Wide Range Of Water Concentrations Research Articles

Unraveling relationship between complex lifetimes and microscopic diffusion in deep eutectic solvents.

Aqueous mixtures of deep eutectic solvents (DESs) have emerged as a subject of interest in recent years for their tailored physicochemical properties. However, a comprehensive understanding of water's multifaceted influence on the microscopic dynamics, including its impact on improved transport properties of the DES, remains elusive. Additionally, the diffusion mechanisms within DESs manifest heterogeneous behavior, intricately tied to the formation and dissociation kinetics of complexes and hydrogen bonds. Therefore, it is imperative to explore the intricate interplay between bond kinetics, diffusion mechanism, and dynamical heterogeneity. This work employs water as an agent to explore their relationships by studying various relaxation phenomena in a DES based on acetamide and lithium perchlorate over a wide range of water concentrations. Notably, acetamide exhibits Fickian yet non-Gaussian diffusion across all water concentrations with Fickian (τf) and Gaussian (τg) timescales following a power-law relationship, τg∝τfγ, γ ∼ 1.4. The strength of coupling between bond kinetics and different diffusion timescales is estimated through various power-law relationships. Notably, acetamide-water hydrogen bond lifetime is linked to diffusive timescales through a single power-law over the entire water concentration studied. However, the relationship between diffusive timescales and the lifetime of acetamide-lithium complexes shows a sharp transition in behavior at 20 wt. % water, reflecting a change from vehicular diffusion below this concentration to structural diffusion above it. Our findings emphasize the critical importance of understanding bond dynamics within DESs, as they closely correlate with and regulate the molecular diffusion processes within these systems.

Влияние состава электролита на морфологию пленок диоксида титана, получаемых анодированием титана в ячейке с циркуляционным перемешиванием

Методом потенциостатического анодирования титана в электрохимической ячейке с проточноциркуляционным потоком раствора и системой его охлаждения, вынесенной за пределы ячейки, при температуре 25 ± 0.5°С получены высокоупорядоченные пленки из отдельных нанотрубок (НТ) TiO2 c контролируемыми геометрическими характеристиками. Продемонстрировано влияние в широком диапазоне концентрации воды (0–15%) и фтористого аммония (0.1–2.0%) в этиленгликоле на морфологию и состав получаемых НТ TiO2 . Установлено, что наиболее упорядоченная структура из НТ TiO2 формируется при содержании воды в растворе анодирования 0.5– 4.0%, доля НТ в гексагональном окружении достигает 75%. Показано, что концентрация фторидионов и воды в этиленгликоле не оказывают влияния на химическое состояние и концентрацию элементов в получаемых наноструктурах. С использованием рентгеновской фотоэлектронной спектроскопии установлено, что в полученных образцах титан находится в форме Ti4+ и Ti3+ с относительной долей последнего 8 ± 2%.

Backbone Hydrogen Bond Energies in Membrane Proteins Are Insensitive to Large Changes in Local Water Concentration.

A hallmark feature of biological lipid bilayer structure is a depth-dependent polarity gradient largely resulting from the change in water concentration over the angstrom length scale. This gradient is particularly steep as it crosses the membrane interfacial regions where the water concentration drops at least a million-fold along the direction of the bilayer normal. Although local water content is often assumed to be a major determinant of membrane protein stability, the effect of the water-induced polarity gradient upon backbone hydrogen bond strength has not been systematically investigated. We addressed this question by measuring the free energy change for a number of backbone hydrogen bonds in the transmembrane protein OmpW. These values were obtained at 33 backbone amides from hydrogen/deuterium fractionation factors by nuclear magnetic resonance spectroscopy. We surprisingly found that OmpW backbone hydrogen bond energies do not vary over a wide range of water concentrations that are characteristic of the solvation environment in the bilayer interfacial region. We validated the interpretation of our results by determining the hydrodynamic and solvation properties of our OmpW-micelle complex using analytical ultracentrifugation and molecular dynamics simulations. The magnitudes of the backbone hydrogen bond free energy changes in our study are comparable to those observed in water-soluble proteins, the H-segment of the leader peptidase helix used in the von Heijne and White biological scale experiments, and several interfacial peptides. Our results agree with those reported for the transmembrane α-helical portion of the amyloid precursor protein after the latter values were adjusted for kinetic isotope effects. Overall, our work suggests that backbone hydrogen bonds provide modest thermodynamic stability to membrane protein structures and that many amides are unaffected by dehydration within the bilayer.

An experimentally-validated numerical model of diffusion and speciation of water in rhyolitic silicate melt

The diffusion of water through silicate melts is a key process in volcanic systems. Diffusion controls the growth of the bubbles that drive volcanic eruptions and determines the evolution of the spatial distribution of dissolved water during and after magma mingling, crystal growth, fracturing and fragmentation, and welding of pyroclasts. Accurate models for water diffusion are therefore essential for forward modelling of eruptive behaviour, and for inverse modelling to reconstruct eruptive and post-eruptive history from the spatial distribution of water in eruptive products. Existing models do not include the kinetics of the homogeneous species reaction that interconverts molecular (H2Om) and hydroxyl (OH) water; reaction kinetics are important because final species distribution depends on cooling history. Here we develop a flexible 1D numerical model for diffusion and speciation of water in silicate melts. We validate the model against FTIR transects of the spatial distribution of molecular, hydroxyl, and total water across diffusion-couple experiments of haplogranite composition, run at 800–1200 °C and 5 kbar. We adopt a stepwise approach to analysing and modelling the data. First, we use the analytical Sauer-Freise method to determine the effective diffusivity of total water DH2Ot as a function of dissolved water concentration CH2Ot and temperature T for each experiment and find that the dependence of DH2Ot on CH2Ot is linear for CH2Ot≲1.8 wt.% and exponential for CH2Ot≳1.8 wt.%. Second, we develop a 1D numerical forward model, using the method of lines, to determine a piece-wise function for DH2OtCH2Ot,T that is globally-minimized against the entire experimental dataset. Third, we extend this numerical model to account for speciation of water and determine globally-minimized functions for diffusivity of molecular water DH2OmCH2Ot,T and the equilibrium constant K for the speciation reaction. Our approach includes three key novelties: (1) functions for diffusivities of H2Ot and H2Om, and the speciation reaction, are minimized simultaneously against a large experimental dataset, covering a wide range of water concentration (0.25≤CH2Ot≤7 wt.%) and temperature (800°C≤T≤1200°C), such that the resulting functions are both mutually-consistent and broadly applicable; (2) the minimization allows rigorous and robust analysis of uncertainties such that the accuracy of the functions is quantified; (3) the model can be straightforwardly used to determine functions for diffusivity and speciation for other melt compositions pending suitable diffusion-couple experiments. The modelling approach is suitable for both forward and inverse modelling of diffusion processes in silicate melts; the model is available as a MATLAB script from the electronic supplementary material.

Improved Kinetic Rate Constants for Nylon 6, Nylon 6,6, and Nylon 6/6,6 Copolymer

AbstractNylon 6 and 6,6 literature data are collected over a wide range of water concentrations and temperatures (0 ≤ [W]0 ≤ 40.8 wt%, 200 ≤ T ≤300 °C) and used to fit parameters in an updated batch reactor model. The resulting copolymerization model uses side reactions to account for the complex influence of water on kinetics and reaction equilibria. The proposed parameter estimates result in a significant improvement in the fit to the data, corresponding to a 73% reduction in the weighted‐least‐squares objective function compared to when the parameters of Arai et al. are used. Copolymerization simulations are conducted at industrially relevant conditions, shedding light on the complex influence of water and on the potential to include waste nylon 6 cyclic dimer in the feedstock. The model and parameter estimates will be helpful in future models of nylon 6/6,6 copolymerization in continuous reactor systems.

Entropic effect implication for change in polymer coils swelling state in the demixing enthalpy recovery of aqueous poly(vinyl methyl ether) solutions

ABSTRACTTime‐dependent demixing enthalpy recovery behavior of aqueous poly(vinyl methyl ether) (PVME) solutions exhibits distinct recovery characteristics in three concentration regions. The absence of recovery behavior below a water concentration of 38.3 wt % indicates that the PVME coil is in a globular state. The typically sigmoidal recovery behavior of demixing enthalpy above 38.3 wt % is ascribed to the reswelling of the collapsed polymer coils induced by the entropic effect. The increase in difference between the upper and lower limits indicates the continued swelling of the PVME coils. Above 65 wt %, a dominant diluting effect can be observed, and a much longer phase separation time is needed to reach the expected lower limit. In contrast, the recovery of demixing enthalpy in a wide range of water concentration (from 38.3 to 90 wt %) exhibits the same feature. The infrared spectroscopy results are in agreement with the above macroscopic differential scanning calorimetry results. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 142–151

Simulation and measurement of water-induced liquid-liquid phase separation of imidazolium ionic liquid mixtures.

The miscibility of ionic liquid (IL) pairs with a common cation (1-ethyl-3-methylimidazolium [C2C1im]) and different anions (bis(trifluoromethylsulfonyl)amide [TFSI], acetate [OAc], and chloride [Cl]) was investigated at a wide range of water concentrations at room temperature. Molecular simulations predicted that the addition of water to the [C2C1im][TFSI]:[C2C1im][OAc] and [C2C1im][TFSI]:[C2C1im][Cl] mixtures would induce a liquid-liquid phase separation and that water addition to the [C2C1im][OAc]:[C2C1im][Cl] mixture would not produce a phase separation. The effect of water on the phase behavior of the IL mixtures was verified experimentally, and the IL and water concentrations were determined in each phase. Of particular importance is the analytical methodology used to determine the species' concentration, where 1H NMR and a combination of 19F NMR, Karl Fischer titration, and ion chromatography techniques were applied.

Effect of Concentration on the Interfacial and Bulk Structure of Ionic Liquids in Aqueous Solution.

Bio and aqueous applications of ionic liquids (IL) such as catalysis in micelles formed in aqueous IL solutions or extraction of chemicals from biologic materials rely on surface-active and self-assembly properties of ILs. Here, we discuss qualitative relations of the interfacial and bulk structuring of a water-soluble surface-active IL ([C8MIm][Cl]) on chemically controlled surfaces over a wide range of water concentrations using both force probe and X-ray scattering experiments. Our data indicate that IL structuring evolves from surfactant-like surface adsorption at low IL concentrations, to micellar bulk structure adsorption above the critical micelle concentration, to planar bilayer formation in ILs with <1 wt % of water and at high charging of the surface. Interfacial structuring is controlled by mesoscopic bulk structuring at high water concentrations. Surface chemistry and surface charges decisively steer interfacial ordering of ions if the water concentration is low and/or the surface charge is high. We also demonstrate that controlling the interfacial forces by using self-assembled monolayer chemistry allows tuning of interfacial structures. Both the ratio of the head group size to the hydrophobic tail volume as well as the surface charging trigger the bulk structure and offer a tool for predicting interfacial structures. Based on the applied techniques and analyses, a qualitative prediction of molecular layering of ILs in aqueous systems is possible.

In Situ Determination of the Water Content of Ionic Liquids

This study examines the applicability of electrochemical methods to the in situ determination of the water content in proton-conducting ionic liquids (PILs). Two proton-conducting ionic liquids with different acidities and hygroscopicities of the cations, sulfoethylmethylammonium trifluoromethanesulfonate, [2-Sema][TfO] and N,N-diethylmethylammonium trifluoromethanesulfonate, [Dema][TfO], were used. At first, PIL water electrolytes with known water concentrations ([2-Sema][TfO]: 0.64-6.1 wt%, [Dema][TfO]: 0.18-99.5 wt%) were prepared. Then, the influence of the water content on the electrochemical properties, namely the electrical conductivity, charge of hydrogen oxidation, charge of Pt oxide reduction and onset potential of Pt oxidation, were investigated. The four parameters were plotted as a function of the water concentration and fitted by exponential, linear or asymptotic functions. These fits serve as calibration curves that can be used to determine the actual water concentration by measuring one or more of the four parameters investigated. It was found that the measurement of specific ion conductivity is a fast and simple method across a wide range of water concentrations. The evaluation of the Pt oxide reduction charge from cyclic voltammograms is more time-consuming, but provides higher accuracy at low water concentrations, although the accuracy also depends on the nature of the ionic liquid.

Novel green PVA-fullerenol mixed matrix supported membranes for separating water-THF mixtures by pervaporation.

This study focuses first on the preparation of mixed matrix supported membranes of polyvinyl alcohol (PVA) and low-hydroxylated fullerenol C60(OH)12 used to create water selective membranes and then on their pervaporation properties for the separation of water-THF mixtures. These novel supported PVA membranes containing nano-carbon particles were prepared to reach high membrane performance for further integration in a dehydration process, such as distillation coupled to pervaporation. The separation of water-THF mixtures was performed with the supported membranes over a wide range of water concentrations in the feed mixture, i.e., from the azeotrope range up to 30wt%, to evaluate the performance and stability of the thin active layer. SEM was used to visualize the internal morphology of the membrane. The influence of temperature on the transport properties was also investigated. All the membranes were highly water selective and stable up to 30wt% water in the feed. The best compromise of transport properties was obtained for the C60(OH)12(5%)-PVA supported composite membrane: a permeate enrichment of 99.3±0.3wt% water and a flux of 0.25±0.02kg/(m2h) for the separation of a mixture containing 5.7wt% water and 94.3wt% tetrahydrofuran (THF) at 30°C. Considering its water stability, this supported membrane with a dense layer thinner than 2μm appears promising for use in hybrid industrial processes to upgrade solvents with a smaller environmental footprint than conventional methods.

Facile fabrication of hollow titania microparticles using wet yeast cells as templates

Abstract Hollow titania microparticles were prepared using the bio-templating method with wet yeast cells as templates. Wet yeast cells were used to eliminate fixation or drying of as-cultured cells, and titania shells were formed on the cells via the sol–gel method with tetraisopropyl titanate (TTIP). When the citric acid was used to stabilize TTIP and catalyze TTIP hydrolysis, hollow titania microparticles with well-defined yeast cell morphologies were successfully synthesized. The diameter of the obtained particles was approximately 1.3 μm, and the crystal structure was anatase. The specific surface area and average pore diameter were 41.5 m2/g and 9.6 nm, respectively. Titania nanoparticles generated by homogeneous nucleation were rarely observed over a wide range of water concentrations, indicating that reaction on the biological cell surface, rather than monomer diffusion toward the surface, was rate-limiting. A significant advantage of our method is that the use of dry cultured cells is not required, in contrast to methods using powdered biological cell templates.

Effects of Dissolved Water on Li+ Solvation in 1-Ethyl-3-methylimidazolium Bis(trifluoromethanesulfonyl)amide Ionic Liquid Studied by NMR

(1)H and (7)Li NMR chemical shifts of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide-water solutions in the presence and absence of lithium bis(trifluoromethanesulfonyl)amide were determined at 293.2 K over a wide range of water concentrations from 0.0156 to 1.16 mol kg(-1). These results revealed the attractive interaction between water molecule and Li(+) as well as the hydrogen bonding among water molecules. Moreover, self-diffusion coefficients of water, 1-ethyl-3-methylimidazolium cation, Li(+), and bis(trifluoromethanesulfonyl)amide anion in the ionic liquid solutions at various water contents were determined by (1)H, (7)Li, and (19)F NMR techniques. It was found that Li(+) is averagely hydrated by eight water molecules in the ionic liquid solutions. Furthermore, (7)Li longitudinal relaxation times of Li(+) in the ionic liquid solutions at 293.2 K were measured with two different magnetic fields and various water contents. The mean one-jump distances of Li(+) in the ionic liquid solutions were estimated from the correlation times and the self-diffusion coefficients. A comparison between the hydrodynamic radius and the mean one-jump distance of Li(+) suggested the formation of water channels in the ionic liquid solutions.

Water Dynamics in Water/DMSO Binary Mixtures

The dynamics of dimethyl sulfoxide (DMSO)/water solutions with a wide range of water concentrations are studied using polarization selective infrared pump-probe experiments, two-dimensional infrared (2D IR) vibrational echo spectroscopy, optical heterodyne detected optical Kerr effect (OHD-OKE) experiments, and IR absorption spectroscopy. Vibrational population relaxation of the OD stretch of dilute HOD in H(2)O displays two vibrational lifetimes even at very low water concentrations that are associated with water-water and water-DMSO hydrogen bonds. The IR absorption spectra also show characteristics of both water-DMSO and water-water hydrogen bonding. Although two populations are observed, water anisotropy decays (orientational relaxation) exhibit single ensemble behavior, indicative of concerted reorientation involving water and DMSO molecules. OHD-OKE experiments, which measure the orientational relaxation of DMSO, reveal that the DMSO orientational relaxation times are the same as orientational relaxation times found for water over a wide range of water concentrations within experimental error. The fact that the reorientation times of water and DMSO are basically the same shows that the reorientation of water is coupled to the reorientation of DMSO itself. These observations are discussed in terms of a jump reorientation model. Frequency-frequency correlation functions determined from the 2D IR experiments on the OD stretch show both fast and slow spectral diffusion. In analogy to bulk water, the fast component is assigned to very local hydrogen bond fluctuations. The slow component, which is similar to the slow water reorientation time at each water concentration, is associated with global hydrogen bond structural randomization.

Vibrational dynamics of the water shell of DNA studied by femtosecond two-dimensional infrared spectroscopy

Vibrational dynamics of the water shell around DNA oligomers are addressed by femtosecond two-dimensional (2D) infrared spectroscopy in a wide range of water concentrations. In the 2D spectra, NH stretching excitations of DNA are clearly separated from OH stretching excitations of water. For full hydration, OH stretching excitations display spectral diffusion on a time scale of 500 fs. Vibrational relaxation results in the build-up of a hot water ground state on a 1–2 ps time scale. A comparison of center line slopes of the 2D spectra with the frequency–time correlation function of bulk water suggests a decay of frequency correlations distinctly slower than in bulk H2O. We attribute this behavior to local DNA–water interactions which reduce structural fluctuations and to the smaller rate of resonant OH stretch energy transfer. In contrast, the kinetics of excess energy dissipation are similar in the two systems.

Formation of Negative Cluster Ions with Water Molecules in Nonpolar Liquid

Formation of negative cluster ions with water molecules in nonpolar liquid is considered in a wide range of water concentration. The experimental approaches based on the photoconductivity technique have been developed which allow one to measure the ion mobility and investigate the electron photodetachment from negative ions as well as the electron autodetachment kinetics for short-lived negative ions. It has been established that, in the range of low water concentrations 10-5-10-4 M, the main part of ions exists in a form of the smallest clusters A-(H2O). The big ion clusters were observed when the water concentration was close to the solubility limit (~10-3 M). The rate constants of formation and decay of the smallest cluster ions were determined. The estimations of the equilibrium constant for formation of the cluster ions with two water molecules were obtained.

Mechanistic Studies of Cu Electropolishing in Phosphoric Acid Electrolytes

Electropolishing of Cu and Cu/Ta/Si wafer samples were studied using a rotating disk electrode in a variety of phosphoric acid-based electrolytes, including several with ethanol and other species added as diluents. Diluents allow a wide range of water concentrations to be accessed and also reduce the dissolution rate during Cu electropolishing, simplifying possible applications to damascene processing. The measured limiting current densities are subject to a Levich analysis, demonstrating that water is the acceptor species involved in the rate-determining step. The effective diffusion coefficient that is determined is in almost exact agreement with that previously obtained from the electrohydrodynamic impedance, which does not require knowledge of the limiting species. © 2004 The Electrochemical Society. All rights reserved.

Interaction of Water with GeCl4 , SnCl4 , and AsCl3

The interaction of water with GeCl4 , SnCl4 , and AsCl3 was studied by IR spectroscopy. The results demonstrate that these chlorides contain molecular water in monomeric form. At water concentrations above 10–2 mol/l, GeCl4 also contains H3O+ ions. The mechanisms of GeCl4 and AsCl3 hydrolysis were studied over a wide range of water concentrations.

Solvatochromism in pure and binary solvent mixtures: effects of the molecular structure of the zwitterionic probe

The solvatochromic behavior of 2,6-dichloro-4-(2,4,6-triphenyl-1-pyridinio)phenolate (WB) was studied by UV–visible spectrophotometry in 32 pure solvents, in binary mixtures of 1-butanol–cyclohexane (BuOH–Cyhx), and of water with methanol, ethanol, 1-propanol, 2-butoxyethanol (2-BE), acetonitrile, 1,4-dioxane and THF. The solvent polarity, ET(33) in kcal mol−1, was calculated from the position of the longest-wavelength intramolecular charge-transfer absorption band of WB and the results were compared with those for 2,6-diphenyl-4-(2,4,6-triphenyl-1-pyridinio)phenolate [RB, ET(30)] and of 1-methyl-8-oxyquinolinium betaine [QB, ET(QB)]. For pure solvents, ET(33) is a linear function of ET(30), with a slope of practically unity. Steric crowding from the two ortho phenyl rings of RB hinders the formation of H-bonds with solvents, which results in similar susceptibilities of WB and RB to solvent acidity. For binary solvent mixtures, all plots of ET versus the mole fraction of 1-butanol or water are non-linear owing to preferential solvation of the probe by one component of the mixed solvent and, when applicable, to solvent micro-heterogeneity. Preferential solvation due to non-specific and specific probe–solvent interactions was calculated for BuOH–Cyhx and water–acetonitrile. Both solvation mechanisms contribute to the non-ideal behavior in the former binary mixture, whereas probe–solvent specific interactions dominate the solvatochromic behavior in the latter. The composition of the probe solvation shell was calculated. In aqueous alcohols, preferential solvation is by the alcohol. In water–aprotic solvent mixtures, preferential solvation of RB and WB is by the solvent which is present in lower concentration, whereas QB seems to form its own, water-rich solvation shell over a wide range of water concentration. Copyright © 2000 John Wiley & Sons, Ltd.

The effect of incorporation of phosphonic acid dibutyl ester in POPC model membranes on the hydration force

The hydration and swelling properties of lipid model membranes formed by mixtures of 1-palmitoyl-2-oleoylglycerophosphatidyl-choline (POPC) and different molar ratios R a l of dodecyl phosphonic acid dibutyl ester (PAB 12) in water were studied at 25°C. It is shown by X-ray diffraction and 31P NMR spectroscopy that the system exists in a fluid lamellar phase at R a l = 0.25 and 0.5 over a wide range of water concentration. Intermembrane forces were determined by the osmotic stress technique. The hydration repulsion was found to decrease exponentially with increasing intermembrane water layer thickness. The values of the pre-exponential factor of the hydration forces which slightly decrease with increasing R a l were discussed according to the theory of water polarization near structured water/lipid interfaces (Cevc).

Perfluoropolyether microemulsions: Conductivity behavior of three-component W/O systems

The formation of water-in-oil (W/O) microemulsions based on perfluoropolyether (PFPE) oil and a surfactant (S) with a similar PFPE hydrophobic chain has been investigated by conductivity and static light scattering. As previously reported, conductivity measurements across the isotropic oil-rich region (W < 30%) allowed the detection of the transition from solution of hydrated surfactant species to microdroplets of water in oil. The quantitative interpretation of the conductivity data was proposed. The hydration and partial dissociation of ionic surfactant molecules were found to be responsible for the variation of conductivity upon addition of water at a constant oil to surfactant ratio. The contribution of charge fluctuation among droplets was negligible over a wide range of water concentration and could explain only the relatively low conductivities at high W/S ratio. In turn, high conductivities, on the scale of percolative systems, were measured at lower water content. Light scattering results confirmed the onset of droplet formation at the compositions where the maxima of the conductivity curves were observed. The droplet formation was driven by the number of water molecules per polar head. Varying systematically the chain length of either surfactant or oil, an increase in oil penetration (higher packing parameter V/al) favored droplet formation over a wider composition range and decreased conductivity, while a decrease in oil penetration (lower V/al) inhibited droplet formation and increased conductivity, according to previous observations in hydrocarbon systems.