °C) for up 20 days. ATR-FTIR was used to characterize the chemical composition change of degraded PET as a function of UV exposure time. The results showed that the cleavage of the ester bond at peak 1713 cm-1 and the formation of the carboxylic acid at peak 1685 cm-1 were significantly influenced by UV radiation. Furthermore, the formation of carboxylic acid was considerably higher at saturated humidity and 50 °C conditions compared with dry conditions. The ester bond cleavage was also more pronounced in saturated humidity conditions. The novelty of this study is to provide insights into the chemical degradation of PET under environmental conditions, including UV radiation, humidity, and temperature. The results can be used to develop strategies to reduce the environmental impact of plastic pollution.

Changes in the Chemical Composition of Polyethylene Terephthalate Under UV Radiation in Various Environmental Conditions.

Polyethylene terephthalate has been widely used in the packaging industry. Degraded PET micro-nano plastics could pose public health concerns following release into various environments. This study focuses on PET degradation under ultraviolet radiation using the NIST SPHERE facility at the National Institute of Standards and Technology in saturated humidity (i.e., ≥ 95 % relative humidity) and dry conditions (i.e., ≤ 5 % relative humidity) with varying temperatures (30 °C, 40 °C, and 50 °C) for up 20 days. ATR-FTIR was used to characterize the chemical composition change of degraded PET as a function of UV exposure time. The results showed that the cleavage of the ester bond at peak 1713 cm-1 and the formation of the carboxylic acid at peak 1685 cm-1 are significantly influenced by UV radiation. Furthermore, the formation of carboxylic acid was considerably higher at saturated humidity and 50 °C conditions compared to dry conditions. The ester bond cleavage was also more pronounced in saturated humidity conditions. The novelty of this study is to provide insights into the chemical degradation of PET under environmental conditions, including UV radiation, humidity, and temperature. The results can be used to develop strategies to reduce the environmental impact of plastic pollution.

Chitosan reduced in-situ synthesis of gold nanoparticles on paper towards fabricating highly sensitive, stable uniform SERS substrates for sensing applications

Surface-Enhanced Raman Spectroscopy (SERS) is a powerful surface-sensitive technique for molecular analysis. Its use is limited due to high cost, non-flexible rigid substrates such as silicon, alumina or glass and less reproducibility due to non-uniform surface. Recently, paper-based SERS substrates, a low-cost and highly flexible alternative, received significant attention. We report here a rapid, inexpensive method for chitosan-reduced, in-situ synthesis of gold nanoparticles (GNPs) on paper devices towards direct utilization as SERS substrates. GNPs have been prepared by reducing chloroauric acid with chitosan as a reducing and capping reagent on the cellulose-based paper surface at 100 °C, under the saturated humidity condition (100 % humidity). GNPs thus obtained were uniformly distributed on the surface and had fairly uniform particle size with a diameter of 10 ± 2 nm. Substrate coverage of resulting GNPs directly depended on the precursor's ratio, temperature and reaction time. Techniques such as TEM, SEM, and FE-SEM were utilized to determine the shape, size, and distribution of GNPs on paper substrate. SERS substrate produced by this simple, rapid, reproducible and robust method of chitosan-reduced, in situ synthesis of GNPs, showed exceptional performance and long-term stability, with a detection limit of up to 1 pM concentration of test analyte, R6G. Present paper-based SERS substrates are cost-effective, reproducible, flexible, and suitable for field applications.

In-plane micro-supercapacitor using polymer nanosheet assembly as a weak acid solid electrolyte

In-plane micro-supercapacitors, in which the electrodes are arranged on the same plane have attracted much attention because of their light weight, simple device structure, etc. In this paper, micro-supercapacitors were fabricated by using polymer nanosheet multilayer film as a solid electrolyte. The micro-supercapacitors were fabricated by sequential deposition poly(N-dodecyl acrylamide-co-acrylic acid) monolayer onto a solid substrate with interdigitated gold electrodes. The capacitor characteristics were investigated by cyclic voltammetry under saturated humidity condition. It was revealed that the micro-supercapacitor showed a capacitance of 33 µF/cm2.

A Comparison Study on the Carbon Corrosion Reaction under Saturated and Low Relative Humidity Conditions via Transmission Line Model-Based Electrochemical Impedance Analysis

In this work, we study the dependence of water content on the carbon corrosion reaction by applying an external potential (1.4 V vs RHE) under saturated and low (30%) relative humidity (RH) conditions via a transmission line model (TLM)-based impedance analysis in a polymer electrolyte membrane fuel cell (PEMFC). High potentials inducing carbon corrosion reaction cause electrode thinning, make the supporting carbon structure less porous, decrease the electrochemical surface area (ECSA), and dehydrate the ionomer, leading to fast performance decay in the cell. Particularly, in this work, we discuss the main cause of performance decay in PEMFCs in view of the structural deformation of supporting carbon using the ionic resistance and double layer capacitance in non-faradaic impedance and charge transfer resistance in faradaic impedance to elucidate the different degradation behaviors of membrane electrode assembly (MEA) under saturated and low humidity (RH 30%) conditions. As a result, it is confirmed that carbon corrosion severely changes the structural properties of the supporting carbon, such as pore depth and circumference, and the specific pore deformation with the evolution of oxygen-containing functional groups on the carbon surfaces subordinately induces the severe degradation in cell performance with the water drainage issues, namely, flooding.

Colloidal monolayers with cell-like tessellations via interface assisted evaporative assembly

Evaporating sessile drops containing surface active colloids is a promising route to self-assemble two-dimensional nanostructures. The standard protocol is to first self-assemble surface active nanoscale particles at the water-vapour interface and subsequently transfer it on to a solid surface. Colloidal monolayers with very few morphologies have been fabricated, exploiting this bottom-up self-assembly technique. However, the evaporation kinetics under controlled humidity conditions may dramatically alter the microstructure of self-assembled colloidal monolayers at the liquid-vapor interface and that on the solid surfaces, an aspect that has not been fully addressed in the prior studies. To this end, we present an experimental study of evaporation driven self-assembly of soft poly(N-isopropylacrylamide) (pNIPAM) microgel particles loaded in a sessile drop. The surface-active microgel particles spontaneously populate the water-vapour interface facilitating the suppression of the coffee-ring effect and the formation of monolayer stains. The role of evaporation kinetics under controlled humidity conditions on the colloid's microstructure adsorbed to the solvent-air interface and on the morphology of the colloidal monolayer transferred onto the solid surface are studied in detail. The formation of particle-free and particle-rich regions at the water-vapor interface is observed for sessile drops evaporated under saturated humidity conditions. We show that the evaporation induced shrinkage of the interface area and the enhancement of the areal density of microgel particles adsorbed onto the interface leads to a restructuring of the particle-laden interface. The rearrangement of microgel particles along the water-vapor interface resembling the de-wetting assisted patterns is transferred to the solid substrate upon complete evaporation of the solvent. The microgel particles in the deposit assemble into domains with enhanced crystalline order. The evolution of Voronoi entropy across the monolayer deposit patterns obtained by the standard and slow evaporation routes are presented.

Humidity responsive single-layered film fabricated by hydrophilic titanium oxide nanotubes

We fabricated a humidity responsive film comprising a bundle of titanium oxide tubes, which changes its curvature corresponding to the relative humidity. The mechanism of changing the curvature of the film can be explained by adsorption, condensation, and evaporation of water molecules within the film. During adsorption, a liquid bridge is formed because of the growth of a water layer between tubes, thus contracting the tubes. When vapor pressure exceeds the equilibrium vapor pressure, condensation occurs at the meniscus of the liquid bridge, thus expanding the gap between tubes. We obtained the adsorption and desorption isotherms for the humidity responsive film by determining physical adsorption. Additionally, we demonstrated the varying motions of the humidity sensing film when a water droplet was applied on the surface. The sensor could distinguish between saturated and oversaturated humidity conditions, such as fog and rain, respectively, which is not possible using resistive humidity sensors. This humidity responsive film can be applied to environmental monitoring systems and possibly even to energy harvesting systems.

A fatty acid synthase gene (FASN3) from the integument tissue of Rhodnius prolixus contributes to cuticle water loss regulation.

Fatty acid synthase is a multifunctional enzyme involved in the formation of fatty acids. Despite the role of fatty acids in cell signalling and energy metabolism, and as precursors to pheromones and hydrocarbons that waterproof the cuticle, the insect fatty acid synthases have been scarcely studied. Here we perform the molecular characterization of three fatty acid synthase genes (fatty acid synthase RPRC000123, RPRC000269 and RPRC002909) in the Chagas disease vector, Rhodnius prolixus. Gene expression screening by reverse transcription quantitative PCR showed that RPRC000123 and RPRC002909 are expressed almost exclusively in the integument tissue whilst RPRC000269 is mostly expressed in the fat body and also in several body organs. Phylogenetic analysis, together with gene expression results, showed that RPRC000269, RPRC002909 and RPRC000123 are orthologues of Drosophila melanogaster fatty acid synthase 1 (FASN1), FASN2 and FASN3 genes, respectively. After RNA interference-mediated knockdown of RPRC000123, insects died immediately after moulting to the next developmental stage. However, mortality was prevented by placing the insects under saturated humidity conditions, suggesting that dehydration might play a role in the insects' death. Lipid analyses in RPRC000123-silenced insects showed reduced amounts of integument fatty acids and methyl-branched hydrocarbons, compared to controls. These data support an important role for FASN3 in the biosynthesis of the precursors to hydrocarbons that waterproof the insect cuticle.

Physiological responses of garden roses to hot and humid conditions

Garden roses do not grow well under hot and humid conditions. The objective of this study was to investigate the physiological responses of ‘Marie Curie’ and ‘Lapjau’ to high temperatures and relative humidity. The study included temperatures of 25/18°C (day/night) and 35/28°C (day/night), and relative humidity of 70% and 100%. ‘Marie Curie’ was more tolerant to heat stress than ‘Lapjau’ based on relative electrolyte leakage (REL), malondialdehyde (MDA), and activities of superoxide dismutase (SOD). The heat tolerance of cultivars also was confirmed by the levels of chlorophyll content and the net photosynthesis rate. Both cultivars were more stressed under more water vapour deficit than saturated vapour at 35/28°C (day/night), while at 25/18°C (day/night) the cultivars were more stressed under saturated humidity condition than at 70% relative humidity. In conclusion, combined hot and saturated humidity does not necessarily result in increased stress over separated heat or humidity elevations to the garden roses. Rose growers can use this information in regions where hot and humid conditions concur.

Using Growth and Transpiration Phenotyping Under Controlled Conditions to Select Water Efficient Banana Genotypes.

Water deficit is one of the world’s major constraints in agriculture and will aggravate in the future. Banana (Musa spp.) is an important crop that needs vast amounts of water for optimal production. The International Transit Center of Bioversity International holds the world’s biggest collection of banana biodiversity (>1,500 accessions). The long-term aim of this research is to evaluate the potential within this collection for climate smart agricultural usage. Therefore, we developed a phenotyping setup under controlled environmental conditions and we selected 32 representatives of the Musa biodiversity (29 cultivars and 3 wild relatives) for evaluation. The best performing genotypes accumulated six to seven times more biomass than the least performing. Eight genotypes (five ABB, one AAB, and two AAA) invest under osmotic stress significantly more in root growth than in leaf growth. We predict therefore that these genotypes have potential for high productivity under rain fed conditions with a short dry season. To gain more insight in the transpiration physiology, we gravimetrically monitored individual plant transpiration over the diurnal period. All analyzed genotypes showed a marked reduction in transpiration rate in the afternoon. Moreover, the timing of this onset, as well as its impact on total transpiration, was genotype dependent. This phenomenon was more pronounced in 13 genotypes (eight ABB, two AAB, two AA, one BB). Banana is a crop originating from the humid tropics and has developed a strong root pressure to maintain an efficient water and nutrient transport even under saturated relative humidity conditions. Therefore, we hypothesize that the diurnal transpiration decline contributes to a higher water use efficiency without compromising the nutrient transport. Of the eight genotypes that had the best growth under osmotic stress, all analyzed ABB cultivars have a lower maximal transpiration rate, keep this maximal transpiration for a shorter time and therefore consume less water per day. We conclude that lab models are very useful to study the biodiversity and to identify different traits that contribute to a better drought tolerance/avoidance. We encourage researchers investigating other crops to start exploring their collections.

Shiitake mushroom packages tuned in active CO2 and moisture absorption requirements

Abstract Active packages of shiitake mushrooms with CO 2 - and moisture-absorbing sachet or pad were designed and tested in their effectiveness in quality preservation for a given shelf life of 5 days at 10 °C. Sachets of sodium carbonate (SC) and mix of SC and calcium hydroxide (CH), and SC-impregnated cotton pad were characterized in their CO 2 and moisture absorption properties to calculate proper amounts of the active components capable of scavenging the required amounts of CO 2 and water vapour. The demands of CO 2 and water vapour absorptions to maintain the desired modified atmosphere (MA) and avoid moisture condensation inside the packages were determined from mass balance relationships comprising the mushroom respiration/transpiration and gas transmission through the package layer. Super-absorbent polymer (SAP) of polyacrylate was added as a supplement material to bring about the water vapour absorption required further to attain non-saturated humidity condition. Sachet combined of SC and SAP attached inside the package of 180 g mushrooms maintained its atmosphere of 10.7–11.6% O 2 and 7.1–8.9% CO 2 concentrations at steady state helping to preserve the quality best. Proper combination of CO 2 and moisture absorbers can be useful tool to create the desired MA and alleviate saturated humidity conditions in packages of the commodities sensitive to high CO 2 and moisture condensation.

Reduction of the Nitrate Content in Baby Spinach Leaves by Vacuum Impregnation with Sucrose

Vacuum impregnation (VI) has been widely utilized as a pre-treatment method prior to, e.g., the minimal processing, freezing, or drying of foods. In many cases, VI has been used to focus on the enrichment of fruits and vegetables with probiotics or micronutrients, texture enhancement, the modification of the sensory attributes, and extension of shelf life by pH reduction. However, little attention has been paid to the exploration of the metabolic consequences of VI that could lead to changes in the quality characteristics of plant tissues. Since nitrate has long been discussed as a compound that is harmful to human health, the aim of this investigation was to reduce the nitrate content in spinach leaves by feeding sucrose into the tissue using VI. The leaves, either non-treated or treated with VI, were stored under saturated humidity conditions and in darkness at 8 °C, for up to 72 h. VI-treated leaves showed a remarkable reduction in nitrate content as compared to the non-treated samples. Upon storage, sucrose was reduced, indicating that this sugar had been respired and had induced metabolization of the stored nitrate. The nitrite content of the treated leaves was unaffected, proving that this toxic compound was not accumulated in the baby spinach leaves upon external sucrose feeding.

Transpiration of Water Molecules through Molecule-Based Porous Crystals with One-Dimensional Nanochannels

Abstract Synthetic molecular crystals with one-dimensional nanoporous channels containing H2O molecules act as model systems for pores such as aquaporin-1 in cell membranes. The structural characteristics of water molecular clusters (WMCs) were investigated using X-ray crystal analysis of {[NiII(cyclam)]3(TMA)2·35–34 H2O}n (2) (TMA: trimesate, cyclam: 1,4,8,11-tetraazacyclotetradecane) in a closed glass capillary to adjust the saturated humidity. The structural phase transition of WMCs with temperature depends only on the H2O structures around the centre, not on those in the primary hydrate layer nearest to the outer wall. The centre of a WMC was filled with H2O molecules under saturated humidity conditions; however, in air, the WMC had a nanotube-like structure with a vacant space. Thus, the centre portion of a WMC probably contains volatile and mobile H2O molecules. Therefore, we investigated the rapid proton conductivity using alternating current impedance and microwave spectroscopy and also carried out a transpiration experiment for transferring the mobile H2O molecules. The microwave spectroscopy results for 2 indicated no isotope effect, which would be observed by the rapid motion of H2O molecules without the breaking of hydrogen bonds between two site-disordering positions above the phase transition temperature. The results indicated reasonable water transpiration ability of the single crystal through its nanochannels; this property can be useful as a working principle to understand applications such as the desalination of seawater.

Surface engineered CuO nanowires with ZnO islands for CO2 photoreduction.

Large arrays of massively parallel (10(8) cm(-2)) CuO nanowires were surface engineered with dense ZnO islands using a few pulsed cycles of atomic layer deposition (ALD). These nanowires were subjected to UV-vis radiation-based CO2 photoreduction under saturated humidity (CO2 + H2O mixture) conditions. We monitored CO2 to CO conversion, indicating the viability of these nanostructures as potential photocatalysts. High-resolution transmission electron microscopy and atomic force microscopy indicated an island growth mechanism of ZnO epitaxially depositing on pristine, single crystal CuO nanowire surface. Photoluminescence and transient absorption spectroscopy showed a very high density of defects on these ZnO islands which trapped electrons and enhanced their lifetimes. Peak CO conversion (1.98 mmol/g-cat/hr) and quantum efficiency (0.0035%) were observed in our setup when the ZnO islands impinged each other at 1.4 nm (8 cycles of ALD) diameter; at which point ZnO island perimeter lengths maximized as well. A mechanism whereby simultaneous H2O oxidation and CO2 reduction occurred in the active perimeter region between CuO nanowire and ZnO islands is proposed to explain the observed photoconversion of CO2 to CO.

High ionic conductivity of Mg–Al layered double hydroxides at intermediate temperature (100–200 °C) under saturated humidity condition (100% RH)

Ionic conduction properties of layered double hydroxides (LDHs), [Mg (1 − x) Al ( x) (OH) 2](CO 3) x/2 · nH 2O (═CO 3-type) and [Mg (1 − x) Al ( x) (OH) 2](OH) x · nH 2O (═OH-type), have been investigated in the temperature range of 25–200 °C under saturated water vapor pressure (100% RH). Conductivity was measured by the complex impedance method using pressed pellet samples. The conductivity of an OH-type sample ( x = 0.25) is as high as 4 × 10 − 3 S cm − 1 already at room temperature. On heating, it increases as slowly (the activation energy E a ∼ 55 meV) as those of liquid electrolyte solutions, suggesting that ions are transported via exchange of protons between OH − and H 2O species in the interlayer space of the LDH (a kind of the Grotthus mechanism). The conductivity at 200 °C reaches 3 × 10 − 2 S cm − 1 . Although the conductivity of the CO 3-type counterpart is considerably low (∼ 10 − 6 S cm − 1 ) at room temperature, it increases with increasing temperature with showing a jump by about four orders of magnitude around 80 °C, after which the compound is turned into an almost the same liquid-like conductor as the OH-type sample; the conductivity jump is probably due to the interlayer reaction CO 3 2− + H 2O = 2OH − + CO 2 (g). Thus those Mg–Al LDH materials show the potential application as solid electrolyte materials for intermediate temperature fuel cells, not only because they have high conductivity but also they should not suffer from the degradation by CO 2 which is a serious problem for conventional anion exchange membranes.

Pathogen‐tested material of grapevine varieties and rootstocks

Pathogen‐tested material of grapevine varieties and rootstocks

Organic–Inorganic Hybrid Membranes for a PEMFC Operation at Intermediate Temperatures

Recently, polymer electrolyte membrane fuel cells (PEMFCs) have been investigated extensively as a future energy source to solve a global energy and environmental problem due to their high energy conversion efficiency. As a membrane is recognized to be a key element for more efficient PEMFCs, new classes of polymer electrolytes have been investigated elsewhere. We have also studied new temperature-tolerant electrolytes using organic–inorganic materials such as polydimethylsiloxane, polytetramethylene oxide (PTMO), zirconia, and titania materials. 12-phosphotungstic (PWA) and phosphoric acids as a proton source were incorporated in the hydrophilic interface of organic–inorganic hybrid membranes. In this paper, they were synthetically displayed, and the cell performance for intermediate temperature PEFC using a single membrane electrolyte assembly cell was also investigated. The maximum power densities for zirconium phosphate–PTMO and titania–PTMO–PWA composite membranes were 13 and , respectively. The cell performance of the membranes increased with increasing cell temperature up to 130°C under saturated humidity conditions. The organic–inorganic hybrid electrolytes synthesized from PTMO with metal alkoxides show promise for applications in intermediate temperature PEFCs.

Highly proton conducting hybrid materials synthesized from 12-phosphotungstic and hexadecyltrimethylammonium salt

12-phosphotungstic acids were mixed with hexadecyltrimethylammonium chloride to form self-assembled organic/inorganic nanostructures. The composite materials are thermally stable and exhibited large proton conductivity when the composite was annealed at higher temperatures. High proton conductivity of 0.01 S/cm at 150 °C under a saturated humidity condition was obtained for the PWA ammonium salt product, which was formed by annealing the initial nanostructures at 400 °C.