Cavities in molecular liquids and the theory of hydrophobic solubilities

Thermal configurational data on neat liquids are used to obtain the work of formation of hard spherical cavities of atomic size in six molecular solvents: n-hexane, n-dodecane, n-undecyl alcohol, chloroform, carbon tetrachloride, and water. These results are used to test a recent suggestion that the differences between nonaqueous solvents and liquid water in solvation of inert gases are not principally due to the hydrogen-bonded structure of liquid water but rather to the comparatively small size of the water molecule. The frequencies of occurrence of cavities in liquid water can be meaningfully distinguished from those in the organic solvents. Liquid water has a larger fractional free volume, but that free volume is distributed in smaller packets. With respect to cavity work, water is compared to a solvent of the same molecular density and composed of hard spheres of the same size as the water molecule. That comparison indicates that the hard-sphere liquid finds more ways to configure its free volume in order to accommodate an atomic solute of substantial size and thus, would be more favorable solvent for inert gases. The scaled particle model of inert gas solubility in liquid water predicts cavity works 20% below the numerical data for TIP4P water at 300 K and 1.0 g/cm3 for cavity radii near 2.0 angstroms. It is argued that the sign of this difference is just the sign that ought to be expected and that the magnitude of this difference measures structural differences between water and the directly comparable hard-sphere liquid. In conjunction with previous data, these results indicate that atomic sized cavities should be considered submacroscopic.     

Modification of the Scaled Particle Theory for Solubility of Non-Polar Gases in Water

In this work based on the modified scaled particle theory (SPT), the solubility of non-polar gases (He, Ar, N₂, H₂, O₂, CO₂ and CH₄) in water has been studied over a wide range of temperatures. Calculations of Henry’s law constant by the SPT are related to the inherent physical properties and parameters of solvent and solute, all of which are considered temperature dependent. The temperature dependence of molar volume and hard sphere diameter of solvent and polarizability of solute have the most significant effects on the solubilities of gases in water. The average relative deviation is less than 3 %. Also, the effect of different mixing rules in the application of SPT to prediction of gas solubility has been studied.     

The solubility of ethane, propane, and carbon dioxide in aqueous solutions of sodium cumene sulfonate

Measurements have been made to determine the solubilities of ethane, C2H6, propane, C3H8, and carbon dioxide, CO2, in aqueous solutions of sodium cumene sulfonate (NaCS) at 25 degrees C. The solubilities measured for each gas satisfy Henry's law at all concentrations of NaCS. The solubilities of C2H6 and C3H8 exhibit quite similar behavior with respect to added NaCS. The solubilities of these two gases are very low in pure water and are found to be nearly independent of NaCS concentration over a concentration range of 0-0.4 mol NaCS/kg H2O. At intermediate concentrations of NaCS, the solubilities of C2H6 and C3H8 exhibit a gradual increase with added NaCS concentrations ranging from 0.4 to 2.0 mol NaCS/kg H2O. At NaCS concentrations greater than 2.0 mol NaCS/kg H2O, the solubilities of these two gases increase with added NaCS in an approximately linear manner, with the solubility of C3H8 increasing more rapidly than that for C2H6 (by a factor of approximately 2.5). CO2 is much more soluble in pure water than the hydrocarbon gases and exhibits markedly different behavior with respect to added NaCS. The solubility of CO2 decreases with added NaCS over a concentration range of 0-0.9 mol NaCS/kg H2O, passes through a minimum at a concentration of approximately 1.0 mol NaCS/kg H2O, and then increases with added NaCS at higher NaCS concentrations in a manner similar to that observed with C2H6 and C3H8. The trends in solubility observed for these three gases dissolved in aqueous solutions of NaCS resemble those found previously with aqueous solutions of ordinary surfactants. The solubility data measured for these three gases can be interpreted surprisingly well in terms of the mass-action model for micellization, in which salting-out effects due to monomer salt ions suppress gas solubility at low NaCS concentrations and gas solubilization by small micelles of NaCS acts to enhance gas solubility at the higher NaCS concentrations.     

Structural contribution to the effect of hydrophobic hydration of noble gases

Within the concepts of structurally-thermodynamic characteristics of solvation and pseudo-chemical potential, the sample collection of the most authentic experimental data on solubility of gaseous He, Ne, Ar, Kr, Xe, and Rn in H₂O and D₂O is analysed at ≈0.1 MPa and T = 278–318 K. The conclusion is drawn that at deuteration of water molecules and also with increasing molar mass of noble gas, the relative contribution of effect of its hydrophobic hydration decreases. However in case of pass from lightweight noble gases (He, Ne, Ar) to heavy ones (Kr, Xe, Rn), structural transformations in their aqueous solutions become more expressed as a whole due to strengthening interaction between dissolved substance and solvent.     

KAlF_4熔盐的结构特征

根据已取得的实验数据和间接论据,通过熔度对比、相关系分析和ＫＡｌＦ４熔态电化学分析结果,对ＫＡｌＦ４的熔态结构特征进行了探讨。结果表明,ＫＡｌＦ４在液相和气相中均比较稳定,整个熔融体的结构重要表现为分子态的ＫＡｌＦ４和分子基因。     

Culation of partial molar volume and its components for molecular dynamics models of dilute solutions

This paper is a review of our recent computational studies of volumetric characteristics using computer models of dilute solutions. Partial molar volume (PMV) and its components are calculated for simple and complex molecules in water (methane, noble gases, surfactants, polypeptides). Advantages and disadvantages of various computational methods are discussed. It is proposed to use the Voronoi-Delaunay technique to determine the reasonable boundary between a solute molecule and solvent molecules and to identify the PMV components related to the molecule, the boundary layer, and the solvent. It is noted that the observed increase in PMV with temperature for large molecules is due to an increase in the volume of voids in the boundary layer, i.e., due to the “thermal volume.” In this case, the solvent gives a negative contribution to the PMV. In contrast, for simple molecules (methane), the contribution from the solvent is positive and is the main factor in the increase in the PMV, which is associated with a specific change in water structure around a spherical hydrophobic particle outside the boundary layer. For surfactant molecules, the contribution from the solvent changes sign (from negative to positive) with increasing temperature.     

A new approach in modelling phase equilibria and gas solubility in electrolyte solutions and its applications to gas hydrates

This paper presents a new predictive model for phase equilibria and gas solubility calculations in the presence of electrolyte solutions. It treats salts as pseudo-components in an equation of state (EoS) by defining the critical properties and acentric factor for each salt. The water–salt, gas–salt and salt–salt binary interaction parameters (BIP) have been determined by using available experimental data on freezing point depression and boiling point elevation as well as gas solubility and salt solubility data in saline solutions.The methodology has been applied in modelling sodium chloride, potassium chloride and their mixtures, as well as solubility of methane and carbon dioxide in aqueous single and mixed electrolyte solutions.The developed model is capable of accurately predicting the phase behaviour, gas hydrate stability zone and potential salt precipitation in single and mixed electrolyte solutions. The model predictions are compared with available independent experimental data, including hydrate inhibition characteristics of single and mixed electrolyte solutions, and good agreement is demonstrated.     

The solubility of the noble gases He,Ne, Ar,Kr, and Xe in water up to the critical point

The solubility of the noble gases Ar, He, Ne, Kr, and Xe in pure water was measured from 298 to 561°K. These data in turn were extrapolated to the critical point of water, thus providing a complete set of Henry's law constants from 274 to 647°K when combined with the existing literature data. Equations describing the behavior of the Henry's law constants over this temperature range are also given. The data do not confirm extrapolations of empirical correlations based on low-temperature solubility data.     

Thermodynamic Analysis and Experimental Investigation into Nonflame Combustion Technology（NFCT） with Thermal Cyclic Carrier

The utilization of fossil fuels causes serious negative impacts on the environment and human life. To mitigate greenhouse gases and other pollutants, a novel combustion process-the nonflame combustion technology with a thermal cyclic carrier of molten salt is introduced. In this technology, a whole combustion is divided into two steps, i.e. , the section of producing oxide and the section of combustion. In the first step, oxygen is separated from air, and pure N2 is simultaneously formed which is easily recovered. In the other step, the fuels react with lattice oxygen in the oxides formed in the first step, and at the same time, thermal energy, CO2 and H2O vapor are produced. It is noted that the CO2 is easily separated from water vapor and ultimately captured. Theoretically, there are no environmental-unfriendly gases such as CO2, NOx and SO2 discharged in the whole combustion process. Some metal oxides scattered into molten salts play the roles of oxygen carriers in the combustion system, and they can constantly charge and discharge oxygen element from air to fuels during the combustion process. A nonflame combustion system with Li2CO3 K2CO3 Na2SO4 as the molten salt system, CH4 as the fuel and CuO as the catalyst was experimentally investigated. The experimental resuits show that the combustion process proceeded as it was theoretically analyzed, and CO2 with a high volume fraction of 77.0M--95.0M and N2 with a high volume fraction of 91.9%-99.3% were obtained. The high concentration of CO2 is favorable for capturing and storing subsequently. Therefore, the potential of reducing CO2 emissions of this nonflame combustion technology is huge.     

An investigation of the high gas permeability of poly (1-Trimethylsilyl-1-Propyne)

The permeability of poly (1–trimethylsilyl–1−propyne), PMSP, to light gases is higher than that of any other nonporous synthetic polymer at ambient temperatures. PMSP is in the glassy polymer state at these temperatures. Permeability, diffusion, and solubility coefficients were determined for N₂, O₂, CH₄, and CO₂ in PMSP, and are compared with values reported for these gases in poly (dimethyl siloxane). The higher gas permeability of PMSP results primarily from a substantial gas solubility, which appears to be due, in turn, to a large “excess” free volume in the unrelaxed (Langmuir) domains of this glassy polymer. The structure of PMSP, which consists of relatively rigid backbone chains separated by bulky trimethylsilyl side groups, probably is responsible for this large free volume.     

On the dissolution of vapors and gases

The captive bubble technique in combination with axisymmetric drop shape analysis (ADSA-CB) and with micro gas chromatography is used to study the dynamics of dissolution of different gases and vapors in water in situ. The technique yields the changes in the interfacial tension and bubble volume and surface. As examples, the dissolution of methanol and hexane vapors, inhaled anesthetic vapors, and gases, that is, diethyl ether, chloroform, isoflurane, enflurane, sevoflurane, desflurane, N2O, and xenon, and as nonimmobilizers perfluoropentane and 1,1,2-trichloro-1,2,2-trifluoro-ethane (R113) were investigated. The examination of interfacial tension-time and bubble volume-time functions permits us to distinguish between water-soluble and -insoluble substances, gases, and vapors. Vapors and gases generally differ in terms of the strength of their intermolecular interactions. The main difference between dissolution processes of gases and vapors is that, during the entire process of gas dissolution, no surface tension change occurs. In contrast, during vapor dissolution the surface tension drops immediately and decreases continuously until it reaches the equilibrium surface tension of water at the end of dissolution. The results of this study show that it is possible to discriminate anesthetic vapors from anesthetic gases and nonimmobilizers by comparing their dissolution dynamics. The nonimmobilizers have extremely low or no solubility in water and change the surface tension only negligibly. By use of newly defined molecular dissolution/diffusion coefficients, a simple model for the determination of partition coefficients is developed.     

KAlF4熔盐的结构特征

根据已取得的实验数据和间接论据,通过熔度对比、相关系分析和KAIF4熔态电化学分析结果,对KAIF4的熔态结构特征进行了探讨。结果表明,KAIF4在液相和气相中均比较稳定,整个熔融体的结构重要表现为分子态的KAIF4和分子基团。     

To the thermodynamics of saturation of liquids with inert gases

In continuation of the earlier advanced point of view concerning the non-true character of solutions of inert gases in liquids, a thermodynamic analysis of the transfer of particles of these gases to the liquid at constant temperature and sum of volumes of coexisting phases was performed. The analysis is based on the linearity of the concentration dependences of the enthalpy and entropy of noble gases and nitrogen and approximation of the real process by the hypothetical one including two stages: transfer of some number of moles of the gas from the intrinsic phase to the physical microvolume numerically equal to the volume of the intermolecular space of the liquid accessible for gas particles and the distribution of these particles over particular cavities of the latter. The contact of inert gases with liquids results in the formation of a thermodynamically unstable two-phase binary system, whose liquid phase can be considered as internally strained dispersion of gas clusters.     

稀有气体的前世今生

In this paper, many elements are personified and a kingdom of elements is constructed. Noble gas elements are compared to hermits in the kingdom. Through the dialogue between noble gases, the process of discovering noble gases and noble gaseous compounds is described. The article tells the discovery and some properties of noble gases in a vivid language.     

In-situ synthesis of nanoparticles via supersolubilizing micelle self-assembly

In-situ synthesis of nano-particles using the self-assembly of molten salt and super soluble micellae was proposed based on a phenomenon of super solubilization of molten salt in reverse micellae and its self-assembly when the concentration reached up to 95%(w/w).The mechanism of the self-assembly indicates that the self-assembly of molten salt occurs in a reverse micelle where a homogenous phase is established between 5%(w/w)of a surfactant with a VB value of less than 1 and a hydrocarbon spe- cies.This synthesis has some unique features,such as being free of water,highly effective deposition and narrow distribution of particle size.