Humidity Dependence Research Articles

A-C/Au Film with Low Humidity Sensitivity of Friction by Forming Au Transfer Film.

Amorphous carbon is recognized as an excellent lubricating material; however, its tribological properties are significantly influenced by humidity. To elucidate the mechanism underlying this humidity dependence and to propose a novel enhancement method, we investigated and compared the tribological properties of hydrogenated amorphous carbon (a-C:H) and amorphous carbon/gold (a-C/Au) composite films. First, the friction coefficient of these carbon films under different humidity conditions was tested using a rotational ball-on-disk tribometer. Subsequently, we analyzed the morphology and structure of the sliding interface employing optical microscopy (OM), Raman spectroscopy, transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM). Finally, first-principle calculations were carried out to calculate the adsorption energy of water molecules on different surfaces. The results indicate that the friction coefficient of a-C:H film and the area of transfer film increase with the increase of humidity. This phenomenon can be attributed to the fact that water molecules enhance the interaction between the a-C:H film and steel counterfaces. Notably, in contrast, the friction coefficient of a-C/Au film demonstrates low sensitivity to humidity due to the formation of an Au transfer film that exhibits weak interaction with water molecules. These findings provide a promising strategy for developing environment-adaptive amorphous carbon films and play an important role in promoting the development of intelligent lubricating film.

Evaluation of a reduced-pressure chemical ion reactor utilizing adduct ionization for the detection of gaseous organic and inorganic species

Abstract. Volatile organic compounds (VOCs) and volatile inorganic compounds (VICs) provide critical information across many scientific fields including atmospheric chemistry and soil and biological processes. Chemical ionization (CI) mass spectrometry has become a powerful tool for tracking these chemically complex and temporally variable compounds in a variety of laboratory and field environments. It is particularly powerful with time-of-flight mass spectrometers, which can measure hundreds of compounds in a fraction of a second and have enabled entirely new branches of VOC and/or VIC research in atmospheric and biological chemistry. To accurately describe each step of these chemical, physical, and biological processes, measurements across the entire range of gaseous products is crucial. Recently, chemically comprehensive gas-phase measurements have been performed using many CI mass spectrometers deployed in parallel, each utilizing a different ionization method to cover a broad range of compounds. Here we introduce the recently developed Vocus AIM (adduct ionization mechanism) ion–molecule reactor (IMR), which samples trace vapors in air and ionizes them via chemical ionization at medium pressures. The Vocus AIM supports the use of many different reagent ions of positive and negative polarity and is largely independent of changes in the sample humidity. Within the present study, we present the performance and explore the capabilities of the Vocus AIM using various chemical ionization schemes, including chloride (Cl−), bromide (Br−), iodide (I−), nitrate (NO3-), benzene cations (C6H6+), acetone dimers ((C3H6O)2H+), and ammonium (NH4+) reagent ions, primarily in laboratory and flow tube experiments. We report the technical characteristics and operational principles, and compare its performance in terms of time response, humidity dependence, and sensitivity to that of previous chemical ionization approaches. This work demonstrates the benefits of the Vocus AIM reactor, which provides a versatile platform to characterize VOCs and VICs in real time at trace concentrations.

Impact of compound warm and wet events on dengue fever infection in South and Southeast Asian countries

BackgroundMultiple studies have reported the profound influence of various climate factors on dengue fever infection, while the effects of joint exposure to warm and wet environment, a condition favouring dengue vectors, on disease transmission were less evaluated. This study aims to investigate the impact of various compound temperature, rainfall, and relative humidity exposures on dengue fever infection in the South and Southeast Asia regions. MethodsWeekly dengue fever surveillance data from 2012 to 2020 were collected from 48 locations in four countries named Singapore (1 location), Sri Lanka (15 locations), Malaysia (9 locations), and Thailand (23 locations, with 11 locations having different study periods). The distributed lag non-linear models were built to assess the impacts of compound temperature, rainfall, and relative humidity exposures on dengue fever infection risks. ResultsA total of 1,359,993 dengue fever cases were reported with 9.33%, 24.02%, 48.73%, and 17.91% cases contributed by Singapore, Sri Lanka, Malaysia, and Thailand, respectively. Compared to non-warm-non-wet, compound warm-wet was associated with an increased dengue risk (RR:1.32, 95% CI:1.21–1.44). Compared to moderate temperature-humidity, warm-wet environment was also associated with an increase in dengue risk (RR:1.37, 95% CI:1.22–1.55). In comparison to weeks with moderate temperature-rainfall, warm-wet weeks was linked to an elevated dengue risk (RR:1.39, 95% CI:1.27–1.52), whereas cold-dry weather would significantly reduce the infection risk (RR:0.70, 95% CI:0.62–0.80). Modification effects showed that the hot effect on dengue infection was more pronounced under higher humidity, while the impact of rainfall increased with warmer temperature. ConclusionWarm-wet events were associated with an increased dengue fever risk, while the infection risk would decline in cold-dry environment, and modification effects exist among exposures. Findings from this study highlight the importance of considering joint temperature, humidity, and rainfall dependency of dengue fever infection in disease prevention and control.

Thermo-hydro-mechanical viscoplastic constitutive model for polyester strap reinforcement long-term response

Polymeric materials have been shown to be rate-dependent materials, that is, their response will vary depending on the conditions to which they are subjected. The present work details the formulation, validation and implementation of a viscoplastic constitutive model with stress, strain, temperature, and relative humidity dependencies aimed to simulate the long-term response of polymeric materials, particularly that of polyester. The model is capable of predicting primary and secondary creep, often observed in geosynthetic materials. Both creep mechanisms can be modelled independently if needed. For calibration, a wide data-set of polyester strap reinforcement creep measurements was used. The validation process was done using parameters for load-, product-, and material-specific scenarios. Load- and product-specific scenarios showed suitable agreement between simulated and measured data. The coupled capabilities of the model are shown via variable temperature and relative humidity boundary conditions. Due to lack of data, temperature and relative humidity dependencies represent idealized scenarios. Simulations of stress-relaxation response for constant rate of strain scenarios are also provided. The proposed formulation is aimed at modelling the mechanical response of reinforced soil structures while accounting for the effect of in-air or in-soil conditions to which reinforcement materials can be exposed to throughout the structure’s life-cycle.

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.

THE BIOLOGICAL DEVELOPMENT CYCLE AND THE DAMAGE OF THE PEST OF THE SLIDERWORM (LEMA MELANOPUS L) IN THE CONDITIONS OF OUR REPUBLIC

In this article, the dependence of temperature and relative humidity on the developmental phenology of Lema melanopus, a serious pest of wheat, is studied. As a result of the increase in the number of Lema melanopus, the level of damage to the leaves increases, the yield of wheat decreases.

Effects of Relative Humidity and Phase on the Molecular Detection of Nascent Sea Spray Aerosol Using Extractive Electrospray Ionization.

Online mass spectrometry techniques, such as extractive electrospray ionization mass spectrometry (EESI-MS), present an attractive alternative for analyzing aerosol molecular composition due to reduced aerosol sample collection and handling times and improved time resolution. Recent studies show a dependence of EESI-MS sensitivity on particle size and mixing state. This study measured authentic sea spray aerosol (SSA) components generated during a phytoplankton bloom, specifically glycerol, palmitic acid, and potassium ions. We demonstrate temporal variability and trends dependent on specific biological processes occurring in seawater. We found that the EESI-MS sensitivity, after adjusting for pressure variations at the inlet and normalizing to the reagent ion, critically depends on the sample's relative humidity. Relevant SSA species exhibited heightened sensitivity at an elevated relative humidity near the deliquescence relative humidity of sea salt and poorer sensitivity with sparse detection below the efflorescence relative humidity. Modeling the reagent ion's diffusive depth demonstrates that the sample aerosol particle viscosity governs the relative humidity dependence because it modulates the particle's coagulation efficiency and distance the reagent ion diffuses and reacts with components in the particle bulk. The effects of particle size and mixing state are discussed, revealing improved sensitivity of phase-separated components present along the particle surface. This work highlights the importance of the particle phase state in detecting and quantifying molecular components within authentic and complex aerosol particles and the utility of EESI-MS for measuring SSA composition.

Ultraefficient Ammonia Gas Sensors Based on Pt‐Loaded WO3 Nanobars

Herein, unloaded WO3 (WO3) and Pt‐loaded WO3 (Pt‐WO3) nanobars are successfully synthesized through simple hydrothermal and impregnation methods. X‐ray diffractometer analysis confirms the formation of a monoclinic WO3 structure. Surface analysis reveals that the Pt impregnation results in a significant increase in the specific surface area of WO3 nanobars. The gas‐sensing performance of sensors based on nanobars is measured toward ammonia (NH3) with varying NH3 concentrations at different operating temperatures. Compared with the pristine WO3 sensor, the Pt‐WO3‐based sensor with an optimal Pt content of 1 wt% exhibits a relatively low optimum operating temperature of 250 °C and a superior response of 960–50 ppm NH3. Furthermore, the Pt‐WO3‐based sensor also displays fast response, excellent NH3 selectivity to ammonia, moderate humidity dependence, and good stability. Therefore, the developed hydrothermal and impregnation methods could be a suitable alternative procedure for the synthesis of Pt‐WO3 nanobars useful for advanced NH3‐sensing applications.

Stickiness: A New Variable to Characterize the Temperature and Humidity Contributions toward Humid Heat

Abstract Extreme wet-bulb temperatures (Tw) are often used as indicators of heat stress. However, humid heat extremes are fundamentally compound events, and a given Tw can be generated by various combinations of temperature and humidity. Differentiating between extreme humid heat driven by temperature versus humidity is essential to identifying these extremes’ physical drivers and preparing for their distinct impacts. Here we explore the variety of combinations of temperature and humidity contributing to humid heat experienced across the globe. In addition to using traditional metrics, we derive a novel thermodynamic state variable named “stickiness.” Analogous to the oceanographic variable “spice” (which quantifies the relative contributions of temperature and salinity to a given water density), stickiness quantifies the relative contributions of temperature and specific humidity to a given Tw. Consistent across metrics, we find that high magnitudes of Tw tend to occur in the presence of anomalously high moisture, with temperature anomalies of secondary importance. This widespread humidity dependence is consistent with the nonlinear relationship between temperature and specific humidity as prescribed by the Clausius–Clapeyron relationship. Nonetheless, there is a range of stickiness observed at moderate-to-high Tw thresholds. Stickiness allows a more objective evaluation of spatial and temporal variability in the temperature versus humidity dependence of humid heat than traditional variables. In regions with high temporal variability in stickiness, predictive skill for humid heat-related impacts may improve by considering fluctuations in atmospheric humidity in addition to dry-bulb temperature. Significance Statement Extreme humid heat increases the risk of heat stress through its influence over humans’ ability to cool down by sweating. Understanding whether humid heat extremes are generated more due to elevated temperature or humidity is important for identifying factors that may increase local risk, preparing for associated impacts, and developing targeted adaptation measures. Here we explore combinations of temperature and humidity across the globe using traditional metrics and by deriving a new variable called “stickiness.” We find that extreme humid heat at dangerous thresholds occurs primarily due to elevated humidity, but that stickiness allows for thorough analysis of the drivers of humid heat at lower thresholds, including identification of regions prone to low- or high-stickiness extremes.

Evolution behavior of adhesion force with continually changed relative humidity revealed on AFM

ABSTRACT Adhesion forces on various surfaces with different hydrophilicity were measured by atomic force microscopy in the force-volume mode and at a location to study the relative humidity (RH) dependence. With an increasing-stable-decreasing trend in RH, the force in the force-volume mode usually exhibits a constant-increase-constant-decrease-constant variation. Surfaces with partial or complete hydrophobicity exhibited a much larger increase compared to a hydrophilic one. However, the behavior on some surfaces was distorted due to a decrease at high stable RHs. Contrastively, the behavior at a location could also display the same behavior. Both gradual and sudden changes were observed at a single location as RH changed. At high stable RHs, the force displayed complex behaviors, indicating unique characteristics at each location. Therefore, the measurement at a location is not suitable to study the RH dependence. Specially, the force measured on silica in the force-volume mode has the mentioned behavior. However, the force at a location can remain stable, gradually/sharply increase or decrease, and suddenly jump or drop with RH. These observations are attributed to the evolution of a water bridge, which is largely influenced by thin-film flow. The findings provide deeper insights into adhesion mechanisms at different RHs.

Polarization Analysis and Humidity Dependence of Dielectric Properties of Aromatic and Semialicyclic Polyimides Measured at 10 GHz

Polarization Analysis and Humidity Dependence of Dielectric Properties of Aromatic and Semialicyclic Polyimides Measured at 10 GHz

Superprotonic conductivity of ketoenamine covalent-organic frameworks grafted by imidazole-based units

The achievement of covalent organic frameworks (COFs) with high stability and exceptional proton conductivity is of tremendous practical importance and challenge. Given this, we hope to prepare the highly stable COFs carrying CN connectors and enhance their proton conductivity via a post-modification approach. Herein, one COF, TpTta, was successfully synthesized by employing 1,3,5-triformylphloroglucinol (Tp) and 4,4′,4″-(1,3,5-triazine-2,4,6-triyl)-trianiline (Tta) as starting materials, which has a β-ketoenamine structure bearing a large amount of –NH groups and intramolecular H-bonds. TpTta was then post-modified by inserting imidazole (Im) and histamine (His) molecules, yielding the corresponding COFs, Im@TpTta and His@TpTta, respectively. As a result, their proton conductivities were surveyed under changeable temperatures (30–100 °C) and relative humidities (68–98 %), revealing a degree of temperature and humidity dependence. Impressively, under identical conditions, the optimum proton conductivities of the two post-modified COFs are 1.14 × 10−2 (Im@TpTta) and 3.45 × 10−3 S/cm (His@TpTta), which are significantly greater than that of the pristine COF, TpTta (2.57 × 10−5 S/cm). Finally, their proton conduction mechanisms were hypothesized based on the computed activation energy values, water vapor adsorption values, and structural properties of these COFs. Additionally, the excellent electrochemical stability of the produced COFs was expressed, as well as the prospective application value.

Study of the ZnO/MoS2 heterostructures-based gas sensor for humidity-independent response

In this study, several strategies including coating with a hydrophobic MoS2 layer, UV light illumination, raising temperature, alternating current (AC), and four-probe measurement have been systematically studied to overcome humidity dependence response behavior for the ZnO sensor. Catalyst-free CVD method was used to prepare pure ZnO nanorods and ZnO/MoS2 heterostructures, and the prototypes were then fabricated on the substrates with Pt interdigital (ID) electrodes, respectively. The gas sensing properties of two sensors were systematically investigated. The ZnO/MoS2 heterostructures-based sensor with four-probe measurement operating at 150 °C shows stable responses during a wide humidity variation range. Furthermore, the ZnO/MoS2 sensor obtains excellent sensing performance to NO2 with a high sensitivity of 12.6 %/ppm and high sensor responses at 150 °C and UV light illumination. Additionally, a low theoretical LoD of 6.5 ppb NO2 is achieved for ZnO/MoS2 heterostructures-based sensor.

Mechanical properties of wall soils for predicting damage to the substrate of Hiten wall paintings in the Horyu‐ji Temple main hall caused by humidity fluctuation: Measurements with mock‐up materials

AbstractSafe and efficient conservation of cultural artifacts requires preventing artifacts deterioration and energy‐saving environmental control. To achieve this, predicting deterioration caused by environmental conditions is necessary. Predicting the mechanical damage caused by humidity fluctuations necessitates knowledge of the mechanical properties of cultural artifacts materials. Although the mechanical properties of several artifacts have been extensively studied, no investigations have focused on the soils underlying wall paintings. This study aims to clarify some mechanical properties of the upper‐ and middle‐coat soils serving as the substrates for Hiten wall paintings at Horyu‐ji Temple. Mock‐up materials were prepared, and splitting tensile and uniaxial compressive tests were performed. Simultaneously, specimens with various equilibrium humidities were tested to clarify their humidity dependency. The tensile and compressive strengths, Young's modulus, proportional limit, and Poisson's ratio of the upper‐coat soil were 0.103–0.239 MPa, 1.16–2.55 MPa, 0.115–0.209 GPa, and 1.10–2.49 MPa, and 0.152, respectively. Moreover, the humidity‐induced strains for the upper‐ and middle‐coat soils were measured, and the moisture expansion coefficients were approximately 1240 and 2337 μST/−, respectively. The results of this study provide vital data for the conservation of the wall paintings and contribute to a deeper understanding of wall soil properties.

Hydrogen and Oxygen Permeability through PEFC Membrane and Membrane Electrode Assembly

IntroductionThe permeation of feed gas through a proton exchange membrane (PEM) affects a PEFC performance [1, 2]. The temperature and relative humidity (RH) dependences of the hydrogen and oxygen permeability through the perfluorinated sulfonic-acid (PFSA) membrane were investigated. A membrane is considered to consist of a bulk layer sandwiched between skin layers [3]. In this study, by measuring the hydrogen and oxygen permeation flux through a membrane and plotting the permeation resistance against the membrane thickness, the bulk layer effective diffusion coefficients and the skin layer mass transport coefficients of PEM and membrane electrode assembly (MEA) were examined.ExperimentalNafion™ NR-211, NR-212, and N115 (Chemours) with different thickness (at RH of 50 %), 25.8, 51, and 127 μm, respectively, were used as PEM. Catalyst layers made of Pt-loaded carbon (Pt 50 wt%) and Nafion ionomer (I/C = 1.0) with a thickness of 8.5-10 μm on both sides of PEMs were prepared as MEA. They were installed separately in a Japan Automobile Research Institute (JARI) standard cell whose active area was 5.0 cm×5.0 cm. The cell was placed in the constant temperature and humidity oven (ESPEC, LHL-113) and the relative humidity of the supplied gas was controlled by the bubbler temperature. The hydrogen and oxygen fluxes through a membrane were measured at cell temperatures of 60-90 °C and RH of 0.2-1.0 (moisture content λ = 1.7-10.5) with different partial pressures of nitrogen diluent gas. Permeate gas was quantified by a gas chromatograph (Agilent 990 micro GC, column: MSieve5A, detector: TCD). The schematic drawing of the measurement system is shown in Fig. 1.Results and discussionThe permeate gas flux through a membrane, Nj (j = H, O), is expressed asNj = k pj Δpj , where k pj is the gas permeance and Δpj is the partial pressure difference between the supply side and the permeate side.Fig. 2 shows the temperature and RH dependences of O2 permeance through PEM and Fig. 3 shows the permeation resistance against the membrane thickness. k pO increases with increasing RH and 1/k pj becomes lower at higher temperature. The permeation resistance through MEA tends to be lower than PEM. By assuming that Nafion has a bulk layer and skin layers [3], the bulk layer and skin layer resistances were separated from a slope and an intercept of trend lines in Fig. 3. The permeation resistances through MEA do not have y-axis intercept. The fused layer can be created by hot press process in manufacturing MEA and an x-axis intercept might be a fused layer thickness. It is easier to permeate gas through the fused layer than the skin layer of PEM. The temperature dependences of the bulk layer effective diffusion coefficient, D ej (B), are shown in Fig. 4. D eH (B) and D eO (B) of PEM and MEA are on the same line, with activation energies, E a, of 23.9 and 20.6 kJ/mol, respectively at λ = 6. D ej (B) can be formulated as follows: D eH (B) = (4.26×10-11 + 6.50×10-11RH) exp(-E aH/R (1/T-1/T ref)) m2/s D eO (B) = (8.16×10-12 + 3.39×10-11RH) exp(-E aO/R (1/T-1/T ref)) m2/s T ref = 353.15 K, E aH = 0.65 λ + 20.0 kJ/mol, E aO = 21.2 kJ/mol,Reproduced D eH (B) and D eO (B) are shown in Fig. 5. The skin layer mass transport coefficient, k pj (S), can be obtained from the y-axis intercept of a trend line in Fig. 4 and it shows that only PEM has skin layers. It is necessary to consider the gas permeation through MEA not through PEM in designing PEFCs because using the transport properties through PEM may lead to overestimate the performance.ConclusionsBy measuring the hydrogen and oxygen permeation flux through PEM and MEA in PEFC, the bulk layer effective diffusion coefficients and the skin layer mass transport coefficients of hydrogen and oxygen were obtained. The bulk layer effective diffusion coefficients of PEM and MEA were found to be the same and the temperature and RH dependences of D ej (B) were formulated as a function of temperature and RH. The skin layer mass transport coefficient appears only in PEM.AcknowledgementThis work was supported by the FC Platform Program: Development of design-for-purpose numerical simulators for attaining long life and high-performance project (FY 2020–FY 2023) conducted by the New Energy and Industrial Technology Development Organization (NEDO), Japan.

Hydrogen and Oxygen Permeability through PEFC Membrane and Membrane Electrode Assembly

A proton exchange membrane (PEM) is an important component of a polymer electrolyte fuel cell (PEFC) from the viewpoint of proton transport. Only protons are desired to be transported through a membrane, but the feed gases also permeate. The permeation of the feed gas through a membrane affects the PEFC performance. Temperature and relative humidity dependencies of the hydrogen and oxygen permeability through a perfluorosulfonic acid (PFSA) membrane were measured. By considering that a membrane consists of three layers, i.e. a bulk layer sandwiched between skin layers, the transport properties of each layer were separated. The bulk layer effective diffusion coefficients of hydrogen and oxygen through both a PEM and an MEA were formulated as a function of temperature and RH. The oxygen transfer coefficient in the skin layer increased with RH, whereas the hydrogen transfer coefficient was almost constant regardless of RH.

In-situ observation of an anion exchange membrane at various humidity by X-ray scattering

In-situ observation of an anion exchange membrane (AEM), QPAF-4, synthesized by the group of University of Yamanashi, was performed under various humidity conditions by synchrotron X-ray scattering measurements. The absorption process of water vapor into the AEM was slow, taking even a few hours. When the environmental humidity decreased, the amount of water contained in the membrane decreased also very slowly. Hysteresis was clearly observed during the absorption and desorption processes. Although the amount of absorbed water was very small, a meaningful difference in the X-ray scattering intensity was found between water-absorbed and dry membrane. The radial distribution functions (RDFs) of the membrane under various humidity conditions were obtained by subtracting the scattering of the chamber, where the humidity and the temperature were contorted from the scattering intensity from the membrane in the chamber. The peak at 2.8 Å was assigned to the hydrogen bonding interaction of O(water)-O(water) and non-hydrogen bonded interaction of water molecules. These peaks increased under a high humidity condition. In-situ observation in the present study clarified the humidity dependence of the bonding state of water in the AEM.

Characterization of Temperature and Humidity Dependence in Soft Elastomer Behavior.

Soft robots are predicted to operate well in unstructured environments due to their resilience to impacts, embodied intelligence, and potential ability to adapt to uncertain circumstances. Soft robots are of further interest for space and extraterrestrial missions, owing to their lightweight and compressible construction. Most soft robots in the literature to-date are made of elastomer bodies. However, limited data are available on the material characteristics of commonly used elastomers in extreme environments. In this study, we characterize four commonly used elastomers in the soft robotics literature-EcoFlex 00-30, Dragon Skin 10, Smooth-Sil 950, and Sylgard 184-in a temperature range of -40°C to 80°C and humidity range of 5-95% RH. We perform pull-to-failure, stiffness, and stress-relaxation tests. Furthermore, we perform a case study on soft elastomers used in stretchable capacitive sensors to evaluate the implications of the constituent material behavior on component performance. We find that all elastomers show temperature-dependent behavior, with typical stiffening of the material and a lower strain at failure with increasing temperature. The stress-relaxation response to temperature depends on the type of elastomer. Limited material effects are observed in response to different humidity conditions. The mechanical properties of the capacitive sensors are only dependent on temperature, but the measured capacitance shows changes related to both humidity and temperature changes, indicating that component-specific properties need to be considered in tandem with the mechanical design. This study provides essential insights into elastomer behavior for the design and successful operation of soft robots in varied environmental conditions.

RTILs as Electrolytes in Electrochemical Gas Sensors for O2 and Other Gases

Oxygen is the third-most abundant element on this planet and is essential to life, the lifestyle of humans and virtually all sentient life. We need O2 to live and additionally use it for both heating and transportation. Since O2 is so essential in our everyday life, there are several applications where the oxygen levels need to be controlled or maintained within a certain range. To make sure that the O2 level is within the necessary range, devices are needed that can monitor and feedback/communicate O2 levels continuously. There are several types of chemical gas sensors for O2 which include chemoresistive gas sensors and electrochemical gas sensors. The Clark-type electrochemical sensor is the oldest and probably the most used sensor for oxygen especially in medical applications. One of the most well-known industrial applications for gas-phase oxygen sensors is probably the control of oxygen levels in combustion engines with the help of a Lambda probe, a solid-state electrochemical cell operated in amperometric and potentiometric modes.Electrochemical sensors have evolved over the past decades. By finding the suitable combination of electrolyte, electrode material, cell design and operation conditions, electrochemical sensors are tunable to meet the specific requirements of the many different applications. For example, by changing the electrode material from gold to platinum while keeping everything else the same, you can reduce the response to CO by orders of magnitude improving the selectivity in low level measurements. Further, by adjusting the thermodynamic voltage of the sensing electrode, the electrochemical reactivity is adjusted to maximize the sensor’s selectivity for the target analyte. While these developments have occurred over time, recent work implements room temperature ionic liquids (RTILs) as electrolytes. This idea has some serious merit to it for multiple reasons. Firstly, many electrochemical sensors have aqueous electrolytes which freeze at low temperatures and rapidly evaporate at elevated temperatures. Additionally, aqueous electrolytes can change in real time with variations in background humidity levels. To be more exact, aqueous electrolytes dry out when operated in low humidity backgrounds and significantly increase in volume (swell) in high humidity background levels. While drying out is an issue because this leads to poor ionic conductivities, swelling is an issue because the electrolyte needs expansion room in the sensor, typically an extensive cavity within the cell body. RTILs have shown promise because they can extend the operating temperature range as well as lead to new sensor designs operatable over a wider range of environmental conditions. The implementation of RTILs might even allow for smaller sensor designs due to a smaller volume change of the electrolyte in dependence of changing humidity levels.Several research groups have investigated the oxygen sensing capabilities of RTILs in electrochemical devices. Silvester et al. investigated the oxygen solubility in several different imidazolium cations combined with [bis(trifluoromethylsulfonyl)imide] ([NTf2]-) anions and found a high oxygen solubility in 3-butyl-1-methyl imidazolium [NTf2]- [1]. They further investigated the influence of humidity on the oxygen reduction reaction and found the most stable behavior for [3-etyhl-1-methyl imidiazolium] [NTf2]- over a broad range of different humidity levels [2]. Yin et al. investigated 1-butyl-1-methylpyrrolidinium [NTf2]- as an electrolyte in oxygen sensors and found good linear correlation of the sensor output to the oxygen concentration [3].In this work, we investigated different RTILs, including the before mentioned 1-butyl-1-methylpyrrolidinium [NTf2]- and 3-butyl-1-methyl imidazolium [NTf2]-, regarding their suitability for thin layer electrochemical oxygen sensors in a background of mostly nitrogen. The performance was investigated using CV (cyclic voltammetry) and other time dependent voltametric techniques. The ability to detect oxygen of sensors with different RTILs as electrolyte was compared to that of aqueous H2SO4.[1] S. Doblinger, D.S. Silvester, M. Costa Gomes, Functionalized Imidazolium Bis(trifluoromethylsulfonyl)-imide Ionic Liquids for Gas Sensors: Solubility of H2, O2 and SO2, Fluid Phase Equilib. 549 (2021). https://doi.org/10.1016/j.fluid.2021.113211.[2] S. Doblinger, J. Lee, D.S. Silvester, Effect of Ionic Liquid Structure on the Oxygen Reduction Reaction under Humidified Conditions, Journal of Physical Chemistry C. 123 (2019) 10727–10737. https://doi.org/10.1021/acs.jpcc.8b12123.[3] H. Yin, H. Wan, L. Lin, X. Zeng, A.J. Mason, Miniaturized Planar RTIL-based Electrochemical Gas Sensor for Real-Time Point-of-Exposure Monitoring, 2016 IEEE Healthcare Innovation Point-Of-Care Technologies Conference (HI-POCT). (2016) 85–88. https://doi.org/10.1109/HIC.2016.7797703.

Hydrogen-bonded nickel(II)-organosulfonate framework: Thermal expansion behavior, proton conduction, and magnetic properties

Metalo Hydrogen-bonded organic frameworks are emerging supramolecular platforms for designing functional molecular materials. Herein, we reported the supramolecular structure, thermal, magnetic, and proton conduction properties of a hydrogen-bonded nickel(II)-organosulfonate framework, [Ni(H2O)6][NPS]2 (NiHOF, HNPS = naphthalene-2-sulphonic acid). Single-crystal X-ray diffraction studies reveal a two-dimensional hydrogen-bonded network sustained by multiple and charge-assisted OH···O H bonds between hexaaquanickel(II) cations and organosulfonate anions. Additionally, continuous ca. 0.47 × 0.70 nm2 windows were formed within the framework. The thermal stability of the NiHOF was confirmed by thermal gravimetric analysis and variable temperature single-crystal and powder X-ray diffraction patterns. N2 sorption isotherms suggest an ultramicroporous supramolecular framework of NiHOF with permanent porosity. The anisotropic positive thermal expansion behavior of NiHOF was evidenced by the dynamic crystallography experiments. Magnetic measurements indicate easy-axis magnetic anisotropy (D = -10.5 cm−1) of the NiHOF while no slow magnetic relaxation behavior. Electrochemical impedance spectroscopy indicates the temperature and humidity dependence of conductivities of NiHOF. At 50 °C and 70% relative humidity, the conductivity is 1.13 × 10−4 S·cm−1, revealing a supramolecular proton conductor of NiHOF. This work provides a potential way for designing novel thermal, magnetic, and electrical molecular materials through the supramolecular assembly of inorganic and organosulfonate synthons.