Density Of Liquid Phase Research Articles

Thermodynamic property correlation of pure hydrogen fluoride

Empirical methods are proposed to correlate the thermodynamic properties of pure hydrogen fluoride. The methods hinge on the application of a multi-constant equation of state previously derived by the author, whose analytical form can be adapted to the complexity of the studied systems.The correlation of pure HF properties requires the application of the chosen EOS endowed with a number of empirical parameters which range from 8 to 11.Among the pure HF properties correlated in the full experimental range are: vaporization enthalpies, orthobaric densities of both liquid and vapor phases, the PVT data reported by Stromeier and Briegleb in the subcritical range and by Frank and Spalthoff in both in the subcritical and supercritical range up to 300bars and 573K.The method followed to insert the association models in the context of an EOS is also briefly discussed.

Solid–liquid equilibrium (SLE) of ternary system 3-nitrophthalic acid + 4-nitrophthalic acid + 1,4-dioxane at (283.15, 293.15, 303.15, 313.15 and 323.15) K

In this work, solid–liquid equilibria (SLE) data for ternary 3-nitrophthalic acid+4-nitrophthalic acid+1,4-dioxane system was determined at (283.15, 293.15, 303.15, 313.15 and 323.15)K, respectively. The solid–liquid phase diagrams of the ternary system were constructed based on the measured solubility data. The solid phases formed in the studied system were determined by Schreinemaker's wet residue method. In addition, the density of equilibrium liquid phase was obtained. At each temperature, there are two pure solids formed which correspond to 3-nitrophthalic acid and adduct of 4-nitrophthalic acid with 1,4-dioxane, in which the mole ratio of the two components is 2:3, in the ternary 3-nitrophthalic acid+4-nitrophthalic acid+1,4-dioxane system. The solubility data for the ternary system were regressed and calculated using the NRTL model which gives acceptable results for the investigated systems.

Studies on ultrathin films of tricycloquinazoline (TCQ) based discotic liquid crystal molecules

The assembly of disk-shaped molecules on surfaces has drawn considerable attention because of their unique electro-optical properties. We have studied the monolayer of the tricycloquinazoline based disk-shaped (TCQCB) molecules at air-water and air-solid interfaces. The TCQCB molecules form a stable Langmuir monolayer at the air-water interface. The monolayer exhibits gas, low density liquid (L1), and high density liquid (L2) phases. In L1 and L2 phases, the molecules prefer edge-on conformation. The atomic force microscope study on the Langmuir-Blodgett films of the molecules reveals a structural transformation. The elongated domains in the film deposited in L1 phase transformed to a compact grainy texture in the film deposited in the L2 phase.

Free energy surface of ST2 water near the liquid-liquid phase transition

We carry out umbrella sampling Monte Carlo simulations to evaluate the free energy surface of the ST2 model of water as a function of two order parameters, the density and a bond-orientational order parameter. We approximate the long-range electrostatic interactions of the ST2 model using the reaction-field method. We focus on state points in the vicinity of the liquid-liquid critical point proposed for this model in earlier work. At temperatures below the predicted critical temperature we find two basins in the free energy surface, both of which have liquid-like bond orientational order, but differing in density. The pressure and temperature dependence of the shape of the free energy surface is consistent with the assignment of these two basins to the distinct low density and high density liquid phases previously predicted to occur in ST2 water.

Biomineralization Mechanisms: A New Paradigm for Crystal Nucleation in Organic Matrices

There is substantial practical interest in the mechanism by which the carbonated apatite of bone mineral can be initiated specifically in a matrix. The current literature is replete with studies aimed at mimicking the properties of vertebrate bone, teeth, and other hard tissues by creating organic matrices that can be mineralized in vitro and either functionally substitute for bone on a permanent basis or serve as a temporary structure that can be replaced by normal remodeling processes. A key element in this is mineralization of an implant with the matrix and mineral arranged in the proper orientations and relationships. This review examines the pathway to crystallization from a supersaturated calcium phosphate solution in vitro, focusing on the basic mechanistic questions concerning mineral nucleation and growth. Since bone and dentin mineral forms within collagenous matrices, we consider how the in vitro crystallization mechanisms might or might not be applicable to understanding the in vivo processes of biomineralization in bone and dentin. We propose that the pathway to crystallization from the calcium phosphate-supersaturated tissue fluids involves the formation of a dense liquid phase of first-layer bound-water hydrated calcium and phosphate ions in which the crystallization is nucleated. SIBLING proteins and their in vitro analogs, such as polyaspartic acids, have similar dense liquid first-layer bound-water surfaces which interact with the dense liquid calcium phosphate nucleation clusters and modulate the rate of crystallization within the bone and dentin collagen fibril matrix.

An image analysis procedure for measuring the surface tension of pendant micro-drops

A method based on an image analysis procedure was developed to calculate the shape and surface tension of pendant droplets hanging down in air from the tip of a syringe. In contrast to most existing methods, a numerical solution of the Young-Laplace equation of capillarity for the calculation of the drop contour is not required. Apart from local gravity and densities of liquid and fluid phases, the only input information needed to determine the surface tension is given by the maximum equatorial radius of the drop and its degree of deformation defined by a shape factor. Specifically it is not necessary to determine the radius of curvature at the apex of the experimental drop profile, the drop height, or the contact angles. When the drops are formed from the tip of a capillary tube, the software obtains direct digitization of the drop image, performs edge detection, and reconstructs the three-dimensional drop from its digitized profile to accurately determine its volume. Surface tension measurements have been performed for distilled water drops suspended in air to test the reliability and accuracy of the method. The results show that reliable values of the surface tension can be obtained for drops larger than about 2--3 μl, with relative errors less than 0.08--0.29 mN m^{-1}, depending on the size of the holder.

Numerical estimate for boiling points via Wang–Landau simulations

We show how molecular simulations, based on the Wang–Landau (WL) sampling method, can be used to determine the boiling points of a wide range of fluids. The simulations presented here rely on an efficient sampling of the isothermal–isobaric ensemble. This circumvents the difficult deletion/insertion of molecules in dense liquid phases, such as those encountered at the standard boiling point. Using a combination of the WL sampling and hybrid Monte Carlo simulations, we show how we can determine the standard boiling point of atomic fluids, such as liquid metals. We then apply WL configurational bias Monte Carlo simulations to determine the boiling points for a series of long n-alkane chains (icosane, tetracosane and triacontane). The results obtained in this work are in good agreement with the available experimental data and simulation results.

A model for molecular emulsions: Water and “weak water” mixtures

The SPC/E water model is mixed with three 《weaker》 versions of it, obtained by reducing the initial partial charges by multiplicative factors of 1/3, 2/3 and 4/5, respectively, while keeping the same diameter as water, and adjusting only the energy parameters such as to keep each neat substance in a dense liquid phase under ambient conditions. These models cover the observed behaviour of many realistic aqueous mixtures, ranging from demixing (the 1/3 model) to fully mixed hydrophobic-like (2/3) or hydrophilic-like (4/5) situations, the latter both showing strong and weak micro-heterogeneity, respectively. The simulations show that micro-segregation arises even when all constituents have the same length scale, under the sole influence of hydrogen bonding interactions. However, this micro-heterogeneity itself introduces a second length scale by producing domain oscillations in the distribution functions in the nanometer range, that can be captured by making a formal analogy with micro-emulsions. This approach explains the origin of the anomalously large Kirkwood–Buff integrals, often obtained in simulations of realistic aqueous mixtures, as a transient behaviour in the domain range. The analogy can be used to calculate the correct integrals by accounting for domain statistics, without the need to perform expensive large scale simulations.

Swaging of liquid phase sintered 90W–7Ni–3Fe tungsten heavy alloy

The aim of this study was to investigate the effect of swaging on the microstructure and mechanical properties of vacuum sintered 90W–7Ni–3Fe alloys. Cold isostatically pressed samples were sintered under vacuum at 1510°C, for 30min. Samples were then 15% cold rotary swaged. The study has shown that, mechanical properties of relatively low density (<98% theoretical) liquid phase sintered 90W–7Ni–3Fe alloy can be considerably improved by swaging due to increase in density and strain hardening.

Measurement and correlation of saturated liquid properties and gas solubility for decane, tetradecane and their binary mixtures saturated with carbon dioxide

The solubilities of carbon dioxide (CO2) in decane, tetradecane and their binary mixtures have been measured at a temperature of 373.2K and pressures up to 6MPa using a rocking mechanism pressure–volume–temperature apparatus. The measurements presented in this paper were undertaken to determine the solubility and liquid saturated properties (density and viscosity) when a liquid hydrocarbon (decane, tetradecane and their mixtures) was saturated with CO2. The generated data for compositions and densities were correlated with the Soave–Redlich–Kwong and Peng–Robinson equations of state (EOSs). The binary interaction parameters were adjusted, and the volume translation technique was employed to correlate the experimental compositions and densities. The generated ternary data were correlated with the adjusted binary parameters from the data of binary pairs (CO2+decane) and (CO2+tetradecane). The calculated ternary compositions were found to be in good agreement with the experimental data using the binary parameters from the data of binary pairs for both EOSs. The results for the density of the saturated liquid phase indicated that volume translation should be applied to all components in the binary and ternary systems to accurately describe the saturated liquid densities for mixtures.

Nonmonotonic Dependence of the Absolute Entropy on Temperature in Supercooled Stillinger-Weber Silicon

Using a recently developed thermodynamic integration method, we compute the precise values of the excess Gibbs free energy (G e ) of the high density liquid (HDL) phase with respect to the crystalline phase at different temperatures (T) in the supercooled region of the Stillinger-Weber (SW) silicon (Stillinger and Weber in Phys. Rev. B 31:5262–5271, 1985). Based on the slope of G e with respect to T, we find that the absolute entropy of the HDL phase increases as its enthalpy changes from the equilibrium value at T≥1065 K to the value corresponding to a non-equilibrium state at 1060 K. We find that the volume distribution in the equilibrium HDL phases become progressively broader as the temperature is reduced to 1060 K, exhibiting van-der-Waals (VDW) loop in the pressure-volume curves. Our results provides insight into the thermodynamic cause of the transition from the HDL phase to the low density phases in SW silicon, observed in earlier studies near 1060 K at zero pressure.

Liquid Crystals at Interfaces

AbstractThe ordering in liquid crystals (LCs) can be influenced by an interface. Some of these molecules adsorbed at the air‐water interface yield a stable Langmuir monolayer. They exhibit numerous surface phases, which are classified on the basis of intermolecular separation and ordering. These surface phases are governed by the molecular interactions and the ambient experimental conditions such as temperature, humidity, pH, and ion content of the subphase. In this article, the role of molecular interactions on the surface behavior of several rodlike LCs are discussed. The Langmuir monolayer of a cholesteric LC exhibits an interesting low density liquid (L1′) phase with tilted molecules. Brewster angle microscopy reveals stripe patterns, which arise due to the precession of the tilted molecules. It is demonstrated that this molecular precession can be controlled by the relative humidity, presence of cations in the subphase, and incorporation of appropriate molecular species. The Langmuir monolayer and Langmuir‐Blodgett films of a novel rod‐disc hybrid LC are discussed.

Phase composition and saturated liquid properties in binary and ternary systems containing carbon dioxide, n-decane, and n-tetradecane

Experimental phase equilibrium data have been measured for the binary and ternary systems containing (carbon dioxide, n-decane, and n-tetradecane) at 323.2K over the pressure range (1 to 6)MPa using a designed PVT apparatus. The measurements presented in this paper were undertaken to determine liquid phase composition and liquid saturated properties (density and viscosity) when a liquid hydrocarbon (n-decane, n-tetradecane, and their mixtures) was saturated with carbon dioxide. The generated data for compositions and densities were correlated with the Soave–Redlich–Kwong (SRK) and Peng–Robinson (PR) equations of state (EOS). The adjustment of binary interaction parameters and volume translation technique has been employed to correlate the experimental compositions and densities. The adjusted binary parameters from the data of binary pairs (carbon dioxide+n-decane) and (carbon dioxide+n-tetradecane) were used to correlate the generated ternary data. The calculated ternary compositions were found to be in good agreement with the experimental data using the binary parameters from the data of binary pairs for both EOSs. The results for the density of saturated liquid phase indicated that the volume translation should be applied to all components in the binary and ternary systems to describe accurately the saturated liquid densities for mixtures.

Effect of Electric Field on Water Confined in Graphite and Mica Pores

We examined the influence of external electric field on the vapor–liquid coexistence curve and on structural properties of TIP4P/2005 water confined in hydrophobic and hydrophilic pores using all-atom molecular dynamics simulations. While the electric field increases the critical temperature of bulk water, the effect is contrary on the confined water. We clearly observe that the critical temperature of confined water decreases with increasing field strength. The current work strongly indicates that using electric field results in a decrease in the saturated liquid phase density and increase in the saturated vapor phase density of the confined water and can be used to modulate the evaporation rate of water under confinement. The effect of an electric field on the confined fluids is more pronounced at higher temperature. We also report that the critical density of water behaves differently in hydrophobic and hydrophilic pores. With increasing electric field, the critical density increases in hydrophobic pores; however, it is found to decrease in hydrophilic pores. We analyze the results using pair correlation functions and orientational, tetrahedral, and hydrogen bond distributions. Our investigation indicates that the presence of an electric field enhances the coordination number N(r) of the bulk phase. In contrast, the presence of an electric field reduces N(r) of the confined fluid. This is clearly reflected in the behavior of the critical temperature of bulk and confined water. Our structural analysis reveals that the application of an external field induces orientational order of dipole vector parallel to the field direction in bulk water, whereas its effects on dipole orientation is much less in confined systems. We also report that the hydrogen-bonding behavior in the vapor phase is responsible for the difference in critical density of water confined in hydrophobic and hydrophilic pores.

Solubility Measurements and Saturated Liquid Properties of Ternary Systems (Methane + Decane + Octadecane) at 295 K

Experimental vapor–liquid equilibrium (VLE) data have been measured for the ternary system (methane + decane + octadecane) at 295 K over the pressure range (1 to 8) MPa using a PVT apparatus that was designed in-house. Three different (decane + octadecane) binary mixtures were prepared, and the solubility and phase equilibria of these prepared mixtures with methane were studied. The experimental information of saturated liquid phase composition, density, and viscosity was reported at each pressure. The VLE data were correlated with the Soave–Redlich–Kwong (SRK) and Peng–Robinson (PR) equations of state (EOS's). The adjustment of binary interaction parameters and the volume translation technique has been employed to correlate the experimental compositions and densities. The adjusted binary parameters from the VLE data of binary pairs (methane + decane) and (methane + octadecane) were used to correlate the generated ternary VLE data. The calculated ternary VLE compositions were found to be in good agreement with the experimental data using the binary parameters from the VLE data of binary pairs for both EOS's. According to the results for the saturated liquid densities, more accurate predictions of the experimental data were obtained using the PR EOS than the SRK EOS.

Two-phase simulation of the crystalline silicon melting line at pressures from –1 to 3 GPa

Results of a numerical investigation of crystalline silicon melting line within the range of pressures from -1 to 3 GPa are presented. A two-phase molecular dynamics method is applied to obtain temperature, pressure, and densities of solid and liquid phases on the melting line. Using a special procedure we ensure the strict control of the two-phase equilibrium in the simulation cell. To describe the interaction between the atoms four classic potentials have been chosen: the Stillinger-Weber one and three modified variants of the Tersoff potential. For the Stillinger-Weber and Tersoff potentials in the modification by Kumagai-Izumi-Hara-Sakai a good coincidence with experimental data on crystalline Si melting temperature is obtained within the range of pressure from 0 to 3 GPa. Calculations of the solid and liquid phase densities on the silicon melting line for the Stillinger-Weber potential are also in close agreement with experiments.

Experimental and thermodynamic modeling study on (vapor + liquid) equilibria and physical properties of ternary systems (methane + n-decane + n-tetradecane)

The vapor–liquid equilibrium (VLE) data of ternary systems (methane+n-decane+n-tetradecane) at ambient temperature and various pressures, 1–8MPa, have been measured using a designed pressure–volume–temperature (PVT) apparatus. The phase compositions and saturated liquid phase properties, density and viscosity, have been measured for each pressure. The densities of three different (n-decane+n-tetradecane) binary mixtures have also been measured at ambient temperature over a wide range of pressures (1–10MPa). The generated experimental data have been correlated with two cubic equations of state (EoS), Peng–Robinson (PR) and Soave–Redlich–Kwong (SRK). The binary interaction parameters and the volume shift values from the experimental information on the binary pairs, (methane+n-decane) and (methane+n-tetradecane), have been used to predict the VLE data of ternary system (methane+n-decane+n-tetradecane). Both equations of state have been found to be capable of describing the phase equilibria of binary pairs as well as ternary systems over the range of studied conditions.

Haloing in bimodal magnetic colloids: The role of field-induced phase separation

If a suspension of magnetic micrometer-sized and nanosized particles is subjected to a homogeneous magnetic field, the nanoparticles are attracted to the microparticles and form thick anisotropic halos (clouds) around them. Such clouds can hinder the approach of microparticles and result in effective repulsion between them [M. T. López-López, A. Yu. Zubarev, and G. Bossis, Soft Matter 6, 4346 (2010)]. In this paper, we present detailed experimental and theoretical studies of nanoparticle concentration profiles and of the equilibrium shapes of nanoparticle clouds around a single magnetized microsphere, taking into account interactions between nanoparticles. We show that at a strong enough magnetic field, the ensemble of nanoparticles experiences a gas-liquid phase transition such that a dense liquid phase is condensed around the magnetic poles of a microsphere while a dilute gas phase occupies the rest of the suspension volume. Nanoparticle accumulation around a microsphere is governed by two dimensionless parameters--the initial nanoparticle concentration (φ(0)) and the magnetic-to-thermal energy ratio (α)--and the three accumulation regimes are mapped onto a α-φ(0) phase diagram. Our local thermodynamic equilibrium approach gives a semiquantitative agreement with the experiments on the equilibrium shapes of nanoparticle clouds. The results of this work could be useful for the development of the bimodal magnetorheological fluids and of the magnetic separation technologies used in bioanalysis and water purification systems.

Studies on Langmuir monolayer of tricycloquinazoline based disk-shaped liquid crystal molecules

The assembly of disk-shaped molecules on surfaces has drawn considerable attention because of their unique electronic and optical properties. We have studied the monolayer of the amphiphilic tricycloquinazoline (AmTCQ) based disk-shaped molecules at the air–water and air–solid interfaces. The AmTCQ molecules form a stable Langmuir monolayer at the air–water interface. The monolayer exhibits gas phase, low density liquid (L1) phase, and high density liquid (L12) phase. In L1 phase, the molecules prefer face-on conformation with their flexible side-chain being interdigitated with the neighboring molecules. Interestingly, the molecular conformations in L12 phase were found to be both the face-on and edge-on. The structure of the aggregates of the molecules on a surface can be influenced by the intermolecular and molecule–substrate interactions. The deficiency in π-electrons of the AmTCQ molecule may lead to a weak intermolecular interaction. The observation of both the conformations of the molecules in L12 phase can be attributed to the weak intermolecular interaction.

Dependence of diffusivity on density and solute diameter in liquid phase: A molecular dynamics study of Lennard-Jones system

Investigations into the variation of self-diffusivity with solute radius, density, and degree of disorder of the host medium is explored. The system consists of a binary mixture of a relatively smaller sized solute, whose size is varied and a larger sized solvent interacting via Lennard-Jones potential. Calculations have been performed at three different reduced densities of 0.7, 0.8, and 0.933. These simulations show that diffusivity exhibits a maximum for some intermediate size of the solute when the solute diameter is varied. The maximum is found at the same size of the solute at all densities which is at variance with the prediction of the levitation effect. In order to understand this anomaly, additional simulations were carried out in which the degree of disorder has been varied while keeping the density constant. The results show that the diffusivity maximum gradually disappears with increase in disorder. Disorder has been characterized by means of the minimal spanning tree. Simulations have also been carried out in which the degree of disorder is constant and only the density is altered. The results from these simulations show that the maximum in diffusivity now shifts to larger distances with decrease in density. This is in agreement with the changes in void and neck distribution with density of the host medium. These results are in excellent agreement with the predictions of the levitation effect. They suggest that the effect of disorder is to shift the maximum in diffusivity towards smaller solute radius while that of the decrease in density is to shift it towards larger solute radius. Thus, in real systems where the degree of disorder is lower at higher density and vice versa, the effect due to density and disorder have opposing influences. These are confirmed by the changes seen in the velocity autocorrelation function, self part of the intermediate scattering function and activation energy.