Properties Of Interfacial Water Research Articles

Qualifying interfacial properties of crude oil−water system with the synergistic action of a nano Gemini ionic liquid and conventional surfactants

Surface-active ionic liquids (SAILs) have gained much attention due to their green, stable, and efficient properties. The high costs associated with SAILs have raised concerns in their applications; however, blending with conventional surfactants like sodium dodecyl benzene sulfonate (SDBS) can bring about desired outcomes. Gemini surface-active ionic liquids (GSAILs) have been recognized as more efficient surfactants. Accordingly, this study investigates the influence of a mixture of an imidazolium-based GSAIL, [C4im-C6-imC4][Br2], and SDBS on different aspects of crude oil−water interfacial properties. The findings show remarkable synergy in interfacial tension (IFT) reduction up to 98.8% together with incredibly low IFT value of 0.05 mN m−1. This was with an optimal GSAIL mole fraction of 0.2 in the mixture. Further, the surfactant mixture gives synergies of 52.6% in emulsification and 51.8% in wettability of a quartz surface. These amazing results can be explained by the dominant interactions between the oppositely charged components. In theoretical study, the adsorption of individual surfactants and their mixtures was analyzed based on the Frumkin isotherm and the Rosen model, respectively, further supporting the findings.

Impact of interfacial curvature on molecular properties of aqueous interfaces.

The curvature of soft interfaces plays a crucial role in determining their mechanical and thermodynamic properties, both at macroscopic and microscopic scales. In the case of air/water interfaces, particular attention has recently focused on water microdroplets, due to their distinctive chemical reactivity. However, the specific impact of curvature on the molecular properties of interfacial water and interfacial reactivity has so far remained elusive. Here, we use molecular dynamics simulations to determine the effect of curvature on a broad range of structural, dynamical, and thermodynamical properties of the interface. For a droplet, a flat interface, and a cavity, we successively examine the structure of the hydrogen-bond network and its relation to vibrational spectroscopy, the dynamics of water translation, rotation, and hydrogen-bond exchanges, and the thermodynamics of ion solvation and ion-pair dissociation. Our simulations show that curvature predominantly impacts the hydrogen-bond structure through the fraction of dangling OH groups and the dynamics of interfacial water molecules. In contrast, curvature has a limited effect on solvation and ion-pair dissociation thermodynamics. For water microdroplets, this suggests that the curvature alone cannot fully account for the distinctive reactivity measured in these systems, which are of great importance for catalysis and atmospheric chemistry.

Orientational dynamics of the water layer adjacent to Au surface accelerated by polarization effect.

The orientation and rearrangement of water on a gold electrode significantly influences its physicochemical heterogeneous performance. Despite numerous experimental and theoretical studies aimed at uncovering the structural characteristics of interfacial water, the orientational behavior resulting from electrode-induced rearrangements remains a subject of ongoing debate. Here, we employed molecular dynamics simulations to investigate the adaptive structure and dynamics properties of interfacial water on Au(111) and Au(100) surfaces by considering a polarizable model for Au atoms in comparison with the non-polarizable model. Compared to the nonpolarizable systems, the polarization effect can enhance the interaction between water molecules and the gold surface. Unexpectedly, the rotational dynamics directly associated with the orientational behavior of water adjacent to the gold surface is accelerated, thereby reducing the hydrogen bond lifetime. The underlying mechanism for this anomalous phenomenon originates from the polarization effect, which induces the attraction of the positive hydrogen atoms to the surface by the negative image charge. This leads to a change in orientation that disrupts the hydrogen bonds in the first water layer and subsequently accelerates reorientation dynamics of water molecules adjacent to the gold surface. These results shed light on the intricate interplay between polarization effects and water molecule dynamics on metal surfaces, establishing the foundation for the rational regulation of the orientation of interfacial water.

Adsorption of Asphaltenes at Model Oil/Brine Interface: Influence of Solvent Polarity.

With the exploitation of heavy oil worldwide, the influence of asphaltene aggregation in the oil phase on the stability of crude oil emulsion has been paid more and more attention. Under this background, the effects of solvent polarity on model oil/brine water interfacial properties and emulsion stability are investigated in this study. It is demonstrated that there is a critical asphaltene concentration for the formation of a stable emulsion. This critical concentration is then found to increase from 80 to 500 ppm with the mixing ratio of methylnaphthalene to n-decane changed from 2:3 to 7:3. The dynamic light scattering experiment shows that the average aggregate size increases abruptly from 132.8 to 261.1 nm at 2:3 mixing ratio of methylnaphthalene to n-decane once the asphaltenes are added to above the critical concentration. Accordingly, the diffusion coefficient of the asphaltenes decreases sharply from 4.36 × 10-12 to 5.68 × 10-13 m2/s. Similar conclusions are also found for the other mixing ratios of 1:1, 3:2, and 7:3. Besides, the aggregation degree of asphaltenes weakens, and the diffusion coefficient enlarges at the same asphaltene concentration with the enhancement of the solvent polarity. Further, the interfacial experiments manifest that the equilibrium interfacial dilation modulus decreases from 38.42 to 23.65 mN/m with the mixing ratio of methylnaphthalene to n-decane increased from 2:3 to 7:3. It can thus be inferred that the structural strength of the interfacial film decreases with the enhancement of the solvent polarity.

Water structure at coal/water interface: Insights from SFG vibrational spectroscopy and MD simulation

The coal/water interface plays a significant role in coal processing and utilization, and hydrogen bonds (HBs) are the primary factors affecting the interfacial water structure. Sum frequency generation (SFG) vibrational spectroscopy was used in this study to analyze HBs at the coal/water interface, and molecular dynamics (MD) simulations were conducted to investigate the molecular dynamics properties of interfacial water. The results showed that water molecules formed strong HBs with the lignite surface using both oxygen and hydrogen atoms, whereas HBs at bituminous coal/water and anthracite/water interfaces mainly occurred through the hydrogen atoms of water molecules. Fewer HBs existed at the bituminous coal/water interface, resulting in more free hydroxyl groups of water molecules. HBs at the anthracite/water interface were weaker than those at the lignite/water interface but stronger than those at the bituminous coal/water interface. Stronger HBs facilitated the adsorption of water molecules onto coal surfaces, reducing the number density and diffusion coefficient of water molecules within the water layer. For both properties, the MD simulation results showed the following order of decreasing magnitude: bituminous coal/water interface > anthracite/water interface > lignite/water interface. The combination of SFG vibrational spectroscopy and MD simulation offers a scientific approach to understanding the coal/water interface.

Experimental characterization technique to probe interfacial water

Water is a fundamental substance in the natural world, playing a central role in various fields such as energy, catalysis and the environment. Broadly speaking, the diverse applications of water in different domains are all reliant on its interactions at surfaces. This mini-review aims to provide a comprehensive overview of advanced characterization techniques employed in the examination of interfacial water. Through the presentation of recent findings regarding water’s behavior on various surfaces, we elucidate how these newly developed characterization methods enable precise determination of the physical and chemical properties of interfacial water. Additionally, we delve into how these discoveries enhance our comprehension of the physical and chemical processes involving water. Of particular interest is the intricate relationship between interfacial water and catalytic activity in electrocatalytic reactions. Furthermore, we offer insights into the challenges and prospects within this captivating field of study.

The Surface of Ionic Liquids in Water: From an Ionic Tug of War to a Quasi-Ordered Two-Dimensional Layer.

The sustainable development encompasses the search for new materials for energy storage, gas capture, separation, and solvents in industrial processes that can substitute conventional ones in an efficient and clean manner. Ionic liquids (ILs) emerged and have been advanced as alternative materials for such applications, but an obstacle is their hygroscopicity and the effects on their physical properties in the presence of humidity. Several industrial processes depend on the aqueous interfacial properties, and the main focus of this work is the water/IL interface. The behavior of the aqueous ionic liquids at the water-vacuum interface is representative for their water interfacial properties. Using X-ray photoelectron spectroscopy in combination with molecular dynamics simulations we investigate four aqueous IL systems, and provide molecular level insight on the interfacial behaviour of the ionic liquids, such as ion-pair formation, orientation and surface concentration. We find that ionic liquids containing a chloride anion have a lowered surface enrichment due to the low surface propensity of chloride. In contrast, the ionic liquids containing a bistriflimide anion are extremely surface-enriched due to cooperative surface propensity between the cations and anions, forming a two-dimensional ionic liquid on the water surface at low concentrations.

Effect of hydrolyzed polyacrylamide on oil droplet stability in polymer-flooding produced water: variation of oil droplets diameter and oil–water interfacial properties

Hydrolyzed polyacrylamide (HPAM) in polymer flooding leads to stable oil-in-water emulsions, making the oil removal from polymer-flooding produced water (PFPW) more difficult. To elucidate HPAM’s effects on the oil separation performance of conventional physical separation process for PFPW, the stability, and diameter of oil droplets of simulated PFPW were accurately determined using the Turbiscan LAB expert. The results demonstrated that an increase in HPAM’s molecular weight and concentration led to a significant decrease in the diameter of oil droplets in simulated PFPW. When the molecular weight of HPAM increased from 6 to 18 MDa, there was a decrease in the Turbidity Scanning Index (TSI) values from 22.5 to 8.7, along with a significant decline in the diameter of oil droplets from 72.7 to 32.6 µm after a settling period of 40 min. Furthermore, a rise in HPAM concentration inhibited the enlargement of oil droplets. As HPAM concentration increased from 0 to 500 mg/L, the diameter of the oil droplets reduced by 42.1 µm after a 40 min settling period. HPAM's effect on restricting the growth of oil droplets remained relatively constant across oil concentrations ranging from 500 to 2500 mg/L. Moreover, increasing the molecular weight of HPAM from 6 to 18 MDa led to a 41.6% increase in PFPW's viscosity and a 38.9% decrease in oil-water interfacial tension, thereby inhibiting oil droplet coalescence. Our findings provide valuable fundamental guidance for the design of innovative separation methods for PFPW treatment.

Evaluation of pH, NaCl and CaCl2 salts on Solubility, Zeta Potential and air - water interfacial properties of the protein isolate from lupin seeds

Lupin is a legume seed rich in proteins and presents high nutritional and health benefits but is little used in the human diet. In this work, lupin proteins were extracted using an alkaline-saline solution followed by dialysis. Then, globulins were separated by isoelectric precipitation to give lupin globulin isolate (LGI). The solubility, zeta potential and interfacial properties of LGI were evaluated at pH of 3.4 and 6.8 in the presence of NaCl or CaCl2. The solubility of LGI was dependent on the pH and type of salt, with lower solubility in the isoelectric region (pH ∼ 5), with lower solubility in the presence of NaCl (42.81 ± 1.23 %). The lowest value of interfacial tension was at pH 3.4 and absence of salts (41.79 ± 0.63 mN m−1). Indicating the type of salt changes the electrostatic shielding of the LGI electrical double layer, which leads to a decrease in electrostatic potential at the surface of LGI. The rate of diffusion is highest at pH 6.8 under conditions without salts or in the presence of NaCl (0.57 ± 0.01 and 0.55 ± 0.05 mN m−1 s−0.5 respectively). When the salt was changed to CaCl2 diffusion was decreased, probably due to protein-protein interactions. On the other hand, the protein adsorption rate is lower at pH 6.8 under all conditions studied. Apparently, it is influenced by the type of surface electrical charge of the proteins and the rate of rearrangement is greater than the rate of adsorption. The results obtained demonstrate that the lupin protein isolate can be used in multiphase food systems, such as foams, due to its interfacial properties.

Spin-lattice relaxation time in water/graphene-oxide dispersion.

We present the results of the calculations of the spin-lattice relaxation time of water in contact with graphene oxide by means of all-atom molecular dynamics simulations. We fully characterized the water-graphene oxide interaction through the calculation of the relaxation properties of bulk water and of the contact angle as a function of graphene oxide oxidation state and comparing them with the available experimental data. We then extended the calculation to investigate how graphene oxide alters the dynamical and relaxation properties of water in different conditions and concentrations. We show that, despite the diamagnetic nature of the graphene oxide, the confining effects of the bilayers strongly affect the longitudinal relaxation properties of interfacial water, which presents a reduced dynamics due to hydrogen bonds with oxygen groups on graphene oxide. This property makes graphene oxide an interesting platform to investigate water dynamics in confined geometries and an alternative contrast-agent for magnetic resonance imaging applications, especially in view of the possibility to functionalize graphene oxide from theranostic perspectives.

Atomic-scale characterisation of dielectric properties and structured water molecules at the interface of lipid membranes.

Water molecules play a major role in determining the structure and function of biomolecules and their assembly. Hydration layers occurring at the interface of macromolecules strongly depend on their molecular charge distribution and dielectric polarization, which in turn determine their electrostatic and electrodynamic properties. At a greater scale, water molecules surrounding and permeating the cell membrane have been demonstrated organising on the cell membrane components themselves, i.e. lipids and transmembrane proteins. For instance, evidences showed that lipid head groups are supposed to be surrounded by more than one hydration layer, being the first layer formed by a tightly bound shell, and outer layers likely to be displaced due to protein-lipid interactions. Hence, it is of fundamental importance to understand the physical properties of interfacial water in order to gain information on the structure and function of biological systems.

Water adsorption on planar interfaces: Classical density functional study

• A new cDFT based on SAFT with an explicit account for dipole-dipole interactions was formulated. • Our model provides a good description of binodal, liquid-vapor surface tension, latent heat of vaporization, and wetting contact angles. • The energy distribution functions for non-porous silica and alumina were calculated. Theoretical modeling of water adsorption in micro- and mesoporous materials remains a challenging problem for physical chemistry and chemical engineering despite its great importance for industrial applications. Here, we present the theoretical study of bulk and inhomogeneous water within the classical density functional theory. Our model includes all important intermolecular interactions, such as dispersion, association, and dipole-dipole. We validated the model via comparison with existing literature experimental and computer simulation data. Among the others, the following water properties were compared: liquid-vapor binodal (T - ρ ), surface tension, latent heat of vaporization, wetting contact angle, and adsorption isotherms on nonporous silica and alumina. Our computational results demonstrate good agreement with the experimental literature data and show similar trends compared to the several commonly used water models (SPC/E, TIP4P, TIP4P/2005). Because the presented model can accurately describe the thermodynamic and interfacial properties of water then it can be of interest to the adsorption community. Also, the model may serve as a starting point for further works regarding porous adsorbents characterization employing classical density functional theory.

Some Interfacial Properties of Water and CO2/H2S at Quasireservoir Conditions: A Molecular Dynamics Study

Summary Interfacial properties are important in the process of geosequestering acid gases in the presence of formation water. However, to a considerable extent, the information from molecular interactions is not obtainable experimentally. Theoretically, this limitation is due to a dearth of data at reservoir conditions (i.e., high pressures and elevated temperatures). Hence, molecular dynamics (MD) is used to study interfacial interactions such as interfacial tension (IFT) as a function of temperature and pressure through the mechanical pressure tensor method, acid gas adsorption onto water and absorption into water, pair correlation functions, and density profiles. Simulations were carried out isothermally at 77°C with pressures ranging from 0.5 to 15.6 MPa. The predicted water densities, ρ, and acid gas [CO2/H2S, with the NERD (Nath, Escobedo and de Pablo) H2S potential] densities matched the experimental values well. The two force fields used to simulate water-acid gas IFTs, γ, both overpredict the experimental values, especially at the higher pressures, but the water-OPLS (optimized potentials for liquid simulations) H2S acid gas combination’s γ is closer to the experimental ideal. The overpredictions are primarily due to the supercritical nature of the fluids and the force fields used. Radial distribution functions (RDFs) of the various combinations were also examined, and they were found to demonstrate the supercritical nature of the fluids and the molecular interaction between the constituent components of the acid gas and water. The interfacial thickness, δ, revealed further insights into the molecular structure and was found to be typically in the 4.0–7.5 Å range and is influenced by mainly the acid gas adsorption onto the water surface and to a lesser extent absorption into the bulk water. It was found that CO2 is more dominant than H2S at the water interfacial layer and that CO2-water interactions contributed more toward the overall interfacial properties. Our findings further suggest that the predomination of interactions by CO2 in the system, coupled with the weak interactivity between CO2 and H2S, means that CO2 geosequestration, at least in the 70 mol%CO2 and 30 mol%H2S used in this work, and by extension for higher CO2 mole percentages, does not face any meaningful impediment from the H2S presence during the process. In the absence of nigh impossible to achieve experiments at these extreme temperature and pressure conditions, the findings of this MD study thus offer a better understanding of some of the geological interactions of fluid-fluid mixtures in the presence of formation water and the application of this information during geosequestration.

Emulsifying properties and oil–water interface properties of succinylated soy protein isolate: Affected by conformational flexibility of the interfacial protein

This work aims to investigate the effect of succinylated modification of soy protein isolate (SPI) on its emulsifying and oil–water interfacial properties. The structure–effect mechanism was further analyzed between the emulsifying properties and the interfacial protein conformational flexibility of SPI. After succinylation, the ζ-potential of emulsion droplets increased, the particle size decreased, the turbidity and flocculation index decreased, and their macroscopic stability improved. The interfacial protein adsorption increased and the interfacial tension decreased, reaching their optimum when the degree of succinylation (DS) was 89.71%. As the increase of DS, the content of β-turn and random coil of interfacially adsorbed proteins increased to 16.27% and 25.15%, respectively, and the flexibility increased and the particle size decreased, while the opposite changes were observed for the unadsorbed proteins. Correlation analysis showed that the emulsifying and interfacial properties of SPI emulsions were closely related to the conformational flexibility of the interfacially adsorbed proteins, while the interfacial adsorption process was also affected by the ζ-potential and particle size of the unabsorbed proteins. This research could provide theoretical guidance on the regulation of protein-emulsifying properties by succinylation and reference data for the conformational characterization of interfacial proteins.

The dielectric function profile across the water interface through surface-specific vibrational spectroscopy and simulations

The dielectric properties of interfacial water on subnanometer length scales govern chemical reactions, carrier transfer, and ion transport at interfaces. Yet, the nature of the interfacial dielectric function has remained under debate as it is challenging to access the interfacial dielectric with subnanometer resolution. Here we use the vibrational response of interfacial water molecules probed using surface-specific sum-frequency generation (SFG) spectra to obtain exquisite depth resolution. Different responses originate from water molecules at different depths and report back on the local interfacial dielectric environment via their spectral amplitudes. From experimental and simulated SFG spectra at the air/water interface, we find that the interfacial dielectric constant changes drastically across an ∼1 Å thin interfacial water region. The strong gradient of the interfacial dielectric constant leads, at charged planar interfaces, to the formation of an electric triple layer that goes beyond the standard double-layer model.

Ionic liquid-based reverse micelles. Use of hydrogen–deuterium exchange as a tool for surfactant self-assembly characterization

We report the study of the rate for hydrogen–deuterium (H-D) exchange in the cation of the ionic liquid-surfactant 1-butyl-3-methylimidazolium 1,4-bis-2-ethylhexylsulfosuccinate (bmim-AOT) when it forms reverse micelles (RMs). The results were compared with those found for bmim-AOT dissolved in D2O showing an inhibition larger than 500-fold on going from bulk D2O to the reverse micelle. Also, the effect of varying water content and surfactant concentration of the RMs on the deuterium exchange was evaluated by 1H NMR technique. The results demonstrate that the H-D exchange at the C(2) position of bmim+ when it forms RMs significantly reflects the properties of the micellar microenvironment, specifically of the micellar interface due to the localization of bmim+ in the interfacial region, intercalated between the AOT moiety. The rate of deuterium exchange is directly related to the properties of interfacial water, which, in turn, is closely related to the water-surfactant interaction. Thus, the analysis of deuterium exchange in the 2-position of bmim+ is proposed as a useful tool to explore the properties of RMs formed by this cation, with the advantage of being a non-invasive technique since the ionic liquid-surfactant itself acts as the molecular probe.

Influence of polymer concentration on the stability of the polymer flooding wastewater: Oil droplets floating behaviour and oil–water interfacial properties

Polymer flooding is considered as a promising technology in enhanced oil recovery process. However, a large amount of oil-in-water (O/W) emulsion with high stability is generated during this process. In order to clarify the stability mechanism of the polymer flooding wastewater, we investigate the effect of polymer concentration on the floating behaviour of the oil droplets and oil–water interfacial properties. The experimental results demonstrate that increasing the polymer concentration can improve the viscosity of system, which results in a low rising velocity of oil droplets. Besides, the hydrophilic polymer molecules can absorb on the oil–water interface, and enhance the electrostatic repulsive force between oil droplets, leading to a low collision efficiency of oil droplets, making oil droplets difficult to approach and coalesce. The viscoelasticity is also improved, indicating that oil–water interfacial film strength is enhanced, and ultimately, the emulsion stability is improved.

Microfluidic platforms for characterization of crude oil emulsion stability

Microfluidic technology has gained significant scientific interest in the characterization of crude oil emulsions that are often formed in the process of oil production. Microfluidic platforms can be used to mimic the pores of natural rock and study multiphase displacement, as well as emulsion formation at a microscale level. This paper focuses on the applications of microfluidics to probe the stability of emulsified droplets against coalescence (e.g., in the presence of additives, electric field) for both water-in-oil (W/O) and oil-in-water (O/W) emulsion systems. Additionally, this study summarizes the recent efforts made to identify the effects of various experimental factors, including crude oil composition, aging, salinity, and pH on the interfacial properties of water–oil interface and their ultimate roles in the formation and stability of emulsions. Finally, main findings and some recommendations for future work related to the potential of microfluidics in different aspects of crude oil emulsion studies are discussed.

Study of interfacial properties of water + methane + oil three-phase systems by a simple molecular simulation protocol

A straightforward molecular simulation protocol has been proposed to study the interfacial properties of the three-phase fluid systems. With this protocol, the interfctcial tension (IFT) can be calculated based on the pressure tensor of the entire simulation box of the two-phase systems split from the three-phase system without calculating the debatable pressure tensor profile. Water + methane + oil (decane, hexadecane, and toluene) three-phase systems was studied at different temperatures (323–423 K) and pressures (up to around 20 MPa). Reasonable agreement was found among the results obtained from molecular simulation, density gradient theory with the cubic-plus-association equation of state, and available experimental data in the literature. The IFT of the aqueous phase + vapor phase in the three-phase systems is smaller than the IFT in water + methane two-phase systems. Importantly, the reduction of IFT of aqueous phase + vapor phase in the three-phase systems containing decane or hexadecane is moderate while that in the three-phase systems containing toluene is significant, which can be explained by the stronger enrichment of toluene in the interfacial region in contrast to that of decane or hexadecane. Meanwhile, methane accumulates in the interfacial region of the aqueous phase + decane/hexadecane-rich phase in the three-phase systems, which causes the reduction of IFT with pressure while the opposite pressure effect was reported in the water + decane/hexadecane two-phase systems. The interfacial properties of the oil-rich phase + vapor phase in the three-phase systems are hardly affected by water due to the small amount of dissolved water. Furthermore, the calculated spreading coefficient of different types of oil in contact with water + methane under three-phase conditions follows this order: toluene > decane > hexadecane.

Molecular Dynamics Study on Performance of Olefin Sulfonate at the Decane–Water Interface: Effect of Molecular Architecture

Surfactant flooding has been widely employed to recover the residual oil in the oilfields. Among the various oil-displacing chemicals, olefin sulfonate isomers have been identified as effective chemical agents by many experiments due to the realization of low interfacial tension (IFT) at the oil–water interface, and tolerance for high salinity and high temperature under reservoir conditions. The molecular architecture (e.g. degree of branching) of the surfactant can significantly affect the oil–water interfacial properties and hence its performance. Herein, molecular dynamics simulations were performed to investigate the adsorption processes of alpha olefin surfactant (AOS with single-tailed structure) and internal olefin surfactant (IOS with twin-tailed structure) at the oil (n-decane) - water interface under oil reservoir condition. The results show that IOS can significantly reduce the IFT at high concentrations, and the formed monolayers at the interface are more stable compared with AOS. The steric hindrance effect by the short chain of IOS can inhibit the aggregation behavior, thus leading to larger interfacial coverage, which are favorable to separation of the water and decane phases. The larger distance between the headgroups of IOS molecules is conducive to formation of hydrogen bonds between the surfactant and water molecules, and hence enhances the interaction between the IOS and water molecules at the inerface. Based on the analysis of order parameter, the middle segment of AOS molecules and the long chain of IOS molecules are mainly contributed to the Van der Waals’ interaction between the surfactant alkyl tails and decane molecules. Meanwhile, the twin-tailed structure of IOS has more favorable effective alkyl tail length (i.e. better miscibility with the oil phase) compared with the single-tailed structure of AOS. Consequently, the twin-tailed structure is superior to the single-tailed structure in terms of interfacial performance, and it is strongly suggested for the design of advanced surfactants in EOR implementation.