Non-ideal Behavior Of Mixture Research Articles

Densities and Viscosities for the Ternary Mixtures of n-Undecane (1) + Butylcyclohexane (2) + 1-Pentanol (3) and Corresponding Binaries at T = (293.15 to 333.15) K

The actual composition is known to be highly responsible for the physical and chemical properties of a fuel. To understand the foundational physical properties of an aviation kerosene substitute mixture for hypersonic aircraft, n-undecane, butylcyclohexane, and 1-pentanol were used to construct a ternary system. The values of density (ρ) and viscosity (η) for the ternary system and three corresponding binaries were measured at temperatures T = (293.15 to 333.15) K and pressure p = 0.1 MPa. The Redlich–Kister equation was used to fit the excess molar volumes (VmE) and viscosity deviations (Δη) of the binary systems, while those of the ternary system were correlated with four semi-empirical formulas (Cibulka, Singh, Redlich–Kister, and Nagata–Tamura equations). The experimental results show that the VmE values of the three binary mixtures have a positive relationship with the mole fraction of nonpolar components, while Δη values have a negative relationship. The non-ideal behavior of mixtures is discussed from the perspective of molecular interactions and structural effects. This work provides data support and guidance for fuel compatibility research.

Mixed Micellization, Thermodynamic and Adsorption Behavior of Tetracaine Hydrochloride in the Presence of Cationic Gemini/Conventional Surfactants.

In this approach, tensiometry and UV-visible techniques are used to determine the effect of cationic gemini and conventional surfactants on tetracaine hydrochloride (TCH), an anesthetic drug. We have estimated micellar, interfacial, and energetic constraints. To gain a deep understanding of their mixed association behavior, the outputs were examined using different theoretical models. The critical micelle concentration for single and mixed amphiphiles was estimated. The cmc values of mixed amphiphiles were found between the individual amphiphiles due to strong attractive interaction (synergism) between the components after mixing. The non-ideal behavior of mixtures was confirmed by the larger values of ideal cmc than the experimental cmc values. The negative values of interaction parameter (β) and values of activity coefficients less than unity indicate strong synergistic interaction between drug and surfactant. The stability of the mixed systems is demonstrated by the negative Gibbs free energy of micellization and excess free energy of micellization. In contrast to a single chain surfactant, a double chain surfactant (gemini) exhibits better interactions with the drug. Spectral measurements (UV-visible spectra) were used to monitor the binding of the drug with surfactant (conventional as well as gemini). Studying these mixed aggregates could help to optimize their compositions and find synergistic properties between TCH monomers and surfactants.

Impact on micellization between promethazine hydrochloride and ester bonded gemini surfactant in distinct solvents: A multi-faceted procedure

Ester bonded bio-cleavable gemini surfactant - ethane-1,2-diylbis(N,N-dimethyl-N-hexadecylammonium acetoxy)dichloride (16-E2-16) influences the micellization of promethazine hydrochloride (PMT) studied through surface tension, UV and FT-IR measurements in various media (aqueous, 50 mmol/kg sodium chloride (NaCl), 500 mmol/kg urea (U) and 500 mmol/kg thiourea (TU)) solutions. The solution and interfacial behavior show synergism between PMT and gemini surfactant in all the media. The addition of urea (U) and thiourea (TU) to the PMT, 16-E2-16, and PMT + 16-E2-16 mixture solution exhibit both increase and decrease in cmc hangs on concentration of [U] and [TU] and here the employed concentration of [U] or [TU] increases the cmc value of system while NaCl always decreases the cmc value. In mixed micelles, the micellar composition of 16-E2-16 is found higher than PMT. The micelle phase is found rich in surfactant monomers as compared to drug molecules. Activity coefficients in each case were attained below one in solution and interface, which authorized an interaction between constituents along with non-ideal behavior of mixtures. Different evaluated thermodynamic parameters depicted spontaneity as well as stability of mixed systems. UV–visible spectra showed that the absorption intensity of PMT increased with the addition of 16-E2-16 owing to interaction amongst them. FTIR investigation confirmed that the peak shifting in spectra of the pure component was detected also addressed the interaction amongst both components (PMT and 16-E2-16). Mixed micelles formation enhances solubility and permeability, so favorable for drug delivery purposes across the membrane.

Rapid Vapor-Collection Method for Vapor Pressure Measurements of Low-Volatility Compounds.

Dynamic vapor microextraction (DVME) is a new method that enables rapid vapor pressure measurements on large molecules with state-of-the-art measurement uncertainty for vapor pressures near 1 Pa. Four key features of DVME that allow for the rapid collection of vapor samples under thermodynamic conditions are (1) the use of a miniature vapor-equilibration vessel (the "saturator") to minimize the temperature gradients and internal volume, (2) the use of a capillary vapor trap to minimize the internal volume, (3) the use of helium carrier gas to minimize nonideal mixture behavior, and (4) the direct measurement of pressure inside the saturator to accurately account for overpressure caused by viscous flow. The performance of DVME was validated with vapor pressure measurements of n-eicosane (C20H42) at temperatures from 344 to 374 K. A thorough uncertainty analysis indicated a relative standard uncertainty of 2.03-2.82% for measurements in this temperature range. The measurements were compared to a reference correlation for the vapor pressures of n-alkanes; the deviation of the measurements from the correlation was ≤2.85%. The enthalpy of vaporization of n-eicosane at 359.0 K was calculated to be ΔvapH = 91.27 ± 0.28 kJ/mol compared to ΔvapH(corr) = 91.44 kJ/mol for the reference correlation. Total measurement periods as short as 15 min (3 min of thermal equilibration plus 12 min of carrier gas flow) were shown to be sufficient for high-quality vapor pressure measurements at 364 K.

Poly(ethylene glycol) diacrylate as a novel chaotropic compound for design of aqueous biphasic systems

In this work novel solvent, poly(ethylene glycol) diacrylate (PEGDA) of average number molecular weight 700, is proposed for design of aqueous biphasic systems with salting-out agents: K3PO4/Na3C6H5O7/K2CO3/MnSO4/Li2SO4/ZnSO4. Ternary liquid-liquid equilibrium experiments were conducted at constant temperature 298.15K and 0.1MPa, where binodal curves and tie-lines were determined. The consistency of equilibrium data were checked and confirmed using Othmer-Tobias and Bancroft equations. Density ρ, viscosity η and refractive index nD have been experimentally measured for PEGDA 700+water system over the temperature range T=(293.15 to 323.15) K with temperature step 5K and at atmospheric pressure. Excess molar volumes VE, viscosity deviations Δη, deviations in refractive index ΔnD, excess Gibbs free energy of activation of viscous flow ∆G⁎E, partial molar volumes V¯i, excess partial molar volumes V¯iE and it's values at infinite dilutions V¯iE,∞ were calculated from experimental data and used to analyze non-ideal behavior of polymer aqueous solution. Fourier-transform infrared analysis (FT-IR) of PEGDA+water mixture and corresponding pure components was performed at T=298.15K in order to gain insight into the molecular structure of the mixture. FT-IR analysis indicates the absence of hydrogen bonding between PEGDA 700 and water. This leads to the conclusion that non-ideal behavior of mixture is contributed to geometrical packing or van der Waals forces of different species.

Group contribution method for multicomponent evaporation with application to transportation fuels

Transportation fuels consist of a large number of species that belong to different families of compounds. Predictions of physical and chemical properties of such multicomponent fuels require the accurate description of evaporation rates of all species initially contained in the liquid phase. Existing computational approaches are yet to do this without difficulty due to the lack of experimental data for physical properties of fuel components. In addition, a vast number of assumptions, which include idealized compositions and interpolation equations calibrated using experiments, are being introduced to make the problem tractable. By addressing this issue, an approach based solely on functional groups that are present in the components of the fuel is developed. This formulation is coupled to a multicomponent evaporation model to account for non-ideal behavior of mixtures and the consideration of pressure and temperature variations. This is done by using the fuel composition to evaluate the acentric factor and critical properties of each fuel component followed by the evaluation of certain physical properties using a group contribution method. This procedure thus allows the evaluation of evaporation rates of practical fuels based only on the intrinsic functional groups and their relative abundance. Studies of common fuel blends including those belonging to the Jet-A and JP-8 classes related to evaporation rates, distillation characteristics and speciation are presented. A discussion of the effect of polar species on evaporation properties utilizing the UNIFAC approach for non-ideal mixtures is presented. Due to the generalized nature of this approach, the proposed method provides an effective alternative to existing computational techniques dedicated to multicomponent droplet evaporation.

Thermodynamic and spectroscopic interpretation of molecular interactions of nicotine + alcohol binary mixtures

Density ρ, viscosity η and refractive index nD have been experimentally measured for four binary mixtures nicotine+1-butanol, nicotine+2-butanol, nicotine+1,2-propanediol and nicotine+1,3-propanediol over the temperature range T=(293.15–323.15)K with temperature step 5K and at atmospheric pressure. Excess molar volumes VE, viscosity deviations Δη, deviations in refractive index ΔnD, excess Gibbs free energy of activation of viscous flow ΔG∗E, thermal expansion coefficients α, excess thermal expansion coefficients αE, partial molar volumes V‾i, excess partial molar volumes V‾iE and it’s values at infinite dilutions V‾iE,∞ were calculated from experimental data and used to analyze non-ideal behavior of mixtures. Fourier-transform infrared analysis of binary mixtures and corresponding pure components was performed at 298.15K in order to gain insight into the molecular structure of mixtures and possible intermolecular interactions. Performed infra-red analysis confirms the presence of hydrogen bonding between unlike compounds, except for the system nicotine+1-butanol. Here, the non-ideal behavior of mixtures is contributed to strong intermolecular interaction or in the case of nicotine+1-butanol due to geometrical packing or dispersion forces of different species.

Thermodynamic study of (anthracene + phenanthrene) solid state mixtures

Polycyclic aromatic hydrocarbons (PAH) are common components of many materials, such as petroleum and various types of tars. They are generally present in mixtures, occurring both naturally and as byproducts of fuel processing operations. It is important to understand the thermodynamic properties of such mixtures in order to understand better and predict their behavior (i.e., fate and transport) in the environment and in industrial operations. To characterize better the thermodynamic behavior of PAH mixtures, the phase behavior of a binary (anthracene+phenanthrene) system was studied by differential scanning calorimetry, X-ray diffraction, and the Knudsen effusion technique. Mixtures of (anthracene+phenanthrene) exhibit non-ideal mixture behavior. They form a lower-melting, phenanthrene-rich phase with an initial melting temperature of 372K (identical to the melting temperature of pure phenanthrene) and a vapor pressure of roughly lnP/Pa=−2.38. The phenanthrene-rich phase coexists with an anthracene-rich phase when the mole fraction of phenanthrene (xP) in the mixture is less than or equal to 0.80. Mixtures initially at xP=0.90 consist entirely of the phenanthrene-rich phase and sublime at nearly constant vapor pressure and composition, consistent with azeotrope-like behavior. Quasi-azeotropy was also observed for very high-content anthracene mixtures (2.5<xP<5) indicating that anthracene may accommodate very low levels of phenanthrene in its crystal structure.

Experimental Investigation of Interactions and Thermodynamic Properties of Poly(ethylene glycol) 200/400 + Dimethyl Adipate/Dimethyl Phthalate Binary Mixtures

Density ρ, viscosity η, and refractive index nD have been experimentally measured for four binary mixtures dimethyl adipate + poly(ethylene glycol) 200, dimethyl adipate + poly(ethylene glycol) 400, dimethyl phthalate + poly(ethylene glycol) 200, and dimethyl phthalate + poly(ethylene glycol) 400 in the temperature range T = (288.15 to 323.15) K with a temperature step of 5 K and at atmospheric pressure. Excess molar volumes VE, viscosity deviations Δη, and deviations of refractive index ΔnD were calculated from experimental data and fitted using Redlich–Kister polynomial. Fourier-transform infrared analysis of binary mixtures and corresponding pure components was performed at 298.15 K in order to gain insight into the molecular structure of mixtures and possible intra- and intermolecular interactions. Performed IR analysis confirms an absence of intermolecular interactions between unlike compounds. Consequently, the nonideal behavior of mixtures is contributed to geometrical packing or dispersion forces ...

On the hydrogen bond networks in the water–methanol mixtures: topology, percolation and small-world

Statistical mechanics based topological analysis and island (or cluster) statistics were used to study the hydrogen bond (H-bond) networks in the water-methanol mixtures with the following methanol mole fractions (x(m)): 0.00, 0.10, 0.20, 0.25, 0.28, 0.30, 0.32, 0.36, 0.38, 0.42, 0.50, 0.60, 0.70, 0.80, 0.90, 1.00. NPT-Monte Carlo simulations were performed at room conditions using the TIP5P model potential for water and united-atoms (OPLS) for methanol to generate the H-bond networks. We have found evidence for non-ideal behavior of mixtures with x(m) ≈ 0.3. Several structural and topological properties present strong dependence with the mixture composition. Island statistics indicate a change from the percolated to non-percolate regime at x(m) ≈ 0.5. Statistical analysis of the islands' nature (homo-clusters: same type of molecules × hetero-clusters: two types of molecules) yields a preferential formation of homo-clusters that quantifies the local composition and preferential solvation ("microimmiscibility"). The topology of the hydrogen bond networks was characterized by local (clustering coefficients, average degrees), semi-global (path lengths) and global (spectral densities) properties. Small-world patterns (highly clustered and small path lengths) appear for x(m) in the range 0.40-0.70, and the momenta in the spectral densities correlate quite well with previous analysis based on rings, chains and branched chains topologies. It also seems that small quantities of methanol in water cause disruption of the continuous fully connected H-bond networks formed by water molecules.

Phase equilibria for strongly nonideal liquid mixtures at low temperatures

AbstractInvestigation of the nonideal behavior of mixtures of simple molecules is an important step toward improved understanding of the theory of solutions. This work describes an equilibrium apparatus suitable for the measurement of vapor‐liquid and vapor‐liquid‐liquid equilibria of simple fluid mixtures at cryogenic temperatures. Vapor‐liquid data are reported for the argonethane and nitrogen‐carbon tetrafluoride systems. Contrary to expectations, limited liquid‐phase miscibility was not observed for either of these mixtures. These results and those for other nonideal mixtures of simple molecules are compared with predictions of upper critical solution temperatures by the theory of regular solutions. Usefulness of this theory is impaired by its neglect of the order‐disorder phenomenon and, more seriously, by the geometric‐mean assumption for the intermolecular forces between dissimilar molecules.