Concentration-concentration Structure Factor Research Articles

Thermodynamics of chlorobenzene, or bromobenzene, or 1-chloronaphthalene or 1,2,4-trichlorobenzene + alkane mixtures

The systems C6H5Cl, or C6H5Br, or 1-chloronaphthalene, or 1,2,4-trichlorobenzene, or 1-methylnaphthalene, or 1,2,4-trimethylbenzene + alkane have been investigated by means of the their excess molar properties, including, when the needed data are available, those at constant volume, internal energies (UVmE) and heat capacities (CVmE), and using the DISQUAC, and Flory models, and the concentration-concentration structure factor formalism. The position of the mixtures within the GmE (excess molar Gibbs energy) vs. HmE(excess molar enthalpy) diagram has been also determined. Interactions between C6H5X molecules become stronger in the sequence X = H ≈ F ≈ Cl < Br. These interactions are weaker than those between 1-chloronaphtahlene or 1,2,4-trichlorobenzene molecules. It is shown that the considered systems have some common features: dispersive interactions are dominant, structural effects for solutions with shorter n-alkanes are large and UVmE decreases when the number (n) of C atoms of the alkane increases. This variation is held when an n-alkane is replaced by a branched alkane with the same n in systems with C6H5Cl or 1-chloronaphthalene. This suggests that larger alkanes are poorer breakers of the interactions between aromatic halogenated compounds. Viscosity and CVmE data support this conclusión. The parabolic dependence of CVmE with n indicates that the short orientational order of long n-alkanes is destroyed. Aromacity and proximity effects are discussed.

Thermodynamics of mixtures containing a fluorinated benzene and a hydrocarbon

Fluorobenzene, or 1,4-difluorobenzene or hexafluorobenzene + alkane mixtures and hexafluorobenzene + benzene, or + toluene, or + 1,4-dimethylbenzene systems have been investigated using thermodynamic properties from the literature and through the application of the DISQUAC and UNIFAC (Dortmund) models and the concentration-concentration structure factor (SCC(0)) formalism. DISQUAC interaction parameters for the contacts F/alkane and F/aromatic have been determined. UNIFAC interaction parameters available in the literature for these contacts have been used along calculations. Both models predict double azeotropy for the C6F6 + C6H6 system, although in different temperature ranges. TheHmE values of the fluorobenzene, or 1,4-difluorobenzene + n-alkane systems are positive and are accurately described by the models using interaction parameters independent of the n-alkane. This means that no Patterson’s effect exists in such mixtures. DISQUAC calculations allow state that such conclusion is still valid for C6F6 + n-alkane mixtures. DISQUAC provides better results than UNIFAC on CpmE of solutions involving n-alkanes, or on HmE of C6F6 + aromatic hydrocarbon systems. Mixtures with alkanes are characterized by interactions between like molecules, which are mainly of dispersive type, which is supported, e.g, by the negative CpmE values of these systems. It is shown that structural effects can contribute largely to HmE. This is investigated in terms of the excess molar internal energy at constant volume, UVmE, whose values are determined for the investigated solutions. For mixtures with a given n-alkane, the relative variation of HmE and UVmEwith the fluorohydrocarbons is different.HmEvalues change in the sequence C6F6 > 1,4-C6H4F2 > C6H6 > C6H5F, while UVmE changes in the order: 1,4-C6H4F2 > C6H6≈ C6H5F > C6F6 . C6F6 + aromatic hydrocarbon mixtures are characterized by interactions between unlike molecules as it is demonstrated by their negative HmE values. The application of the SCC(0) formalism reveals that homocoordination is more important in C6F6 + n-alkane mixtures than in the corresponding systems with C6H5F, and that heterocoordination is dominant in the solutions of C6F6 with an aromatic hydrocarbon.

Density, speed of sound, refractive index and relative permittivity of methanol, propan-1-ol or pentan-1-ol + aniline liquid mixtures. Application of the Kirkwood-Fröhlich model

Densities (ρ) and speeds of sound (c) at a temperature T = 298.15 K, relative permittivities at 1 MHz (εr) and refractive indices at the sodium D-line (nD) at T = (293.15 K to 303.15 K), all of them at a pressure p = 0.1 MPa, are reported for binary liquid mixtures alkan-1-ol + aniline. The alkan-1-ols considered are methanol, propan-1-ol and pentan-1-ol. Also, the values of the excess molar volume (VmE), excess isentropic compressibility (κSE), excess speed of sound (cE), excess refractive index (nDE), excess relative permittivity (εrE) and its temperature derivative (∂εrE/∂T)p are calculated and fitted to Redlich-Kister polynomials. The agreement among the reported data and other literature sources is analysed by comparing VmE, nDE, εrE and the deviation of c from mole-fraction linearity (Δc). The positive excess molar internal energies at constant volume (Um, VE) show the dominance of the breaking of interactions between like molecules in the energy balance on mixing, particularly the breaking of strong dipolar interactions between aniline molecules. This contribution is also dominant for the εrE values, as they are negative and decrease with the length of the alkan-1-ol chain. Calculations on the concentration-concentration structure factor are consistent with these statements, revealing homocoordination in the studied systems. The VmE are negative, which together with the positive Um, VE indicate the existence of important structural effects in the studied mixtures. The application of the Kirkwood-Fröhlich model shows that the average relative orientation of neighbouring dipoles is similar in the mixtures methanol + aniline or + pyridine, in spite of the different character of the predominant interactions in the latter mixture (heterocoordination).

Theoretical and experimental study of 1-butyl-3-methylimidazolium nitrate with 1-pentanol, 1-hexanol and 1-heptanol: COSMO-RS and structure factor

In this paper, some thermodynamic and structural properties of the binary mixtures containing [Bmim][NO3] and 1-alkanols (1-pentanol, 1-hexanol, and 1-heptanol) was studied using theoretical and experimental methods. Density and viscosity for the mixtures above were measured at temperatures (293.15 K to 323.15 K), and values of excess molar volumes, VmE and viscosity deviations Δη were calculated. For binary mixtures of [Bmim][NO3] with 1-octanol, 1-nonanol, and 1-decanol a miscibility gap was observed in the mole fraction regions between 0.1 and 0.9. Findings indicate that strong interactions occur in the binary solutions containing short-range 1-alkanol, and increasing the length of the alcohol causes the weakening of the intermolecular interactions. To obtain more information about the molecular structure of aforesaid mixtures, the conductor-like screening model for real solutions (COSMO-RS) method was applied, and the D parameter, the concentration-concentration structure factor, Scc(0), and the chemical short-range order parameter α′, were calculated for the binary mixtures.

Theoretical and experimental study of valeric acid and 1-alkanol: COSMO-RS method and structure factors

Abstract This paper attempts to describe the types and nature of interactions present in binary mixtures containing valeric acid and 1-alkanols (1-pentanol up to 1-decanol) using theoretical and experimental methods. The density and viscosity of the mixtures above were measured at temperatures of 293.15 K to 323.15 K. Values of excess molar volumes (VmE) and viscosity deviations(Δη) were calculated. The findings indicate that strong interactions occur in binary solutions containing short-range 1-alkanol, and increasing the length of the alcohol chain causes a weakening of intermolecular interactions. To confirm the experimental results, the conductor-like screening model for real solutions (COSMO-RS) method was used to calculate the activity coefficients of the compounds in the liquid mixtures and the contact probability (CP) of alcohols with the valeric acid. Then, the D parameter, the concentration-concentration structure factor (SCC(0)), and the chemical short-range order parameter (α') were obtained and used to describe the existing interactions for binary mixtures. For binary systems, viscosity and density data are novel and have not previously been reported.

Study of interactions in binary mixtures containing normal alkanols; KB integrals and structure factor

ABSTRACT In this paper, the investigation on the structure and molecular interactions in the binary systems containing aniline and 1-alkanol (1-pentanol up to 1-decanol) was performed in the framework of Kirkwood-Buff (KB) integrals and experimental techniques. The interpretation of obtained parameters shows that in binary mixtures with shorter chain alcohols, unlike molecules tend to form strong interactions, while increasing in the carbon atom of 1-alkanols reduces the strength of bonds and tendency of the heterogeneous molecules to stay along side. Mixtures structure was studied using the concentration-concentration structure factor, . Results from the application of this parameter show that the heterocoordination occurs in solutions involving 1-pentanol up to 1-heptanol, while for mixtures containing 1-octanol to 1-decanol, homocoordination is predominant. Also, the chemical short-range order parameter, α′which is an important function to understand the complex formation and phase segregation in the liquid mixtures was obtained and discussed for mentioned mixtures.

Kirkwood-Buff integrals and structure factor for binary mixtures of ionic liquid with 1-alkanol

In this paper, we have tried to describe the factors affecting molecular interactions and structure of binary systems including 1-Hexyl-3-methylimidazolium Nitrate ([Hmim][NO3]) and 1-alkanol (1-hexanol, up to 1-decanol) using Kirkwood-Buff (KB) integrals and structure factor. Obtained results indicate that unlike molecules tend to form favorable interactions via forming hydrogen bonds or dipolar interactions and stay alongside, while an increase in the carbon chain of 1-alkanols reduces the strength of bonds and tendency of the unlike molecules to stay together. Moreover, the structure of mixtures was studied using the concentration-concentration structure factor, SCC(0). Results from the application of this parameter show that in all binary mixtures, heterocoordination is predominant, ordering occurs in solutions and fluctuations are less than random orientation. In addition, the chemical short-range order parameter α′, which is an important function to understand the complex formation and phase segregation in the liquid mixtures, was calculated and discussed for mentioned mixtures. For current binary mixtures, experimental data and theoretical investigations are novel and reported for the first time.

Thermodynamic study of interactions between 1-alkanol and butanone

To obtain the new perspectives on the molecular interactions in the binary systems of butanone and a homologous series of 1-alkanol from 1-pentanol up to 1-decanol, these mixtures were studied using the Kirkwood–Buff (KB) formalism and preferential solvation analysis. The results were confirmed using the experimental excess molar volumes. KB integralsGij, the excess or deficit numberΔnij, and solvation coefficients δijare reported here. Analysis of obtained data regarding the KB formalism and preferential solvation reveals that interactions strength in mixtures depends on the butanone concentration and size of 1-alkanol. Also, interactions between similar molecules are remarkable and become stronger as the length of the alcohol increases. Furthermore, mixtures structure was studied using the concentration-concentration structure factor, SCC(0). Results from application of this parameter show that the homocoordination occurs in solutions. Steric effects lead to the stronger orientations in the mentioned mixtures.

Thermodynamics of mixtures containing a very strongly polar compound. 12. Systems with nitrobenzene or 1-nitroalkane and hydrocarbons or 1-alkanols

Mixtures involving nitrobenzene and hydrocarbons, or 1-alkanols and 1-nitroalkane, or nitrobenzene have been investigated on the basis of a whole set of thermophysical properties available in the literature. The properties considered are: excess molar functions (enthalpies, entropies, isobaric heat capacities, and volumes), vapour-liquid and liquid-liquid equilibria, permittivities or dynamic viscosities. In addition, the mixtures have been studied by means of the application of the DISQUAC, ERAS, and UNIFAC models, and using the formalism of the concentration-concentration structure factor. The corresponding interaction parameters in the framework of the DISQUAC and ERAS models are reported. In alkane mixtures, dipolar interactions between 1-nitroalkane molecules are weakened when the size of the polar compound increases, accordingly with the relative variation of their effective dipolar moment. Dipolar interactions are stronger in nitrobenzene solutions than in those containing the smaller 1-nitropropane, although both nitroalkanes have very similar effective dipole moment (aromaticity effect). Systems with 1-alkanols are characterized by dipolar interactions between like molecules which sharply increases when the alkanol size increases. Simultaneously, interactions between unlike molecules become weaker, as the OH group is then more sterically hindered. Interactions between unlike molecules are stronger in systems with nitromethane than in nitrobenzene solutions. The replacement of nitromethane by nitroethane in systems with a given 1-alkanol leads to strengthen those effects related with the alcohol self-association. Permittivity data and results on Kirkwood's correlation factors show that the addition of 1-alkanol to a nitroalkane leads to cooperative effects, which increase the dipolar polarization of the solution, in such way that the destruction of the existing structure in pure liquids is partially counterbalanced. This effect is less important when longer 1-alkanols are involved.

Calorimetric Measurements of Liquid Al-Zn Alloys

The integral molar enthalpies of mixing were determined by the drop calorimetric method for binary AL-Zn liquid solutions and compared with the Miedema model as well as the earlier experimental data. The measurements were conducted at two temperatures: 957 K and 1001 K (684 °C and 728 °C), in the entire concentration range. Based on the experimental calorimetric data of this study as well as those available in the literature and the results of the activity studies, the interaction parameters of the Redlich-Kister equation for the liquid Al-Zn phase were worked out with the use of the least square method. The partial and integral Gibbs energies, entropies and enthalpies were calculated and presented in tables and figures. Additionally, the concentration-concentration partial structure factors for the ideal and real Al-Zn solutions were calculated and graphically presented.

Thermodynamic properties of liquid Ag-Li alloys

The electrochemical concentration cell method was used in the measurements of the activities of Li in the Ag-Li liquid and solid alloys. Activity measurements were performed with the use of electrochemical cells with liquid LiCl-LiF and LiCl-KCl electrolytes for 9 alloys in the xLi concentration range from 0.1 to 0.9 and at temperatures between 643K and 916K. The linear temperature dependencies of EMF of the Ag-Li alloys were observed and described by the equation EMF(T)=a+bT. The calculated partial thermodynamic functions of Li showed negative deviations from the ideal behaviour. With the application of all the available literature thermodynamic data, the interaction parameters of the Redlich-Kister equation for the liquid Ag-Li phase were worked out with the use of the least square method. The partial and integral Gibbs energies, entropies and enthalpies were calculated and presented in tables and figures. Additionally, the concentration-concentration partial structure factors for the ideal and real Ag-Li solutions were calculated and graphically presented.

Liquid-liquid phase separation of N-isopropylpropionamide aqueous solutions above the lower critical solution temperature.

We investigate driving forces of the liquid–liquid phase separation of N-isopropylpropionamide (NiPPA) aqueous solutions above the lower critical solution temperature using molecular dynamics simulations. Spontaneous phase separations of the model aqueous solution with a modified OPLS-AA force field are observed above the experimentally determined cloud point. The destabilization toward the phase separation is confirmed by temperature dependence of the long-wavelength limit of the concentration-concentration structure factor, the dominant component of which is found to be an increasing effective attraction between NiPPA molecules. At varying temperatures, the potentials of mean force (PMFs) between a pair of NiPPA molecules at infinite dilution are obtained and decomposed into the nonpolar and Coulombic contributions. The nonpolar contribution, arising essentially from molecular volume, promotes association of NiPPA molecules with increasing temperature while the Coulombic one antagonizes the association. Thus, our analysis leads to a conclusion that the driving force of thermally induced aggregation of NiPPA molecules is the temperature dependence of the nonpolar contribution in PMF between NiPPA molecules, not the temperature dependence of the number or strength of hydrogen bonds between NiPPA and water molecules.

Thermodynamics And Atomic Order In Molten Mg-Bi Alloy

The quasi-lattice model based on pairwise interactions has been used to study the large deviation from the ideal mixture and the concentration dependent asymmetry in the thermodynamic properties of Mg-Bi liquid alloy. This has been utilised to extract microscopic information such as concentration-concentration structure factor in long wavelength limit [Scc(o)] and warren-cowley short range order parameter 1 of Mg-Bi liquid alloy at 975K. The analysis suggests that heterocoordination leading to the formation of complex Mg3Bi2 is likely to exist in the melt, and is of strongly interacting nature. The theoretical analysis reveals that the pairwise interaction energies between the species depend considerably on temperature and the alloy is chemically more ordered in Mg-rich region of the phase diagram. The alloy behaves like a segregating system in Bi-rich region. Copyright © 2013 VBRI press.

Simulation and reference interaction site model theory of methanol and carbon tetrachloride mixtures

We report molecular dynamics and reference interaction site model (RISM) theory of methanol and carbon tetrachloride mixtures. Our study encompasses the whole concentration range, by including the pure component limits. We majorly focus on an analysis of partial, total, and concentration-concentration structure factors, and examine in detail the k-->0 limits of these functions. Simulation results confirm the tendency of methanol to self-associate with the formation of ring structures in the high dilution regime of this species, in agreement with experimental studies and with previous simulations by other authors. This behavior emerges as strongly related to the high nonideality of the mixture, a quantitative estimate of which is provided in terms of concentration fluctuation correlations, through the structure factors examined. The interaggregate correlation distance is also thereby estimated. Finally, the compressibility of the mixture is found in good agreement with experimental data. The RISM predictions are throughout assessed against simulation; the theory describes better the apolar solvent than the alcohol properties. Self-association of methanol is qualitatively reproduced, though this trend is much less marked in comparison with simulation results.

Short and intermediate range order in amorphousGeSe2

By using first-principle molecular dynamics within density functional theory, we study the structural properties of amorphous GeSe2 at a temperature T of 300 K. For each property, a statistical average is obtained from six independent partial averages taken on temporal trajectories, each one lasting 12 ps. Each trajectory stems from an initial configuration of the liquid phase at T=1100 K and is generated by extensive annealing at T=300 K. Overall, our level of theory provides a picture of this prototypical disordered network-forming glass that is quantitatively consistent with neutron diffraction data. Very satisfactory agreement with experiments is obtained for the pair correlation functions g(GeSe)(r) and g(SeSe)(r) in terms of peak intensities and positions. This holds true also for the amount of Se-Se homopolar bonds and the Ge-Se and Se-Se coordination numbers. Conversely, the g(GeGe)(r) pair correlation function is much less structured around the main peak position and the concentration of Ge-Ge homopolar bonds is lower than in the experiment. The network organizes itself through the predominant presence of GeSe4 tetrahedra. However, other coordinations occur in non-negligible proportions for both Ge and Se. Total and partial structure factors reproduce very well the experimental patterns for wave numbers k larger than 2 A(-1). For smaller k values, the largest difference between theory and experiment is exhibited by the S-GeGe(k) structure factor, showing a FSDP of lower intensity in the simulation. In agreement with experimental results, a sizeable feature is found at the FSDP location in the Bhatia-Thornton concentration-concentration structure factor S-CC(k).

Microscopic origin of concentration fluctuations over intermediate range distances in network-forming disordered systems

Ab initio molecular dynamics simulations of liquid GeSe2 show that the first sharp diffraction peak in the concentration-concentration structure factor S-CC(k) is due to a sequence of connected fourfold rings. These subunits can be viewed as chains of edge-sharing tetrahedra. Ge atoms at the opposite tails of these chains are mostly miscoordinated and separated from each other by intermediate range distances. This result correlates a specific structural subunit to a subtle intermediate range order property, involving both the structural and chemical composition of the disordered network.

Intermediate-range order in molten network-forming systems

The structural origin of intermediate-range order in two archetypal network-forming liquids, $\mathrm{Ge}{\mathrm{Se}}_{2}$ and $\mathrm{Zn}{\mathrm{Cl}}_{2}$, is investigated via molecular dynamics computer simulation. Relatively simple ionic models, in which a proper description of ion polarization effectively controls the network connectivity, are shown to be capable of showing a first-sharp diffraction peak in the Bhatia-Thornton concentration-concentration structure factor. This feature is shown to arise from the presence of percolating edge-sharing polyhedral units which act to disrupt a corner-sharing network and introduce addition cation density fluctuations on both short- and intermediate-range length scales.

Structure of liquid Rb-Se mixtures: void and fluctuation

Neutron diffraction and EXAFS measurements, and the detailed structural modeling by reverse Monte Carlo simulation have been performed in order to study the short-and intermediate-range structures of liquid Rb-Se mixtures. The Se chains in the liquid mixture are strongly bent to form horseshoe-like Se chains with Rb atoms at the chain ends, creating a large amount of voids. The interaction between Rb and Se atoms is weak and Rb atoms come close together. Near the boundary of the miscibility gap at low temperature the short Se chains link up to form a large cluster, and Rb atoms sit around it. The structure factor S(Q) in the liquid mixture has a small pre-peak at 1.3Å-1. The computed partial Sij(Q) for the RMC model indicates that the pre-peak is associated with the Se-Se interchain component of S(Q). From the void analysis using Delaunay simplices it has been revealed that the observed pre-peak corresponds to a pre-peak in the concentration-concentration structure factor due to the chemically ordered packing of the voids and Se chains in the structure.

Charge fluctuations and concentration fluctuations at intermediate-range distances in the disordered network-forming materialsSiO2,SiSe2, andGeSe2

We calculate the concentration-concentration partial structure factor ${S}_{\mathrm{CC}}(k)$ and the charge-charge structure factor ${S}_{\mathrm{zz}}(k)$ of liquid $\mathrm{Si}{\mathrm{O}}_{2}$, amorphous $\mathrm{Si}{\mathrm{Se}}_{2}$ and liquid $\mathrm{Ge}{\mathrm{Se}}_{2}$ using first-principles molecular dynamics. These systems are characterized by the occurrence of intermediate range order, as evidenced by a first sharp diffraction peak (FSDP) at low $k$ values in the total neutron structure factor. We show that a FSDP in the concentration-concentration partial structure factor ${S}_{\mathrm{CC}}(k)$ is generally associated with a small departure from chemical order. This feature tends to vanish either when sufficiently high levels of structural disorder set in, or, oppositely, when the chemical order is essentially perfect. For none of these networks, a FSDP is observed in the charge-charge structure factor ${S}_{\mathrm{zz}}(k)$, i.e., fluctuations of charge do not occur over intermediate range distances. The constraint of charge neutrality is at the very origin of the appearance of fluctuations of concentration. These are observed when the atoms occur in configurations with different coordinations.

Absence of charge-charge correlations at intermediate-range distances in disordered network-forming materials

Applying a first-principles scheme to liquid ${\mathrm{GeSe}}_{4},$ we show that the charge-charge structure factor does not present any feature at the location of the first sharp diffraction peak (FSDP), despite a clear FSDP in the concentration-concentration structure factor ${S}_{\mathrm{CC}}(k).$ The origin of this effect is assigned in part to the finite extent of the electron density and in part to electron rearrangements. Our result provides evidence in favor of the postulate that, in binary network-forming systems, charge-charge correlations are absent on intermediate-range length scales. A FSDP in the ${S}_{\mathrm{CC}}(k)$ then signals the occurrence of structural defects.