Critical Mole Fraction Research Articles

Numerical Study on the Effect of Pressure on Biodiesel/N-Pentanol Blended Droplet Homogeneous Micro-Explosion

A three-dimensional droplet evaporation model using VOF is developed to study the influence of pressure on biodiesel/n-pentanol blended droplet homogeneous nucleation and evaporation characteristics. Numnerical results reveal that the homogeneous nucleation ratereduces while the homogeneous superheating limit temperature increases with increase of the pressure and the critical n-pentanol mole fraction. The minimum n-pentanol mole fraction of 0.65 is required for homogeneous nucleation when the ambient pressure is 12 atm. Higher pressure also weakens surface evaporation of droplets, which reduces the increase rate of vapor concentration around droplets, and increases the peak vapor value. The homogeneous micro-explosion can only occur when the ambient pressure is greater than 3 atm. As pressure increases, the temperature and temperature rise rate of droplets increases, and the homogeneous micro-explosion delay reduces.

Influence of competitive adsorption, diffusion, and dispersion of CH4 and CO2 gases during the CO2-ECBM process

The displacement mechanisms of adsorbed CH4 by injected CO2 at high pressures in CO2-enhanced coalbed methane (CO2-ECBM) processes involve competitive adsorption, diffusion, and dispersion. Inherent coal heterogeneity and the complexity of the CO2-CH4 displacement model make CO2-ECBM modelling and optimal process design challenging. The pure gas isotherms and Langmuir adsorptions constants for CO2 and CH4 were determined using the manometric method. Notably, CO2 shows higher adsorption capacity than methane, and Langmuir volume (VL) for CO2 is 2 to 2.3 times that of methane. High pressure adsorption isotherms and experimentally determined diffusion coefficients set the sorption kinetics. The diffusion coefficient of CH4 for all four samples was in the range between 1.35×10-12 and 7.42×10-12 m2/s, while for CO2, it varied from 10.9×10-12 to 15.48×10-12 m2/s. The new concept of caucus time was introduced in the sorption kinetics of CO2 and CH4. Each sample has distinct caucus time and was positively correlated with Langmuir volumes of CO2 and CH4 with R2 > 0.9. The critical desorption pressure above which CH4 exhibits retrograde adsorption behaviour is evaluated from co-adsorption isotherms adopting Ideal Adsorption Solution Theory (IAST). The critical desorption pressure for the four samples were 1220, 460, 575 and 740 psi respectively. IAST also predicts a critical mole fraction (∼30 %) in the gas phase above which CO2 becomes the dominant adsorbed phase on coal surfaces. The results of Advective-Dispersion modelling at a larger scale illustrate the value of the Dispersion coefficient in forecasting and screening. Since the time available for diffusion versus dispersion depends upon flowrate, high values of dispersion coefficient can negatively influence favourable competitive adsorption expectations through higher operational cost in CO2 separation. This work suggests the existence of both an optimal operational pressure and flowrate to maximize the potential of CO2-ECBM technology demonstrated in competitive adsorption modelling.

Incipient sooting tendency of oxygenated fuels doped in ethylene counterflow diffusion flames

The incipient sooting tendencies of oxygenated fuels in counterflow diffusion flames were systematically assessed by doping selected oxygenate fuels into the baseline fuel of ethylene with various mixing ratios. Laser light scattering and planar laser-induced fluorescence (PLIF) techniques were adopted. The critical oxygen mole fractions at different mixing ratios were identified with the use of laser scattering. It is found that the critical oxygen mole fraction varies with oxygenates, suggesting that the effect of mixing ethylene with oxygenates is highly sensitive to the types of oxygenate. While the doping of acetone moderately promoted the incipient sooting tendency, the doping of methanol, acetic acid, formic acid, and diethyl carbonate suppressed the formation of incipient soot. On the other hand, the doping of ethanol, dimethyl carbonate, diethyl ether, and dimethoxymethane had weak influences on the incipient sooting tendency. The production of polycyclic aromatic hydrocarbons (PAHs) of different sizes were measured by PLIF. The results show there was a strong correlation between the incipient sooting tendency and the production of large PAHs. One important finding is that, at their sooting limits, the total oxygen-to-carbon ratio of a stoichiometric fuel/oxygen mixture is linearly correlated with the mixing ratio of the ethylene-oxygenate mixture. This slope of these two quantities can be defined as an incipient sooting index (ISI) of oxygenated fuels for ranking their tendency of incipient sooting formation. Having the slopes correlated well with the oxygenates’ hydrogen/oxygen ratio, a reasonably accurate prediction of critical oxygen mole fractions from the molecule information of oxygenated fuels can be achieved.

Flame edge dynamics in counterflow nonpremixed flames of CH4/He versus air at low strain rates: An experimental and numerical study

The characteristics of the flame structure, stabilization, and extinction of counterflow nonpremixed flames of CH4/He versus air at low strain rates are investigated by performing a series of experiments and two-dimensional (2-D) numerical simulations. By adopting an experimental methodology using He curtain flow, we can locate the flames near the center of the counterflow burner and measure the critical He mole fraction in the fuel stream, XHe,cr, for flame extinction at very-low strain rates. XHe,cr obtained from 2-D numerical simulations in normal and zero gravity show a good agreement with those from the experiments, which substantiates that the experimental methodology can effectively reduce the buoyancy effect at low strain rates. It is found from various steady and unsteady 2-D numerical simulations that the dynamics of flame edge plays a critical role in determining the flame stabilization and extinction, and the edge flame is stabilized at a location where negative edge flame propagation speed, Se, balances positive local flow velocity, Ue. The transport budget analysis reveals that despite the negative Se by the diffusive loss of heat and radicals, the edge flame can survive by the help of the convective gain of heat and radicals from the trailing diffusion flame. It is also found that the counterflow flame can survive the increase of He mole fraction in the fuel stream, XHe, by shrinking its flame length since the local chemical reaction at the flame edge is enhanced with decreasing the flame length. However, as XHe exceeds XHe,cr, a slight inward movement of the edge flame induces a large magnitude of negative Se compared to positive Ue such that the counterflow flame is totally extinguished by the shrinkage of the outer edge flame toward the flame center.

Effects of CO addition on laminar flame characteristics and chemical reactions of H2 and CH4 in oxy-fuel (O2/CO2) atmosphere

An experimental study is conducted to investigate the effect of CO addition on the laminar flame characteristics of H2 and CH4 flames in a constant-volume combustion system. In addition, one-dimensional laminar premixed flame propagation processes at the same conditions are simulated with the update mechanisms. Results show that all mechanisms could well predict the laminar flame speeds of CH4/CO/O2/CO2 mixtures, when ZCO is large. For mixtures with lower CO, the experimental laminar flame speeds are always smaller than the calculated ones with Han mechanism. For mixtures with larger or smaller ZCO2, GRI 3.0, San diego and USC 2.0 mechanisms all overvalue or undervalue the laminar flame speeds. When CO ratio in the CH4/CO blended fuels increases, laminar flame speed firstly increases and then decreases for the CH4/CO/O2/CO2 mixtures. For H2/CO/O2/CO2 mixtures, San diego, Davis and Li mechanisms all undervalue the laminar flame speeds of H2/CO/CO2/CO2 mixtures. Existing models could not well predict the nonlinear trend of the laminar flame speeds, due to complex chemical effects of CO on CH4/CO or H2/CO flames. Then, the detailed thermal, kinetic and diffusive effects of CO addition on the laminar flame speeds are discussed. Kinetic sensitivity coefficient is far larger than thermal and diffusive ones and this indicates CO addition influences laminar flame speeds mainly by the kinetic effect. Based on this, radical pool and sensitivity analysis are conducted for CH4/CO/O2/CO2 and H2/CO/O2/CO2 mixtures. For CH4/CO/O2/CO2 mixtures, elementary reaction R38H + O2 ↔ O + OH and R99 OH + CO ↔ H + CO2 are the most important branching reactions with positive sensitivity coefficients when CO ratio is relative low. As CO content increases in the CH4/CO blended fuel, the oxidation of CO plays a more and more important role. When CO ratio is larger than 0.9, the importance of R99 OH + CO ↔ H + CO2 is far larger than that of R38H + O2 ↔ O + OH. The oxidation of CO dominates the combustion process of CH4/CO/O2/CO2 mixtures. For H2/CO/O2/CO2 mixtures, the most important elementary reaction with positive and negative sensitivity coefficients are R29 CO + OH ↔ CO2 + H and R13H + O2(+M) ↔ HO2(+M) respectively. The sensitivity coefficient of R29 CO + OH ↔ CO2 + H is increasing and then decreasing with the addition of CO in the mixture. Chemical kinetic analysis shows that the chemical effect of CO on the laminar flame propagation of CH4/CO/O2/CO2 and H2/CO/O2/CO2 mixtures could be divided into two stages and the critical CO mole fraction is 0.9.

Gramicidin Lateral Distribution in Phospholipid Membranes: Fluorescence Phasor Plots and Statistical Mechanical Model.

When using small mole fraction increments to study gramicidins in phospholipid membranes, we found that the phasor dots of intrinsic fluorescence of gramicidin D and gramicidin A in dimyristoyl-sn-glycero-3-phosphocholine (DMPC) unilamellar and multilamellar vesicles exhibit a biphasic change with peptide content at 0.143 gramicidin mole fraction. To understand this phenomenon, we developed a statistical mechanical model of gramicidin/DMPC mixtures. Our model assumes a sludge-like mixture of fluid phase and aggregates of rigid clusters. In the fluid phase, gramicidin monomers are randomly distributed. A rigid cluster is formed by a gramicidin dimer and DMPC molecules that are condensed to the dimer, following particular stoichiometries (critical gramicidin mole fractions, Xcr including 0.143). Rigid clusters form aggregates in which gramicidin dimers are regularly distributed, in some cases, even to superlattices. At Xcr, the size of cluster aggregates and regular distributions reach a local maximum. Before a similar model was developed for cholesterol/DMPC mixtures (Sugar and Chong (2012) J. Am. Chem. Soc. 134, 1164–1171) and here the similarities and differences are discussed between these two models.

Cluster formation of network-modifier cations in cesium silicate glasses

Natural abundance 29Si two-dimensional magic-angle flipping (2D MAF) NMR spectra were measured in a series of ten cesium silicate glass compositions xCs2O·(1 − x)SiO2, where x is 0.067, 0.113, 0.175, 0.179, 0.218, 0.234, 0.263, 0.298, 0.31, and 0.36. The Q3 shielding anisotropy decreases with increasing Cs content—interpreted as an increase in the non-bridging oxygen (NBO) bond length from increasing Cs coordination (clustering) around the NBO. The 29Si 2D MAF spectra for four glass compositions x = 0.218, 0.234, 0.263, 0.298 exhibit a second co-existing and distinctly smaller shielding anisotropy corresponding to a significantly longer Si–NBO length arising from a higher degree of Cs clustering around the NBO. This second Q3 site appears at a Cs2O mole fraction close to the critical mole fraction of x = 0.24 associated with the percolation threshold of non-bridging oxygen in random close packing of oxygen, thus suggesting that the longer Si–NBO length is associated with an infinite size spanning cluster while the sites with larger anisotropies are associated with shorter Si–NBO lengths and belong to finite size clusters. The equilibrium constant of the Q3 disproportionation reaction was determined as k3 = 0.005, indicating a Qn anionic species distribution close to a binary model as expected for a low field strength modifier such as cesium. It is also found that evolution of the isotropic Q4 and line shapes with increasing Cs content are consistent with a random connectivity model between Qn of differing number of bridging oxygen, n.

New Parameterizations for Neutral and Ion‐Induced Sulfuric Acid‐Water Particle Formation in Nucleation and Kinetic Regimes

AbstractWe have developed new parameterizations of electrically neutral homogeneous and ion‐induced sulfuric acid‐water particle formation for large ranges of environmental conditions, based on an improved model that has been validated against a particle formation rate data set produced by Cosmics Leaving OUtdoor Droplets (CLOUD) experiments at European Organization for Nuclear Research (CERN). The model uses a thermodynamically consistent version of the Classical Nucleation Theory normalized using quantum chemical data. Unlike the earlier parameterizations for H2SO4‐H2O nucleation, the model is applicable to extreme dry conditions where the one‐component sulfuric acid limit is approached. Parameterizations are presented for the critical cluster sulfuric acid mole fraction, the critical cluster radius, the total number of molecules in the critical cluster, and the particle formation rate. If the critical cluster contains only one sulfuric acid molecule, a simple formula for kinetic particle formation can be used: this threshold has also been parameterized. The parameterization for electrically neutral particle formation is valid for the following ranges: temperatures 165–400 K, sulfuric acid concentrations 104–1013 cm−3, and relative humidities 0.001–100%. The ion‐induced particle formation parameterization is valid for temperatures 195–400 K, sulfuric acid concentrations 104–1016 cm−3, and relative humidities 10−5–100%. The new parameterizations are thus applicable for the full range of conditions in the Earth's atmosphere relevant for binary sulfuric acid‐water particle formation, including both tropospheric and stratospheric conditions. They are also suitable for describing particle formation in the atmosphere of Venus.

Ionic Liquid Influenced Synergistic Interaction between Amitriptyline Hydrochloride and Cetyltrimethylammonium Bromide

The mixed micellization behavior of amitriptyline hydrochloride (AMT) with cetyltrimethylammonium bromide (CTAB) has been studied at different mole fractions in the presence of imidazolium based ionic liquid 1-butyl-3-methyl imidazolium hydrochloride (Bmim·Cl), by using electrical conductivity at different temperatures from 298 to 318 K. A shift in the Tmax value (i.e., the temperature at which the cmc value is maximized) has been observed with the rise in CTAB mole fraction. Synergistic interaction is explained by the deviations in critical micelle concentration (cmc) from an ideal critical micelle concentration (cmc*) and micellar mole fraction (Xm) from ideal micellar mole fraction (Xideal) values. The calculated thermodynamic parameters (viz., the standard Gibbs energy change, ΔGm°, the standard enthalpy change, ΔHm°, and the standard entropy change, ΔSm°) suggest the dehydration of hydrophobic part of the drug at higher temperatures in the case of AMT as well as in CTAB-AMT binary systems in the pres...

Two-Dimensional Infrared Spectroscopy Reveals Cosolvent-Composition-Dependent Crossover in Intermolecular Hydrogen-Bond Dynamics.

Cosolvents have versatile composition-dependent applications in chemistry and biology. The simultaneous presence of hydrophobic and hydrophilic groups in dimethyl sulfoxide (DMSO), an industrially important amphiphilic cosolvent, when combined with the unique properties of water, plays key roles in the diverse fields of pharmacology, cryoprotection, and cell biology. Moreover, molecules dissolved in aqueous DMSO exhibit an anomalous concentration-dependent nonmonotonic behavior in stability and activity near a critical DMSO mole fraction of 0.15. An experimental identification of the origin of this anomaly can lead to newer chemical and biological applications. We report a direct spectroscopic observation of the anomalous behavior using ultrafast two-dimensional infrared spectroscopy experiments. Our results demonstrate the cosolvent-concentration-dependent nonmonotonicity arises from nonidentical mechanisms in ultrafast hydrogen-bond-exchange dynamics of water above and below the critical cosolvent concentration. Comparison of experimental and theoretical results provides a molecular-level mechanistic understanding: a distinct difference in the stabilization of the solute through dynamic solute-solvent interactions is the key to the anomalous behavior.

Hydrogen bonding mediated ion pairs of some aprotic ionic liquids and their structural transition in aqueous solution

Ion pair speciation of ionic liquids (ILs) has an important effect on the physical and chemical properties of ILs and recognition of the structure of ion pairs in solution is essential. It has been reported that ion pairs of some ILs can be formed by hydrogen bonding interactions between cations and anions of them. Considering the fact that far-IR (FIR) spectroscopy is a powerful tool in indicating the intermolecular and intramolecular hydrogen bonding, in this work, this spectroscopic technique has been combined with molecular dynamic (MD) simulation and nuclear magnetic resonance hydrogen spectroscopy (1H NMR) to investigate ion pairs of aprotic ILs [Bmim][NO3], [BuPy][NO3], [Pyr14][NO3], [PP14][NO3] and [Bu-choline][NO3] in aqueous IL mixtures. The FIR spectra have been assigned with the aid of density functional theory (DFT) calculations, and the results are used to understand the effect of cationic nature on the structure of ion pairs. It is found that contact ion pairs formed in the neat aprotic ILs by hydrogen bonding interactions between cation and anion, were still maintained in aqueous solutions up to high water mole fraction (say 0.80 for [BuPy][NO3]). When water content was increased to a critical mole fraction of water (say 0.83 for [BuPy][NO3]), the contact ion pairs could be transformed into solvent-separated ion pairs due to the formation of the hydrogen bonding between ions and water. With the further dilution of the aqueous ILs solution, the solvent-separated ion pairs was finally turned into free cations and free anions (fully hydrated cations or anions). The concentrations of the ILs at which the contact ion pairs were transformed into solvent-separated ion pairs and solvent-separated ion pairs were transformed into free ions (fully hydrated ion) were dependent on the cationic structures. These information provides direct spectral evidence for ion pair structures of the aprotic ILs in aqueous solution. MD simulation and 1H NMR results support the conclusion drawn from FIR spectra investigations.

Alternative EoS-based model for predicting water content, metastable phases and hydrate formation in natural gas systems

Methods for determination of water content in natural gas are a very important asset for the oil and gas industry. However, predicting water content can be a challenging task in some conditions. This is the case when acid gases are present in natural gas mixtures or when ice or hydrate formation is taken into account.In this work, we propose a methodology based on modified cubic equations of state (Peng-Robinson and Soave-Redlich-Kwong) as an alternative of greater accuracy than other standard approaches and simpler than SAFT or other more complex equations of state. The modifications used are a three-parameter alpha function and new binary interaction parameters. The parameters were regressed from bubble point experimental data for several compounds and mixtures. Then, the model was extrapolated to liquid water, ice and hydrate formation conditions. The calculations were compared to other common methods for water content prediction. The modified equations of state performed successfully, despite presenting some limitations.Finally, we used the alternative model to discuss the role of metastable phases in hydrate formation. We studied phase equilibrium of water + methane mixtures to extract information about hydrate formation in total absence of free water. Results show that there is a critical water mole fraction for every binary mixture, above which hydrates will not form directly from the vapor phase. In lower mole fractions, surface phenomena have to be taken into account in order to fully understand hydrate formation.

Chemical and radiation effects on flame extinction and NOx formation in oxy-methane combustion diluted with CO2

Oxy-methane counterflow diffusion flames diluted with CO2 were investigated to clarify impact of radiation heat loss and chemical effects of additional CO2 to oxidizer stream on flame extinction and NOx formation caused by air infiltration. Flame stability maps were presented with a functional dependency of critical diluents mole fraction upon global strain rate at various oxidizer stream temperatures in CH4–O2/N2, CH4–O2/CO2, and CH4–O2/CO2/N2 counterflow diffusion flames. The effects of radiation heat loss on the critical diluent mole fractions for flame extinction are not significant even at low strain rate in CH4–O2/N2 flame whereas those are significant at low strain rate and are negligible at high strain rate (>200s−1) in CH4–O2/CO2 and CH4–O2/CO2/N2 flames. Chemical effects of additional CO2 to oxidizer stream on the critical diluent mole fractions for flame extinction were appreciable in CH4–O2/CO2 and CH4–O2/CO2/N2 flames. A scaling analysis based on asymptotic solution of stretched flame extinction was applied. A specific radical index, which could reflect the OH population in main reaction zone via controlling the mixture composition in the oxidizer stream, was identified to quantify the chemical kinetic contribution to flame extinction. A good correlation of predicted extinction limits to those calculated numerically were obtained via the ratio between radical indices and oxidizer Lewis numbers for the target and baseline flames. This offered an effective approach to estimate extinction strain rate of oxy-methane diffusion flames permitting air infiltration when the baseline flame was taken to CH4–O2/N2 flame. Further study was conducted to investigate NOx formation in air infiltration environments. NOx formation could be suppressed by radiation heat loss and chemical effects of additional CO2 in oxy-methane combustion permitting air infiltration. The effect of air infiltration on NOx emission is addressed, and chemical effects of CO2 on NOx emission are discussed.

메탄 산소 연소에 있어서 화염 소화에 대한 연구

ABSTRACTOxy-methane nonpremixed flames diluted with CO 2 were investigated to clarify impact of radiation heat loss and chemical effects of additional CO 2 to oxidizer stream on flame extinction. Flame stability maps were presented with functional dependencies of critical diluents mole fraction upon global strain rate at several oxidizer stream temperatures in CH 4 -O 2 /N 2 , CH 4 -O 2 /CO 2 , and CH 4 -O 2 /CO 2 /N 2 counterflow flames. The effects of radiation heat loss on the critical diluent mole fractions for flame extinction are not significant even at low strain rate in nonpremixed CH 4 -O 2 /N 2 diffusion flame, whereas those are significant at low strain rate and are negligible at high strain rate (> 200 s -1 ) in CH 4 -O 2 /CO 2 and CH 4 -O 2 /CO 2 /N 2 counterflow flames. Chemical effects of additional CO 2 to oxidizer stream on the flame extinction curves were appreciable in both CH 4 -O 2 /CO 2 and CH 4 -O 2 /CO 2 /N 2 flames. A scaling analysis based on asymptotic solution of stretched flame extinction was applied. A specific radical index, which could reflect the OH population in main reaction zone via controlling the mixture composition in the oxidizer stream, was identified to quantify the chemical kinetic contribution to flame extinction. A good correlation of predicted extinction limits to those calculated numerically were obtained via the ratio between radical indices and oxidizer Lewis numbers for the target and baseline flames. This offered an effective approach to estimate extinction strain rate of non-premixed oxy-methane flames permitting air infiltration when the baseline flame was taken to nonpremixed CH

(Liquid + liquid) phase equilibria of binary mixtures 1-butyl-3-methylimidazolium tetrafluoroborate and tert-butanol or 1,2-butanediol

Precise (liquid+liquid) coexistence curves of binary mixtures {1-butyl-3-methylimidazolium tetrafluoroborate ([C4mim][BF4])+tert-butanol or RS-1,2-butanediol} have been measured. Critical exponent β and critical amplitude B̂0Z were deduced from the (liquid+liquid) equilibria data in the critical regions, and it was found that the critical exponent β coincided well with the 3D-Ising value. The complete scaling theory was applied to describe the asymmetry behavior of the diameter of the coexistence curves, which suggested that the heat capacity related term showed significant importance. The reduced critical temperature and density were calculated by the restricted primitive model (RPM), which were used to discuss the driven force of phase separation. Moreover, the dependences of the critical temperature, the critical mole fraction, the reduced critical temperature and the reduced critical density on the permittivity of alcohol for a series of binary solutions of RTIL in alcohols are discussed.

Effect of nitrogen mole fraction on hydrogenated amorphous silicon nitride deposited by DC magnetron sputtering: transition between metallic and reactive sputtering

AbstractThe hydrogenated amorphous silicon nitride thin films are deposited by DC magnetron sputtering in argon, molecular hydrogen and nitrogen plasma mixture. The films are deposited at 150 °C and at 130 W sputtering power with wide range of nitrogen mole fraction. The plasma is characterized by the target voltage measurement. The samples are characterized by the optical transmission measurements and the physicochemical structure is studied by the FTIR absorption spectroscopy. When the nitrogen mole fraction increases from 0.075 to 0.24 the target voltage decrease from 413 to 325 V and increases suddenly to 450 V when nitrogen mole fraction increases to 0.69. The decrease of target voltage may be due to the transition from metallic to reactive sputtering process and its increase can be explained by the implantation of reactive ions in the target. Sputtering rate and refractive index decrease respectively from 8.33 to 1.73 Å/sec and from 2.52 to 1.68 with nitrogen mole fraction. The value of refractive index at critical nitrogen mole fraction is about 1.8. When the nitrogen mole fraction increases the frequency related to Si‐H band, on FTIR spectrum, shift from 2097 cm‐1 to reach 2209 cm‐1 at the critical nitrogen mole fraction. Thereafter it varies sharply to 2190 cm‐1 and remains constant. A sudden change is observed on the sputtering rate, on the intensity of the band attributed to the stretching vibration of N‐H and Si‐H bonds. From these results we believe that the stoichiometric composition is reached at the critical nitrogen mole fraction and beyond this the deposited films are rich of nitrogen and hydrogen. This is consistent with the explanation given of the variation of the target voltage. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Mesoscopic structuring and dynamics of alcohol/water solutions probed by terahertz time-domain spectroscopy and pulsed field gradient nuclear magnetic resonance.

Terahertz and PFG-NMR techniques are used to explore transitions in the structuring of binary alcohol/water mixtures. Three critical alcohol mole fractions (x1, x2, x3) are identified: methanol (10, 30, 70 mol %), ethanol (7, 15, 60 mol %), 1-propanol (2, 10, 50 mol %), and 2-propanol (2, 10, 50 mol %). Above compositions of x1 no isolated alcohol molecules exist, and below x1 the formation of large hydration shells around the hydrophobic moieties of the alcohol is favored. The maximum number of water molecules, N0, in the hydration shell surrounding a single alcohol molecule increases with the length of the carbon chain of the alcohol. At x2 the greatest nonideality of the liquid structure exists with the formation of extended hydrogen bonded networks between alcohol and water molecules. The terahertz data show the maximum absorption relative to that predicted for an ideal mixture at that composition, while the PFG-NMR data exhibit a minimum in the alkyl chain self-diffusivity at x2, showing that the alcohol has reached a minimum in diffusion when this extended alcohol-water network has reached the highest degree of structuring. At x3 an equivalence of the alkyl and alcohol hydroxyl diffusion coefficients is determined by PFG-NMR, suggesting that the molecular mobility of the alcohol molecules becomes independent of that of the water molecules.

Liquid–liquid phase equilibria of ionic liquid solutions in the critical region: 1-Methyl-3-octylimidazolium tetrafluoroborate with 1-pentanol or 1-hexanol

The liquid–liquid coexistence curves for the binary solutions of the room temperature ionic liquid (RTIL) 1-methyl-3-octylimidazolium tetrafluoroborate ([C8mim][BF4]) in 1-pentanol and 1-hexanol were measured in the critical region. The critical exponent β and the critical amplitude B were deduced and the former was found to be consistent with the 3D-Ising value. The complete scaling theory was applied to describe the asymmetry of the diameters of the coexistence curves. Moreover, the dependences of the critical temperature, the critical mole fraction, the reduced critical temperature and the reduced critical density on the permittivity of alcohol for a series of binary solutions of RTIL in alcohols were discussed.

Micellization behavior of the amphiphilic drug promethazine hydrochloride with 1-decyl-3-methylimidazolium chloride and its thermodynamic characteristics

The micellization behavior of promethazine hydrochloride (PMT) with 1-decyl-3-methylimidazolium hydrochloride, [C10mim] [Cl], at different temperatures was investigated by using electrical conductivity. The system thermodynamic properties were also studied by calculating various thermodynamic parameters (viz., the standard Gibbs energy change, ΔG°m, the standard enthalpy change, ΔH°m, the standard entropy change, ΔS°m), that favor the micellization in binary mixtures of PMT–[C10mim][Cl] compared with the pure counterparts, at two mole fractions of PMT. The synergistic interaction is examined using Regular Solution Theory for PMT–[C10mim] [Cl] binary mixtures, through the interaction parameter (β) and activity coefficient (f1 and f2) values. The synergism is also revealed in the deviations in the critical micelle concentration (cmc) from the ideal critical micelle concentration (cmc*) and micellar mole fraction (X1) from ideal micellar mole fraction (X1ideal) values. The value of excess free energy (ΔGex) for α1=0.6 at 308K favor the better condition for the formation of the most stable and compact mixed micelles.

Concentration-dependent dynamics of hydrogen bonding between acetonitrile and methanol as determined by 1D vibrational spectroscopy.

Solutions of acetonitrile (MeCN) in methanol (MeOH) at various concentrations have been investigated by variable temperature Raman spectroscopy. In the ν(CN) region of the spectrum, the variable temperature spectra at each concentration show two overlapping bands from hydrogen bound and free MeCN. These two species undergo dynamic exchange that gives rise to increasing coalescence of the two bands with increasing temperature. By simulation of the band shape, the rate of exchange was determined at each temperature. Arrhenius plots yielded values for the activation energy, Ea, and the natural log of the pre-exponential factor, ln[A/s(-1)], for the hydrogen bond formation/cleavage. Both of these dynamic parameters were found to depend on the relative amounts of MeCN and MeOH in the solutions. In particular, two different concentration regimes of dynamic hydrogen bonding were observed. First, at low MeCN concentration, the dynamics are largely independent of changes in MeCN concentration. Second, at higher MeCN concentration (above ∼0.2 MeCN mole fraction) the dynamics are strongly dependent on further increases of MeCN content. Over the range of MeCN mole fractions that we studied (0.03-0.5), the ln[A/s(-1)] changes from 32.5 ± 0.1 to 30.1 ± 0.2 and Ea changes from 3.73 ± 0.08 to 2.7 ± 0.1 kcal/mol. We suggest the observed changes in dynamics arise from changes in the local solvent microstructure that occur above a critical mole fraction of MeCN.