Properties Of Aqueous Systems Research Articles

Application of Nanofibrous Clay Minerals in Water-Based Drilling Fluids: Principles, Methods, and Challenges

Nanofibrous clay minerals, specifically palygorskite (Pal) and sepiolite (Sep), have been becoming a new generation of rheological additives for drilling fluid systems due to their unique nanostructure, high performance, environmentally benign nature, and cost-effectiveness. These nanoclay minerals exhibit excellent colloidal and rheological properties in aqueous systems, even in saline and high-temperature environments. Although Pal and Sep have been employed as auxiliary rheological additives in a few cases to enhance the salt resistance of conventional water-based drilling fluids (WBDFs), these two clay minerals have not yet been used on a large scale due to a lack of understanding of their structures and properties, as well as the control of their performance. This paper presents a comprehensive review of the clay mineralogy, colloidal chemistry, rheological behaviors, and filtration properties of nanofibrous clay minerals in WBDFs, with critical comments. It also discusses the challenges and prospects for further research. This review provides new insights into fundamental and applied studies of nanofibrous clay minerals and helps promote the large-scale application of nanofibrous clay products in drilling fluids.

Comparison of the Thermal and Rheological Properties of Frontière Brown Rice Flour, Tapioca Starch, and Potato Starch and Mixture Effects on Pasting Properties in Aqueous Systems

AbstractGluten‐free blends utilize starches, gums, hydrocolloids, and proteins for viscoelasticity, gas holding ability, and crumb structure of dough and batter without gluten. This study examines Frontière brown rice flour (HPBRF), a new high protein rice cultivar, with tapioca starch (TS) and potato starch (PS) in an aqueous model system in a mixture design, to study interaction effects on pasting properties. The effect of the flour from this new cultivar on the pasting properties of other starches typically used in gluten‐free products has not yet been tested. Pasting properties are analyzed with a Rapid Visco Analyzer (RVA). Rheological and thermal characterization of the flour and starches are also done using differential scanning calorimetry (DSC) and a rheometer. The blends of HPBRF and PS affect the pasting properties compared to each alone, and it is observed that the application of HPBRF with PS decreases breakdown viscosity and peak viscosity, significantly compared to PS alone. Also, the ternary mixture considerably decreases the retrogradation potential for HPBRF, which indicates more stability during storage. These positive and negative effects can indicate how combined usage of these ingredients for the development of bakery products can impact physiochemical properties of gluten‐free bakery products.

The Electrochemical Characterization of Nanostructured Bi2Se3 Thin Films in an Aqueous Na Electrolyte

Due to their layered structure and high theoretical capacity, bismuth chalcogenides have been proposed as anodes in organic electrolyte Li- and Na-ion batteries. On the other hand, their electrochemical properties in aqueous systems have not been reported. Here, the electrochemical performance of Bi2Se3 thin films in 1 M NaNO3 aqueous electrolyte is presented. This aqueous Bi2Se3 system was found to have up to two orders of magnitude increased diffusion coefficients, compared to other anode materials in Na electrolyte-based systems, as well as limited anode electrode degradation over 5 CVs and significant changes in the anode after 30 CVs.

Peculiarities of the Physicochemical Properties of Hydrated C60 Fullerene Solutions in a Wide Range of Dilutions

Hydrated fullerene C60 (HyFn) is a supramolecular object in which the nanosized fullerene molecule is enclosed in a multilayer shell of water molecules. Despite the fact that fullerene C60 is chemically rather inert, aqueous solutions of HyFn exhibit a wide spectrum of biological activity in particular in low and ultra-low concentrations. Thus, physical and chemical properties of aqueous solutions of HyFn in a wide range of its dilutions are of interest. Here we compared some physical and chemical properties of aqueous systems prepared by successive 100-fold dilutions of HyFn (10–7 M) with deionized water, with their intensive shaking at each stage up to the calculated HyFn concentration of 10–31 M and of the corresponding “dilutions” of deionized water prepared in the same manner (controls). We studied the character of рН changes in dilutions when titrating them with HCl and NaOH. It turned out that HyFn dilutions had significantly higher buffering capacity against acidification with HCl than control water “dilutions.” At the highest acidity reached pH in all HyFn dilutions was almost 0.3 units higher than in the respective controls. Average buffering capacity of HyFn dilutions and water controls when titrated with NaOH did not differ. However, differences in buffering capacity could be seen between consecutive dilutions of HyFn at their titration either with NaOH or with HCl. Most prominent differences were observed between consecutive HyFn dilutions in the range of calculated concentrations 10–17–10–31 M titrated with NaOH while no significant differences in pH between equivalent “dilutions” of control water were observed. Similar though less prominent variations in buffering capacity between consecutive HyFn dilutions titrated with HCl were also noticed. Thus, titration with an acid and especially with an alkali made it possible to reveal differences between individual dilutions of HyFn, as well as differences between HyFn dilutions and corresponding dilutions of water. These features may be due to complexity in the structural properties of aqueous systems, which, supposedly, can arise due to the emergence of heterogenous aqueous regions (“clouds”) in the course of their dilutions with intensive mixing at each stage. In order to find out if such heterogeneity is a characteristic for HyFn dilutions we used the method of drying microsphere-containing droplets, whose aqueous base were either HyFn dilutions in the range of calculated HyFn concentration 10–7–10–31 M or respective water controls. It was found that a significant part of HyFn dilutions is characterized by mesoscopic heterogeneity. It showed up by the tendency of microspheres to concentrate in a specific way resembling ornaments once the droplets had dried. As the degree of HyFn dilution increased, the number of dried droplets with an ornament-like microsphere distribution increased. Same was also observed in water control drops. However, for the dilutions of HyFn equivalent to concentrations 10–19–10–31 M the percentage of complexly structured dried up droplets reached 60–80%, while for dried out drops of respective water controls it did not exceed 15–20%. Thus, the physicochemical properties of high dilutions of hydrated fullerene differ not only from each other dependently on the dilution level, but also from those of high dilutions of water, which can be explained by the structuredness and heterogeneity of these aqueous systems. Therefore, upon dilution process the properties of the solutions change according to complex and non-linear laws so that final dilutions cannot be identical in their properties and features to those of the initial solutions (before dilutions process) and to the untreated water. Dilution process, in view of the aforementioned, should not be underestimated when analyzing properties of the solutions, having shown to be able to affect dramatically properties of the solutions.

Field-Induced Tunneling Ionization and Terahertz-Driven Electron Dynamics in Liquid Water.

Liquid water at ambient temperature displays ultrafast molecular motions and concomitant fluctuations of very strong electric fields originating from the dipolar H2O molecules. We show that such random intermolecular fields induce the tunnel ionization of water molecules, which becomes irreversible if an external terahertz (THz) pulse imposes an additional directed electric field on the liquid. Time-resolved nonlinear THz spectroscopy maps charge separation, transport, and localization of the released electrons on a few-picosecond time scale. The highly polarizable localized electrons modify the THz absorption spectrum and refractive index of water, a manifestation of a highly nonlinear response. Our results demonstrate how the interplay of local electric field fluctuations and external electric fields allows for steering charge dynamics and dielectric properties in aqueous systems.

The Behavior of H2 in Aqueous Fluids under High Temperature and Pressure

The presence of H2 and H2O in planetary interiors prompts the need for fundamental studies on these compounds under corresponding conditions. Here, we summarize data on H2 properties in aqueous systems under conditions of high temperature and pressure. We explain how to measure important H2 fugacities in hydrothermal systems. We present available experimental data and thermodynamic models for H2 solubility and vapor–liquid partitioning under hydrothermal conditions. In addition, we introduce the fascinating world of H2–H2O clathrate hydrates under extreme temperatures and pressures. The properties of the H2–H2O system are well established below the critical point of water (374 °C and 22.06 MPa), but far less is known under higher temperatures and pressures, or the effect of salt.

LiFePO4‐Accelerated Change in Surface and Electrochemical Properties in Aqueous Systems Induced by Mechanical Agitation

Switching from organic to aqueous solvents for battery electrode processing is desirable due to both safety and cost advantages. Lithium iron phosphate (LFP) is considered a cathode material for aqueous processing due to its demonstrated chemical compatibility with water, in addition to its favorable cost, safety, electrochemical performance, and environmental advantages as a battery active material. All research on LFP stability in water has been conducted in a scenario where LFP is aged in stagnant water, or surrounded by water when confined within a composite electrode. However, a much accelerated degradation in the electrochemical performance of LFP when it is in contact with water and exposed to mechanical agitation is demonstrated. Changes to LFP are probed using a combination of materials characterization methods. Although there are no significant changes to the bulk particle structure and morphology, significant particle surface damage and compositional modifications are observed. These results suggest that the systems where LFP is exposed to agitation in an aqueous environment, such as in aqueous battery electrode processing or in aqueous slurry electrodes, need to be carefully investigated for potential changes to the LFP surface environment under relevant processing conditions.

A reactive force field molecular dynamics simulation of the dynamic properties of hydrogen bonding in supercritical water

Dynamic properties especially lifetime and connectivity of hydrogen bonds in supercritical water play essential roles in physical and chemical properties in aqueous systems. Although average lifetime of hydrogen bonds in supercritical water derived using computer simulation has been reported, detailed distribution and survival analyses have yet to be performed. Here, we performed classical molecular dynamics (MD) simulations with a recently developed reactive force field method to investigate the detailed dynamic process of hydrogen bond forming, cracking, re-bonding and exchanging in supercritical water. We analyzed the MD-calculated trajectories with a sample interval equal to the MD time-step to obtain detailed lifetime information. The calculated lifetime distributions indicate that hydrogen bonds in supercritical water exhibit the newborn instability which is independent of temperature. Supercritical water shows non-exponential kinetics with a gradually decreasing failure rate. We also investigated the connectivity of hydrogen bonding by analyzing the fractions of water molecules involved in a certain number of hydrogen bonds and found that the fractions at high densities remarkably deviate from the widely applied simple binomial distribution. On the basis of the assumption that the maximal coordination number can be a non-integer w, we proposed a non-integer binomial distribution with a maximum coordination number of 4.4 for an enhanced prediction.

Dimensionless Models for Predicting the Effective Area, Liquid-Film, and Gas-Film Mass-Transfer Coefficients of Packing

A total of 11 structured packings with surface areas (ap) from 125 to 500 m2/m3 and corrugation angles (θ) from 45 to 70° were studied to explore the effects of the packing geometry on mass transfer. A new concept, the mixing point density, was proposed to represent the effects of ap and θ. A generalized method to calculate the mixing point density from aP and θ was developed. Dimensionless mass-transfer models are developed to predict the effective area, liquid-film, and gas-film mass-transfer coefficients, with the mixing and Reynolds numbers imbedded into the correlations. Compared with literature models, the models developed in this work capture the effects of the packing geometry and predict the mass-transfer properties in aqueous systems.

Express analysis of the structural properties of water clusters containing more than 12 water molecules and impurities

An express analysis technique for the determination of the structural properties of water clusters with impurities and the number of contained water molecules more than 12 is developed. The technique is based on the derivation of three matrices for a water cluster, which makes it possible to write down the unique code characterizing its structure. The technique significantly decreases the computation time (approximately 104 times) in comparison with the procedure developed previously [1], and consequently, allows the analysis of the structural properties of aqueous systems with a large number of molecules on usual PCs. In order to illustrate the technique the code for the typical configuration of the (H2O)13 cluster is determined within the water model at a temperature of 268 K and a density of 0.99930 g/cm3.

Synthesis of mesoporous Mn/TiO2 nanocomposites and investigating the photocatalytic properties in aqueous systems.

Mesoporous 20 wt% Mn/TiO2 nanocomposites were synthesized adopting modified sol-gel method at different pH (pH = 2, 7 and 11) conditions and calcined at 400 °C. Based on the characteristics of the 20 wt% Mn/TiO2 nanocomposites synthesized at pH 11, same procedure was adopted for the synthesis of different wt% Mn/TiO2. The nanocomposite samples and their surface properties were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), mapping, inductively coupled plasma optical emission spectrometry (ICP-OES), Fourier transform infrared (FTIR), and fluorescence spectrometry. The nanocomposites existed in the anatase phase of TiO2 with no peak assigned to Mn on the diffractogram. The photocatalytic activities of the materials were evaluated by monitoring degradation of a model dye (methylene blue (MB)) in presence of visible light and ozone. The nanocomposite synthesized under neutral condition (pH = 7) exhibited the best photocatalytic activity resulting from its relatively smaller crystal size (5.98 nm) and larger pore volume (0.30 cm(3)/g). One percentage of weight Mn/TiO2 showed 100% decolouration of MB in the presence of O3 after 100 min.

A thermodynamic model for predicting mineral reactivity in supercritical carbon dioxide: I. Phase behavior of carbon dioxide–water–chloride salt systems across the H2O-rich to the CO2-rich regions

Phase equilibria in mixtures containing carbon dioxide, water, and chloride salts have been investigated using a combination of solubility measurements and thermodynamic modeling. The solubility of water in the CO2-rich phase of ternary mixtures of CO2, H2O and NaCl or CaCl2 was determined, using near infrared spectroscopy, at 90atm and 40 to 100°C. These measurements fill a gap in the experimental database for CO2–water–salt systems, for which phase composition data have been available only for the H2O-rich phases. A thermodynamic model for CO2–water–salt systems has been constructed on the basis of the previously developed Mixed-Solvent Electrolyte (MSE) framework, which is capable of modeling aqueous solutions over broad ranges of temperature and pressure, is valid to high electrolyte concentrations, treats mixed-phase systems (with both scCO2 and water present) and can predict the thermodynamic properties of dry and partially water-saturated supercritical CO2 over broad ranges of temperature and pressure. Within the MSE framework the standard-state properties are calculated from the Helgeson–Kirkham–Flowers equation of state whereas the excess Gibbs energy includes a long-range electrostatic interaction term expressed by a Pitzer–Debye–Hückel equation, a virial coefficient-type term for interactions between ions and a short-range term for interactions involving neutral molecules. The parameters of the MSE model have been evaluated using literature data for both the H2O-rich and CO2-rich phases in the CO2–H2O binary and for the H2O-rich phase in the CO2–H2O–NaCl/KCl/CaCl2/MgCl2 ternary and multicompontent systems. The model accurately represents the properties of these systems at temperatures from 0°C to 300°C and pressures up to ~4000atm. Further, the solubilities of H2O in CO2-rich phases that are predicted by the model are in agreement with the new measurements for the CO2–H2O–NaCl and CO2–H2O–CaCl2 systems even though the new data were not used in the parameterization of the model. Thus, the model can be used to predict the effect of various salts on the water content and water activity in CO2-rich phases on the basis of parameters determined from the properties of aqueous systems. Given the importance of water activity in CO2-rich phases for mineral reactivity, the model can be used as a foundation for predicting mineral transformations across the entire CO2/H2O composition range from aqueous solution to anhydrous scCO2. An example application using the model is presented which involves the transformation of forsterite to nesquehonite as a function of temperature and water content in the CO2-rich phase.

Excluded volume versus hydrogen bonding: complementary or incompatible concepts?

An attempt has been made to assess individual effects of the repulsive and attractive interactions on the structure of associating fluids using short-range models descending from parent realistic models. It is shown that neither the excluded volume (repulsive interactions) nor the hydrogen bonding (attractive interactions) considered separately are able to produce the correct structure. However, when both these types of interactions are considered together, they faithfully reproduce the structure of water and other associating fluids. Consequently, although some properties of aqueous systems can be explained qualitatively/intuitively by hydrogen bonding only, disregarding simultaneously the excluded volume effects may be misleading.

Formation of mesoscopic water networks in aqueous systems

Formation of the macroscopically-infinite hydrogen-bonded water network in various aqueous systems occurs via 3D percolation transition when the probability of finding a spanning water cluster exceeds 95%. As a result, in a wide interval of water content below the percolation threshold, rarefied quasi-2D water networks span over the mesoscopic length scale. Formation and topology of spanning water networks, which affect various properties of aqueous systems, can be described within the framework of the percolation theory.

Photochemical behavior of inorganic and organic selenium compounds in various aqueous solutions

Selenium possesses interesting chemical, biochemical and geochemical behaviors. However, studies of its photochemical properties in aqueous systems are scarce. A better understanding of these phenomena is of great importance for further application of such properties to selenium speciation. In this work, the photochemical behavior of selenium and some of its organic compounds have been systematically studied in various aqueous matrices under UV irradiation at 300 nm. It was observed that the photochemical oxidation rate of Se(IV) to Se(VI) was greatly enhanced in the presence of HN0 3 at ≥1 × 10 −3 M, but not by NaNO 3. However this photo-oxidation could be inhibited by the presence of Cl −. Under UV irradiation, organoselenium compounds went through two successive photochemical reactions in pure water: a direct photolysis (photo-cleavage) followed by a photo-oxidation to form Se(VI). These two steps could also be greatly accelerated in presence of NO 3 − although the second step required an acidic condition. The photo cleavage rates varied from one organic compound to another and 10-fold differences were observed. Similarly to Se(IV), the further oxidation to Se(VI) could be prevented by Cl − for all studied organoselenium compounds. Detailed reaction mechanisms involving OH radicals are proposed to explain Se photochemical behaviors in different matrices.

Characterisation and functional properties of Australian rice protein isolates

Albumin, globulin, glutelin and prolamin fractions were isolated from an Australian rice variety (cv. Langi) and characterised by yield, protein content and molecular weight profile using both capillary electrophoresis (SDS-CE) and sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). The influence of pre-extraction enzymatic hydrolysis of starch and heating to 70 °C was also investigated, as was the extraction of the glutelin fraction without prior removal of the albumin and globulin fractions. Pre-extraction treatment affected mainly the albumin fraction, increasing dry matter yield but reducing protein content. SDS-CE was able to separate the protein fractions over a wider molecular weight range than SDS-PAGE, and the peaks from SDS-CE showed slightly higher molecular weight compared to equivalent bands from SDS-PAGE. The glutelin fraction extracted without prior removal of albumin and globulin fractions had different characteristics compared to those obtained by conventional extraction methods. Pre-extraction hydrolysis of starch did not significantly affect the emulsifying, foaming and gelling properties of extracted protein. Although rice glutelin had poor solubility, emulsifying and foaming properties in aqueous systems, it had good gelling properties which could be important for food applications.

Some Recent Developments in Headspace Gas Chromatography

In this study, recent developments in headspace gas chromatography (HSGC) are briefly reviewed. Several novel HSGC techniques developed recently are presented in detail. These techniques were developed using the unique characteristics of the headspace sampling process implemented in commercial HSGC systems and therefore can be easily applied in laboratory and industrial practices. These techniques greatly expand the capability of traditional HSGC from simply analysis of volatile species to the measurements of nonvolatile species in solid systems and their properties in aqueous systems. The basic principles of the techniques along with specific applications are presented. These HSGC techniques are practical, accurate, and simple for both laboratory and industrial applications.

Partially carboxymethylated feather keratins. 1. Properties in aqueous systems.

Feather keratins were extracted from chicken feathers with an aqueous solution of urea and 2-mercaptoethanol. The keratin solution obtained was dialyzed to remove the reagents. Upon dialysis, extensive protein aggregation occurred. To obtain stable solutions or dispersions in water, cysteine residues were modified prior to dialysis with iodoacetamide, iodoacetic acid, or bromosuccinic acid, thereby blocking free thiol groups and introducing hydrophilic groups. For the development of biodegradable materials with good mechanical properties from these biopolymers, disulfide bonds between the keratin molecules are needed. Therefore, cysteine residues were only partially modified by using different reagent/cysteine molar ratios. The reaction rate constants of iodoacetate with glutathione and 2-mercaptoethanol were successfully used to predict the degree of modification of keratin cysteine. It was shown that, for carboxymethylated keratin, fewer aggregates were formed for higher degrees of cysteine modification, while more protein was present as oligomers. Aggregates and oligomers were stabilized through intermolecular disulfide bonds.

On the role of short- and long-range forces in aqueous systems

Effects of short- and long-range forces upon the properties of aqueous systems is examined using a decomposition into trial potentials which can be constructed from any realistic water-water potential. Both pure water and diluted aqueous solutions of nonelectrolytes are considered over a wide range of thermodynamic conditions. It is shown that, regardless of the thermodynamic conditions, the structure of water is determined by short range forces which may be both repulsive and attractive; however, with increasing temperature the effect of the short range attractive forces rapidly lessens. As regards the aqueous solutions of non-polar compounds, it is shown that only the short range water-water interactions and simple exclusion effects are essential for the arrangement and orientation of water molecules in the hydration shell.

Synthesis and characterization of amphiphilic poly(ethylene glycol) graft copolymers and their potential application as drug carriers

Amphiphilic graft copolymers comprising monomeric units of stearyl methacrylate, methyl acrylate, acrylic acid and poly(ethylene glycol) acrylate were synthesized and their properties in aqueous systems characterized. The structures of these copolymers were analysed by Fourier transform infra-red and nuclear magnetic resonance spectroscopies while their molecular weights were estimated by static light scattering. The study of critical micelle concentrations and micellar sizes indicated that the formation of micelles is primarily determined by the hydrophobic/hydrophilic properties of these copolymers. Encapsulation of pyrene (as a drug model) into the micelles was found to be dependent on their stearyl methacrylate content. These copolymers also exhibited a sustained release pattern for pyrene in aqueous solutions and might indicate their future applications as potential drug delivery systems.