Quasi-lattice Structure Research Articles

Pseudo-Optical Modes in Room-Temperature Ionic Liquids.

The terahertz spectrum encodes information about dynamics, structure, and intermolecular interactions of liquids being probed both experimentally and computationally by techniques such as Raman and far-infrared spectroscopies and molecular dynamics (MD) simulation. In the case of room temperature ionic liquids (RTILs), there has been a debate whether a mode observed at about 1.5-2.7 THz (50-90 cm-1) is due to a quasi-lattice structure or the formation of complex ions. Here we show through the analysis of Raman and far-infrared spectra and MD simulation of a typical RTIL that this mode has a collective optic-like character. Then, employing a simple model based on the theory for optical phonons in crystals, we show that a correlation between the frequency of this mode and material parameters holds for different RTILs. These results, which encompass a wide range of samples, reinforce a quasi-lattice view of the liquid phase.

Using FT-IR Spectroscopy to Measure Charge Organization in Ionic Liquids

A major goal in the field of ionic liquids is correlating transport property trends with the underlying liquid structure of the compounds, such as the degree of charge organization among the constituent ions. Traditional techniques for experimentally assessing charge organization are specialized and not readily available for routine measurements. This represents a significant roadblock in elucidating these correlations. We use a combination of transmission and polarized-ATR infrared spectroscopy to measure the degree of charge organization for ionic liquids. The technique is illustrated with a family of 1-alkyl-3-methylimidazolium trifluoromethanesulfonate ionic liquids at 30 °C. As expected, the amount of charge organization decreases as the alkyl side chain is lengthened, highlighting the important role of short-range repulsive interactions in defining quasilattice structure. Inherent limitations of the method are identified and discussed. The quantitative measurements of charge organization are then correlated with trends in the transport properties of the compounds to highlight the relationship between charge and momentum transport and the underlying liquid structure. Most research laboratories possess infrared spectrometers capable of conducting these measurements; thus, the proposed method may represent a cost-effective solution for routinely measuring charge organization in ionic liquids.

Liquid structure of benzene and its derivatives as studied by means of X-ray scattering

The liquid structures of benzene, toluene, aniline, benzaldehyde and nitrobenzene were investigated by the X-ray scattering method. The X-ray scattering data were analysed by a method without constructing any structure models. The obtained liquid structure of benzene is different from the previous X-ray scattering results which were derived from the quasi-lattice structure for the liquid based on the crystal structure of benzene. This is because a molecular arrangement which is not found in the crystal structure is left out of consideration. In liquid toluene, benzaldehyde and nitrobenzene, two molecules are associated with the dipole–dipole interaction in the antiparallel fashion. Two aniline molecules are hydrogen-bonded in liquid aniline. The third molecule weakly interacts with the other two in liquid toluene, aniline and benzaldehyde. In liquid nitrobenzene, the parallel dipole–dipole interaction of the third molecule with another one is present in the coplanar form. The substituent effect on the liquid structures is discussed.

Modified Eyring viscosity equation and calculation of activation energy based on the liquid quasi-lattice model

Viscosity is an important physical parameter of fluid, and the Eyring viscosity equation is a popular viscosity theory. Based on the Eyring reaction rate equation and Boltzmann statistical theory, and including the probabilities of creating a hole in liquid and the transition to the neighboring hole, a modified Eyring viscosity equation was proposed. According to the structural characteristics of short-range order, liquid is treated as a quasi-lattice structure in a small region. The activation energy, which is the minimum energy needed for the molecule to jump to its neighboring hole because of the restriction of other molecules around it, was analytically calculated from an intermolecular Lennard-Jones potential function and a Stockmayer potential function. The viscosity values of 37 kinds of typical liquids at 25°C and the dependence of viscosity of three kinds of liquids on temperatures were calculated with this modified viscosity equation, and the calculated results agree with the experimental values to some extent. This work not only enriches the understanding of the mechanism of liquid viscosity, but also could provide some theoretical guides for the relevant studies and applications.

Simultaneous Correlation of Saturated Viscosities of Pure Gases and Liquids Using the Significant Structure Theory

The significant structure theory (SST) for liquid viscosities, originally proposed by Eyring, coupled with a cubic equation of state was used for the simultaneous correlation of gas and liquid viscosities of pure fluids (polar and nonpolar) at saturated conditions. The SST visualizes a liquid as having both solidlike and gaslike degrees of freedom with fluidized vacancies of molecular size randomly distributed throughout a quasi-lattice structure. In this context, the viscosity of a liquid is calculated from two main components: a gaslike η g and a solidlike η s contribution. The first viscosity contribution η g represents the viscosity of a pure fluid at dilute gas conditions (low-pressure viscosity). The method of Chung et al. based on the Chapman-Enskog kinetic theory of gases was used to calculate η g . The second contribution η s captures the solidlike effects on viscosity. This quantity was calculated by means of Eyring's absolute rate theory. All the thermodynamic properties required in the viscosity model were computed via the use of a well-known cubic equation of state (Soave-Redlich-Kwong or Peng-Robinson) thus allowing the simultaneous correlation of gas-liquid viscosities along their coexistence curve. The resulting model was satisfactorily validated in the representation of experimental saturated gas and liquid viscosities of a highly polar compound (water) and a nonpolar fluid (propane) over a wide range of temperatures (from near the triple point up to the critical region of the fluid of interest).

Leakage behavior of the quasi-superlattice stack for multilevel charge storage

The leakage behavior of the quasi-superlattice structure has been characterized by current–voltage measurements at room temperature and 50 K. A resonant tunnelinglike leakage characteristic is observed at low temperature. The resonant tunneling occurs at around 2, 5.2, and 7 V under a gate voltage swept from 0 to 10 V. A concise physical model is proposed to characterize the leakage mechanism of tunneling for the quasi-lattice structure and suggests that the considerations of the operating voltage for the two-bit per cell nonvolatile-memory device need to be taken into account.

Emf studies of a ternary molten AgNO 3KNO 3NaNO 3 system

The excess chemical potentials of AgNO 3 have been measured using a suitable formation cell over a wide composition range of the ternary AgNO 3KNO 3NaNO 3 system. The coefficients of series expansions in the composition variables of ▪ and x AgNO 3 for isothermal excess chemical potential of AgNO 3 were determined. The experimental data show a minimum at t = 0.500 for all the temperatures and mole fractions of silver nitrate. Such an anomalous phenomenon in a ternary AgNO 3KNO 3NaNO 3 molten system is explained on the basis of the behavior of the subsidiary binary systems, as well as by change in the quasi-lattice structure of the melt, as a consequence of increasing the mole fraction of AgNO 3 in the mixture. The conformal ionic solution (CIS) theory has been tested with respect to its capability to predict the excess chemical potential in a ternary AgNO 3KNO 3NaNO 3 molten system. From the linear temperature dependence of emf values in pure AgNO 3 and in ternary molten salt mixtures, the partial excess enthalpies and partial excess entropies of silver nitrate in the AgNO 3KNO 3NaNO 3 melts were calculated.

Construction of the Quasi-Lattice Structure According to Local Equivalence Postulate: Packing of Helical Polymer Molecules

The unperiodic quasi-lattice structure has been constructed of the helical polymer molecules starting from the interaction potentials of the molecules. The process of the construction is explained in detail. The construction is carried out according to the local equivalence postulate which requires that all pairs of the nearest neighbor molecules in the system are packed in the equivalent way. The construction is based on the symmetry of the molecules and not dependent on the shape of the potential function of each material. The obtained quasi-lattice structure is the ground state of the system. Both the one dimensionally unperiodic structure and the two dimensionally unperiodic structure are found. Geometric features of the quasi-lattice structure are investigated.

Hole theories for liquids and compressed gases: a theoretical comparison of equations of state

The theoretical expressions for the equation of state of a pure component, derived from the hole theory of Simha and Somcynsky and the lattice gas model of Kleintjens and Koningsveld, are examined in detail. Similarities and differences are discussed. From this, the comparable quality of description for experimental data offered by both theories can be appreciated. For the Kleintjens-Koningsveld theory, a scaled equation of state is derived. However, no principle of corresponding states is obtained. I. Introduction A few years ago, an effort was made to compare the hole theory' of Simha and Somcynsky (S-S) with the lattice gas model2 of Koningsveld and Kleintjens (K-K). At that time a numerical comparison was offered, based on ex- perimental data for eth~lene.~ The experimental data consisted of the critical conditions and a series of isotherms for both gaseous and liquid states. It was observed that both theories have a similar overall quality of agreement with experimental data. However, a detailed comparison of the theoretical expressions was not made. 11. The Configurational Partition Function Both theories model a pure component in its liquid state as a quasi-lattice structure with sites either vacant or oc- cupied by a segment of a linear s-mer. The quasi-lattice allows the evaluation of the configurational partition function Z which is factored into three contributions:

Ultrasonic nonlinear parameters and sound speed of alcohol-water mixtures.

Changes in the nonlinear parameter B/A caused by the addition of monohydric alcohols to water have been investigated. The measurements, made by using an aqueous solution of n-propanol, isopropanol, and t-butanol, show that as the alcohol concentration is increased, B/A decreases to a minimum at approximately 10% concentration (by volume). Further increase in alcohol concentration raises B/A rapidly to a maximum at about 80% by volume. This complex variation in B/A is attributed to solute-solvent interaction which is believed to be due to an enhancement of water structure in the water-rich region. These results suggest that the magnitude of B/A may be closely related to the quasilattice structure of water, which to a first approximation can be expressed by relative amounts of bound and unbound water.

Monte Carlo calculations of thermodynamic properties of alloys in the case of the surrounded atom model

Monte Carlo calculations are carried out to give exact values of some thermodynamic properties of alloys. The calculations are performed within the framework of the surrounded atom model the main assumptions of which are: quasilattice structure of the alloy, nearest neighbour interactions, description of the configuration in terms of “surrounded atoms”. The results are then compared with those obtained using current approximations: the Bragg-Williams treatment and the quasichemical treatment. This work enables us to generalize the previous conclusions drawn in the study of the regular solution model. In every case, whatever the sign of the interactions (ordering or clustering tendency) Monte Carlo calculations yield a local order that both approximations fail to reproduce. In order to compare the calculations with some experimental data, Cowley's short range order parameter α 1, is calculated by Monte Carlo and by the approximate methods (the parameters of the surrounded atom model are derived from thermodynamic data). The Monte Carlo values compare better than the quasichemical ones with the data obtained by X-ray or neutron diffraction in three actual systems.

Liquidus calculation of II–VI compound semiconductors

The pair approximation (which is equivalent to the quasi-chemical method) is used to calculate liquidus of II–VI compound semiconductors. For the liquid phase, a quasi-lattice structure is assumed and the pressure and the association property are taken into account. Vieland's formula is used for the free energy difference between liquid and solid. Numerical calculation was made with the Hg-Te and Cd-Te systems. For each system, one set of parameters is found which computes the liquidus in good agreement with experiments for the entire composition and temperature ranges. A particular attention is paid to the shape of the liquidus curve near its top. Experimentally it looks pointed, although thermodynamics requires it to be rounded. Our calculation shows that when the AB-A and AB-B interactions are repulsive, the theoretical curve looks pointed and the top region has a very small radius of curvature.

Radial distribution function of liquid argon according to significant structure theory

The significant structure theory of liquids is tested by evaluating the radial distribution function. The calculations are based on face-centered cubic quasi-lattice structure, and the fluctuation in volume is used to describe the thermal displacements of molecules. It is shown that the local structure of liquids has inhomogeneous distributions. The correlation at long ranges becomes negligible because of the fluidized vacancies in our model. The calculations are performed for liquid argon, and the results are in good agreement with experiments.

Small-angle maxima and cation-cation distances. Differences between iron nitrate and perchlorate solutions

X-ray diffraction data of aqueous solutions of iron(III) nitrate show a small-angle peak at an s value of about 0.5–0.9 A−1. A constant relationship between peak position and concentration leads to reject the hypothesis of a quasi-lattice structure for the solutions investigated. On the contrary, no peak is present in the same s range of diffraction data of iron (III) perchlorate solutions.

ChemInform Abstract: FORMATION CONSTANTS OF CHLOROCADMIUM(II) AND CADMIUM DICHLORIDE IN AQUEOUS MELTS OF CALCIUM DINITRATE AND CALCIUM DINITRATE‐POTASSIUM NITRATE

AbstractAus EMK‐ Messungen in Konzentrationsketten des Typs A werden die Bildungskonstanten von CdCl sowie CdClz in den wasserhaltigen Schmelzen von Ca[NO3]2°C xHzO und Ca[NO3]2°K[NO3] ‐ xHzO (x = 3,5‐7) bei 50, 65 und 80°C bestimmt.

Formation constants of chlorocadmium(II) and cadmium dichloride in aqueous melts of calcium dinitrate and calcium dinitrate–potassium nitrate

Formation constants of [CdCl]+ and CdCl2 in aqueous melts of Ca[NO3]2·xOH2 and Ca[NO3]2·K[NO3]·xOH2(x= 3.5–7) have been determined at 50, 65, and 80 °C from e.m.f. measurements in suitable concentration cells. The results are discussed in terms of a quasi-lattice structure of aqueous melts, and a model is proposed which predicts the dependence of thermodynamic data for [CdCl]+ formation on the temperature and water content of the molten salt.

The quasi-lattice structure in concentrated aqueous solutions

The total neutron diffraction pattern from an aqueous solution of nickel chloride shows a pre-peak at a q value of approximately 1 A −1, which has been identified as the principal peak in the NiNi partial structure factor. In this paper we report an investigation of the position of the pre-peak as the molarity ( C) of the solution is changed. The data show that the peak position is proportional to C 1/3, which argues strongly in favour of the quasi-lattice model for aqueous solutions.

Electrical Conductivities and Molar Volumes in the Binary Systems MnCl2 ‐ LiCl , MnCl2 ‐ NaCl , MnCl2 ‐ KCl , MnCl2 ‐ RbCl , MnCl2 ‐ CsCl

The densities and the electrical conductivities of the five binary , have been measured. The molar volumes exhibit increasing positive deviations from additivity, as the size of the alkali metal cation in ACl is increased from , and have a maximum positive deviation at approximately . The molar conductances exhibit an increasing negative deviation from ideality, with a minimum occurring approximately at . The concentration dependence of the molar volumes and of the electrical conductivities in these systems is interpreted in terms of a complex ion model (1) proposed previously for the purpose of interpreting their thermodynamic properties. According to this model the solutions of with alkali chlorides are characterized by the presence of the complex anions. The difference between a “free” chloride anion and a chloride anion bonded within a complex configuration, lies in differences in the strength of the anion‐to‐cation bonds in these two configurations. In this respect, the continuity of the quasilattice structure of a molten salt is not disrupted by the presence of complex species and the latter are not expected to occupy single “lattice” sites within the liquid, as local electrical neutrality is always maintained. Good agreement is obtained between the experimental and the theoretical values for the electrical conductivities and the molar volumes in the systems , , and . The deviations from ideal behavior are small in the systems and . The coefficients for thermal expansion and the activation energies for specific and molar conductances were also calculated from the experimental results and their concentration dependences are also indicative of complex formation.

Water in melts: Raman spectral investigation of the molten Ca(NO3)2�4H2O?KNO3 system

The Raman spectra of molten mixtures of Ca(NO3)2\4H2O−KNO3 have been examined, covering the concentration range of 0–70 mole% KNO3. The frequencies in the spectra of the mixtures have been found to change slightly with concentration. Striking variations in the band shapes have been observed in the regions corresponding to the O−H stretching mode (2850–3850 cm−1) and the v4-NO 3 − mode (700–750 cm−). The results are discussed in terms of perturbed quasi-lattice structure for the melt, in which there could be a displacement of water molecules in the first coordination sphere around Ca2+ by the NO 3 − ion.

Raman Spectra of Molten NaBF4 to 606°C and 8% NaF-92% to 503°C

The Raman spectra of molten NaBF4 samples have been measured to 606°C, and spectra of samples of the eutectic mixture of 8 mole % NaF in NaBF4 were recorded to 503° using 4880-Å radiation from an argon-ion laser for excitation. The BF4− ion appeared to retain its tetrahedral symmetry under all the conditions studied in this investigation. The frequency of the ν1(a1) mode of BF4− decreased with increasing melt temperature, and weak, asymmetric features on the bands from the ν2(e) and ν4(f2) modes were observed in molten NaBF4 and in the melts with 8 mole % NaF. The interpretation of the Raman spectra of molten NaBF4 does not require postulating the existence of a quasilattice structure or phonons in the molten state.