Increasing Mole Fraction Research Articles

Investigation of aggregation behavior and surface properties of cationic surface-active ionic liquids and sodium carboxymethylcellulose mixed systems

Abstract The impact of different concentrations of sodium carboxymethyl cellulose (NaCMC) on the micellization process in cationic, ester-functionalized, ethyl-substituted imidazolium-based surface-active ionic liquids (SAILs) ([C n Eeim]Br where, n = 12, 14, 16) were investigated using specific conductivity and surface tension measurements at 298 K. The study focused on determining the critical micelle concentration (CMC) of the three pure SAILs and their mixtures with NaCMC to evaluate various thermodynamic and interfacial parameters. The results showed that the CMC values decreased significantly with increasing hydrophobicity of the SAILs, while the CMC increased with a gradual increase in the NaCMC mole fraction in the SAIL–NaCMC mixed systems. It was observed that the excess free energy of micellization ( ∆ G e x m ${{\increment}G}_{ex}^{m}$ ) and the minimum free energy of surface at equilibrium ( ∆ G min s ${{\increment}G}_{\mathrm{min}}^{s}$ ) exhibited an opposite behaviour, indicating that the formed mixed micelles were stable while the formed surface was unstable. The results of this study are useful for evaluating the properties of SAIL–NaCMC mixed systems to improve and better understand their applications in the food, medical and cosmetic industries.

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.

Study on the ignition characteristics of CH4/H2/air mixtures in a micro flow reactor with a controlled temperature profile

The ignition characteristics of stoichiometric CH4/H2/air mixtures with different H2 dilution ratios were studied by using a micro flow reactor (MFR) with a controlled temperature profile. The weak flame positions of the mixtures were determined by the luminosity of CH∗, and the ignition temperatures (defined as the corresponding wall temperatures) were obtained. The ignition temperature of the mixture is smoothly decreased with a small amount of H2 addition, while the decrease of the ignition temperature is more rapid with increasing H2 dilution. One-dimensional computation with a detailed reaction mechanism was also conducted to study the ignition characteristics of the CH4/H2/air mixtures. The computational ignition temperature which is defined as the wall temperature at the peak of the heat release rate (HRR) peak is also obtained. Both the experimental and computational results show that the weak flame shifts to the lower temperature region with an increase of the H2 mole fraction. And the non-linear decrease of the ignition temperature of the CH4/H2/air weak flame versus increasing H2 dilution was also well reproduced by the numerical computation. The flame structures, primary exothermic and endothermic reactions of the CH4/H2/air weak flames were studied in detail. The importance of H and OH in the ignition process of the mixtures was analyzed, and the kinetic effects of H2 on the ignition of the mixture in the intermediate-temperature region (1000–1200 K) and high-temperature region (1200–1300 K) were elucidated. The analysis of the computational results reveals that the OH production routes in the intermediate-temperature region are substantially changed with different H2 dilutions, while the OH production routes at the peak of the heat release rate are not obviously influenced. In the end, the primary mechanism for the non-linear effects of H2 addition on the ignition temperatures of the CH4/H2 mixtures was clarified.

Design and optimization of stress/strain in GAA nanosheet FETs for improved FOMs at sub-7 nm nodes

Stress/strain engineering techniques are employed to boost the performance of Gate-all-around (GAA) vertically stacked nanosheet field-effect transistors (NSFETs) for 7 nm technology nodes and beyond. In this work, we report on the 3D numerical simulation study of the impacts of source/drain epitaxial and uniaxial strained-SiGe channel stresses on p-type NSFETs. It is shown that the uniaxial strained-SiGe channel improves the drive current by up to 107% due to higher compressive stress while the 3-stack NSFET can achieve an enhancement in drive current even up to 187% using a 30% Ge mole fraction. Furthermore, we compare the multiple stacked channel NSFETs and nanowire FETs (NWFETs) considering different strain techniques. As compared to a 3-stack strained-SiGe NWFET, NSFETs show 27% and 10% enhancements in ION and SS, respectively. Vertically stacked NSFETs are shown to be the best option to improve the hole mobility under biaxial and uniaxial compressive strain rather than NWFETs. We also look at how the Ge mole fraction affects various electrical properties in a uniaxial strained-SiGe channel with shrinking dimensions of scaled NSFETs. It is observed that for a fixed Lg, ION/IOFF ratio, SS and DIBL decrease with the increase in Ge mole fraction.

Solid-liquid phase equilibrium of 2, 4-epibrassinolide in binary mixed solvents: Solubility determination, model correlation, preferential solvation and thermodynamic properties

The solubility of 2, 4-epibrassinolide in four binary mixed solvents including (ethanol + water, isopropanol + water, acetone + water, and acetonitrile + water) with numerous compositions was determined at temperature of 283.15 K to 323.15 K by a laser dynamic method. The solubility of 2, 4-epibrassinolide in all four binary solvent mixtures increases with increasing temperature. At a given temperature, it shows a trend of increasing and then decreasing with increasing mole fraction of water. In the same solvent composition, the order of solubility is isopropanol + water > ethanol + water > acetone + water > acetonitrile + water. The experimental solubility data of 2, 4-epibrassinolide was correlated with the modified Apelblat, Van’t Hoff, NRTL, Wilson, and three-suffix Margules model. The preferential solvation mechanism of 2, 4-epibrassinolide in four aqueous solutions was also discussed by IKBI method. Furthermore, the Wilson model was worked to analyze the thermodynamic mixing properties of the solutions, including ΔmixG, ΔmixH and ΔmixS. All ΔmixG values are negative indicating that the mixing process of 2, 4-epibrassinolide in these solvents is spontaneous.

Abnormal thermal expansion coefficients in (Nd1−xDyx)2Zr2O7pyrochlore: The effect of low-lying optical phonons

Chemical doping is a normal strategy to tune thermal expansion coefficient (TEC) of ceramics in engineering applications, but the resultant TEC values usually follow Vegard’s law, as doping does not modify the nature of chemical bonding in ceramics and its anharmonicity. In this paper, we report abnormal TEC behavior in (Nd_1−<i>x</i>Dy_<i>x</i>)₂Zr₂O₇ ceramics, where the TEC values remarkably exceed the values predicted by Vegard’s law and even exceed the values obtained for two constituents Nd₂Zr₂O₇ and Dy₂Zr₂O₇. In addition to a reduction in lattice energy with an increasing molar fraction of Dy (<i>x</i>) value, we attribute the additional increase in the TEC to the high concentration of Dy dopants in a pyrochlore (P) region, which can soften low-lying optical phonon modes and induce strongly avoided crossing with acoustic phonon branches and enhanced anharmonicity. We believe that this finding can provide a new route to break through the restriction imposed by the conventional Vegard’s law on the TEC values and bring new opportunities for thermal barrier coatings (TBCs) or ceramic/metal composites towards realizing minimized thermal mismatch and prolonged service life during thermal cycling.

High-pressure supersonic carbon dioxide (CO2) separation benefiting carbon capture, utilisation and storage (CCUS) technology

Carbon capture, utilisation and storage (CCUS) is of unique significance for building a green and resilient energy system, and it is also a key solution to tackle the climate challenge. The concept of supersonic decarburization, a joint product of non-equilibrium condensation and swirling separation, can contribute to CCUS technology in a clean way. In this paper, a numerical model is established and validated to investigate the complex physical phenomena of supersonic decarbonization in a high-pressure environment based on the real gas equation of state. The model is compatible with the pure CO2 model and CH4-CO2 model. Through the simulation of the supersonic nozzle and supersonic separator, the condensation and separation performance of supersonic decarbonization technology was evaluated. For the condensation performance of carbon dioxide, the results show that higher pressure makes it much easier to achieve the condensation process. When the pressure is supercritical, the decrease of inlet temperature or the increase of inlet mole fraction of CO2 leads to a higher liquid fraction. For separation performance, when the mass concentration of inlet heterogeneous droplets increases from 0.1 kg/m3 to 7.5 kg/m3, the carbon separation amount increases from 3.33 ton/h to 4.43 ton/h, while the exergy loss of condensed CO2 drops from 436.57 kJ/kg to 329.56 kJ/kg. It demonstrates that the decarburization process is easier, and exergy required for condensation decreases when the concentration of the foreign core is larger. This new concept is beneficial to CCUS technology and can be applied to carbon capture in offshore natural gas processing.

Effects of X (X = H2S, SO2 and N2O) mole fractions on adsorption behavior and phase equilibrium properties of CO2 + X mixed gas hydrate

As a remedy for air pollution caused by flue gas, Hydrate Based Gas Separation (HBGS) technology is under development. Among many issues in HBGS, the prediction for the adsorption and dissociation conditions of hydrate and the impact from mixed gas on the formation of carbon dioxide hydrate are crucial to understand the sequestration and separation of CO2. In this work, the occupancy isotherms of the mixed systems of CO2 + H2S, CO2 + SO2 and CO2 + N2O with different mole fractions of H2S, SO2 and N2O in sI and sII hydrates are examined. The results show that X (H2S, SO2 and N2O) in flue gases can increase the absorption of mixed gas; CO2 + H2S in the sI and sII hydrates can be categorized as the one-site Langmuir type. The calculated abundance ratio of CO2 to X vary with the mole fraction of impurity gas and pressure, which provide the prerequisite information for prediction of gas recovery yield at different conditions during the CO2 + X gas separate process. The phase equilibria of clathrate hydrates of mixed gases are predicted and the hydration numbers are determined. The results show that the dissociation pressure of mixed hydrates decreases as the impurity gas mole fraction increases, indicating that SO2, H2S and N2O gases can all promote the formation of CO2 hydrate. Additionally, inspection indicates that the mixed flue gas can be efficiently separate by clathrate hydrate.

Modelling and analysis of a compression/resorption heat pump system with a zeotropic mixture of acetone/CO2

Industrial processes represent one of the most energy-consuming activities, which are related to fossil fuel utilization and the growing environmental problems. In this way, the heat waste energy recovery has been presented as an efficient solution, to take advantage of low-grade residual heat, where the compressor -resorption heat pump technology has proven to achieve high-temperature levels with a considerable Coefficient of Performance. However, known working fluids such as hydrofluorocarbons represents an environmental hazard due to its Global Warming potential, these have been replaced by natural fluids such as ammonia, but they also have disadvantages like its toxicity. In this way, the CO2 is an available waste heat compound product of fossil combustions, therefore, this research is based on the utilization of novel fluids such as the zeotropic mixture of CO2/Acetone as an eco-friendly working fluid with low Global Warming Potential. Even more, the utilization of the mentioned compound represents the opportunity to explore the utilization of low-grade residual heat that sometimes is not used in subsequent applications. In this sense, the modelling of the binary vapor–liquid equilibria of the mixture CO2/Acetone has been performed based on a thermodynamic model using the Peng-Robinson equation regarding the conditions of pressure, temperature, and concentration of the fluids for operational industry applications. The modelling of the compression/resorption heat pump cycle is based on the mass and energy balance for each component with Engineering Equation Solver software (EES). In this way, the adjustment of equilibria for the mixture determinates the maximum average square deviation of 4.28 % and 8.70 % for a temperature range between 291 and 303 K and 333 to 393 K. The concentration of CO2 from 20 % to 50 % showed that the increasing molar fraction delivers a more efficient cycle, even reaching a coefficient of performance of 3 for a difference of 0.2 between the global concentration of CO2 and the poor solution, and a 20 °C temperature difference between source and sink. Even more, the COP obtained in the simulation was not affected by variations of steam mass flow rate and it was proven that the mathematical model proposed has a correlation with the literature.

Synthesis of α-Fe2O3 nano-rod/sheet: Volumetric and electrical conductivity properties of their nanofluids

Physico-chemical properties of synthesized α-Fe2O3 nano-rods/sheets using the co-precipitation method and 3-sulfanylpropane-1,2-diol as a capper and shape-directing agent were studied. The synthesized nanomaterials were characterized using UV–visible, powder X-ray diffraction (pXRD), High-resolution transmission electron microscopy (HR-TEM), Field emission scanning electron microscopy (FE-SEM), Fourier transform infrared spectroscopy (FTIR), and Thermogravimetry analysis (TGA) techniques. Characterized nanomaterials revealed the formation of the pure rhombohedral crystal structure of nano-rod having a diameter of 33 nm and length of 76 nm, apart from the formation of nano-sheets with a diameter of 86 nm. An average absorption maximum (λmax) of 396.5 nm was observed. The properties of the prepared α-Fe2O3 nanofluids were investigated from 298.15 K to 338.15 K temperatures. The density of nanofluids was observed to increase with an increase in mole fraction of α-Fe2O3 nano-rods/sheets but decreases with an increase in temperature. Excess molar volume data shows positive and negative values revealing van der Waals interactions, packing effect, and hydrogen bonding forces. This volumetric property has revealed a significant impact of intermolecular interactions present in nanofluids on various thermodynamic properties. Results revealed an increment in electrical conductivity with an increase in volume fraction. A maximum enhancement of 2195 % was observed for 0.000728 mol fraction at 338.15 K in ethylene glycol/double-distilled water nanofluid. These electromagnetic nanofluids have great scope for application as smart electrolytes in electronic devices.

Determination of Solubility and Thermodynamic Analysis of Solubility Behavior of 2,5-Furandicarboxylic Acid in Water and Ether Binary Solvent System

2,5-Furandicarboxylic acid (FDCA) is a promising biomass-derived monomer, and the study of FDCA dissolution behavior is of paramount importance to its purification. In this study, the solubility of FDCA in four different ethers (1,4-dioxane, tetrahydrofuran, 1,2-dimethoxyethane, and diethylene glycol dimethyl ether), as well as four binary solvent systems containing these above ethers with water, was measured by a gravimetric method. The solubility of FDCA could be improved in binary solvent systems as compared to corresponding pure solvents. More interestingly, the solubility of FDCA increased first and then gradually dropped back with the increasing mole fraction of water in binary solvent systems. The KAT-LSER model was used to explore the influence of solvent effect on solubility. The Hansen solubility parameter was utilized to probe the solute–solvent molecular interactions. Apelblat equation, van’t Hoff equation, λh equation, Wilson model, and nonrandom two-liquid model were applied to analyze the experimental solubility data in pure ether solvents and binary solvent systems. Furthermore, the dissolution thermodynamic characteristics of FDCA in particular binary solvent systems were analyzed by the van’t Hoff equation, which revealed that the dissolving process of FDCA is endothermic, entropy-driven, and spontaneous in the other three examined solvent systems, with the exception of the 1,4-dioxane/water mixture.

Trend and Multi‐Frequency Analysis Through Empirical Mode Decomposition: An Application to a 20‐Year Record of Atmospheric Carbonyl Sulfide Measurements

AbstractThe Empirical Mode Decomposition (EMD) is a fully non‐parametric analysis of frequency modes and trends in a given series that is based on the data alone. We have devised an improved strategy based on a series of best practices to use EMD successfully in the analysis of the monthly time series of carbonyl sulfide (OCS) atmospheric mole fractions measured at NOAA network stations (2000–2020). Long‐term trends and intra‐ and inter‐annual variability has been assessed. After a phase of generally increasing mole fractions up to 2015, with a temporary decline around 2009, we found that the OCS atmospheric mole fraction subsequently decreased at all stations, reflecting a recent imbalance in its total sources and losses. Our analysis has revealed a characteristic time scale for variation of 8–10 years. The variance associated with this long‐term behavior ranges from 15% to 40% of the total strength of the signal, depending on location. Apart from this complex long‐term behavior, the OCS time series show a strong annual cycle, which primarily results from the well‐known OCS uptake by vegetation. In addition, we have also found one more frequency of minor variance intensity in the measured mole fraction time‐history, which corresponds to periods in the range of 2–3 years. This inter‐annual variability of OCS may be linked to the Quasi‐Biennial Oscillation.

Impacts of core parameters on the capability of Cf-252 production in an MSR

Californium-252 (Cf-252) is a powerful neutron source for various applications including neutron radiography, reactor startup, cancer therapy, etc. However, the demand for Cf-252 exceeds its supply at present, and therefore becomes one of the most important restrictions on its applications. Molten salt reactor (MSR) has unique advantages of no fuel rod fabrication, online reprocessing and very deep burnup, which permits flexible core design, substantial target loading into the fuel salt and sufficient depletion time, and is therefore expected to provide an effective solution for Cf-252 production. In this study, four different targets (DU, Pu, Am and Cm) and various mole fractions of the Am target in an MSR are proposed to evaluate the Cf-252 conversion capability. The results indicate that an alluring quality factor of Cf-252 with its mass fraction of over 80% in Cf can be obtained for the selected targets. The highest inventory and conversion rate for Cf-252 with the Cm target can achieve about 700 g and 0.14%, respectively, during the first 10-year operation. The Cf-252 production can be further improved with the increased mole fraction of target but with a deteriorated conversion rate of Cf-252 due to the hardened neutron spectrum and the weakened neutron captures of most isotopes in the reaction chains of Cf-252 formation.

Density and Dynamic Viscosity of Perfluorodecalin-Added n-Hexane Mixtures: Deciphering the Role of Fluorous Liquids

Fluorous solvents are deputed as prominent solvent systems owing to their salient features, unique physical properties, and ecological importance. In this study, the temperature- and composition-dependence of physical properties, density (ρ/g·cm−3), and dynamic viscosity (η/mPa·s), of neat perfluorodecalin (PFD) and PFD-added n-hexane mixtures with select compositions are reported. Density follows a linear decrease with temperature and a quadratic increase with the mole fraction of PFD. The sensitivity or dependence of density on temperature increases with an increase in PFD mole fraction. The temperature-dependence of the dynamic viscosity of the investigated mixtures follows the Arrhenius-type expression from which the resultant activation energy of the viscous flow (Ea,η) is determined. Interestingly, the composition-dependence of dynamic viscosity shows exponential growth with an increase in PFD mole fraction. Excess molar volumes (VE) and deviation in the logarithmic viscosities ∆(ln η) of the mixtures are calculated to highlight the presence of strong repulsive interactions between the two mixture components.

An Improved Correlation of Compressibility Factor Prediction of Variable CO2-Content Condensate Gases

The injection of carbon dioxide (CO2) into gas reservoirs has become an important way to enhance gas recovery and reduce CO2 emissions. Large discrepancies are observed when predicting natural gas compressibility factors with high CO2 content by several well-known empirical correlations. An explicit correlation is proposed to improve the prediction accuracy in the estimation of compressibility factors on condensate gases with variable CO2 contents. The analysis of the results is carried out on the basis of 202 experimental data from 9 various mixtures of natural gases. The results show that relative deviations of compressibility factors predicted by conventional empirical correlations increase with the increase in CO2 mole fraction with an average error of 8%. The average error of the new method is less than 4%. The effect of compressibility factors on the estimations of dynamic reserves is studied and the compressibility factor causes a 3% reduction in dynamic reserves estimation. The proposed correlation has fewer uncertainties and more accurate results than other correlations that involve the iterative process in calculating compressibility factors of natural gases with variable CO2 contents.

Interfacial properties of the hexane + carbon dioxide + water system in the presence of hydrophilic silica.

Molecular dynamics simulations were conducted to study the interfacial behavior of the CO2 + H2O and hexane + CO2 + H2O systems in the presence of hydrophilic silica at geological conditions. Simulation results for the CO2 + H2O and hexane + CO2 + H2O systems are in reasonable agreement with the theoretical predictions based on the density functional theory. In general, the interfacial tension (IFT) of the CO2 + H2O system exponentially (linearly) decreased with increasing pressure (temperature). The IFTs of the hexane + CO2 + H2O (two-phase) system decreased with the increasing mole fraction of CO2 in the hexane/CO2-rich phase xCO2 . Here, the negative surface excesses of hexane lead to a general increase in the IFTs with increasing pressure. The effect of pressure on these IFTs decreased with increasing xCO2 due to the positive surface excesses of carbon dioxide. The simulated water contact angles of the CO2 + H2O + silica system fall in the range from 43.8° to 76.0°, which is in reasonable agreement with the experimental results. These contact angles increased with pressure and decreased with temperature. Here, the adhesion tensions are influenced by the variations in fluid-fluid IFT and contact angle. The simulated water contact angles of the hexane + H2O + silica system fall in the range from 58.0° to 77.0° and are not much affected by the addition of CO2. These contact angles increased with pressure, and the pressure effect was less pronounced at lower temperatures. Here, the adhesion tensions are mostly influenced by variations in the fluid-fluid IFTs. In all studied cases, CO2 molecules could penetrate into the interfacial region between the water droplet and the silica surface.

Study of molecular interactions of monoethanolamine with some higher alcohols at 298.15 K

Abstract Experimental measurements of the viscosity, density, and ultrasonic parameters of monoethanolamine (MEA) with 1-butanol, 1-pentanol, and 1-hexanol were carried out at 298.15 K. The excess molar volume (V E), viscosity change (Δη), and isentropic compressibility (ΔK s) are calculated using the viscosity, density, and ultrasonic velocity data. A polynomial equation of the Redlich-Kister type was used to fit these values. With increasing mole fraction, the viscosity, the density and the ultrasonic velocity increase. As the concentration of MEA rises, the excess molar volume falls. All V E values for MEA and 1-hexanol are positive, meaning that V E increases. At all concentrations, isentropic compressibility and viscosity change exhibit negative values.

Impact of CH4 addition on the electron properties and electric field dynamics in a Ar nanosecond-pulsed dielectric barrier discharge

Non-equilibrium plasmas derive their low temperature reactivity from producing and driving energetic electrons and active species under large electric fields. Therefore, the impact of reactants on the plasma properties including electron number density, electric field, and electron temperature is critical for applications such as plasma methane (CH reforming. Due to experimental complexity, electron properties and the electric field are rarely measured together in the same discharge. In this work, we combine time-resolved Thomson scattering and electric field induced second harmonic generation to probe electron temperature, electron density, and electric field strength in a 60 Torr CH4/Ar nanosecond-pulsed dielectric barrier discharge while varying the CH4 mole fraction from 0% to 8%. These measurements are compared to a 1D numerical model to benchmark its predictions and identify areas of uncertainty. Nonlinear coupling between CH4 addition, electron temperature, electron density, and the electric field was directly observed. Contrary to previous measurements in He, the electron temperature increased with CH4 mole fraction. This rise in electron temperature is identified as electron heating by residual electric fields that increased with larger CH4 mole fraction. Moreover, the electron number density has been found to decrease rapidly with the increase of methane mole fraction. Comparison of these measurements with the model yielded better agreement at higher CH4 mole fractions and with the usage of ab initio calculated Ar electron-impact cross-sections from the B-spline R-matrix database. Furthermore, the calculated plasma properties are shown to be sensitive to the residual surface charge implanted on the quartz dielectric surfaces. Without considering surface charge in the simulations, the calculated electric field profiles agreed well with the measurements, but the electron properties were underpredicted by more than a factor of three. Therefore, measurements of either the electric field or electron properties measurements alone are insufficient to fully validate modeling predictions.

Efficient hydrogen recovery and purification from industrial waste hydrogen to high-purity hydrogen based on metal hydride powder

Flow-through reaction model of metal hydride powder for hydrogen recovery and purification from industrial by-product hydrogen to high-purity hydrogen is proposed. The hydriding mechanism of hydrogen storage alloy in the flow-through reactor is expounded. The results show that the evolution of bed temperature field leads to a unique increase in outlet hydrogen mole fraction compared to the case of pure hydrogen. In addition, the effects of operating parameters and reactor geometrical parameters are systematically investigated for performance optimization. The indexes of hydrogen absorption efficiency and effective metal hydride utilization ratio are introduced to evaluate the hydrogen recovery and purification performance of reactor. The optimum hydrogen absorption efficiency of 65 % with the effective metal hydride utilization ratio of about 0.8 could be achieved at the cooling water temperature of 373 K. This work contributes to the design and development of advanced hydrogen separation and purification technology.

Water Miscibility, Surface Tension, Density, and Dynamic Viscosity of Hydrophobic Deep Eutectic Solvents Composed of Capric Acid, Menthol, and Thymol

Deep eutectic solvents (DESs) are rapidly emerging as environmentally benign and viable alternatives not only to common organic solvents but to relatively toxic ionic liquids as well. By judicious selection of the constituents and subsequent variation in their composition, the key physicochemical properties of the DESs can be easily tailored for a specific application. Impact of variation in constituents as well as their composition on important physical properties of natural DESs (NADESs) prepared using a common fatty acid n-decanoic acid (DA) and two naturally occurring monoterpenoids, thymol (Thy) and L(−)-menthol (Men), is assessed. Specifically, water miscibility, surface tension, density, and dynamic viscosity of 17 different DESs of three combinations of constituents, Men:DA, Thy:DA, and Thy:Men in four, four, and nine compositions, respectively, are measured. The water intake by the DESs under ambient conditions varies from 0.6 to 2.7 mol·kg–1 offering a means to gauge their hydrophobicity. Water miscibility is relatively lower for Men:DA DESs and higher for Thy:DA DESs. Surface tension values are within 28.37 mN·m–1 to 31.14 mN·m–1 under ambient conditions; they are higher for the DESs with the Thy constituent and vary systematically with DES composition. The densities of all the DESs are lower than that of water and decrease linearly with increasing temperature. While density does not vary with composition for Men:DA, it is found to increase linearly with an increase in Thy mole fraction for Thy:DA and Thy:Men DESs. The dynamic viscosity of the DESs are relatively lower as compared to the common tetralkylammonium salt- and metal salt-based DESs, and exhibit strong constituent and composition dependence. Rather than the Arrhenius-type expression, the temperature-dependence of the dynamic viscosity better conforms to the Vogel–Fulcher–Tammann (VFT) model with activation energy of the viscous flow varying systematically with the constituent and composition. Reported physical properties and their dependence on constituents/composition of the NADESs will enhance their utility and help establish them as novel alternate media in science and technology.