Water Mole Research Articles

Vesicle-to-micelle transition in a double chain quaternary ammonium surfactant system: Interfacial behavior and molecular insights

Vesicles have emerged as promising drug carriers with excellent compatibility with cell membranes, holding immense potential for biomedical applications. While most reported micelle-to-vesicle transitions involve increasing surfactant or additive concentrations, the reverse vesicle-to-micelle transition remains less explored. In this study, we investigate the vesicle-to-micelle transition of hexyldimethyloctylammonium bromide (C6C8Br) using dynamic light scattering, transmission electron microscopy, and fluorescence spectroscopy. Tetradecyltrimethylammonium bromide (TTABr), a single-chain tetraalkylammonium surfactant with the same chain-length, is studied for comparison. Through the chemical trapping (CT) method, we explore the interfacial composition changes during the vesicle-to-micelle transition. Notably, C6C8Br exhibits a unique characteristic setting it apart from TTABr and other cationic surfactants. At lower concentration ranges, there is a simultaneous increase in interfacial molarities of water and bromide ions, signifying a decrease in interfacial headgroup molarity and surfactant molecule packing. Moreover, our dissipative particle dynamics (DPD) simulation results show that, as the surfactant concentration rises, the interior angle between surfactant chains widens, and the molecular configuration of C6C8Br approaches a straight line. These combined CT and DPD findings underscore the prominent role of steric effects arising from the rigidity of the double-chain. These effects become more pronounced at higher C6C8Br concentrations, leading to looser interfacial packing of surfactant monomers and driving the transition from vesicles to micelles. Interestingly, the breakage of vesicles was not observed when replacing the counterion of C6C8Br with acetate in C6C8Ac solutions. CT results suggest that the elevated interfacial acetate molarity may faciliate the compact packing of surfactant monomers and hinder vesicle-to-micelle transformation. Our study provides a molecular-level understanding of the vesicle-to-micelle transitions in C6C8Br solutions and establishes a theoretical basis for morphological control of surfactant aggregates.

Modelling of convective drying of potatoes polyhedrons

Abstract This work aimed to develop numerical models to predict the moisture content and deformation of potato slices during convective drying (40–80 °C, 0.5 m·s−1). Three-dimensional slices were considered in cylindrical, cubic, parallelepiped, and prism geometries. The first classic model coupled the linear constant drying rate period with the analytical solution of Fick’s law in spherical coordinates, evaluating the mass diffusion coefficients (4.2–15.5·10−10 m2·s−1), critical drying time (1640–5085 s), and critical moisture content (1.8–2.4 kg·kg−1). The Finite Element Method (FEM) was a more robust model, that combined momentum and mass transfer to three-dimensional solid deformation of polyhedrons by ALE method, evaluating the mass diffusivity (1.4–6.5·10−10 m2·s−1). The FEM model could predict the shrinkage due to water molar flux removal on moving solid boundaries and explain the pseudo-constant drying rate detected in experimental data. The developed models accurately described the drying of food materials with a high shrinkage ratio.

Absorption of Water Vapor by Bambus[6]uril and a Density Functional Theory Study of Its Aqua Complexes

The absorption/desorption of water vapor by bambus[6]uril (Bu[6]) has been studied. According to kinetic experiments, the absorption capacity of Bu[6] is 4 moles of water per 1 mole of Bu[6] with the absorption duration of 20 min and the complete desorption duration of 100 min. Experimental rate constants for water vapor absorption and desorption by Bu[6] have been determined to be 0.166 min−1 and 0.0221 min−1, respectively. The obtained results are in agreement with theoretical calculations using the DFT method. A hypothetical structure of bambus[6]uril tetrahydrate (Bu[6]·4H2O) has been proposed based on the experimental and DFT data.

1H, 31P NMR, Raman and FTIR spectroscopies for investigating phosphoric acid dissociation to understand phosphate ion kinetics in body fluids

The study investigates the formation and transportation of ionic charge carriers in phosphoric acid-water system. This investigation encompasses an analysis of 1H and 31P NMR chemical shifts, self-diffusion coefficients, spin-lattice relaxation rates, spin-spin relaxation rates, activation energies, dissociation constants, electrical conductivity, and Raman shifts, along with FTIR spectra across various water concentrations. Significantly, the maxima observed in these curves at around 0.8 water molar fraction predominantly from the unique molecular arrangement between phosphoric acid and water molecules, influenced by a hydrogen bonding network. These findings yield valuable insights into phosphate ion kinetics within body fluids, covering essential aspects like hydrogen bonding networks, ionization processes, and the energy kinetics of phosphoric dissociation. A customized semiempirical model is applied to calculate dissociated species (water, phosphoric acid, and hydronium ion) at different water contents within a wide range of water mole fraction. Furthermore, this investigation extends to the dissociation of phosphoric acid in DMEM cell culture media, offering a more precise model for phosphate ionic kinetics within body fluids, especially at nominal phosphate concentrations of approximately 1:700μL.

Trace Water Changes Metal Ion Speciation in Deep Eutectic Solvents: Ce3+ Solvation and Nanoscale Water Clustering in Choline Chloride-Urea-Water Mixtures.

Eutectic mixtures of choline chloride, urea, and water in deep eutectic solvent (DES)/water molar hydration ratios (w) of 2, 5, and 10, with dissolved cerium salt, were measured using neutron diffraction with isotopic substitution. Structures were modeled using empirical potential structure refinement (EPSR). Ce3+ was found to form highly charged complexes with a mean coordination number between 7 and 8, with the shell containing mostly chloride, followed by water. The shell composition is strongly affected by the molar ratio of dilution, as opposed to the mass or volume fraction, due to the high affinity of Cl- and H2O ligands that displace less favorable interactions with ligands such as urea and choline. The presence of Ce3+ salt disrupted the bulk DES structure slightly, making it more electrolyte-like. The measured coordination shell of choline showed significant discrepancies from the statistical noninteracting distribution, highlighting the nonideality of the blend. Cluster analysis revealed the trace presence of percolating water clusters (25 ≥ n ≥ 2) in solvent compositions of 5 and 10w for the first time.

Thermodynamic Analysis of Capillary and Electric Field Effects on Liquid-Vapor Equilibrium: A Study on the Water-Ethanol Mixture.

This study investigates phase equilibrium manipulation in nonideal mixtures through a combined capillary and external electric field approach. Utilizing thermodynamic principles, an expression is established for estimating the equilibrium liquid mole fraction in a confined system subjected to a localized electric field within a capillary that is filled with a liquid phase in equilibrium with its vapor counterpart. Applied to a water-ethanol system, the model suggests large shifts in the equilibrium liquid mole fraction of water due to the electric field and capillary effects. These findings reveal that while the capillary's influence remains negligible for radii exceeding 10 nm, capillaries of smaller dimensions, when exposed to electric fields of around 300 MV/m, can amplify the equilibrium liquid water mole fraction by up to 55%. This suggests the potential for phase equilibrium control through larger capillaries and lower electric fields, while intriguing complexities arise at very small radii.

Effects of interfacial molarity on salts inducing vesicle-to-micelle transitions in acyl taurines

Specific ion effects (SIEs) are crucial in engineering, chemistry and biology. N-acyl taurine (NAT) exists naturally in organisms and may have various physiological functions. However, compared with other acyl amino acid-based surfactants bearing carboxylate headgroups, the SIEs on NATs have received little research. Here, sodium lauroyl taurate (SLT) and sodium methyl lauroyl taurate (SMLT) bearing secondary and tertiary amides, respectively, were synthesized by a green method. The interfacial molarities of water, amides and sulfonate groups in SLT and SMLT aggregates were estimated simultaneously in the presence of tetraalkylammonium cations (TAA+) of different chain lengths. With increasing salt concentration, the interfacial water molarity increased, whereas the interfacial amide molarity decreased in all cases. However, at a fixed salt concentration, the interfacial water molarity increased with the hydrophobicity of cations, while the interfacial amide bond molarity followed the reverse order. The combined TEM and DLS results show that the majority of SLT and SMLT molecules formed vesicles spontaneously in the absence of salts, and some of these vesicles turned into micelles with TAA+ addition. Tertiary amides of SMLT may also absorb protons at the interface and interact with each other by hydrogen bonding. Such hydrogen bonds facilitate the tight packing of surfactant molecules and induce vesicle formation, just like the intermolecular amide-amide hydrogen bonds between SLT. Added TAA+ cleaves the hydrogen bonds between NAT and induces vesicle-to-micelle transitions. This hypothesis is supported by CT results showing that vesicle-to-micelle transitions were accompanied by decreases in interfacial amide molarity.

Measurement of Critical Temperatures, Critical Pressures and Densities of Acetone–Water Solutions for Simulation

Critical temperature, critical pressure and P–T–ρ–X data of acetone–water solutions with water mole fractions in a range of 0–60% were measured to provide fundamental data for CFD simulations. Critical temperatures were determined via observing critical opalescence in fused quartz capillary tubes. Meanwhile, critical pressures were measured by heating acetone–water solutions to its critical temperature in an autoclave. The standard deviations of critical temperature and critical pressure were 0.55 K and 0.029 MPa, respectively. The results indicate that only one phase exists during mixing of acetone with water. Moreover, P–T–ρ–X data under 15 and 20 MPa in the temperature range of 460–550 K were measured in the autoclave. The relative deviation of density was 0.32%. Volume-translated Peng-Robinson and Soave–Redlich–Kwong state equations were used to illustrate the P–V–T–X relationship of acetone–water solutions, and the Peng–Robinson state equation with an average absolute relative deviation of 1.19% between fitting and experimental densities was found more accurate.

The Spontaneous Vesicle-Micelle Transition in a Catanionic Surfactant System: A Chemical Trapping Study.

Typically, the formation of vesicles requires the addition of salts or other additives to surfactant micelles. However, in the case of catanionic surfactants, unilamellar vesicles can spontaneously form upon dilution of the micellar solutions. Our study explores the intriguing spontaneous vesicle-to-micelle transition in catanionic surfactant systems, specifically cetyltrimethyl ammonium bromide (CTAB) and sodium octylsulfonate (SOS). To gain insights into the changes occurring at the interface, we employ a chemical trapping method to characterize variations in the molarities of sulfonate headgroups, water, and bromide ions during the transition. Our findings reveal the formation of ion pairs between the cationic component of CTAB and the anionic component of SOS, leading to tight interfacial packing in CTAB/SOS solutions. This interfacial packing promotes vesicle formation at low surfactant concentrations. Due to the significant difference in critical micelle concentration (cmc) between CTAB and SOS, an increase in the stoichiometric surfactant concentration results in a substantial rise in the SOS-to-CTAB ratio within the interfacial region. This enrichment of SOS in the aggregates triggers the transition from vesicles to micelles. Overall, our study may shed new light on the design of morphologies in catanionic and other surfactant systems.

Tetraalkylammonium counterion effects on lauroyl β-alanine: A chemical trapping study

The use of acyl amino acid surfactants has gained significant interest due to increasing environmental pressure from both the government and customers. Understanding the ion-specific effects (SIE) in these surfactant systems not only contributes to their practical applications in complex systems but also provides a theoretical basis for investigating SIE in protein systems. In this study, we synthesized four types of lauroyl β-alanine tetraalkylammonium salts (TAA-LA) with tetramethylammonium (TMA-LA), tetraethylammonium (TEA-LA), tetrapropylammonium (TPA-LA), and tetrabutylammonium (TBA-LA) as counterions. The SIE on their surface activities, aggregation behaviors, and interfacial molarities were examined. The critical micelle concentration of TAA-LA decrease with an increase in the size of the counterions. Chemical trapping revealed that the interfacial molarity of water and carboxylate groups followed the order TBA-LA > TPA-LA > TEA-LA > TMA-LA, whereas the interfacial amide bond molarity followed the reversed order. These results were consistent with their differences in aggregation behaviors. Specifically, LA bearing smaller TAA+ counterions formed uni-lamellar vesicles (ULVs) spontaneously, while LA with TBA+ self-assembled into double-lamellar vesicles (DLVs) of comparable sizes. Both CT and MD confirmed that TBA-LA DLVs with relatively smaller “average curvature” were more hydrated than other TAA-LA ULVs. Our results suggested that TBA+ tends to break the intermolecular hydrogen bond between amide bonds, which results in looser interfacial packing and larger “average curvature”. Our findings provide new insights into the tetraalkylammonium counterion effects on acyl amino acid surfactants and elucidate the SIE on protein systems at the molecular level.

Nanostructure of aqueous ternary amino-acid-based natural deep eutectic solvents by water bridging

Natural deep eutectic solvents (NADESs) have drawn significant attention as green solvents for their special properties like biodegradability and biocompatibility. Nevertheless, the high viscosity of NADESs tends to prevent their implementation in industry. Even though dilution with water will lower the viscosity of NADESs effectively, fundamental knowledge of the intermolecular network in NADESs as well as the effect of water on the cooperative hydrogen-bonding network has not been evaluated systematically. Herein, solutions spanning a range of molar ratios of DL-Malic acid, L-Serine and water were synthesized. The experimental results demonstrate that it takes at least three moles of water to achieve a stable NADES. Besides, density functional theory (DFT) calculations indicate that water molecules connect DL-Malic acid and L-Serine by a water bridge framework. Furthermore, the progressive addition of water facilitates the proton transfer, making the hydrogen atom of the carboxyl group gradually ionize and approach the amino group. We hope the findings would provide a better understanding of the structural characteristics of NADESs and shed light on the applications.

Anomalous Dependence of Translational Diffusion on the Water Mole Fraction for Solute Molecules Dissolved in a 1-Butyl-3-methylimidazolium Tetrafluoroborate/Water Mixture.

Translational diffusion coefficients of carbon monoxide (CO), diphenylacetylene (DPA), and diphenylcyclopropenone (DPCP) were determined in mixtures of 1-butyl-3-methylimidazolium tetrafluoroborate ([C4mim]BF4) and water using transient grating spectroscopy at different mole fractions of water (xw). While DPA exhibited a larger diffusion coefficient than DPCP at low water mole fractions (xw < 0.7), as observed for conventional liquids and ionic liquids (ILs), it was smaller at high mole fractions (xw > 0.9). The apparent molecular radius of DPA determined using the Stokes-Einstein equation at xw > 0.9 is close to the radius of an IL cluster in a water pool as determined from small-angle neutron scattering experiments (J. Bowers et al., Langmuir, 2004, 20, 2192-2198), suggesting that the DPA molecules are trapped in IL clusters in the water pool and move together. The solvation state of DPCP in the mixture was studied using Raman spectroscopy. Dramatically strong water/DPCP hydrogen bonding was observed at higher water mole fractions, suggesting that DPCP is located near the cluster interfaces. The large diffusion coefficient of DPCP suggests that hopping of DPCP between IL clusters occurs through hydrogen bonding with water.

Determination and correlation of solubility and solution thermodynamics of β-HMX in binary solvent mixtures

Experimental solubility data of β-octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (β-HMX) in three binary solvent mixtures of water + (acetic acid, acetone or DMSO) over the temperature ranges of (283.15–368.15 K) were measured with a gravimetric method under atmospheric pressure. The results all showed that the solubility of β-HMX monotonously decreases with the increase of water mole fraction except for that in mixture of water + acetic acid through all given temperatures investigated, which exhibited the trends reach maximum then descending according to the increase of water mole fraction. In the temperature ranges examined, it was found that the solubility of β-HMX in all the tested solvents increased with the rising of temperature. Furthermore, the experimental solubility data in binary solvents was correlated with the modified Apelblat equation, the CNIBS/R-K model and the Jouyban-Acree model, which all gave satisfactory results. Additionally, the mixing Gibbs free energy, enthalpy and entropy of β-HMX in those binary solvent systems were predicted with the correlation of experimental data on basis of the multicomponent NRTL model.

SYNTHESIS AND CHARACTERISATION OF NI(II) COMPLEX OF L-LEUCINE

Synthesis of [NiL2 ].2H2O (L = L-leucine) was carried out in basic solution and the complex was analysed using gravimetric analysis, molar conductivity measurements, UV-Visible and IR spectroscopies. Molar conductivity measurements showed that the composition of the metal complex corresponds to a metal-amino acid ligand ratio of 1:2. The IR spectrum showed that L-leucine functions as bidentate ligand with coordination involving the carboxyl oxygen and the nitrogen of the amino group. The result also suggests the presence of water of crystallization in the complex. Electronic spectrum and magnetic susceptibility measurements suggested a four-coordinate local symmetry around Ni (tetrahedral) ions. The results also intimate that the ligand, L-leucine, is a weak field ligand as it formed high spin complex with Ni(II) ions. Metal content and hydration water analyses showed that the complex of Ni contains two moles of water of crystallization. The results also hinted that the Ni(II) complex has no aqua ligand in their inner coordination sphere.

The temperature of maximum density of diluted aqueous solutions of non-polar solutes: A molecular simulation study using TIP4P/2005 water and LJ point solutes

The effect of non polar solutes on the temperature of maximum density of water, TMD, is analyzed in detail by means of molecular simulations over an ample pressure interval ranging from negative to very high pressures. Non polar solutes are represented by single Lennard-Jones (LJ) sites, whose non-polar character is tuned with the width and depth of the Lennard-Jones water-solute potential parameters. Our analysis is focused on the behavior of the partial molar volume of the solute at infinite solution, whose thermal dependence is correlated with changes in the TMD. We find that for pressures below −200 bar all possible LJ water-solute potential parameters decrease the TMD, i.e. the solute acts as a “structure breaker”. At higher pressures, it is always possible to find a range of LJ parameters which induce an increase of the TMD, whose magnitude rises gradually with pressure. Our results are consistent with previous simulations of non polar gases in solution and with theoretical studies in the case of small LJ centers. It will be shown that the partial molar volume of an ideal gas at infinite dilution can provide information concerning the existence and size of the LJ parameter space that induces TMD increases for a given water model. Finally, we analyze the changes in the TMD in terms of the competition between low density and high density water states. We find that the temperature dependence of the variation of the low density water mole fraction with the addition of LJ solutes seems to be at the source of the changes in the TMD.

Self-Sustaining Control Strategy for Proton-Exchange Membrane Electrolysis Devices Based on Gradient-Disturbance Observation Method

This paper proposes a self-sustaining control model for proton-exchange membrane (PEM) electrolysis devices, aiming to maintain the temperature of their internal operating environment and, thus, improve the electrolysis efficiency and hydrogen production rate. Based on the analysis of energy–substance balance and electrochemical reaction characteristics, an electrothermal-coupling dynamic model for PEM electrolysis devices was constructed. Considering the influence of the input energy–substance and the output hydrogen and oxygen of PEM electrolysis devices on the whole dynamic equilibrium process, the required electrical energy and water molar flow rate are dynamically adjusted so that the temperature of the cathode and the anode is maintained near 338.15 K. The analytical results show that the hydrogen production rate and electrolysis efficiency are increased by 0.275 mol/min and 3.9%, respectively, by linearly stacking 100 PEM electrolysis devices to form a hydrogen production system with constant cathode and anode operating temperatures around 338.15 K in the self-sustaining controlled mode.

Near-MHz temperature and H2O measurements in post-detonation fireballs of 25 g hemispherical explosives using scanned-wavelength-modulation spectroscopy.

A laser absorption spectroscopy diagnostic integrated within a hardened optical probe was used to measure temperature and water mole fraction at 500kHz in post-detonation fireballs of explosives. In the experiments, an exploding-bridgewire detonator initiated a 25g hemisphere of explosive (N5 or PETN). This produced a hemispherical fireball that traveled radially towards a hardened measurement probe. The probe contained a pressure transducer and optical equipment to pitch fiber-coupled laser light across a 12.6cm gap onto a detector. Tunable diode lasers emitting near 7185.6 and 6806c m -1 were used to measure the absorbance spectrum of H 2 O utilizing peak-picking scanned-wavelength-modulation spectroscopy with a scan frequency of 500kHz and modulation frequencies of 35 and 45.5MHz, respectively. This enabled measurements of temperature and X H 2 O in the shock-heated air and trailing fireball at 500kHz. Time histories of pressure, temperature, and H 2 O mole fraction were acquired at different standoff distances to quantify how the fireball evolved in space and time as well as to compare measured quantities between PETN and N5 fireballs. The standard deviation of temperature and X H 2 O during one representative test were found to be 17K (1.3%) and 0.011 (5%), respectively. These measurements demonstrate this diagnostic's ability to provide rapid and reliable measurements in harsh, highly transient post-detonation environments produced by solid explosives.

Impact and structure of water in aqueous octanol mixtures: Hz-GHz dielectric relaxation measurements and computer simulations

Temperature (283 ≤ T/K ≤ 323) dependent dielectric relaxation (DR) measurements of aqueous binary mixtures of octanol at three different water mole fractions (XH2O = 0.05, 0.10, 0.20) were performed employing two different frequency windows: 0.00002 ≤ν/MHz≤ 10 and 0.2 ≤ν/GHz≤ 50. In addition, DR measurements were carried out for pure octanol and water saturated octanol at 298 K. All these measurements showed, irrespective of solution temperature, a small decrease of the static dielectric constant (εs) upon addition of water in octanol. Two-step relaxation process with time constants ∼ 3–0.3 ns and ∼ 120–40 ps characterized the measured DR spectra with no signature of bulk water-like DR time constant (∼10 ps). Differential scanning calorimetric (DSC) measurements of octanol + water mixtures reflect only water concentration dependent depression of octanol freezing temperature. Our computer simulations of aqueous octanol mixtures with SPC/E water suggests a dramatic decrease of the average number of water-water H-bonds 〈NHBw-w〉 per water molecule and a spectacular increase of water populations possessing OOO angles distributed over 0°≤θ≤ 60°. Consequently, a negative value for the average tetrahedral order parameter (〈Q〉) and an εs as low as ∼ 2 for water have been predicted. A severe damage to the global tetrahedrality of water in these mixtures has been predicted and the angle distributions corresponding to negative and positive Q values explicitly shown. These simulation results therefore explain the microscopic origin for small effects of water at low mole fractions on εs of octanol + water binary mixtures.

Study on Viscosity and density of Crown ether (15C5) Complexes in aqueous Solutions at 25oC

This paper reports on the viscosity and density study of the 1,4,7,10,13 pentaoxcyclopentadecane (15C5) as binary system and 15C5 in present of KBr (the ternary system) in aqueous solutions at 25oC. The results of the viscosity and density depend on type of system, and concentration rang. The relative viscosity obtain was fitted well by the use of Jones-Dole and Falkenhagen equations to the viscosity parameters i.e. the apparent molar volume and the effective rigid molar volume at infinite dilution. The results indicate that 4.2 mole of water are engaged in one mole of 15C5 and the complexation volume 0.015 dm3mol-1 K+ with 15C5 has been determine. The results are interpreted in terms of molecular and occupation of crown ether cavity by solvent molecules.

Study on Purging Strategy of Polymer Electrolyte Membrane Fuel Cell under Different Operation Conditions

The commercial proton exchange membrane fuel cell (PEMFC) system needs to be equipped with the capacity to survive a harsh environment, including sub-freezing temperatures. The cold start of PEMFC brings about great technical challenges, mainly due to the ice blockage in the components, which seriously hinders the multi physical transmission process. A multiscale, two-dimensional model was established to explore the gas purging in PEMFC under different electrochemical reaction intensities. The results indicate that the optimal case is obtained by B3-1 with a power density of 0.796 W cm−2, and the power density increases first and then decreases, followed by stoichiometric flow ratio (ξ) changes. It is worth noting that the water mole fraction in the PEM is closely related to the water concentration gradient. However, the differences in the initial water distribution in porous media have little bearing on the condensed water in the gas channel, and the liquid water in the gas diffusion layer (GDL) is preferably carried away ahead of other porous parts. The results also show that the increase in the purge speed and temperature can remove the excess water on GDL and the catalytic layer in a short time. For a nitrogen-based purge, the operating condition in case B3-1 is shown as the best strategy based on the output performance and economic analysis during the shutdown and purge process.