Changes In Liquid Structure Research Articles

Viscosity of liquid Fe at high pressure

Synchrotron x-ray radiography has been used to measure the viscosity of pure liquid Fe at high pressure and temperature in a large volume press. A probe sphere rising through liquid Fe at high pressure and temperature is imaged, in situ, allowing for the derivation of sample viscosity through a modified form of Stokes' equation. The effect of pressure on viscosity is fit by the semi empirical framework for transport coefficients in liquid metals, providing experimental verification of constant viscosity at the pressure-dependent melting temperature of liquid Fe where no change in liquid structure occurs.

Relative Energy Dissipation: Sensitive to Structural Changesof Liquids

Energy dissipation techniques, widely used in solid physics previously, are provento be sensitive also to changes in liquid structure. It has beensuggested from relative energy dissipation that changes in liquid structure canoccur as a function of temperature in some ordinary binary systems such asPb-Sn, In-Sn and In-Bi. This finding may be helpful to understand liquidstructure changing patterns, therefore enriching the phenomenology of liquidstate physics. This is significant for engineering practices.

Kinetics and thermodynamic behavior of carbon clusters under high pressure and high temperature

Physical processes that govern the growth kinetics of carbon clusters at high pressure and high temperature are: (a) structural sp 3-to-sp 2 and sp 2-to-sp bonding changes and (b) cluster diffusion. Our study on item (a) deals with ab initio and semi-empirical quantum mechanical calculations to examine effects of cluster size on the relative stability of graphite and diamond clusters and the energy barrier between the two. We have also made molecular dynamics simulations using the Brenner bond order potential to show that the melting line of diamond based on the Brenner potential is reasonable and that the liquid structure changes from mostly sp-bonded carbon chains to mostly sp 3-bonding over a narrow pressure interval. We examined item (b) by using the time-dependent cluster size distribution function obtained from the relevant Smoluchowski equations. The resulting surface contribution to the Gibbs free energy of carbon clusters was implemented in a thermochemical equilibrium code and also to a new detonation model in a hydrodynamic code to examine the behavior of carbon-rich explosives. We find that carbon-rich explosives are sensitive to the metastability of graphitic carbon clusters and also to a delayed release of the surface energy of carbon clusters by the slow diffusive clustering processes.

Dielectric Relaxation of NaClO4Solutions in Formamide, N-Methylformamide, and N,N-Dimethylformamide

Complex permittivity spectra in the frequency range 0.95 ≤ v/[GHz] ≤ 89 for N,N-dimethylformamide (DMF), N-methylformamide (NMF), formamide (FA) and their solutions of NaClO4 are investigated to study the change of liquid structure and dynamics arising from the availability of one hydrogen-bond acceptor site together with no (DMF), one (NMF), or two (FA) donor sites on the same molecule. Three solvent relaxation processes are observed for NMF and two for FA and DMF. The relaxation parameters are used to determine solvation numbers. They show that ion-solvent interactions lead to a reduction of the average length of the H-bonded NMF chains but have only moderate influence on the FA structure. An additional solute relaxation process in DMF solutions is due to the diffusion-controlled formation and decomposition of solvent-shared ion pairs.

Acceptor Numbers for Binary Mixtures of Dipolar Aprotic Solvents with Methanol

Using bis(cyano)bis(9,10-phenanthroline)iron(II) as solvatochromic indicator, the acceptor numbers, AN, were determined for binary mixtures of benzene, benzonitrile, acetonitrile, acetone, N,N-dimethylformamide, dimethyl sulfoxide and hexamethylphosphoric triamide with methanol. Deviations from linearity of the plots of AN values against the molar fraction of the components were interpreted both in terms of changes in solvent liquid structure and in cathegories of preferential solvation.

Correlation of Aqueous Two‐Phase Partitioning of Proteins with Changes in Free Volume

AbstractPhase separation and protein partitioning in polymer‐salt aqueous two‐phase systems have been correlated with changes in free volume. Both solute partitioning and phase stability are proposed to be related to those changes in liquid structure that can be described by measurements of the free volume of the mixture upon phase splitting.

Study on liquid–vapor interface of water. I. Simulational results of thermodynamic properties and orientational structure

Molecular dynamics simulations have been carried out for liquid–vapor interface of water and also of Lennard-Jones system. Surface tension and surface excess energy are calculated, from which surface excess entropy is evaluated. These thermodynamic quantities suggest the existence of some liquid-structural change near the surface of water, which is not seen in Lennard-Jones system. For water, orientational structuring near the surface is studied and two types of orientation are found. In the vapor side, a water molecule has a tendency of projecting one hydrogen atom toward the vapor, and in the liquid side, a molecule prefers to lie down on the surface with both hydrogen atoms slightly directed to the liquid. From these results, surface potential χ can be evaluated to be about +0.16 V at T=300 K, which confirms recent experimental results. The ellipticity coefficient is also discussed and the assumption often used in analysis of experimental results of ellipsometry is found to be inadequate for water due to the structural change. These observed orientational orderings are qualitatively consistent with results of molecular theory of surface recently developed and also with simulational results of water near hydrophobic walls.

SSOZ integral equation for polar hard dumbbell fluids

We present the solution of the site-site Ornstein-Zernike equation (SSOZ) for polar hard dumbbell fluids with site-site mean spherical-like (MSA) and hypernetted chain-like (HNC) closures. Numerical solution of this matrix equation is performed using Gillan's method with a renormalization to remove divergences arising from the long-range potentials. The results are compared with Monte Carlo results for pure fluids, and the agreement is good. We consider polar/nonpolar hard dumbbell mixtures where both components have the same elongation and study the change of liquid structure and internal energy with composition.

Proton spin–lattice relaxation study of intermolecular interactions in the methanol + dimethylsulphoxide liquid system

The intra- and inter-molecular contributions to the proton spin-lattice relaxation rate [(1/T1)expt] for the methyl and hydroxyl groups of methanol as well as for dimethylsulphoxide (DMSO) in the methanol + DMSO liquid system were determined as a function of composition at temperatures between 0 and 41.4°C. The distances of closest approach between two groups [d(R–R′)] for various intermolecular interactions were evaluated from the intermolecular contributions to (1/T1)expt. A comparison of the d(R–R′) values reveals that the order of magnitude in the intermolecular interactions in the equimolar and methanol-rich mixtures is: OH–OH > OH–DMSO > Me–DMSO ∼ Me–Me. In the methanol-poor mixtures the order changes to: OH–DMSO ≳ OH–OH > Me–DMSO > Me–Me. There seems to be a distinct change in liquid structure going from the methanol-rich to -poor mixtures.

Emf's across CdI2 ‐ Cd2 I 2 Electrolytes Using Electrodes of Bare W, Molten Cd, and Molten Au‐Cd: Bare Electrode Effects, Use of n ≠ 2 , Premonitory Phenomena and Liquid Structure in Au‐Cd, and the Cd ‐ CdX2 Phase Diagrams

Emf measurements have been made on cells with mixed‐valence electrolytes (a) to establish structural and thermodynamic properties for molten Au‐Cd alloys and (b) to study the source and behavior of some unexpected voltages associated with bare W electrodes dipping into these electrolytes. Changes with temperature and composition of the partial molal entropies, enthalpies, and free energies of the Cd component in the Au‐Cd melts point out the existence of premonitory changes a few degrees above the liquidus as well as of liquid structural changes far from the liquidus; these changes correlate with earlier studies by vapor pressure and by electrical conductivity in the Au‐Cd system at higher temperatures. is used to evaluate the effective valence for these electrolytes when saturated with Cd; this appears in calculation of . Apparently the mixed‐valence electrolyte, plus probable oxide impurities, reacts with the bare electrode (in this case W) surfaces by direct chemical action to form surface films which protect the metal below against direct chemical attack. These films are in equilibrium with the electrolytes. When, however, electrochemical attack is permitted, as when an emf measurement is made, then the underlying metal becomes subject to attack and another reactant enters the reaction. This effect leads to anomalous voltages in electrodes which are normally considered to be inert in molten salts, e.g., W, Mo, and graphite. If these sources of voltage are recognized, then proper determinations of activities and phase boundaries can be made; some earlier measurements of this type which neglected these voltages, however, must be reevaluated. Application of these proper techniques to the system is made.

Electric Strength and Liquid Structure

Recent work on the electric strength of pure hydrocarbon liquids has shown that the strength is probably determined by the amount of energy lost by conduction electrons exciting molecular vibrations by collisions while moving under the applied field through the liquid. The strength can then be determined in terms of a mean free path for the collisions involved. The present paper attempts to show that the liquid structure, i.e., the molecular arrangements in the liquid phase, is also influencing the strength, and this is illustrated by measurements of the temperature effect on the strength of some n-paraffins, the molecules of which are known to pack with their long axes parallel producing a degree of anisotropy. Distinct breaks in the electric strength vs temperature characteristics are found, even when density changes are accounted for, and these occur at temperatures which are in very good agreement with similar breaks in the characteristics of other properties such as density, viscosity, and heat capacity. These breaks have already been associated with changes in liquid structure from quasi-crystallinity to molecular libration (245°K) and from molecular libration to free rotation (288–353°K). If molecular orientation takes place in the applied field then the electron energy loss will be different in the three liquid ``phases'' and would account for the observed transitions in the breakdown characteristics.