Formation Of Hydration Shell Research Articles

Unravelling molecular origins of improved tribological properties of amino acid ionic liquid water-based lubricants

In the quest for sustainable lubrication, this study explores the potential of water-based lubricants (WBLs) with amino acid ionic liquid (AAIL) additives. The research combines experimental and reactive molecular dynamics (MD) simulations to assess the tribological and rheological enhancements provided by AAILs. Specifically, tetrabutylphosphonium (P4444) cations paired with Serine (Ser) and Tryptophan (Trp) anions were mixed into water to create AAIL WBLs. The introduction of AAILs significantly improved the lubricants’ rheological properties and reduced the coefficient of friction by up to 34 %. This reduction is attributed to the formation of hydration shells around the amino acid anions, which create a chemically adsorbed tribofilm on iron oxide surfaces, and P4444 cations that establish a load-bearing layer in the middle regions of the lubricant. This dual-layer structure, supported by hydration lubrication, effectively maintains lubricant fluidity while bearing substantial loads. Among the AAIL WBLs tested, those with a thicker, more stable, hydrated amino acid tribofilm demonstrated more significant friction reduction. These insights into the molecular mechanisms behind AAIL WBLs’ tribological behaviour underscore their promise as eco-friendly lubricants, contributing to advancing a circular economy in industries reliant on lubrication.

Selective mass transport mediated by two-dimensional confined water: A comprehensive review

Confined mass transport based on two-dimensional (2D) materials breaks the trade-off effect between permeability and selectivity, significantly enhancing the efficiency of mass transport. However, the prevailing view that mass transport performance is primarily determined by the structural design of molecules or ions within channels and the regulation of channel walls has led to the neglect of surrounding hydration layers. Recent studies indicate that the interactions between confined water and transport substances, particularly the formation of hydration shells, significantly influence the mass transport process. Therefore, a thorough investigation of the behavior and properties of confined water, especially its presence, regulation methods, and the enhanced mechanisms of mass transport in 2D channels is particularly urgent and constitutes an indispensable research direction for the future development of materials science and engineering technologies. This review summarizes the latest progress on 2D confined water including its structure, properties, and behavior under natural conditions or environmental influences, the mechanisms enhancing mass transport, and regulatory approaches, as well as multiple applications such as membrane separation, drug delivery, and confined reactions. Lastly, we present instructive perspectives on the current challenges and future directions in the study of confined water.

Rheological properties of water-based amino acid ionic liquids

The rheological properties and zero-shear viscosity of water-based lubricants (WBLs) containing amino acid ionic liquids (AAILs) were investigated using both equilibrium (EMD) and non-equilibrium molecular dynamics (NEMD) simulations. We also performed experimental measurements to validate the simulations. The simulations demonstrated that adding AAIL additives to water increased both the shear viscosity and zero-shear viscosity. We added tetrabutylphosphonium (P4444) as a cation and three different amino acids, serine (Ser), lysine (Lys), or phenylalanine (Phe), as anions. We varied the AAIL concentration from 5 to 10 wt. % for tetrabutylphosphonium-serine (P4444-Ser) ionic liquid additives, showing that AAILs increased water viscosity by 68%–125%, depending on concentration. The P4444-Ser WBLs also exhibited a significantly higher first normal stress difference than water, meaning they could support more load in lubrication. The improved rheology persisted over a wide range of shear rates up to ∼1011 s−1. We have extracted full rheological parameters by fitting data into Cross, Carreau–Yasuda, and Eyring models, including zero-shear viscosity and critical shear rates of onset shear thinning. The experimental values of zero-shear viscosity were close to zero-shear viscosity results obtained from fitting NEMD results to these models, demonstrating the high fidelity of the molecular model. We explored the formation of hydration shells around amino acid anions as a marker for low friction behavior. These findings suggest that AAIL WBLs can be potentially low-friction and biodegradable lubricants in tribological applications.

Revisiting the structure and dynamics of hydrated Cd2+ in aqueous solutions: Insights from the RI‐SCS‐MP2/MM molecular dynamics simulation

AbstractThe spin component scale MP2/molecular mechanics molecular dynamics simulation investigated the hydration shell formation and hydrated Cd2+ dynamics in the water environment. At the first hydration shell, six water molecules with 2.27 Å for the average distance between water and Cd2+. Dynamical properties were analyzed by computing the water molecule's mean residence time (MRT) in its first and second hydration shells. The MRT of each shell was determined to be 31.8 and 1.92 ps, suggesting the strong influence of Cd2+ in the first hydration shell. The second shell was labile, with an average number of water molecules being 18. Despite the strong interaction between Cd2+ and water molecules in the first shell, the influence of ions in the second hydration shell remained weak.

Protein hydration shell formation: Dynamics of water in biological systems exhibiting nanoscopic cavities

This work explores the singular scenarios emerging from nanoscopic cavities, located in aqueous solutions, that include biomolecules and, as a consequence, the process of biomolecule hydration shell formation. The research presents a nano-scale study, performed in various systems related with protein-water solutions, using all-atoms molecular dynamics simulations. This research shows that if a protein falls within an empty nanoscopic cavity located in an aqueous solution, it will take a time, with a magnitude significant for biological processes, to rebuild its whole network of hydrogen bonds with the solvent molecules. During that protein isolation time the dynamics of the biomolecule, and therefore the corresponding bioactivity, will be seriously compromised. In the case of the protein barstar (radius of gyration of 1.17 nm) located in the centre of cavities with radius r from 2.5 to 4.5 nm, and solvent diffusion coefficients for bulk and physiologic water (2.4 and 1.5 μm2/ms, respectively), that time is found to be of the order of tens-hundreds of picoseconds, a significant temporal range concerning the dynamics and bioactivity of proteins. On the other hand, the dynamics of formation of the inner protein hydration shell has been followed using an atomic view. The required time has been found to decrease with r, as the network of water molecules approaching the biomolecule resembles that of the biological water corresponding to that biomolecule. That resemblance increases as those water molecules have previously been in close contact with the protein. The dynamics of those systems has been modelled using a two states model. Isolated bulk water is taken as reference for the computer simulations. Comparison with experimental data is also provided.

Methane Hydrate Crystallization on Sessile Water Droplets

This paper describes a method to form methane hydrate shells on water droplets. In addition, it provides blueprints for a pressure cell rated to 10 MPa working pressure, containing a stage for sessile droplets, a sapphire window for visualization, and temperature and pressure transducers. A pressure pump connected to a methane gas cylinder is used to pressurize the cell to 5 MPa. The cooling system is a 10 gallon (37.85 L) tank containing a 50% ethanol solution cooled via ethylene glycol through copper coils. This setup enables the observation of the temperature change associated with hydrate formation and dissociation during cooling and depressurization, respectively, as well as visualization and photography of the morphologic changes of the droplet. With this method, rapid hydrate shell formation was observed at ~-6 °C to -9 °C. During depressurization, a 0.2 °C to 0.5 °C temperature drop was observed at the pressure/temperature (P/T) stability curve due to exothermic hydrate dissociation, confirmed by visual observation of melting at the start of the temperature drop. The memory effect was observed after repressurizing to 5 MPa from 2 MPa. This experimental design allows the monitoring of pressure, temperature, and morphology of the droplet over time, making this a suitable method for testing various additives and substrates on hydrate morphology.

Ratiometric fluorescent sensing of ethanol based on copper nanoclusters with tunable dual emission

Copper nanoclusters (Cu NCs) have attracted a surge of interest in fluorescent sensors as their outstanding physicochemical and optical properties. However, most of the reports have focused on single-signal fluorescent sensors, which are susceptible to background interferences and affect accuracy of the results. Herein, we constructed a facile ratiometric fluorescent sensor for monitoring ethanol based on Cu NCs with tunable dual emission. Polyvinylpyrrolidone (PVP)-modified Cu NCs were simply prepared in water, which exhibit ratiometric dual emission, including a strong green emission at 520 nm and a weak blue emission at 450 nm. The PVP-Cu NCs in water with strong green emission display monodisperse state due to the formation of hydration shell around Cu NCs. In ethanol where the hydration shell is destructed, Cu NCs tend to aggregate and show strong blue emission. This emission shift might attribute to the enhancement of Cu–Cu metallophilic interaction with the aggregation of Cu NCs, which induces the excited-state level increasing. Thus, a ratiometric fluorescent probe for ethanol based on the PVP-Cu NCs is fabricated, which possesses rapid response (<1 min), and realize full-range detection from 0 to 100%. In addition, this ratiometric probe is successfully applied to determine the alcohol strength of alcohol beverages, demonstrating the great potential in practical application.

Neutron total scattering investigation on the dissolution mechanism of trehalose in NaOH/urea aqueous solution.

Trehalose is chosen as a model molecule to investigate the dissolution mechanism of cellulose in NaOH/urea aqueous solution. The combination of neutron total scattering and empirical potential structure refinement yields the most probable all-atom positions in the complex fluid and reveals the cooperative dynamic effects of NaOH, urea, and water molecules in the dissolution process. NaOH directly interacts with glucose rings by breaking the inter- and intra-molecular hydrogen bonding. Na+, thus, accumulates around electronegative oxygen atoms in the hydration shell of trehalose. Its local concentration is thereby 2–9 times higher than that in the bulk fluid. Urea molecules are too large to interpenetrate into trehalose and too complex to form hydrogen bonds with trehalose. They can only participate in the formation of the hydration shell around trehalose via Na+ bridging. As the main component in the complex fluid, water molecules have a disturbed tetrahedral structure in the presence of NaOH and urea. The structure of the mixed solvent does not change when it is cooled to −12 °C. This indicates that the dissolution may be a dynamic process, i.e., a competition between hydration shell formation and inter-molecule hydrogen bonding determines its dissolution. We, therefore, predict that alkali with smaller ions, such as LiOH, has better solubility for cellulose.

Solvation of Ethanol, Phenol, and o-Methoxyphenol in Dilute Aqueous Solutions under Normal and Supercritical Conditions

The structure of 2 wt % aqueous solutions of ethanol, phenol, and o-methoxyphenol (guaiacol) was modeled in NVT ensemble using the classical molecular dynamics method at densities of 0.997 and 0.133 g/cm3 corresponding to the normal (298 K, 0.1 MPa) and supercritical (673 K, 23.0 MPa) conditions. The self-diffusion coefficients were calculated for individual components in solutions; the radial distribution functions were calculated for the oxygen atoms of water molecules, oxygen atoms of hydroxyl groups, and centers of mass in phenol molecules. The possibility of clusterization of solute molecules was analyzed. The data obtained suggest heterogeneity of solutions, in which clusters of different compositions and structures can exist. Clusterization of up to seven ethanol and phenol molecules can occur under normal conditions, and dimerization was detected under SC conditions. The structural features of solutions under normal and SC conditions were compared. The difference in the formation of hydration shells of ethanol and phenols molecules was demonstrated. Stable shells of water molecules form around ethanol molecules under normal conditions. For phenols, the solvation shells are unstable, with a pronounced tendency toward clusterization of organic molecules.

Acoustic characteristics of cold-seep methane bubble behavior in the water column and its potential environmental impact

The amount of methane leaked from deep sea cold seeps is enormous and potentially affects the global warming, ocean acidification and global carbon cycle. It is of great significance to study the methane bubble movement and dissolution process in the water column and its output to the atmosphere. Methane bubbles produce strong acoustic impedance in water bodies, and bubble strings released from deep sea cold seeps are called “gas flares” which expressed as flame-like strong backscatter in the water column. We characterized the morphology and movement of methane bubbles released into the water using multibeam water column data at two cold seeps. The result shows that methane at site I reached 920 m water depth without passing through the top of the gas hydrate stability zone (GHSZ, 850 m), while methane bubbles at site II passed through the top of the GHSZ (597 m) and entered the non-GHSZ (above 550 m). By applying two methods on the multibeam data, the bubble rising velocity in the water column at sites I and II were estimated to be 9.6 cm/s and 24 cm/s, respectively. Bubble velocity is positively associated with water depth which is inferred to be resulted from decrease of bubble size during methane ascending in the water. Combined with numerical simulation, we concluded that formation of gas hydrate shells plays an important role in helping methane bubbles entering the upper water bodies, while other factors, including water depth, bubble velocity, initial kinetic energy and bubble size, also influence the bubble residence time in the water and the possibility of methane entering the atmosphere. We estimate that methane gas flux at these two sites is 0.4×106−87.6×106 mol/a which is extremely small compared to the total amount of methane in the ocean body, however, methane leakage might exert significant impact on the ocean acidification considering the widespread distributed cold seeps. In addition, although methane entering the atmosphere is not observed, further research is still needed to understand its potential impact on increasing methane concentration in the surface seawater and gas-water interface methane exchange rate, which consequently increase the greenhouse effect.

Experimental Investigation of Methane Hydrate Formation in the Carboxmethylcellulose (CMC) Aqueous Solution

Summary In the development of deepwater crude oil, gas, and gas hydrates, hydrate formation during drilling operations becomes a crucial problem for flow assurance and wellbore pressure management. To study the characteristics of methane hydrate formation in the drilling fluid, the experiments of the methane hydrate formation in water with carboxmethylcellulose (CMC) additive are performed in a horizontal flow loop under flow velocity from 1.32 to 1.60 m/s and CMC concentration from 0.2 to 0.5 wt%. The flow pattern is observed as bubbly flow in experiments. The experiments indicate that the increase of CMC concentration impedes the hydrate formation while the increase of liquid velocity enhances formation rates. In the stirred reactor, the hydrate formation rate generally decreases as the subcooling condition decreases. However, in this work, with the subcooling condition continuously decreasing, hydrate formation rate follows a “U” shaped trend—initially decreasing, then leveling out and finally increasing. It is because the hydrate formation rate in this work is influenced by multiple factors, such as hydrate shell formation, fracturing, sloughing, and bubble breaking up, which has more complicated mass transfer procedure than that in the stirred reactor. A semiempirical model that is based on the mass transfer mechanism is developed for current experimental conditions, and can be used to predict the formation rates of gas hydrates in the non-Newtonian fluid by replacing corresponding correlations. The rheological experiments are performed to obtain the rheological model of the CMC aqueous solution for the proposed model. The overall hydrate formation coefficient in the proposed model is correlated with experimental data. The hydrate formation model is verified and the predicted quantity of gas hydrates has a discrepancy less than 10%.

Methane hydrate formation in a water-continuous vertical flow loop with xanthan gum

Hydrate phase transition in drilling fluid is a non-ignorable problem for developing deep-water oil, natural gas and natural gas hydrate resources. Once gas hydrates form during drilling, it will increase the difficulty of wellbore pressure management and flow assurance, which enlarges the risk of hydrate blockage and causes serious property damage and casualties. Methane hydrate formation experiments are conducted in xanthan gum (XG) aqueous solution to mimic the drilling fluid flowing condition in a vertical flow loop. The experiments reveal that the hydrate formation process is a mass transfer process and experiences four different hydrate formation periods, because of the kinetics formation and slough of hydrate shells. The subcooling temperature has a weaker impact on the hydrate formation than the flow velocity and XG. The increase of flow velocity can enhance the hydrate formation rate in drilling fluid but the increase of XG concentration can inhibit the hydrate formation. The influence mechanisms of hydrate shell kinetic slough, flow velocity and XG concentration on hydrate formation are analyzed and discussed in detail. We built a mass-transfer hydrate formation model based on the mechanism of methane molecule diffusing from gas phase to liquid phase. The empirical overall mass transfer coefficient is introduced involving the influence of hydrate shell kinetic slough, flow velocity and XG concentration. In model validation, the maximum discrepancy of the developed model decreases from 146.85% to 11.03% after using the overall mass transfer coefficient.

Hydrate Growth on Methane Gas Bubbles in the Presence of Salt.

Methane bubble dispersions in a water column can be observed in both vertical subsea piping as well as subsea gas seepages. Hydrate growth has been shown to occur at the gas-water interface under flowing conditions, yet the majority of the current literature is limited to quiescent systems. Gas hydrate risks in subsea piping have been shown to increase in late life production wells with increased water content and with gas-in-water bubble dispersions. The dissolution of subsea methane seepages into seawater, or methane release into the atmosphere, can be affected by hydrate film growth on rising bubbles. A high-pressure water tunnel (HPWT), was used to generate a turbulent, continuous water flow system representative of a vertical jumper line to study the relationship between bulk methane hydrate growth and bubble size during a production-well restart. The HPWT comprises a flow loop of 19.1 mm inner diameter and 4.9 m length, with a vertical section containing an optical window to enable visualization of the bubble and hydrate flow dynamics via a high-speed, high-resolution video camera. Additional online monitoring includes the differential pressure drop, viscosity, temperature, flow rates, and gas consumption. Experimental conditions were maintained at 275 K and 6.2 MPa during hydrate formation and 298 K and 1.4 MPa during hydrate dissociation. Hydrate growth using freshwater and saltwater (3.5 wt % NaCl) was measured at four flow velocities (0.8, 1.2, 1.6, and 1.9 m s-1). The addition of salt is shown in this work to alter the surface properties of bubbles, which introduces changes to bubble dynamics of dispersion and coalescence. Hydrate volume fractions and growth rates in the presence of salt were on average ∼32% lower compared to that in freshwater. This was observed and validated to be due to bubble size and dynamic factors and not due to the 1.5 K thermodynamic inhibition effect of salt. Throughout hydrate growth, methane bubbles in pure freshwater maintained larger diameters (2.4-4.2 mm), whereas the presence of salt promoted fine gas bubble dispersions (0.1-0.7 mm), increasing gas-water interfacial area. While gas bubble coalescence was observed in all freshwater experiments, the addition of salt limited coalescence between gas bubbles and reduced bubble size. Consequently, earlier formation of solid hydrate shells in saltwater produced early mass-transfer barriers reducing hydrate growth rates. While primarily directed toward flow assurance, the observed relationship between hydrates, bubble size, and saltwater also applies to broader research fields in subsea gas seepages and naturally occurring hydrates.

Comprehensive Picture of Water Dynamics in Nafion Membranes at Different Levels of Hydration.

1H NMR spectroscopy is employed to study the long-range (diffusion) and short-range (relaxation) motions of water in the hydrophilic channels of Nafion at different stages of hydration, λwater. From Bloembergen, Purcell, and Pound analysis of the temperature-dependent 1H spin-lattice relaxation rates, the coexistence of two motional modes for λwater < 9 was observed, which can be attributed to the nonfreezing behavior of water molecules. At higher hydration levels, a clear transition between two different motional modes was detected associated with the freezing of bulk water. The hydration-level-dependent diffusion 1H NMR studies showed a steep increase in diffusion coefficients at 6 ≤ λwater ≤ 9 followed by a linear increase with the increasing hydration level (λwater ≥ 12). Taken together the correlation of long- and short-range motion studies allowed us to establish a comprehensive picture of the hydration shell formation for the sulfonic acid groups in Nafion dependent on λwater that can be divided into three characteristic regions. These include the formation of the first hydration shell at λwater ≈ 3 (region I), the second hydration shell at λwater ≈ 8 (region II), and finally (iii) the presence of bulk water above λwater ≥ 10 (region III).

Evolution of aqSOA from the Air-Liquid Interfacial Photochemistry of Glyoxal and Hydroxyl Radicals.

The effect of photochemical reaction time on glyoxal and hydrogen peroxide at the air-liquid (a-l) interface is investigated using in situ time-of-flight secondary ion mass spectrometry (ToF-SIMS) enabled by a system for analysis at the liquid vacuum interface (SALVI) microreactor. Carboxylic acids are formed mainly by reaction with hydroxyl radicals in the initial reactions. Oligomers, cluster ions, and water clusters formed due to longer photochemistry. Our results provide direct molecular evidence that water clusters are associated with proton transfer and the formation of oligomers and cluster ions at the a-l interface. The oligomer formation is facilitated by water cluster and cluster ion formation over time. Formation of higher m/z oligomers and cluster ions indicates the possibility of highly oxygenated organic components formation at the a-l interface. Furthermore, new chemical reaction pathways, such as surface organic cluster, hydration shell, and water cluster formation, are proposed based on SIMS spectral observations, and the existing understanding of glyoxal photochemistry is expanded. Our in situ findings verify that the a-l interfacial reactions are important pathways for aqueous secondary organic aerosol (aqSOA) formation.

Effects of ultrasonic pretreatment on particle size and surface topography of lignite and its relationship to flotation response

ABSTRACT The aim of this investigation was to study the effects of different ultrasonic powers and treatment times on particle size and surface topography of low ash fine lignite (<0.125 mm) combined with flotation, wet-screening, surface roughness, scanning electron microscopy (SEM), and induction time tests. Flotation results show the concentrate yield gradually decreased with the increase of ultrasonic power and treatment time except 18 W. The wet-screening results indicate that increasing ultrasonic power and treatment time had more significant crushing effect on lignite particles and produced more fine particles (<0.045 mm), which was harmful for the improvement flotation performance of lignite. SEM results show that crack was gradually expanded into a gap as well as some new cracks and cavities on the surface of lignite are produced with the increase of ultrasonic power. The generation of these gaps, new cracks, and cavities increases the roughness of lignite surface. The higher the ultrasonic power is, the rougher the lignite surface becomes, which promotes its surface to entrap more water during the flotation process resulting in a formation of thick hydration shell. The induction time increased as ultrasonic power and treatment time increased except 18 W. Hence, there will be a negative impact on lignite flotation if the lignite particles are treated by higher ultrasonic power for longer. The findings of this paper may provide some guidance to understand the effects of ultrasound on surface topography of lignite and makebetter use of ultrasound to assist coal flotation.

Characterizing methane hydrate formation in the non-Newtonian fluid flowing system

Developing natural gas hydrates in deep water faces serious well control problem and flow assurance problem, induced by the reformation of gas hydrate in the drilling fluid. In order to solve this problem, developing a hydrate formation predicting model becomes necessary. In this work, the methane hydrate formation experiments are performed in the xanthan gum (XG) aqueous solution under flow velocities from 1.8 to 1.5 m/s, XG concentrations from 0.1 to 0.3% and void fraction of 4.5%. The hydrate formation rates decrease with the XG concentration increasing and increases with the flow velocity increasing. The hydrate formation rate at the moment of the experiment onset will decrease sharply due to the formation of hydrate shell on gas bubbles and gas hydrates will form at the almost constant rate, because the second growth of hydrate shells on the fractures of gas bubbles and collisions between gas bubbles enhances the hydrate formation rates. The hydrate formation rate increases rapidly when the hydrate formation process is near the end of hydrate formation since the breakage rates of gas bubbles increase the hydrate formation rates. A mass transfer model is developed to describe the methane hydrate formation under the non-Newtonian fluid flowing condition. Since the volumetric mass transfer coefficient closely depends on the rheological properties of carrying fluid, the rheological experiments for the XG aqueous solution are conducted and an empirical rheology model is developed correspondingly. An integrated constant is proposed to improve the accuracy of the model which reflects influences of the hydrate shell formation, the second growth of hydrate shell and the bubble breakage on methane hydrate formation. The correlations of the integrated constant are functions of the XG concentration, the flow velocity and the subcooling temperature. Through validation, the proposed mass transfer model shows good agreements with experimental data and the maximum discrepancy is 11.64%.

A theoretical assessment of the primary hydration shell formation for calcium pyrophosphate

The hydration behaviour of calcium pyrophosphate (CPP) was investigated via Density Functional Quantum mechanical calculations (DFT), carried out on isolated monomeric CPP-water complexes. Formation free energies for the first hydration shell shows that hydrates from the di- to octa-hydrate are formed spontaneously whereas the higher hydrates are unstable when hydration occurs via a concerted mechanism (instantaneous hydration). For this mechanism, the most stable hydrate consist of four water molecules which allows for a balance between repulsive steric crowding interactions in the primary hydration shell and CPP-water attractive interactions in addition to water-water attractive interactions. However, step-wise hydration favours the di- and tetra-hydrates, the former being of greatest stability. The results presented in this novel quantum mechanical study of CPP-hydration, could hold the answer for destabilizing CPP crystals in the joints of rheumatic arthritis patients, thereby facilitating a solution/ treatment for pseudo-gout.

Interruption of Hydrogen Bonding Networks of Water in Carbon Nanotubes Due to Strong Hydration Shell Formation.

We present the structures of NaCl aqueous solution in carbon nanotubes with diameters of 1, 2, and 3 nm based on an analysis performed using X-ray diffraction and canonical ensemble Monte Carlo simulations. Anomalously longer nearest-neighbor distances were observed in the electrolyte for the 1-nm-diameter carbon nanotubes; in contrast, in the 2 and 3 nm carbon nanotubes, the nearest-neighbor distances were shorter than those in the bulk electrolyte. We also observed similar properties for water in carbon nanotubes, which was expected because the main component of the electrolyte was water. However, the nearest-neighbor distances of the electrolyte were longer than those of water in all of the carbon nanotubes; the difference was especially pronounced in the 2-nm-diameter carbon nanotubes. Thus, small numbers of ions affected the entire structure of the electrolyte in the nanopores of the carbon nanotubes. The formation of strong hydration shells between ions and water molecules considerably interrupted the hydrogen bonding between water molecules in the nanopores of the carbon nanotubes. The hydration shell had a diameter of approximately 1 nm, and hydration shells were thus adopted for the nanopores of the 2-nm-diameter carbon nanotubes, providing an explanation for the large difference in the nearest-neighbor distances between the electrolyte and water in these nanopores.

Insight into electric field-induced rupture mechanism of water-in-toluene emulsion films from a model system.

This paper presents a model, which we have designed to get insight into the development of electro-induced instability of a thin toluene emulsion film in contact with the saline aqueous phase. Molecular dynamics (MD) simulations demonstrate the role of charge accumulation in the toluene-film rupture induced by a DC electric field. Two ensembles-NVT and NPT-are used to determine the critical value of the external field at which the film ruptures, the charge distribution and capacitance of the thin film, number densities, and the film structure. The rupture mechanism as seen from this model is the following: in both NVT and NPT ensembles, condenser plates, where the charge density is maximal, are situated at the very border between the bulk aqueous (water) phase and the mixed layer. No ion penetration is observed within the toluene core, thus leaving all the distribution of charges within the mixed zone and the bulk phase that could be attributed to the formation of hydration shells. When the critical electric field is reached within a certain time after the field application, electric discharge occurs indicating the beginning of the rupturing process. The MD simulations indicate that the NPT ensemble predicts a value of the critical field that is closer to the experimental finding.