Wide Range Of Relative Humidity Research Articles

Characterization of an Impedance-Type Humidity Sensor Based on Porous SnO2/TiO2 Composite Ceramics Modified with Molybdenum and Zinc.

In this study, we report on the room-temperature characteristics of an impedance-type humidity sensor based on porous tin oxide/titanium oxide (SnO2/TiO2) composite ceramics modified with Mo and Zn. The SnO2/TiO2-based composites synthesized in the solid-state processing technique have been structurally characterized using X-ray diffraction, scanning electron microscopy, energy dispersive, and Raman spectroscopy. Structural analysis indicated the desired porous nature of the synthesized ceramics for sensing applications, with an average crystallite size in the nano range and a density of about 80%. The humidity-sensing properties were evaluated within a wide relative humidity range from 15% to 85% at room temperature, and the results showed that a better humidity response had a sample with Mo. This humidity-sensing material exhibits a linear impedance change of about two orders of magnitude at the optimal operating frequency of 10 kHz. Furthermore, fast response (18 s) and recovery (27 s), relatively small hysteresis (2.8%), repeatability, and good long-term stability were also obtained. Finally, the possible humidity-sensing mechanism was discussed in detail using the results of complex impedance analysis.

High-Barrier, Biodegradable Films with Polyvinyl Alcohol/Polylactic Acid + Wax Double Coatings: Influence of Relative Humidity on Transport Properties and Suitability for Modified Atmosphere Packaging Applications.

Polyvinyl alcohol (PVOH) exhibits outstanding gas-barrier properties, which favor its use as a biodegradable, high-barrier coating on food-packaging films, possibly in combination with modified atmospheres. Nonetheless, its high sensitivity to water can result in a severe loss of barrier properties, significantly limiting its applications with fresh foods and in high-humidity conditions. In this work, the water vapor (PWV) and oxygen permeability (PO2) of high-barrier biodegradable films with PVOH/PLA + wax double coatings were extensively characterized in a wide range of relative humidity (from 30 to 90%), aimed at understanding the extent of the interaction of water with the wax and the polymer matrices and the impact of this on the permeation process. What is more, a mathematical model was applied to the PWV data set in order to assess its potential to predict the permeability of the multilayer films by varying storage/working relative humidity (RH) conditions. The carbon dioxide permeability (PCO2) of the films was further evaluated, and the corresponding permselectivity values were calculated. The study was finally augmented through modified atmosphere packaging (MAP) tests, which were carried out on double-coated films loaded with 0 and 5% wax, and UV-Vis analyses. The results pointed out the efficacy of the PLA + wax coating layer in hampering the permeation of water molecules, thus reducing PVOH swelling, as well as the UV-shielding ability of the multilayer structures. Moreover, the MAP tests underlined the suitability of the double-coated films for being used as a sustainable alternative for the preservation of foods under modified atmospheres.

Self-Powered TENG with High Humidity Sensitivity from PVA Film Modified by LiCl and MXene.

Triboelectric nanogenerators (TENGs) are promising for a variety of applications that require a reliable output performance and stability. In this work, by utilizing the synergistic effect of lithium chloride (LiCl) and MXene, poly(vinyl alcohol) (PVA) based composite films with humidity-sensitive properties were prepared and employed as a friction layer to achieve self-powered TENGs with enhanced output performance under high humidity. The composite material demonstrates exceptional and stable output performance in the humidity range of 30-95% while exhibiting a strong linear correlation with increasing relative humidity (RH). At 95% RH, its short-circuit current increases up to 31.91 μA, which is three times the output of the TENG fabricated by PVA and PTFE (P-TENG). The rich hydroxyl group in PVA, the strong hygroscopicity of LiCl, and the microcapacitor network provided by MXene nanosheets significantly improve the water absorption capacity and surface roughness of the composite material, resulting in an excellent triboelectric output of TENG. Short-circuit current of the TENG in a wide range of RH (from 50% to 98%) responds very sensitively to humidity fluctuations in the environment and superior adsorption-desorption performance as humidity decreases. Furthermore, TENG regarded as a power supply in high humidity conditions was realized and it can light up 240 LEDs instantaneously with the transfer charge density of TENG reaching 194.37 μC m-2. This technology presents an effective method for stable energy harvesting and self-powered sensing in fog, the ocean, and other high-humidity environments.

Phase Behavior and Viscosity in Biomass Burning Organic Aerosol and Climatic Impacts.

Smoke particles generated by burning biomass consist mainly of organic aerosol termed biomass burning organic aerosol (BBOA). BBOA influences the climate by scattering and absorbing solar radiation or acting as nuclei for cloud formation. The viscosity and the phase behavior (i.e., the number and type of phases present in a particle) are properties of BBOA that are expected to impact several climate-relevant processes but remain highly uncertain. We studied the phase behavior of BBOA using fluorescence microscopy and showed that BBOA particles comprise two organic phases (a hydrophobic and a hydrophilic phase) across a wide range of atmospheric relative humidity (RH). We determined the viscosity of the two phases at room temperature using a photobleaching method and showed that the two phases possess different RH-dependent viscosities. The viscosity of the hydrophobic phase is largely independent of the RH from 0 to 95%. We use the Vogel-Fulcher-Tamman equation to extrapolate our results to colder and warmer temperatures, and based on the extrapolation, the hydrophobic phase is predicted to be glassy (viscosity >1012 Pa s) for temperatures less than 230 K and RHs below 95%, with possible implications for heterogeneous reaction kinetics and cloud formation in the atmosphere. Using a kinetic multilayer model (KM-GAP), we investigated the effect of two phases on the atmospheric lifetime of brown carbon within BBOA, which is a climate-warming agent. We showed that the presence of two phases can increase the lifetime of brown carbon in the planetary boundary layer and polar regions compared to previous modeling studies. Hence, the presence of two phases can lead to an increase in the predicted warming effect of BBOA on the climate.

An All-Printed, Fast-Response Flexible Humidity Sensor Based on Hexagonal-WO3 Nanowires for Multifunctional Applications.

The utilization of printing techniques for the development of high-performance humidity sensors holds immense significance for various applications in the fields of the Internet of Things, agriculture, human healthcare, and storage environments. However, the long response time and low sensitivity of current printed humidity sensors limit their practical applications. Herein, a series of high-sensing-performance flexible resistive-type humidity sensors is fabricated by the screen-printing method, and hexagonal tungsten oxide (h-WO3 ) is employed as the humidity-sensing material due to its low cost, strong chemical adsorption ability, and excellent humidity-sensing ability. The as-prepared printed sensors exhibit high sensitivity, good repeatability, outstanding flexibility, low hysteresis, and fast response (1.5s) in a wide relative humidity (RH) range (11-95%RH). Furthermore, the sensitivity of humidity sensors can be easily adjusted by altering the manufacturing parameters of the sensing layer and interdigital electrode to meet the diverse requirements of specific applications. The printed flexible humidity sensors possess immense potential in various applications, including wearable devices, non-contact measurements, and packaging opening state monitoring.

Identification and quantification of soil water components in kaolin by thermogravimetric and kinetic analysis

Different types of soil water, such as bound water and capillary water, have distinct effects on the physicochemical and engineering properties of soils, particularly unsaturated clayey soils. Therefore, it is crucial to develop an accurate and physically meaningful experimental method for identifying and quantifying these components. This study pioneers the use of a multi-step kinetic model to identify and quantify different soil water components across a wide range of relative humidity (RH) using thermogravimetric analysis (TGA) data. To validate the determined kinetic parameters (i.e., activation energy, preexponential factor, and reaction model) and the identification and quantification results of soil water components, TGA with multiple heating rates, nitrogen adsorption method, cation exchange capacity measurement, and nuclear magnetic resonance (NMR) were performed on kaolin samples equilibrated under various RH conditions. These experimental results cross-validate the superior performance of the kinetic model in determining soil water components and predicting the thermal desorption behaviors of soil water. Based on the cross-validation results, the soil water components obtained from the kinetic analysis are further identified as tightly-bound, loosely-bound, and capillary water, which exhibit variations consistent with empirical soil water isotherm models. The T2 cutoff value between bound and capillary water is determined to be 1.79 ms based on TGA and NMR results. The determined thermal kinetic parameters of different soil water components can exhibit their distinct retention mechanisms. The method and results in this study provide a new perspective on identifying different soil water components, as well as understanding the mechanism of soil-water interactions in unsaturated soils.

Laser-direct-writing assisted preparation of flexible humidity sensors based on semi-interpenetrating polymer network for applications in non-contact human-machine interaction

Flexible sensors for non-contact human-machine interaction (HMI) received great attention recently due to increasing requirements for cross-infection of bacteria or virus, which is prominent considering the disaster brought about by COVID-19. Herein, a semi-interpenetrating network of poly(dimethyl diallyl ammonium chloride)/crosslinked poly(vinyl alcohol)/graphene oxide (PDDA/c-PVA/GO) was deposited on polytetrafluoroethylene membrane with interdigital electrodes constructed by reducing GO with laser-direct-writing technology to prepare a flexible humidity sensor (FHS). As-prepared PDDA/c-PVA/GO FHS showed excellent sensing performance, including high response magnitude over wide range of relative humidity (RH) (impedance change of three orders of magnitude between 10 % and 90 % RH), good sensing linearity (R2 = 0.991) on a semi-logarithmic scale, small hysteresis (∼ 4.4 % RH) and resistance to humid environment. Moreover, the FHS exhibited good performance in various scenarios of non-contact HMI, including prompt differentiation of respiration status, speech recognition, accurate measurement of fingertip movement (as small as 2 mm). Specially, a 3 × 3 FHS sensor array could realize accurate non-contact positioning. This work provides a new approach for developing high performance flexible sensors with great application potentials in non-contact HMI.

High-temperature stability of hydrocarbon-based Pemion® proton exchange membranes: A thermo-mechanical stability study

In this work, the ex-situ thermo-mechanical stability of Pemion® – a commercial mechanically-reinforced sulfo-phenylated polyphenylene-based proton exchange membrane – is investigated across a wide range of temperature (30–120 °C) and relative humidity (RH) (10–90%) conditions versus a commercial mechanically-reinforced PFSA material (r-PFSA). The Young's modulus and strain hardening of Pemion® are found to be temperature-independent, whereas r-PFSA exhibits significant decay above 90 °C. Pemion® maintains acceptable resistance against yielding within the tested range, while small mechanical stress values (e.g., 1 MPa) can cause spontaneous yielding in r-PFSA above 110 °C. The modulus of resilience for the r-PFSA membrane is also predicted to approach zero at elevated hygrothermal conditions, rendering them unsuitable for higher operating temperatures. Thermal transition and decomposition of samples are studied using DSC and TGA as well. Overall, Pemion® shows appreciable stability at hygrothermal ambience close to high-temperature PEMFC operating targets, i.e., 110–120 °C and 40–50% RH, likely due to its rigid-rod polyphenylene backbone with reduced intermolecular mobility.

Nanomechanical analysis of Gamma-irradiated cement paste exposed to different humidities

The paper characterizes concurrent effects of gamma-irradiation and presence of water in Portland cement pastes. An extensive nanomechanical quantification (Young’s modulus, hardness, and creep compliance) at two scales is performed after exposure to two gamma-ray doses and a wide range of relative humidities (RH 0%–100%). Competing microstructural mechanisms such as water radiolysis, hydration, carbonation and drying were identified and their effects de-coupled with the aid of nanoindentation and other supporting techniques. Maximum radiation resistance was found for samples in medium humidities (33%–57%). Samples irradiated below 11% RH exhibited compaction of C-S-H phases at the level of 100 nm, ∼25% increase of Young’s modulus and decrease of creep compliance due to water radiolysis and drying. The compaction resulted in microcracking at higher paste scale and caused ∼17% decrease of elastic modulus. Samples irradiated in water showed large (∼26%) decrease of Young’s modulus and increased creep compliance accompanied by 9%–10% Portlandite loss.

An Efficient Ambient-Moisture-Driven Wearable Electrical Power Generator.

Existing devices for generating electrical power from water vapor in ambient air require high levels of relative humidity (RH), cannot operate for prolonged periods, and provide insufficient output for most practical applications. Here a heterogeneous moisture-driven electrical power generator (MODEG) is developed in the form of a free-standing bilayer of polyelectrolyte films, one consisting of a hygroscopic matrix of graphene oxide(GO)/polyaniline(PANI) [(GO)PANI] and the other consisting of poly(diallyldimethylammonium chloride)(PDDA)-modified fluorinated Nafion (F-Nafion (PDDA)). One MODEG unit (1 cm2 ) can deliver a stable open-circuit output of 0.9V at 8µA for more than 10h with a matching external load. The device works over a wide range of temperature (-20 to +50 °C) and relative humidity (30% to 95% RH). It is shown that series and parallel combinations of MODEG units can directly supply sufficient power to drive commercial electronic devices such as light bulbs, supercapacitors, circuit boards, and screen displays. The (GO)PANI:F-Nafion (PDDA) hybrid film is embedded in a mask to harvest the energy from exhaled water vapor in human breath under real-life conditions. The device could consistently generate 450-600mV during usual breathing, and provides sufficient power to drive medical devices, wearables, and emergency communication.

Unlocking efficient and robust ozone decomposition with CNT-confined manganese oxide via synergistic electronic modulation

Manganese oxides (MnO2)-based catalysts are prominent candidates for ozone elimination, which always bear the accumulation of the intermediate oxygen species and water, resulting in unsatisfactory catalytic efficiency. To overcome this critical defect, we propose carbon nanotubes confined MnO2 catalysts (MnO2-in-CNT) for efficient and stable ozone decomposition over a wide relative humidity range (RH, 15–90%). Strikingly, the catalyst exhibits an efficient and sustainable ozone conversion (98%) over 100 h under a gas hourly space velocity (GHSV) of 600,000 mL g−1 h−1 and RH of 15%, and durability under high RH (77% over 50 h, RH 70%), well beyond its unconfined analog and most reported works. This excellent catalytic performance can be attributed to the facilitated intermediate desorption on active sites and the confined structure alleviated the effect of water on inner MnO2. This discovery is expected to drive great progress in the applications of confined-structure catalysts for air purification.

Numerical investigation of novel block flow channel on mass transport characteristics and performance of PEMFC

This study develops a three-dimensional numerical model of a proton exchange membrane (PEM) fuel cell (PEMFC) to investigate the mass transport characteristics and performance of PEMFC with novel two-block structures in the cathode channel. The results reveal that the novel two-block structures improve the efficiency of mass transport and the performance of PEMFC. Effects of the arrangement of two-block structures and the operating conditions on the PEMFC performance are investigated. It is found that the block position closer to the outlet of the channel has greater improvement of the PEMFC performance. The PEMFC performance increases firstly with the block structure number and then decreases, and the best number of block structures is 6 for the present study. The block channel has more evident effect when the PEMFC operated under high current density and small stoichiometric ratio, and the block channel is effective in a wide relative humidity (RH) range.

Biomimetic Hygroscopic Fibrous Membrane with Hierarchically Porous Structure for Rapid Atmospheric Water Harvesting

AbstractSorption‐based atmospheric water generation (SAWG) is a promising strategy to alleviate the drinkable water scarcity of arid regions. However, the high‐water production efficiency remains challenging due to the sluggish sorption/desorption kinetics. Herein, a composite sorbent@biomimetic fibrous membrane (PPy‐COF@Trilayer‐LiCl) is reported by mimicking nature's Murray networks, which exhibits outstanding water uptake performance of 0.77–2.56 g g−1 at a wide range of relative humidity of 30%–80% within 50 min and fast water release capacity of over 95% adsorbed water that can be released within 10 min under one sun irradiation. The superior sorption–desorption kinetics of PPy‐COF@Trilayer‐LiCl are enabled by the novel hierarchically porous structure, which is also the critical factor to lead a directional rapid water transport and vapor diffusion. Moreover, as a proof‐of‐concept demonstration, a wearable SAWG device is established, which can operate 10 sorption–desorption cycles per day in the outdoor condition and produce a high yield of clean water reaching up to 3.91 kg m−2 day−1. This study demonstrates a novel strategy for developing advanced solar‐driven SAWG materials with efficient water sorption–desorption properties.

A Study on the Wide Range of Relative Humidity in Cirrus Clouds Using Large-Ensemble Parcel Model Simulations

This study investigates the possible mechanisms related to the wide range of relative humidity in cirrus clouds (RHi). Under the closed adiabatic assumption, the impacts of vertical motion and ice crystal deposition/sublimation on RHi are investigated through in situ observations and parcel model simulations. Vertical motion is an active external force that changes the RHi, and ice crystal deposition/sublimation plays a role in mitigating the change in the RHi. They are the two most important mechanisms involved in controlling the RHi fluctuation during cirrus evolution and could well explain the wide range of RHi in wave-related cirrus clouds. Furthermore, a comparison of statistical cloud characteristics from both observations and simulations shows that a very low value (e.g., 0.001) for the water vapor ice deposition coefficient is highly unlikely.

Humidity-Tolerant Moisture-Driven Energy Generator with MXene Aerogel-Organohydrogel Bilayer.

Free-standing and film-type moisture-driven energy generators (MEGs) that harness the preferential interaction of ionized moisture with hydrophilic materials are interesting because of their wearability and portability without needing a water container. However, most such MEGs work in limited humidity conditions, which provide a substantial moisture gradient. Herein, we present a high-performance MEG with sustainable power-production capability in a wide range of environments. The bilayer-based device comprises a negatively surface-charged, hydrophilic MXene (Ti3C2Tx) aerogel and polyacrylamide (PAM) ionic hydrogel. The preferential selection on the MXene aerogel of positive charges supplied from the salts and water in the hydrogel is predicted by the first-principle simulation, which results in a high electric output in a wide relative humidity range from 20% to 95%. Furthermore, by replacing the hydrogel with an organohydrogel of PAM that has excellent water retention and structural stability, a device with long-term electricity generation is realized for more than 15 days in a broad temperature range (from -20 to 80 °C). Our MXene aerogel MEGs connected in series supply sufficient power for commercial electronic components in various outdoor environments. Moreover, an MXene aerogel MEG works as a self-powered sensor for recognizing finger bending and facial expression.

High-performance flexible dual-function networks based on MXene hybrid film for human–machine interaction

Flexible multifunctional devices can be used in many fields, but it needs to solve the limitations of their integration and mutual interference, which limits their practical applications. Therefore, it is urgent to develop a flexible sensor that can sense multiple signals at the same time and apply it to human physiological monitoring in real-time. Herein, we developed a flexible dual function sensor which used Ti3C2T x MXene/Ag nanowires (Ag NWs)/tissue hybrid film as the sensing materials. The flexible devices exhibit two types of sensing, including high-performance pressure sensing with a high sensitivity and fast response speed, and high-performance humidity sensing with wide detection range of relative humidity. These new functions enable the device to monitor human motion information and human–machine interaction in a personalized way like an electronic skin. The synthesis of Ti3C2T x MXene/Ag NWs/tissue hybrid film provides a material suitable for large-scale preparation for the development of wearable electronic devices with high performance and high integration.

Influence of Co-amorphization on the Physical Stability and Dissolution Performance of an Anthelmintic Drug Flubendazole.

In this work, the co-amorphization approach was applied to flubendazole (FluBZ), resulting in the formation of two novel solid forms of FluBZ with l-phenylalanine (Phe) and l-tryptophan (Trp). A variety of physicochemical techniques have been used to describe new systems, including powder X-ray diffraction, thermal methods, infrared spectroscopy, and scanning electron microscopy. Co-amorphization has been shown to suppress crystallization tendency and considerably increase the shelf-life storage of amorphous flubendazole solid across a wide range of relative humidities. The dissolution behavior of the amorphous forms in biorelevant media at pH = 1.6, pH = 6.5, and 37 °C has been studied in terms of Cmax (maximum FluBZ concentration), Tmax (time to attain peak drug concentration), and AUC (concentration area under the curve during dissolution). At pH = 6.5, a continuous supersaturation and the highest AUC value of all examined systems were observed for the FluBZ-Phe (1:1) system. The phase solubility diagrams revealed that the reason for the better dissolution performance of FluBZ-Phe (1:1) at pH = 6.5 is a complexation between the components in a solution. This work highlights the applicability of co-amorphous systems in improving the physical stability and dissolution performance of drug compounds with poor biopharmaceutical characteristics.

Distinct Roles of Additives in the Improved Sensitivity to CO of Ag- and Pd-Modified Nanosized LaFeO3

Perovskite-type mixed-metal oxides are of particular interest as semiconductor gas sensors due to the variability in the material composition and the stability of sensing parameters. LaFeO3 is a p-type semiconductor with relatively high conductivity and gas sensitivity. However, less is known about the sensitivity and sensing mechanisms of LaFeO3 modified by catalytic noble metals. In this work, we used a microwave-assisted sol–gel method to synthesize perovskite LaFeO3 nanoparticles with an average size of 20–30 nm and a specific surface area of 6–8 m2/g. LaFeO3 was modified by 2–5 wt.% Ag and Pd nanoparticles via the impregnation route. Using X-ray photoelectron spectroscopy, the additives were observed in the partially oxidized states Ag2O/Ag and PdO/Pd, respectively. Electric conduction and sensitivity to noxious gases were characterized by electrophysical measurements. It was shown that LaFeO3 modified by Ag and Pd had improved sensitivity and selectivity to CO, and the sensing behavior persisted in a wide range of relative humidity. Pristine and Ag-modified LaFeO3 had the maximum sensitivity to CO at a temperature of 200 °C, while modification with Pd resulted in a decreased optimal operating temperature of 150 °C. In situ infrared spectroscopy revealed that supported Pd nanoparticles specifically catalyzed CO oxidation at the surface of LaFeO3 at room temperature, which was the likely reason for the improved sensitivity and decreased optimal operating temperature of LaFeO3/Pd sensors. On the other hand, Ag nanoparticles were deduced to activate CO oxidation by lattice oxygen at the surface of LaFeO3, providing enhanced CO sensitivity at a higher temperature.

Tuning humidity sensing properties via grafting fluorine and nitrogen-containing species on single-walled carbon nanotubes.

The effect of humidity on the electrical conductivity of single-walled carbon nanotube (SWCNT) films depends on both the conductivity of individual nanotubes and the electrical contacts between them. Here, we study these factors by comparing the sensor response of nanotubes with fluorine- and nitrogen-containing groups attached to the sidewalls. Experiments carried out in a wide range of relative humidity (RH) at room and elevated temperatures showed that the conductivity of non-functionalized SWCNTs and contacts between them decreases upon the adsorption of water molecules. Covalent fluorination reduces the conductivity of SWCNTs and significantly increases the sensitivity of the film to low concentrations of water vapor. The response at high RH decreases due to the large number of water molecules adsorbed on the conductive regions of the nanotubes. As a result of substitutional reactions of fluorinated SWCNTs with dimethylformamide and ethylenediamine, nitrogen-containing groups are added, the amount of which, however, is much less than the amount of fluorine. This modification of the SWCNTs improves intertube contacts in the film and increases the surface area for water adsorption. Our results show that an increase in the number of functional groups on the SWCNT surface enhances the sensitivity of the sensor to low water concentrations and worsens the response at high RH. SWCNTs modified with ethylenediamine have the highest sensitivity over the entire range of RH.

Front Cover, Volume 2, Number 1, January 2023

Front Cover: The cover image is based on the Research Article High performance and wide relative humidity passive evaporative cooling utilizing atmospheric water by Wang et al. Passive cooling without energy input is highly desirable for solar panels, which improves the solar-to-electricity conversion efficiency and reduces greenhouse gas emissions. This cover image (DOI: 10.1002/dro2.32) demonstrates a passive evaporative cooling technology for solar panels. The cooling technology possesses high cooling performance in a wide range of relative humidity and solar irradiances.