Surface Enthalpy Research Articles

Investigation of Interfaces by Atom Probe Tomography

We investigated the thermodynamic and transport properties of buried interfaces with atom probe tomography. Owing to the 3D subnanometer resolution and single atom sensitivity of the method, it is possible to obtain composition profiles with high accuracy both along or normal to the interfaces. We have shown that the width of the chemical interface between the Fe and Cr system follows the Cahn–Hilliard relation with a gradient energy coefficient of 1.86 × 10−22 J nm2. Sharpening of the Ni/Cu interface as a result of kinetic control was directly observed. We investigated the grain boundary and triple junction transport in Fe/Cr and Ni/Cu. Cr segregation enthalpy into Fe triple junctions was found to be 0.076 eV, which falls in between the surface (0.159 eV) and grain boundary (0.03 eV) segregation enthalpies. In the investigated 563 K to 643 K (290 °C to 370 °C) range, Ni transport is 200 to 300 times faster in the triple junctions of Cu than in the grain boundaries. The diffusion activation enthalpy in the triple junctions is two-thirds that of the grain boundaries (0.86 and 1.24 eV, respectively). These investigations have shown that triple junctions are defects in their own right with characteristic segregation and diffusion properties: They are preferred segregation sites and can be considered as a diffusion shortcut in the grain boundary network.

Surface tension, surface excess concentration, enthalpy and entropy of surface formation of aqueous salt solutions

Surface tensions of aqueous solutions of sodium salts of chloride, bromide and nitrate; potassium salts of chloride, bromide and nitrate; lithium chloride and potassium iodide has been determined experimentally at different concentrations and temperatures ranging from 0.10 to 2.00molkg−1 and 10–30°C, respectively. Concentration and temperature dependence of the surface tension of the selected salts has been studied for further estimation of surface excess concentration, enthalpy and entropy of surface formation. The results show that the surface excess concentration decreases linearly with concentration but remains almost constant with the variations of temperature. Similarly the enthalpy of surface formation was observed to decrease with concentration but remained almost constant with the change in temperature. The entropy of surface formation was found to decrease with concentration in most cases.

Experimental and Theoretical Study of Two Pyridinium-Based Ionic Liquids

Thermophysical properties of two pyridinium-based ionic liquids, 1-ethyl-2-methylpyridinium bis(trifluoromethylsulfonyl)imide and 1-propyl-2-methylpyridinium bis(trifluoromethylsulfonyl)imide, have been measured from 278.15 to 323.15 K, with a temperature step of 2.5 K. The properties measured were: densities, speeds of sound, refractive indices, surface tensions, isobaric molar heat capacities, electrical conductivities and viscosities. Thermal properties were also recorded in the temperature range from 100 to 320 K. From the experimental results coefficients of thermal expansion, isentropic compressibilities, molar refraction and surface enthalpies and entropies have been determined. Moreover, a theoretical study has been performed using ab initio calculations, level of theory HF/6-31G(d). From this study, we have obtained qualitative information about the magnitude and the directionality of the cation–anion interactions which allows a better understanding of the physico-chemical properties of these ionic liquids.

On the Conundrum of the Heat Capacityof Metallic Nanoclasters

<p>The heat capacity of nanoclusters was investigated using thermodynamics of surfaces, taking into account the surface enthalpy introduced by E. Guggenhein. It is shown that the cluster heat capacity <em>C<sub>p</sub></em> should be greater than the heat capacity of the corresponding bulk phase. However, the ratio should not exceed 50% up to very small clusters containing 100 atoms. Theoretical estimations agree with molecular dynamics results. So, experimental data on metallic nanoclusters and nanostructures demonstrating that <em>C<sub>p</sub></em> exceeds in 2-5 times should be incorrect.</p>

Thermophysical Properties of Five Acetate-Based Ionic Liquids

Ionic liquids (ILs) with improved hydrogen-bonding acceptor abilities, such as acetate-based compounds, have shown great potential for CO2 capture and biomass dissolution. In this context, the knowledge of the thermophysical properties of acetate-based fluids is essential for the design and scale-up of related processes. However, at this stage, acetate-based ILs are still poorly characterized. In this work, four thermophysical properties, specifically, density, viscosity, refractive index, and surface tension, were determined for five acetate-based ILs. Both protic and aprotic ILs were investigated, namely, N,N-dimethyl-N-ethylammonium acetate, 1-ethylimidazolium acetate, 1-ethyl-3-methylimidazolium acetate, 1-butyl-3-methylimidazolium acetate, and 1-butyl-1-methylpyrrolidinium acetate. From the temperature dependence of the measured properties, additional properties, such as the isobaric thermal expansion coefficient, the surface entropy and enthalpy, and the critical temperature, were further estimated.

Effect of Temperature and Cationic Chain Length on the Physical Properties of Ammonium Nitrate-Based Protic Ionic Liquids

We report a systematic study of the effect of the cationic chain length and degree of hydrogen bonding on several equilibrium and transport properties of the first members of the alkylammonium nitrate protic ionic liquids (PILs) family (ethylammonium, propylammonium, and butylammonium nitrate) in the temperature range between 10 and 40 °C. These properties were observed by means of several experimental techniques, including density, surface tension, refractometry, viscosimetry, and conductimetry. The dilatation coefficients and compressibilities, as well as the Rao coefficients, were calculated, and an increase of these magnitudes with alkyl chain length was detected. Moreover, the surface entropies and enthalpies of the studied PILs were analyzed, and the temperature dependence of the surface tension was observed to be describable by means of a harmonic oscillator model with surface energies and critical temperatures that are increasing functions of the cationic chain length. Moreover, the refractive indexes were measured and the thermo-optic coefficient and Abbe numbers were calculated, and the contribution of the electrostrictive part seemed to dominate the temperature dependence of the electric polarization. The electric conductivity and the viscosity were measured and the influence of the degree of hydrogen bonding in the supercooled liquid region analyzed. Hysteresis loops were detected in freezing-melting cycles and the effect of the length of the alkyl chain of the cation on the size of the loop analyzed, showing that longer chains lead to a narrowing of the supercooled region. The temperature dependence of the conductivity was studied in the Vogel-Fulcher-Tamman (VFT) framework and the fragility indices, the effective activation energies, and the Vogel temperatures obtained. A high-temperature Arrhenius analysis was also performed, and the activation energies of conductivity and viscosity were calculated, showing that these transport processes are governed by two distinct mechanisms. The exponents of the fractional Walden rule for the different compounds were obtained. Finally, the ionicities and fragilities of the studied PILs were analyzed, proving that all the studied PILs are subionic and fragile liquids, with propylammonium nitrate showing the lowest fragility and the greater ionicity of all the studied compounds.

Thermodynamics of Nanoscale Lead Titanate and Barium Titanate Perovskites

To explore the surface properties of perovskites with ions of different bond character, the surface and interface enthalpies of nanocrystalline PbTiO 3 and BaTiO 3 perovskites were determined for the first time by a combination of calorimetric, morphological, and structural analyses. PbTiO 3 and BaTiO 3 nanocrystalline samples of varying surface areas and degrees of agglomeration were synthesized by solvothermal and hydrothermal methods, respectively. All synthesized samples were characterized using X‐ray diffraction and Raman spectroscopy. Interface areas were estimated by comparing the surface areas measured by N 2 adsorption to the crystallite sizes refined from X‐ray diffraction data. The integrated heats of water vapor adsorption on the surfaces of the nanocrystalline phases are −62 ± 4 kJ/mol for PbTiO 3, which is less exothermic than the value −72 ± 9 kJ/mol for the isostructural BaTiO 3, both phases having the same chemisorbed water coverage. Similar behavior is observed for the surface and interface enthalpies. The energies of the hydrous and anhydrous surfaces are 1.97 ± 0.67 J/m2 and 1.11 ± 0.23 J/m2 for PbTiO 3, and 3.69 ± 0.22 J/m2 and 3.99 ± 0.28 J/m2 for BaTiO 3, respectively. The interface energies of the hydrous and anhydrous surfaces are 0.55 ± 0.74 J/m2 and 0.73 ± 0.27 J/m2 for PbTiO 3, and 1.11 ± 0.13 J/m2 for BaTiO 3. These observations suggest that PbTiO 3 has lower surface energy and lower affinity for water adsorption on the surface than BaTiO 3 and that surface energy and hydrophilicity of the surface decrease with increasing covalent character of the ions, as was seen previously in comparing TiO 2 and SnO 2.

Synthesis, physical, and thermodynamic properties of 1-alkyl-cyanopyridinium bis{(trifluoromethyl)sulfonyl}imide ionic liquids

Synthesis of new ionic liquids (ILs) viz. 1-butyl-3-cyanopyridinium bis{(trifluoromethyl)sulfonyl}imide, [BCN3Py][NTf2], 1-hexyl-3-cyanopyridinium bis{(trifluoromethyl)sulfonyl}imide, [HCN3Py][NTf2], 1-hexyl-4-cyanopyridinium bis{(trifluoromethyl)sulfonyl}imide, [HCN4Py][NTf2], and 1-octyl-3-cyanopyridinium bis{(trifluoromethyl)sulfonyl}imide, [OCN3Py][NTf2] were performed. The specific basic characterization of new compounds by NMR spectra, elementary analysis, water content and glass transition temperature as well as melting temperature, enthalpy of fusion and decomposition of compounds TG/DTA determined by the differential scanning calorimetry, DSC is presented. The heat capacity was measured at three temperatures (298.15, 323.15, and 353.15)K and at pressure 0.1MPa. The effect of temperature on the density and viscosity is reported over the temperature range from (293.15 to 363.15)K and at 0.1MPa. The density and viscosity correlation for these systems was provided by an empirical polynomial. From the density–temperature dependence, the isothermal expansion coefficient (volume expansivity), α, was calculated. The surface tension of pure ionic liquids was measured at 0.1MPa at five temperatures (298.15, 308.15, 318.15, 328.15, and 338.15)K. The surface thermodynamic functions such as surface entropy and enthalpy, critical temperatures according to the Eötvös and Guggenheim definition and the total surface energy of the ILs studied were derived from the temperature dependence of the surface tension values. The parachor and speed of sound for pure ionic liquids were described within a range of temperature from (298.15 to 338.15)K. A qualitative analysis on these quantities in terms of molecular interactions is reported.

Thermodynamics of manganese oxides: Effects of particle size and hydration on oxidation-reduction equilibria among hausmannite, bixbyite, and pyrolusite

The surface enthalpies of manganese oxide phases, hausmannite (Mn3O4), bixbyite (Mn2O3), and pyrolusite (MnO2), were determined using high-temperature oxide melt solution calorimetry in conjunction with water adsorption calorimetry. The energy for the hydrous surface of Mn3O4 is 0.96 ± 0.08 J/m2, of Mn2O3 is 1.29 ± 0.10 J/m2, and of MnO2 is 1.64 ± 0.10 J/m2. The energy for the anhydrous surface of Mn3O4 is 1.62 ± 0.08 J/m2, of Mn2O3 is 1.77 ± 0.10 J/m2, and of MnO2 is 2.05 ± 0.10 J/m2. Supporting preliminary findings (Navrotsky et al. 2010), the spinel phase (hausmannite) has a lower surface energy than bixbyite, whereas the latter has a smaller surface energy than pyrolusite. Oxidation-reduction phase equilibria at the nanoscale are shifted to favor the phases of lower surface energy—Mn3O4 relative to Mn2O3 and Mn2O3 relative to MnO2. We also report rapidly reversible structural and phase changes associated with water adsorption/desorption for the nanophase manganese oxide assemblages.

Standard entropy, surface excess entropy, surface enthalpy, molar enthalpy of vaporization, and critical temperature of bis(trifluoromethanesulfonyl)imide-based ionic liquids

The density and surface tension of several bis(trifluoromethanesulfonyl)imide-based ionic liquids (ILs) 1-methyl-3-pentylimidazolium bis(trifluoromethanesulfonyl)imide ([MPI][TFSI]), 1,2-dimethyl-3-pentylimidazolium bis(trifluoromethanesulfonyl)imide ([DMPI][TFSI]), 1-ethyl-3-pentylimidazolium bis(trifluoromethanesulfonyl)imide ([EPeI][TFSI]), and 1-ethyl-3-propylimidazolium bis(trifluoromethanesulfonyl)imide ([EPrI][TFSI]) were measured at temperatures from 293.15 to 353.15K and atmospheric pressure. The values of thermal expansion coefficient and surface excess entropy were estimated by extrapolation. In terms of Glasser's semiempirical relation of ILs, the standard molar entropy and the lattice energy of ILs were estimated. Using Kabo's and Sugden's methods, the molar enthalpy values of vaporization of the IL, Δ1gHm°(298 K), and Parachor were estimated. The thermal expansion coefficients of the bis(trifluoromethanesulfonyl)imide-based hydrophobic ILs were estimated by the interstice model and they are in good agreement with experimental values. This indicated that the interstice model is reasonable and may be applied to estimate the coefficient of thermal expansion of ionic liquids.

Viscosity and surface tension of binary systems of N,N-dimethylformamide with alkan-1-ols at different temperatures

Viscosity η and surface tension σ were measured for binary mixtures of N,N-dimethylformamide DMF with pentan-1-ol, hexan-1-ol, and heptan-1-ol at T=(298.15, 303.15, 308.15, and 313.15)K and atmospheric pressure over the entire mole fraction range. Deviations in viscosity Δη and surface tension Δσ were calculated using experimental results. Moreover, the values of the excess Gibbs free energy of activation G∗E, surface enthalpy Hσ and surface entropy Sσ of these mixtures were determined. Viscosity measurements of the binary systems were correlated with Grunberg and Nissan, the three-body and four-body McAllister expressions. Viscosity deviation, surface tension deviation and excess Gibbs energy of activation functions were fitted to the method of Redlich–Kister (R–K) polynomial to estimate the coefficients and standard deviations. The effects of chain length of alkan-1-ols and temperature on the thermodynamic properties of binary systems were studied.

Yttria-stabilized hafnia: Thermochemistry of formation and hydration of nanoparticles

Abstract

Self-Stratification of Tropical Cyclone Outflow. Part II: Implications for Storm Intensification

Abstract Tropical cyclones intensify and are maintained by surface enthalpy fluxes that result from the thermodynamics disequilibrium that exists between the tropical oceans and atmosphere. While this general result has been known for at least a half century, the detailed nature of feedbacks between thermodynamic and dynamic processes in tropical cyclones remains poorly understood. In particular, the spatial relationship between surface fluxes and the radial entropy distribution apparently does not act to amplify the entropy gradient and therefore the surface winds. In previous work, this problem was addressed by accounting for the radial distribution of convective fluxes of entropy out of the boundary layer; this led to the conclusion that a radial gradient of such convective fluxes is necessary for intensification. Part I showed that the assumption of constant outflow temperature is incorrect and argued that the thermal stratification of the outflow is set by small-scale turbulence that limits the Richardson number. The assumption of Richardson number criticality of the outflow allows one to derive an equation for the variation of outflow temperature with angular momentum; this in turn leads to predictions of vortex structure and intensity that agree well with tropical cyclones simulated using a full-physics axisymmetric model. Here it is shown that the variation of outflow temperature with angular momentum also permits the vortex to intensify with time even in the absence of radial gradients of entrainment into the boundary layer. An equation is derived for the rate of intensity change and compared to simple models and to simulations using a full-physics model.

Surface thermodynamics of binary mixtures of aliphatic alcohols in heavy water

The surface tension, σ, of binary mixtures of heavy water and homologous series of aliphatic alcohols (methanol, ethanol, and 1-propanol) were measured over the entire concentration range at various temperatures. The surface tension of these aqueous binary mixtures shows more concentration dependence on the heavy water-rich side. Addition of a small amount of alcohol reduces the surface tension of heavy water drastically. The surface thermodynamic functions such as surface entropy and surface enthalpy have been derived from the temperature dependence of the surface tension values. The magnitude of these thermodynamically quantities is discussed in terms of the nature and type of intermolecular interactions in binary mixtures. The presence of a maximum point in the surface entropy diagram in all systems is explained by the formation of clathrate-like solvates at the surface of these systems. The surface tension of the above mentioned binary systems were correlated with empirical and thermodynamic based models. The Myers–Scott (MS) model with three adjustable parameters gives good results when values of Δσ are large.

The Creation of a High Equivalent Potential Temperature Reservoir in Tropical Storm Humberto (2001) and Its Possible Role in Storm Deepening

Thirty global positioning system dropwindsondes (GPS sondes) were used to identify and examine the creation of a reservoir of high equivalent potential temperature (θe) in the nascent eye of Tropical Storm Humberto (2001). The θe did not increase in the high surface wind portion of the storm as it does in mature hurricanes; instead air spiraled into the light-wind center of the developing storm where it was trapped by subsidence under a mesoscale convectively generated vortex (MCV). An energy budget revealed that the inflow column took 7 h to reach the storm center during which a combined average surface enthalpy flux of ~230 W m−2 was diagnosed via the bulk aerodynamic equations. This estimate is close to the 250 W m−2 required for balance based on the energy acquired by the column. The high θe in the lowest kilometer, overlain by a near dry-adiabatic layer under the anvil base, resulted in convective available potential energy (CAPE) exceeding 2500 m2 s−2. This conditionally unstable air later served as fuel for the convection within the nascent eyewall. The authors speculate that CAPE of such a large magnitude could accelerate the updraft and stretch the vorticity field, essentially turning garden-variety cumulonimbi into the vortical hot towers argued by several researchers to play a role in tropical cyclone formation and intensification.

Fluorite-pyrochlore transformation in Eu2Zr2O7—direct calorimetric measurement of phase transition, formation and surface enthalpies

The energetics of the order-disorder phase transformation in the binary oxide system, Eu2O3–ZrO2, is studied by powder X-ray diffraction and high temperature drop solution calorimetry. The nanocrystalline defect fluorite phase of Eu2Zr2O7 is synthesized on crystallization of an amorphous precursor from aqueous precipitation. The defect fluorite transforms to an ordered pyrochlore above 1200 °C. Aerodynamic levitation combined with laser heating is used to prepare coarse defect fluorite, which is otherwise impossible by conventional synthesis techniques. Formation enthalpies from oxides are −62.4 ± 2.6 and −24.6 ± 3.7 kJ mol−1 for the pyrochlore and defect fluorite phase, respectively. The transformation enthalpy from pyrochlore to defect flourite in the coarse sample is 37.8 ± 3.1 kJ mol−1 at 25 °C. The enthalpy of water vapor adsorption on the surface of the nanocrystalline defect fluorite Eu2Zr2O7 is −75 ± 2.5 kJ mol−1 H2O for coverage of 9.5 ± 0.8 H2O/nm2. The calculated surface enthalpies for the anhydrous and hydrous surfaces of defect fluorite Eu2Zr2O7 are 1.47 ± 0.13 and 1.01 ± 0.15 J m−2, respectively.

Effect of temperature and composition on the density, viscosity, surface tension, and thermodynamic properties of binary mixtures of N-octylisoquinolinium bis{(trifluoromethyl)sulfonyl}imide with alcohols

Density and viscosity were determined for the binary mixtures containing the ionic liquid N-octylisoquinolinium bis{(trifluoromethyl)sulfonyl}imide ([C8iQuin][NTf2]) and 1-alcohol (1-butanol, 1-hexanol, and 2-phenylethanol) at five temperatures (298.15, 308.15, 318.15, 328.15, and 338.15)K and ambient pressure. The density and viscosity correlations for these systems were tested by an empirical second-order polynomial and by the Vogel–Fucher–Tammann equation. Excess molar volumes were described by the Redlich–Kister polynomial expansion. The density and viscosity variations with compositions were described by polynomials. Viscosity deviations were calculated and correlated by the Redlich–Kister polynomial expansions. The surface tensions of pure ionic liquid and binary mixtures of [C8iQuin][NTf2] with 1-hexanol were measured at atmospheric pressure at three temperatures (298.15, 308.15, and 318.15) K. The surface tension deviations were calculated and correlated by the Redlich–Kister polynomial expansion. The surface thermodynamic functions such as surface entropy and enthalpy were derived from the temperature dependence of the surface tension values. The critical temperature, parachor, and speed of sound for pure ionic liquid were described. A qualitative analysis on these quantities in terms of molecular interactions is reported. The obtained results indicate that ionic liquid interactions with alcohols are strong dependent on the special trend of packing effects and hydrogen bonding of this ionic liquid with hydroxylic solvents. As previously observed, an increase by a 1-alcohol carbon chain length leads to lower interactions on mixing.

The effect of vertical shear orientation on tropical cyclogenesis

AbstractThe effect of the relative orientation of the vertical wind shear to the surface wind on tropical cyclogenesis is explored in environments of radiative‐convective equilibrium (RCE) through numerical simulation. This study serves as a companion paper to an earlier study on the thermodynamics of genesis in RCE.It is found, when the mean surface wind and shear are aligned, a negative surface wind anomaly arises from the superposition of the mean and vortex surface flows left of the shear vector. The resulting weak surface enthalpy fluxes and up‐shear quasi‐balanced subsidence leads to dry air being located cyclonically down‐wind of the down‐shear convective anomaly. Thus convection is inhibited from propagating cyclonically around the core leading to a large down‐shear vortex tilt. Conversely, in a counter‐aligned orientation, the negative surface wind anomaly and driest air is found right of the shear vector. Hence the driest air rotates into the down‐shear flank where it moistened by shear‐organized convection. Furthermore, the boundary layer is relatively moist left of shear due to the positive surface wind anomaly, therefore promoting the cyclonic propagation from down‐shear and constraining the magnitude of the vortex tilt.Genesis is intimately tied to the magnitude of the tilt and is found to occur once the mid‐level vortex has precessed into the up‐shear flank. For smaller values of maximum tilt, vortex precession is comparatively rapid, aided by “showerhead” moistening provided by the up‐shear advection of frozen condensate aloft. With the up‐shear flank pre‐moistened, rapid precession of the mid‐level vortex, at smaller radii, leads to near saturation on the mesoscale and the onset of rapid intensification. When the magnitude of the tilt is quite large, precession is much slower and the showerhead effect is significantly reduced until just prior to the emergence of the mid‐level vortex in the up‐shear flank. Copyright © 2011 Royal Meteorological Society

Surface enthalpy and elastic properties of blood vessels

1. Blood vessels form one of the most complicated and important functional systems of humans and other mammals subjected to many risks and poorly amenable to medicinal treatment. The mathematical simulation of blood flow through the aorta, arteries, veins, peripheral vessels, and capillaries both sepa rately and as a whole still remains an important problem. At the same time, the published bloodflow models give no possibility to take into account the complex (composite and anisotropic) structure of walls of vessels. Moreover, the formulation itself of experiments on determining elastic characteristics of walls of ves sels is at the stage of development (see [1, 2] and the review of literature in monograph [3, sect. 8]). This study is devoted to derivation of certain relations for deformable bloodvessel walls on the basis of the conventional representation of their laminar structure (see, for example, [1, 4, 3]). By means of the dimensionreduction procedure and on the basis of the concept of surface enthalpy, we derived a simple formula for the effective elasticmodulus tensor. Contrary to the habitual formulation of the mathematical problem, the blood vessel is not beforehand assumed as a circular cylinder, and the occurrence of a variable curvature, which does not complicate principally the asymptotic analysis, enables us to investigate the deformation of walls of arteries due to damage, such as inhomogeneous calcification (hyalinosis or calcinosis), oblong atherosclerotic deposits (cholesterolplaques), or various surgical treatments (clipping, stenting, and stitching).

Volumetric and surface properties of pure ionic liquid n-octyl-pyridinium nitrate and its binary mixture with alcohol

The density and surface tension for pure ionic liquid N-octyl-pyridinium nitrate were measured from (293.15 to 328.15) K. The coefficient of thermal expansion, molecular volume, standard entropies, and lattice energy were calculated from the experimental density values. The critical temperature, surface entropy, surface enthalpy, and enthalpy of vaporization were also studied from the experimental surface tension results. Density and surface tension were also determined for binary mixtures of (N-octyl-pyridinium nitrate + alcohol) (methanol, ethanol, and 1-butanol) systems over the whole composition range at 298.15 K and atmospheric pressure. Excess molar volumes and surface tension deviations for the binary systems have been calculated and were fitted to a Redlich–Kister equation to determine the fitting parameters and the root mean square deviations. The partial molar volume, excess partial molar volume, and apparent molar volume of the component IL and alcohol in the binary mixtures were also discussed.