Function Of Water Content Research Articles

Performance Losses and Recovery from Cation Contaminants in PEM Water Electrolysis

Water contaminants are extremely common cause of failure for polymer electrolyte membrane (PEM) electrolyzers, potentially accounting for >90% of electrolyzer failures in the field. [1] Water contaminants also commonly impact PEM electrolysis devices in a research setting, confusing measurements of cell performance and durability if they are not recognized and properly addressed. Despite this, relatively little published literature has systematically investigated contaminants in PEM electrolysis cells specifically. Better understanding of contaminant impacts may lead to improved strategies to mitigate or recover performance losses as well as improve the consistency and rigor of electrolysis research.Here we will present an investigation of the performance impacts of cation contaminants and their recoverability. This investigation focuses on cation contaminants that are abundant in tap/ground water, which may enter the cell through a failure of the water processing subsystem, and transition metals that may leach out of system components. We will report performance impacts for a representative selection of cations as a function of water concentration and accumulated contaminant dose, with impedance spectroscopy used to understand the origin of performance losses. We will also present multiple diagnostic signatures to help identify presence of contaminants in PEM electrolysis cells. Finally, we will address the recovery of cells with different contaminants and the prospects for improved recovery procedures.[1] Capuano, Chris “Manufacturing Challenges, Opportunities, and Successes for PEM Electrolysis at Scale”, 3rd International Conference on Electrolysis, Golden, CO, 2022.

The Role of Water in Carbon Dioxide Adsorption in Porphyrinic Metal-Organic Frameworks.

Capturing and converting CO2 through artificial photosynthesis using photoactive, porous materials is a promising approach for addressing increasing CO2 concentrations. Porphyrinic Zr-based metal-organic frameworks (MOFs) are of particular interest as they incorporate a photosensitizer in the porous structure. Herein, the initial step of the artificial photosynthesis is studied: CO2 sorption and activation in the presence of water. A combined vibrational and visible spectroscopic approach was used to monitor the adsorption of CO2 into PCN-222 and PCN-223 MOFs, and the photophysical changes of the porphyrinic linker as a function of water concentration. A shift in CO2 sorption site and bending of the porphyrin macrocycle in response to humidity was observed, and CO2/H2O competition experiments revealed that the exchange of CO2 with H2O is pore-size dependent. Therefore, humidity and pore-size can be used to tune CO2 sorption, CO2 capacity, and light harvesting in porphyrinic MOFs, which are key factors for CO2 photoreduction.

Molecular dynamics of vegetable oil extraction and degumming: Analysis of micelles and phospholipid bilayers in different solvents

AbstractUnderstanding the molecular‐level mechanisms of vegetable oil extraction and degumming remains limited. This study aimed to investigate these processes using molecular dynamics (MD), with a focus on the challenges associated with replacing n‐hexane with ethanol. MD simulations with a coarse‐grained force field (Martini 3) were conducted to examine the behavior of phospholipid mono/bilayers with and without triacylglycerol in various solvents, including water, absolute and aqueous ethanol (with 0%–10% water content by weight), and n‐hexane. Trilinolein and phospholipids with 16–18 carbon tails and 0–2 unsaturations were considered. The degree of unsaturation and tail size of phospholipids did not significantly affect bilayer formation in water. However, they influenced bilayer organization, as measured by the order parameter, bilayer thickness, and area. The phospholipid bilayer, composed of 1‐palmitoyl‐2‐oleoyl‐sn‐glycero‐3‐phosphocholine (POPC), exhibited a well‐defined structure in water, partial disruption in ethanol, and complete disruption in n‐hexane. The presence of triacylglycerol had no effect on phospholipid monolayers in water but increased lipid disorder in ethanol. Minor amounts of water in ethanol did not significantly alter the behavior of the lipid layers. MD simulations, combined with artificial intelligence, identified and quantified the formation of micelles during the degumming process, both in conjunction with n‐hexane extraction and independently as a function of water concentration. The volume and number of micelles were strongly influenced by the water content. Molecular dynamics in food engineering is relatively limited and scarce because of the complex nature of the systems. However, this study successfully demonstrates its applicability in this context.

Effect of water on the dissolution of flax fiber bundles in the ionic liquid 1-ethyl-3-methylimidazolium acetate

This work investigated the dissolution rate of flax fibers in the ionic liquid 1-ethyl-3-methylimidazolium acetate [C2mim] [OAc] with the addition of a cellulose anti-solvent, water. The dissolution process was studied as a function of time, temperature and water concentration. Optical microscopy is used to analyse the resultant partially dissolved fibers. Distilled water was added to the solvent bath at the concentrations of 1%, 2% and 4% by weight in order to understand its influence on the dissolution process. The effect of the addition of even small amounts of water was found to significantly decrease the speed of dissolution, decreasing exponentially as a function of water concentration. The resulting data of both pure (as received from the manufacturers) ionic liquid and ionic liquid/anti-solvent mixtures showed the growth of the coagulated fraction as a function of both dissolution time and temperature followed time temperature superposition. An Arrhenius behavior was found, enabling the measurement of the activation energy for the dissolution of flax fiber. The activation energy of the IL as received (0.2% water) was found to be 64 ± 5 kJ/mol. For 1%, 2% and 4% water systems, the activation energies were found to be 74 ± 7 kJ/mol, 97 ± 3 kJ/mol and 116 ± 0.6 kJ/mol respectively. Extrapolating these results to zero water concentration gave a value for the hypothetical dry IL (0% water) of 58 ± 4 kJ/mol. The hypothetical dry ionic liquid is predicted to dissolve cellulose 23% faster than the IL as received (0.2% water).

High conformational stability of cations in N,N-diethyl-N-methyl-N-(2-methoxyethyl) ammonium ionic liquid–water mixtures

We studied the conformational equilibrium of cations in N,N-diethyl-N-methyl-N-(2-methoxyethyl) ammonium ([DEME][X], X = BF4 and I) ionic liquid (IL)–water mixtures as a function of water concentration using Raman spectroscopy and molecular dynamics (MD) simulations. We found that the folded form of the [DEME] cation was exceptionally stable, irrespective of the anion species, and its proportion in the mixtures remained almost constant throughout the studied concentration region. This behavior is significantly different from that of imidazolium IL–water mixtures, where the equilibrium shifts depending on the water concentration. Interestingly, the states of the water molecules were unrelated to the stability of the [DEME] cations in the mixtures. We speculated whether the intramolecular attractive interaction between the N and O atoms in the [DEME] cation was the key to maintaining the stability of the folded form.

Molecular dynamics simulation studies of 1,3-dimethyl imidazolium nitrate ionic liquid with water.

The fundamental understanding of intermolecular interactions of ionic liquids (ILs) with water is essential in predicting IL-water thermodynamic properties. In this study, intermolecular or noncovalent interactions were studied for 1,3-dimethyl imidazolium [DMIM]+ cation and nitrate [NO3]- anion with water, employing quantum mechanics and molecular dynamics simulations. Molecular dynamics simulations were performed using a revised multipolar polarizable force field. The effect of water on ionic liquids was evaluated in terms of thermodynamic and dynamic properties. Thermodynamic properties included liquid densities ρ, excess molar volumes ΔVE, and liquid structures gr. Dynamic properties included self-diffusion coefficients D of mixture constituents as a function of water concentration. The density of ionic liquid-water mixtures monotonically decrease with increasing concentration of water. A negative excess volume was obtained for low and high water concentrations, demonstrating strong intermolecular interactions of water with ionic liquid components. Liquid structures of ionic liquid-water mixtures revealed a tendency for anions to interact with cations at shorter intermolecular distances when the water concentration is increased. Diffusion rates were found to increase for all mixture components with increase in the fraction of water. A significant change in the diffusion rate was found at ∼0.3 weight fraction of water. However, the water self-diffusion coefficient was dominant at all concentrations. The ratio of water/anion and anion/cation self-diffusion coefficients was found to decrease linearly with increasing concentration of water molecules.

Corn Starch-Based Sandstone Sustainable Materials: Sand Type and Water Content Effect on Their Structure and Mechanical Properties

A new biodegradable, sustainable and environmentally friendly building material is introduced and studied in this work, which can be applied to lightweight architectural structures, aiming for the reduction of the greenhouse gas emissions and mitigation of the climate change effects. The focus was to investigate the effect of water concentration and different types of sand on the mechanical properties of corn starch-based artificial sandstone. A series of cubic, cylindrical and disk specimens were prepared by varying the concentration of water and using different sources of commercial quartz sand. The quasi-static and cyclic compressive properties of starch-based artificial sandstone samples were measured as a function of water concentration and sand type, while the structure of the artificial sandstone specimens was examined by scanning electron microscopy (SEM) and optical microscopy. Moreover, the Brazilian Test was employed as the indirect method to determine the tensile strength of the samples based on the type of the commercial sand they contained. The experimental results showed that the homogeneous grading of sand grains and the latter’s chemical composition have a significant effect on the mechanical properties of the sandstone samples. The highest compression values were obtained using the microwave heating method at a water concentration of about 12 wt%, while the cyclic compression and Brazilian Tests have shown that the granulometric grading of the sand particles and the chemical composition of the sand influence the compressive and tensile strength of the material.

Tuneable fluorescence and structural colour in PNIPAM microgel assemblies

The combination of fluorescence and structural colour in colloidal photonic glasses could be the starting point for the design of dynamic multiple responsive colloidal photonic materials for advanced applications in which the fluorescence intensity could be modulated by stimulus-induced colour changes. The merocyanine functionalization of the PNIPAM-based microgel system made it possible to obtain tuneable photonic colloidal glasses displaying vivid structural colours and fluorescence. For this purpose, the MC was introduced in some of the crosslinking points of the inner structure of a PNIPAM-based microgel system. These building blocks were left to organize in water (pH 4.5) to obtain photonic glasses. The structural colour was studied as a function of water concentration, so that increasing the microgel concentration led to a blue colour shift. The PBG was characterized by diffuse reflectance spectroscopy. Reflection imaging microscopy was used to understand the microstructure responsible for the PBG. It could be determined that the microgel particles decreased their diameter from 430 nm up to 220 nm to adjust to the glass organization. It has been found that MC fluorescence intensity in these assemblies depended on the photonic band gap (PBG) position in such manner, that strong quenching of MC fluorescence was observed when the PBG matched the MC excitation wavelength. Besides, the MC fluorescence excitation band was 10 nm shifted to higher wavelengths.

POSSIBILITY OF WATER-OIL EMULSION COMBUSTION

The article describes a device developed by the authors for wave treatment of water-oil emulsion for preparation of water-oil emulsion for combustion. High efficiency of hydrocarbon fuel combustion is one of the main indicators when choosing a method of fuel mixture preparation. The scheme of an innovative vortex burner for combustion of water-oil emulsion is presented. A review of existing equipment for preparation of high quality emulsion is made. The necessity of forced oil dehydration for high quality combustion in burners is refuted. The choice of material for the dispersant body with regard to corrosion, cavitation and wear resistance requirements is presented. The analysis was carried out in order to reveal the relations of transformation of physical-chemical properties of water-oil emulsion (sedimentation and aggregative stability, structural viscosity) from temperature and from the volume of water in them. Knowledge of these physical-chemical parameters is essential to ensure the efficiency of atomization and stable combustion of the fuel under study. A methodology for determining the dynamic viscosity using a capillary viscometer with results obtained in different ranges of temperature changes of emulsified fuel preparation is presented. Data on the density of oil-water emulsion as a function of water concentration at 70 °C was obtained. The dependence of stability of emulsion based on fuel oil M-100 from settling time at 20 °C has been analysed. When using wave treatment dispersant, stable water-oil emulsions are obtained, suitable for use in power engineering as fuel.

Reactivity of a Carene-Derived Hydroxynitrate in Mixed Organic/Aqueous Matrices: Applying Synthetic Chemistry to Product Identification and Mechanistic Implications

β-hydroxynitrates (HN) are a major class of products formed during OH and NO3 initiated oxidation of terpenes. Their production contributes significantly to secondary organic aerosol (SOA) formation and NOx sequestration. However, studying the condensed phase reactions of this important class of molecules has been hindered by the lack of commercially available authentic standards. The goal of this work was to examine the influence of water concentration and solvent identity on product yields of a tertiary HN derived from 3-carene prepared in house. To assess the role of water on conversion chemistry, bulk-phase reactions were conducted in DMSO-d6, a non-nucleophilic solvent, with a gradient of water concentrations, and analyzed with 1H NMR. Product identifications were made by comparison with authentic standards prepared in house. Four major products were identified, including an unexpected diol produced from carbocation rearrangement, diol diastereomers, and trans-3-carene oxide, with varying yields as a function of water concentration. Product yields were also measured in two protic, nucleophilic solvents, MeOD-d4 and EtOD-d6. Finally, reactions with added chloride formed alkyl chloride products in yields approaching 30%. These results are among the first to highlight the complexities of nucleophilic reactions of hydroxynitrates in bulk, mixed aqueous/organic media and to identify new, unexpected products.

Water molecular state in 1-hexylpyridinium hexafluorophosphate: Water mean cluster size as a function of water concentration

The water sorption behavior of representative pyridinium-based ionic liquid (IL), 1-hexylpyridinium hexafluorophosphate ([C6Py][PF6]), was studied over the whole range of the water activity a using a continuous gravimetric method. The analysis of the water sorption isotherm using the combination of a two-mode sorption (i.e. Henry-clustering) allowed to better understand [C6Py][PF6]-water interactions. At low and intermediate activity (a ≤ 0.8), the water molecules revealed a very low affinity to [C6Py][PF6] and, consequently, the water uptake was rather low. On the contrary, at high water activity (a > 0.8), the water uptake increased exponentially and the water clustering easily occurred. The constant of the Henry-clustering equation as well as the water clustering mechanism in [C6Py][PF6] were discussed and compared to those of imidazolium-based ILs: 1-hexyl-3-methylimidazolium hexafluorophosphate [C6C1im][PF6] (water-immiscible IL) and 1-butyl-3-methylimidazolium tetrafluoroborate [C4C1im][BF4] (water-miscible IL). It is shown that the sorption of water molecules by pyridinium-based ILs is controlled not only by the anion's nature, but also by the cation's nature. Moreover, the Zimm-Lundberg theory was used to determine the water mean cluster size (MCS) in [C6Py][PF6], [C6C1im][PF6] and [C4C1im][BF4]. The MCS results confirmed the strong capacity of water molecules to be aggregated in [C6Py][PF6]. In order to have a deeper insight into the water molecular state, infrared spectroscopy measurements were carried out as a function of the relative humidity value and the obtained results were correlated with the results of water sorption isotherms. It is found that at high water activity (a > 0.8), sorbed water molecules are strongly linked with ILs by hydrogen bonds and, therefore, are easily aggregated.

Trace water affects tris(pentafluorophenyl)borane catalytic activity in the Piers-Rubinsztajn reaction.

Improved methods to control silicone synthesis are required due to the sensitivity of siloxane bonds to acid/base-mediated chain redistribution/depolymerization. The Piers-Rubinsztajn reaction employs tris(pentafluorophenyl)borane as an efficient catalyst (<0.1 mol%) for siloxane bond formation from hydro- and alkoxysilanes - typical reactions proceed in open flasks at room temperature within minutes. While advantageous under ideal conditions, the boron catalyst activity may be affected by age, storage conditions and various environmental factors, particularly humidity. Under conditions of high humidity it may be necessary to apply heat and/or use increased catalyst loading in the reactions; there is often an induction time. We examine induction times in the Piers-Rubinsztajn reaction as a function of water concentrations in the reagent or catalyst solution and show that water in the reagent solution or atmosphere is less problematic than water found in the catalyst stock solution. A relatively linear increase in induction time accompanied higher water concentrations in the catalyst solution - no such effect was observed when the water was in the reagent solution. Reaction rates in both scenarios were similar, i.e., not affected by the induction time. Improvements in the stability of catalyst solutions were observed when B(C6F5)3 was stored in low molecular weight silicone oils, and pre-complexed with HSi(OSiMe3)3. These outcomes are ascribed to the ability of HSi groups to outcompete water in binding with B(C6F5)3 to initiate reaction, unless the boron is pre-complexed with water.

The influence of hydrophilicity on the orientational dynamics and structures of imidazolium-based ionic liquid/water binary mixtures.

The orientational dynamics and microscopic structures of imidazolium-based ionic liquids of varying hydrophilicity were investigated using optical heterodyne-detected optical Kerr effect (OHD-OKE) spectroscopy and atomistic simulations. Hydrophilicity was tuned via anion selection, cation alkyl chain length, and the addition of a strong hydrogen bond donor on the cation (protic ionic liquid). In the hydrophobic samples, which saturate at relatively low water concentration, OHD-OKE data display Debye Stokes Einstein (DSE) behavior as a function of water concentration. The DSE behavior indicates that the microstructures of the hydrophobic ionic liquid/water mixtures do not fundamentally change as a function of water concentration. The hydrophilic samples have two regimes of different DSE behaviors demonstrating the presence of two structural regimes depending on water concentration. These experimental results indicate that in hydrophilic ionic liquid/water samples, significant structural changes occur to accommodate high water concentrations, while hydrophobic samples become water saturated because the restructuring of local ionic structures is unfavorable. Atomistic simulations show that the local ionic microstructures experience distinct changes in these hydrophilic ionic liquid/water binary samples because of the delicate interplay of intermolecular interactions among imidazolium cations, hydrophilic anions, and water molecules.

Specific heat of mixtures of kaolin with sea water or distilled water for their use in thermotherapy

Mixtures of clays and waters of different mineralization have been used for thermotherapy therapies since ancient times. These mixtures are the basis of the most so-called thermal peloids, which are used for therapeutic purposes in the main thermal centres of the world. The thermal properties of peloids are very important to establish their applicability and determine whether they are appropriate for use in thermotherapy. This work focuses on the study of the behaviour of the specific heat capacity of different mixtures of kaolin with sea water or distilled water as a function of water concentration. Sea water is equivalent to high mineralized water, and distilled water corresponds to zero mineralization. Specific heat capacity was measured at atmospheric pressure and in the temperature interval from 293.15 to 317.15 K, using a commercial SETARAM BT 2.15 calorimeter. This device is based on the principle of Calvet calorimetry with temperature control. Furthermore, experimental results were compared to those obtained from mixtures with other clays.

Polymorphs in room-temperature ionic liquids: Hierarchical structure, confined water and pressure-induced frustration

Room-temperature ionic liquids (RTILs) can extract hidden information about water. Various types of hydrogen bonds of water are detected clearly in the liquid, glass, and crystal states. In addition to hydrogen bonding in water, balancing among charge (scalar), dipole (vector), and coordination number (topology) contribute to heterogeneous structure on the multiple scales in RTILs–water systems. The water-mediated hierarchical structure in the liquid is connected to macroscopic properties such as AC impedance, pH oscillations, density, and differential scanning calorimetry trace as a function of water concentration. Nanoscale water confinement was observed inside the RTILs, and the size and distribution of confined water were tuned by water concentration and temperature. The loosely packed confinement plays an important role in the engineering of next generation novel nanoheterogeneous materials. High-pressure crystal polymorphs were identified in pure RTILs by X-ray diffraction and Raman spectroscopy. By further compression, amorphous appeared partially in the deformed crystalline.

Effect of moisture on cationic polymerization of silicone epoxy monomers

ABSTRACTMoisture in polymerization of a cationically cured silicone epoxy monomer blend is an important parameter that affects the resulting polymer properties. We report the kinetics of the cationic polymerization of epoxy monomers as a function of water concentration, directly quantified using Karl Fischer (KF) titration that was characterized using Fourier transform infrared (FTIR) spectroscopy and also the mechanical strength of resulting polymers via diametral tensile strength measurements. Methodology and results for a silicone epoxy monomer material were compared with the same methodology applied to a “control” monomer, 3,4‐epoxycyclohexylmethyl 3,4‐epoxycyclohexyane carboxylate, for which moisture effects have been previously studied. Initially, an increase in moisture during cationic polymerization of epoxy caused increased rate (ROC) and degree of conversion (DOC) that for the silicone epoxy was followed by decreased DOCs for water contents approaching saturation, i.e., [H2O]∼0.19 wt %. Further, the rate of conversion was also affected by the presence of moisture with a trend analogous to the DOC. Diametral tensile strength measurements found that small amounts of water present during polymerization caused small changes in tensile strength but found polymer strengths to be significantly decreased if initial water concentrations approached saturation or were in excess of saturation. Lower strengths corresponded with reduced rates of conversion and DOCs. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41831.

Positron Lifetime and Electrical Conductivity Studies of Bicontinuous Phase in (TTAB+Pentanol)/Water/n-Octane Reverse Micellar System

Reverse micellar (L2) phase in (TTAB+pentanol)/water/n-octane, mapped by using optical method, was investigated by preparing mixtures of 30%, 40%, 50%, 60% and 70% by weight of (TTAB+pentanol)(1:1) in n-octane. Positron annihilation studies were performed in these mixtures as a function of water concentration. Around water concentrations of 13.8%, 11.1%, 8.4%, 7.9% and 9.1% respectively, ortho-positronium pick-off lifetime τ3 shows oscillatory behaviour whereas positronium formation I3 exhibits abrupt change. These changes have been attributed to the setting in of bicontinuous phase. Electrical conductivity measurements support these results. Positron annihilation technique can thus distinguish between droplet-like and bicontinuous structures in L2 phase.

Effect of the drying rate on the complex viscosity of wheat flour dough transforming into crust and crumb during baking

This study aimed at characterizing the effect of hydrothermal dynamics on the dough rheology, in order to develop a complete dough viscosity model valid at different locations during baking. The dough rheology was characterised using dynamic mechanical thermal analysis (DMTA). Temperature and water content (WC) were monitored during DMTA. At high heating rates (15–30°C/min), relevant to the top crust, viscosity behaved as if WC was kept constant, in spite of dehydration (37%); such similarity was valid up to 80°C (stage A). Beyond, the viscosity decrease observed in the samples at constant WC was replaced by a long-lasting plateau (stage B, 3–4 × 106 Pa.s), attributed to WC reduction below ∼37%. Above the boiling water temperature, the logarithm of viscosity increased linearly with decreasing WC (stage C). At lower heating rates (5°C/min), relevant to the bottom crust, viscosity was two-fold higher than that at higher heating rates, suggesting lower oven-rise. The viscosity decrease, observed at high temperatures (>80°C) for samples at constant WC, was not observed if drying occurred late (case of crumb beneath the crust); instead, viscosity increased up to levels close to that of the top crust (2–3 × 107 Pa.s at WC∼20%). Despite these deviations, viscosity as a WC function was modelled with a unique equation set.

A Coarse-Grained MARTINI Model of Polyethylene Glycol and of Polyoxyethylene Alkyl Ether Surfactants

Nonionic surfactants are used for the isolation and purification of membrane proteins, as well as for the study of fundamental aspects of protein diffusion in membranes. Here we present a new coarse-grained model of polyethylene glycol (PEG) and of the family of polyoxyethylene alkyl ether (C(i)E(j)) surfactants. The model is compatible with the MARTINI coarse-grained force-field for lipids and proteins. We validate the model by comparing molecular dynamics simulations with experimental data. In particular, we show that the model reproduces the phase behavior of water-surfactant mixtures as a function of water concentration. We also simulate the self-assembly of two ternary mixtures that have been used for the experimental measure of protein diffusion coefficients. The first includes a cosurfactant that affects the curvature of the surfactant bilayers; the second is a mixture of C(i)E(j) surfactants, alkanes and water. In both cases, the results of self-assembly simulations are in agreement with experimental observations and pave the way to the use of the surfactant model in combination with MARTINI peptides and proteins.

A Highly Efficient Turn-On Fluorescent Sensor for Determination of Water in Organic Solvents

2, 3 biphenyl quinoxaline 6-amine is a fluorescent compound in some organic solvents with an excitation wavelength at 435 nm and a fluorescence emission at 518 nm. The fluorescence intensity of 2, 3 biphenyl quinoxaline 6-amine is significantly reduced in the presence of bis-(2, 4, 6-trichlorophenyl) oxalate (TCPO) and Zn(2+) due to the nonfluorescent complex formation. The low stability of the complex in presence of trace amount of water results in decomposing complex, thereby recovering the photoluminescence of 2, 3 biphenyl quinoxaline 6-amine. Based on this fact, a turn-on fluorescence photoluminescence sensor for determination of water content in organic solvents was introduced for the first time.The fluorescence intensity of 2, 3 biphenyl quinoxaline 6-amine as a function of water concentration was used as a simple, sensitive and rapid method for determining trace amount of water in some organic solvents such as ethanol and methanol. The obtained results showed a good linear relationship between fluorescence intensity and the water content with a dynamic range of 0.0094 -1(v/v%), related coefficient of 0.9922 and limit of detection of 0.0026(v/v%). %).