Critical point estimation of the Lennard-Jones pure fluid and binary mixtures

The apparent critical point of the pure fluid and binary mixtures interacting with the Lennard-Jones potential has been calculated using Monte Carlo histogram reweighting techniques combined with either a fourth order cumulant calculation (Binder parameter) or a mixed-field study. By extrapolating these finite system size results through a finite size scaling analysis we estimate the infinite system size critical point. Excellent agreement is found between all methodologies as well as previous works, both for the pure fluid and the binary mixture studied. The combination of the proposed cumulant method with the use of finite size scaling is found to present advantages with respect to the mixed-field analysis since no matching to the Ising universal distribution is required while maintaining the same statistical efficiency. In addition, the accurate estimation of the finite critical point becomes straightforward while the scaling of density and composition is also possible and allows for the estimation of the line of critical points for a Lennard-Jones mixture.     

Electrical conductance of electrolyte mixtures of any type

An analytical expression for the electrical conductance of a mixed electrolyte solution of any type is derived. A general expression giving the equivalent ionic conductance is derived. This expression is also valid for the case of a pure electrolyte, whether asymmetrical or symmetrical. A comparison is made with the results obtained by other authors in the particular case of symmetrical electrolytes.     

Ionic strength dependence in dilute common-ion electrolyte mixtures

The relation between the coefficients of the Harned's rule behavior and the mixing coefficients in the expression for the total excess free energy of a common-ion mixture is elucidated. The results are used to see if the strong ionic-strength dependence of theg ₁ coefficient is reflected in certain modified Harned's coefficients. This is the case for the system studied; moreover, in this case the experimental data are in agreement with the theoretical model calculation made previously.Contribution in memory of Prof. R. A. Robinson.     

Separation of various electrolyte mixtures by unilateral capillary isotachophoresis

A new electrophysical method is proposed for a rapid diagnosis of liquid products relating quality and identification. The method is widely prospective for practical application.     

The electrophoretic effect for the case of electrolyte mixtures

The ionic electrophoretic effect for solutions of mixed electrolytes of any type is calculated. The calculation is based on the well-known treatment due to Chen with the same distance of closest approach for all the ions in solution. The improved iterative method used for the relaxation-field treatment is applied. For the latter the electrophoretic velocity results are derived to the second iteration in the perturbation method.     

The relaxation field for the general case of electrolyte mixtures

The relaxation field for solutions of mixed electrolytes of any type is calculated. the calculation is based on the well-known treatment due to Fuoss-Onsager with the same distance parameter for all the ions in solution. A general conductance-continuity equation has been established and an improved iterative method of calculation, using Laplace transforms, is proposed. The relaxation-field results are derived to the second iteration in the perturbation method of integration.     

Critical resistivity in impurity doped binary liquid mixtures

The electrical resistance of the critical binary liquid system C₆H₁₂₊(CH₃CO)₂O is measured both in the pure form and when the system is doped with small amounts (≈ 100 ppm) of H₂O impurities. Near T_c, the resistance varies as dR/dT = A₁+A₂ (T-T_c)^-b with b ≈ 0.35. Neither the critical exponent b nor the amplitude ratio A₁/A₂ are affected by the impurities. A sign reversal of dR/dT is noticed at high temperatures T ? T_c.     

Critical point measurement of some polycyclic aromatic hydrocarbons

The critical temperatures and the critical pressures of five polycyclic aromatic compounds, namely, acenaphthene, fluorene, anthracene, phenanthrene, and pyrene have been measured. All the compounds studied decompose at near-critical temperatures. A pulse-heating technique applicable to measuring the critical properties of thermally unstable compounds has been used. The times from the beginning of a heating pulse to the moment of reaching the critical temperature were from (0.06 to 0.85) ms. The short residence times provide little degradation of the substances in the course of the experiments. The experimental critical parameters of the polycyclic aromatic compounds have been compared with those estimated by five predictive methods. The acentric factors of polycyclic aromatic compounds studied have been calculated.     

Cloud point phenomenon in aqueous mixtures of cationic-anionic surfactants

It used to be held that the cloud point phenomenon was only a characteris-tic of nonionic surfactants alone. Such phenomenon is rarely observed in ionicsurfactants. The present study shows that the mixture of cationic-anionic surfac-tants not only has a krafft point which is the characteristic of an ionic surfactant,but also exhibits the cloud point phenomenon obviously at certain concentrations.     

Electric permittivity near the critical point of binary mixtures

Electric permittivity for binary solutions of nitrobenzene in 2,2,4-trimethyl pentane, hexane, cyclohexane and cycloheptane was measured versus temperature for critical concentrations. The critical temperatures were determined. It was observed that the derivative d?/dT decreased with decreasing temperature when the system passed from a single phase to a two-phase state.     

Cloud point temperature of polyoxyethylene-type nonionic surfactants and their mixtures

The cloud point temperature, T(c), was investigated for aqueous solutions of poly(oxyethylene) alkyl ethers, C(n)E(m), and their mixtures. The experimental T(c)'s for single surfactant systems were analyzed according to the Flory-Huggins model for cloud point phenomenon, and the enthalpy and the entropy changes associated with the process of the separation of micellar solution into pure water and pure surfactant were estimated. It was found that the enthalpy-entropy compensation relationship holds for this process. The Flory-Huggins model was extended to the binary surfactant mixtures, and the expression of T(c) as a function of the composition was derived assuming the regular solution for mixed micelles. The experimental results of T(c) obtained for mixtures of C(n)E(m) were well reproduced by the model calculation. Discussion is given concerning the interaction parameters of different surfactant species in mixed micelles determined by this model calculation.     

Nonlinear dielectric effect near the critical point of binary mixtures

The nonlinear dielectric effect (NDE) was measured in two binary systems near the critical point. The effect of independent of specific dipole-dipole interactions in contrast with previous conceptions. Its singular part is proportional to (T ? T_c)^{?$\text{1}\text{2}$} in agreement with Snider's theory as applied to NDE.     

A dielectrically consistent interaction site theory for solvent—electrolyte mixtures

A reformulation of reference interaction site model theory is proposed. The approach makes use of the formally correct asymptotic form of the correlations obtained from the one-center angular expansion technique. A modified closure, or equivalently, a modified propagation equation for site—site correlations is shown to incorporate the necessary information to allow dielectric consistency in finite-concentration salt solutions. Examples of the correlations and thermodynamics are given.     

Electric double layers with electrolyte mixtures: integral equations theories and simulations

A study of a planar electric double layer (EDL) in the presence of mixtures of electrolyte is presented. In particular, results from the Hyper-Netted-Chain/Mean-Spherical-Approximation (HNC/MSA) theory are compared with Monte Carlo (MC) simulations. In this way, the charge inversion induced by mixtures of multivalent and monovalent counterions is probed. Since overcharging phenomena in nature emerge under such conditions, the role of ion-ion correlations in the EDL appears as a crucial point in this kind of study. Unlike previous related works, a realistic hydrated ion size is used in the HNC/MSA calculations and simulations. In this way, a qualitative agreement between the results obtained from the theory and MC simulations is found. However, some discrepancies arise when the charge inversion is expected to be more noticeable, namely at high surface charges and/or elevated concentrations of multivalent electrolytes. Such differences are explained in terms of an overestimation of the charge inversion by the integral equation (IE) formalism.     

Adsorption of nonionic mixtures at the air-water interface: effects of temperature and electrolyte

Specular neutron reflection has been used to investigate the effects of temperature and added electrolyte on the adsorption of nonionic surfactants and nonionic surfactant mixtures at the air-water interface. For the alkyl poly-oxyethylene oxide nonionic surfactants, C(n)EO(m), the adsorption at the air-water interface is independent of temperature for surfactants with shorter ethylene oxide groups, whereas there is an increasing tendency for increased adsorption with temperature for surfactants with longer ethylene oxide groups. The addition of "salting in" (sodium thiocyanate, NaSCN) and "salting out" (sodium chloride, NaCl, sodium sulphate, Na2SO4) electrolyte results in reduced and enhanced adsorption, respectively, for C12EO8, whereas both types of electrolyte result in enhanced adsorption for C12EO12. The addition of electrolyte does not substantially alter the temperature dependence of the adsorption of the pure monolayers. For the nonionic mixtures of C12EO3/C12EO8 increasing temperature results in a surface richer in the least surface-active component, C12EO8. For the same nonionic mixture, the addition of "salting in" and "salting out" electrolyte results in an reduced and increased adsorption, respectively. The addition of "salting in" electrolyte results in a surface more rich in C12EO3, whereas for the addition of both "salting in" and "salting out" electrolyte the surface composition is essentially unaltered.     

Electrode potentials of electrochemical cells with oxide-conducting solid electrolyte in chemically nonequilibrium gas mixtures

A wide range of electrodes for solid oxide electrolyte cells in chemically nonequilibrium gas media simultaneously containing oxygen and combustible gases is systematically studied. The concentration dependences are investigated for the potential response of electrodes made of conducting oxides, noble metals (platinum, gold, silver), and also composite electrodes containing dispersed oxide semiconductor phases, apart from the main conducting material. Besides, dynamic characteristics of these electrodes are investigated. The studies are performed in the temperature range from 450 to 800°C. The content of combustible gases in the mixture was varied from 10 ppm to 2%. The research results are of interest for development of sensors for combustible gases and for studying kinetics and mechanisms of catalytic oxidation reactions.     

Flash point of organic binary mixtures containing alcohols: experiment and prediction

The flash points of three organic binary mixtures containing alcohols were measured in the present work. The experimental data was obtained using the Pensky-Martens closed cup tester. The experimental data were compared with the values calculated by the Liaw model. Activity coefficients were calculated by the Wilson equation and NRTL equation. The accuracy of predicted flash point values is dependent on the thermodynamic model used for activity coefficient.     

Ionic interactions in aqueous electrolyte-polyelectrolyte mixtures: Comparisons with mixtures of sodium chloride with the model electrolyte sodiumpara-ethylbenzenesulfonate at 25°C

Osmotic coefficients for aqueous mixtures of sodium chloride with sodiumpara-ethylbenzenesulfonate NapEBS and lithiumpara-ethylbenzenesulfonate LipEBS with NapEBS obtained by the gravimetric isopiestic vapor pressure comparison method are interpreted with the Scatchard neutral-component and with the Pitzer ion-component equations. Ionic and mean ionic activity coefficients for Na⁺ and Cl^– ions and for NaCl, respectively, were also determined with an electrochemical cell. The ±(NaCl) values at constant unit ionic strength,I=1.00, were compared with those computed from osmotic-coefficient measurements. Strong anion-anion interactions were observed in the NaCl-NapEBS mixtures.