Isentropic expansion and related thermodynamic properties of non-ionic amphiphile-water mixtures

A concise thermodynamic formalism is developed for the molar isentropic thermal expansion, ES,m = ( partial differential Vm/ partial differential T)(Sm,x), and the ideal and excess quantities for the molar, apparent molar and partial molar isentropic expansions of binary liquid mixtures. Ultrasound speeds were determined by means of the pulse-echo-overlap method in aqueous mixtures of 2-methylpropan-2-ol at 298.15 K over the entire composition range. These data complement selected extensive literature data on density, isobaric heat capacity and ultrasound speed for 9 amphiphile (methanol, ethanol, propan-1-ol, propan-2-ol, 2-methylpropan-2-ol, ethane-1,2-diol, 2-methoxyethanol, 2-ethoxyethanol or 2-butoxyethanol)-water binary systems, which form the basis of tables listing molar and excess molar isobaric expansions and heat capacities, and molar and excess molar isentropic compressions and expansions at 298.15 K and at 65 fixed mole fractions spanning the entire composition range and fine-grained in the water-rich region. The dependence on composition of these 9 systems is graphically depicted for the excess molar isobaric and isentropic expansions and for the excess partial molar isobaric and isentropic expansions of the amphiphile. The analysis shows that isentropic thermal expansion properties give a much stronger response to amphiphile-water molecular interactions than do their isobaric counterparts. Depending on the pair property-system, the maximum excess molar isentropic value is generally twenty- to a hundred-fold greater than the corresponding maximum isobaric value, and occurs at a lower mole fraction of the amphiphile. Values at infinite dilution of the 9 amphiphiles in water are given for the excess partial molar isobaric heat capacity, isentropic compression, isobaric expansion and isentropic expansion. These values are interpreted in terms of the changes occurring when amphiphile molecules cluster into an oligomeric form. Present results are discussed from theoretical and experimental thermodynamic viewpoints. It is concluded that isentropic thermal expansion properties constitute a new distinct resource for revealing particular features and trends in complex mixing processes, and that analyses using these new properties compare favourably with conventional approaches.     

Isobaric Vapor-Liquid Equilibrium of t-Butyl Alcohol-Cyclohexanol System

The isobaric vapor-liquid equilibrium data of t-butyl alcohol (1)-cyclohexanol (2) were determined at 0.7 bar and 1.0 bar by using a modified Rose-Williams still. The experimental data were tested for thermodynamic consistency and correlated satisfactorily with Margules equation and NRTL equation.     

Isobaric thermal expansivity of the binary system 1-hexanol + n-hexane as a function of temperature and pressure

The isobaric thermal expansivity against temperature and pressure for the system 1-hexanol + n-hexane was directly determined by means of a calorimetric method. From these data, the excess isobaric thermal expansivity is calculated at representative temperatures and pressures. The obtained results for this excess quantity are qualitatively discussed by applying well-known arguments often used for explaining the thermodynamic behavior of alcohol + alkane mixtures. In order to check the consistency of these data with those of literature, the derivative of excess molar volume against temperature and that of excess isobaric molar heat capacity against pressure are calculated and compared with those obtained from literature data. Very good coherence between both data sources is obtained.     

Isobaric Vapour-Liquid Equilibrium of Some Cyclic Ethers with Bromobenzene at Several Pressures

A dynamic recirculating still was employed to study the isobaric vapour-liquid equilibrium (VLE) at 40.0 and 101.3 kPa for the binary systems tetrahydrofuran, tetrahydropyran, 2-methyl-tetrahydrofuran and 2,5-dimethyl-tetrahydrofuran with bromobenzene. The experimental data were tested for thermodynamic consistency and correlated with the Wilson, NRTL and UNIQUAC equations. Predictions with the UNIFAC method were also obtained.     

A simple methodology for analyzing association effects on response functions via Monte Carlo simulations

A simple methodology was developed to analyze association effects on the thermodynamic response functions for a pure self-associated fluid via Monte Carlo simulations. The procedure essentially involves expressing the residual energy and volume of the fluid in terms of these properties for two hypothetical fluids consisting of monomers and associated molecules, respectively. This allows the thermodynamic response functions to be expressed in a perturbative form as a combination of the values for the property in the monomeric fluid and the contribution of association (the perturbative term). The proposed methodology was used to determine both contributions to the isobaric heat capacity and to the temperature and pressure derivatives of the volume for OPLS methanol along the 50 MPa isobar from 220 to 1500 K. Based on the results, both terms exert a substantial influence on the isobaric heat capacity; by contrast, the association term for the volumetric properties is negligible. These results are consistent with those of a previous work involving simulations with the same model under identical thermodynamic conditions but a different approach. They are also compared with others previously reported in context. Moreover, a comprehensive study of the different types of clusters present in the fluid was performed and the results were related to thermodynamic properties. A strong correlation between the heat capacity of the monomeric fluid and this structural analysis was found.     

Thermodynamic integration at constant pressure from the nonlocal Einstein crystal

The Gibbs free energy of a periodic, d-dimensional crystalline assembly can be estimated using thermodynamic integration at constant pressure from a nonlocal Einstein crystal. The method is demonstrated using a two-dimensional, harmonic crystal with hexagonal symmetry for which the isobaric Gibbs function can be derived analytically.     

Isochoric and isobaric glass formation: Similarities and differences

Pressure-volume-temperature (PVT) studies were performed on a glass-forming polymer, poly(carbonate) (PC), under both isobaric and isochoric (constant volume) conditions. An isochoric glass transition was observed and the formation points were found to be consistent with those obtained isobarically. Although the isobaric and isochoric responses were, as expected, the same in the rubbery state, the glassy state values were found to be different and dependent upon the glass formation history. The isobaric data exhibited larger changes in going from the rubber to the glass, hence a “stronger” glass transition, than did the isochoric data. Inserting the experimental values for the thermal expansion coefficient α and isothermal compressibility β, into appropriate thermodynamic relations, measures of the strength of each transition are defined. Strength estimates based on literature values of α and β are compared to the experimental measures of the isochoric and isobaric transitions. In addition, both the isobaric and isochoric PVT results were analyzed in terms of the Fox and Flory free volume theory which assumes that the glass transition is an iso-free volume state. While the isobaric results were consistent with the Fox and Flory theory, the isochoric results were not consistent with the idea of an iso-free volume glass transition. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 1561–1573, 1997     

Additive estimates of the thermodynamic properties of triene hydrocarbons over a wide temperature range

An increment method for calculating the thermodynamic properties of aliphatic triene hydrocarbons is suggested. The method is based on substituting procedures and additive inclusion of 1,4-and 1,5-carbon-carbon intramolecular interactions. Parameter values for estimating the enthalpies of formation of gaseous alkatrienes at 298.15 K were found. A procedure for determining the thermodynamic properties of conjugated alkatrienes at arbitrary temperatures was developed. This procedure is based on the additive determination of the coefficients of polynomials that describe the temperature dependences of properties. The parameters for determining the isobaric heat capacities, entropies, and reduced enthalpies and Gibbs energies of conjugated triene hydrocarbons in the gas phase were found. Calculations reproduce experimental data with accuracy at the level of measurement errors. A thermodynamic analysis of the rearrangements of 2,6-dimethyloctatrienes (alloocimene isomers) was performed. The compositions of equilibrium mixtures of 14 aliphatic terpenes were determined at five gas phase temperatures from 298.15 to 1000 K.     

The thermodynamic rules governing polymorphism of beryllium oxide

A thermodynamic analysis of qualitative and quantitative rules governing polymorphism of BeO was performed. Equations for the temperature dependences of its polarization and isobaric heat capacity in the low-temperature neighborhood of the wurtzite polymorph-rutile polymorph transition point were suggested. Equations describing the curvature of the line of this transition and mutual correlation of the temperature dependences of the thermodynamic characteristics of beryllium oxide were obtained.     

Thermodynamic properties in the molecular dynamics ensemble applied to the gaussian core model fluid

The thermodynamic properties of pressure, energy, isothermal pressure coefficient, thermal expansion coefficient, isothermal and adiabatic compressibilities, isobaric and isochoric heat capacities, Joule-Thomson coefficient, and speed of sound are considered in a classical molecular dynamics ensemble. These properties were obtained using the treatment of Lustig [J. Chem. Phys. 100, 3048 (1994)] and Meier and Kabelac [J. Chem. Phys. 124, 064104 (2006)], whereby thermodynamic state variables are expressible in terms of phase-space functions determined directly from molecular dynamics simulations. The complete thermodynamic information about an equilibrium system can be obtained from this general formalism. We apply this method to the gaussian core model fluid because the complex phase behavior of this simple model provides a severe test for this treatment. Waterlike and other anomalies are observed for some of the thermodynamic properties of the gaussian core model fluid.     

Equilibrium parameters of a liquid—vapor system and thermodynamic characteristics of adsorption of cyclic and cage hydrocarbons in squalane

The thermodynamic characteristics of adsorption of adamantane molecules and its alkyl derivatives, as well as some mono- and bicyclic hydrocarbons C₁₀H _n , were studied by equilibrium gas liquid chromatography on a column packed with the stationary liquid phase squalane under the conditions of infinitely low concentrations of the sorbate in the gas phase. The influence of specific features of the molecular structure of sorbates on the regularities of their retention on the column with squalane was shown. For the first time we obtained the limiting activity coefficients and excess thermodynamic functions of mixing, which made it possible to study in detail the thermodynamics of dissolution of cage molecules in the nonpolar liquid bulk. The changes in the molar isobaric heat capacity of sorbates during adsorption were determined by the chromatographic method. For reference compounds, these values agree well with the results of direct calorimetric measurements of the change in the molar standard isobaric heat capacity during vaporization.     

Thermodynamic property predictions with the trebble-bishnoi equation of state

Predictions of thermodynamic properties including second virial coefficients, enthalpies, isobaric heat capacities, speed of sound, and Joule-Thomson coefficients are presented for the Trebble-Bishnoi equation of state. These predictions are compared both to experimental data and to predictions from the Peng-Robinson equation of state. Both equations of state give reasonable and consistent values for all of the above properties.     

New calibration methodology for calorimetric determination of isobaric thermal expansivity of liquids as a function of temperature and pressure

A new method for determining isobaric thermal expansivity of liquids as a function of temperature and pressure through calorimetric measurements against pressure is described. It is based on a previously reported measurement technique, but due to the different kind of calorimeter and experimental set up, a new calibration procedure was developed. Two isobaric thermal expansivity standards are needed; in this work, with a view on the quality of the available literature data, hexane and water are chosen. The measurements were carried out in the temperature and pressure intervals (278.15 to 348.15) K and (0.5 to 55) MPa for a set of liquids, and experimental values are compared with the available literature data in order to evaluate the precision of the experimental procedure. The analysis of the results reveals that the proposed methodology is highly accurate for isobaric thermal expansivity determination, and it allows obtaining a precise characterisation of the temperature and pressure dependence of this thermodynamic coefficient.     

Modeling thermodynamic properties of natural gas mixtures using perturbed-chain statistical associating fluid theory

Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT) was employed for predicting thermodynamic properties of natural gas mixture. Thermodynamic properties like density, isobaric and isochoric heat capacity, enthalpy, entropy, and internal energy were calculated with the PC-SAFT. Results are validated against experimental data for natural gas and mixtures similar to natural gas. The validation show that the Average Absolute Deviation (AAD) for density is 1.10% for binary mixture and 1.08% for mixtures similar to natural gas. Also AAD value for enthalpy is 1.42%, for internal energy, 0.77, for entropy, 0.43, for isochoric heat capacity, 1.26%, and for isobaric heat capacity, 2.66%. Results show PC-SAFT to be able to predict all the thermodynamics properties of natural gas and mixtures similar to natural gas with high accuracy in a wide range of temperature and pressure.     

Thermodynamic properties of lithium chloride ammonia complexes for application inahigh-lifthigh temperature chemical heat pump

Ammonia absorption by and desorption from lithium chloride at different pressures has been studied using high-pressure differential scanning calorimetry, for application in a high-lift high temperature chemical heat pump. The measurements were performed under isobaric as well as under isothermal circumstances. Clausius–Clapeyron plots were constructed and used to calculate the thermodynamic parameters and to determine the stability regions of the different complexes. Controversies in literature as to the real existing phases are resolved.     

Pressure–enthalpy driven molecular dynamics for thermodynamic property calculation: I. Methodology

An algorithm is presented which enables the direct simulation of isenthalpic pressure changes and isobaric enthalpy changes using molecular dynamics (MD). The pressure and enthalpy can be controlled using either a constraint or extended system formalism. By controlling the rate with which new state points are approached, reversible or irreversible thermodynamic cycles can be simulated directly. The method can be incorporated easily into a standard MD algorithm, and provides a means for rapidly driving a system to a desired thermodynamic statepoint. In a companion paper [1], the method is applied to compute thermodynamic derivatives, simulate a vapor compression refrigeration cycle, and compute vapor–liquid coexistence curves.     

Thermodynamic Stability of Fenclorim and Clopyralid

The present work reports an experimental thermodynamic study of two nitrogen heterocyclic organic compounds, fenclorim and clopyralid, that have been used as herbicides. The sublimation vapor pressures of fenclorim (4,6-dichloro-2-phenylpyrimidine) and of clopyralid (3,6-dichloro-2-pyridinecarboxylic acid) were measured, at different temperatures, using a Knudsen mass-loss effusion technique. The vapor pressures of both crystalline and liquid (including supercooled liquid) phases of fenclorim were also determined using a static method based on capacitance diaphragm manometers. The experimental results enabled accurate determination of the standard molar enthalpies, entropies and Gibbs energies of sublimation for both compounds and of vaporization for fenclorim, allowing a phase diagram representation of the (p,T) results, in the neighborhood of the triple point of this compound. The temperatures and molar enthalpies of fusion of the two compounds studied were determined using differential scanning calorimetry. The standard isobaric molar heat capacities of the two crystalline compounds were determined at 298.15 K, using drop calorimetry. The gas phase thermodynamic properties of the two compounds were estimated through ab initio calculations, at the G3(MP2)//B3LYP level, and their thermodynamic stability was evaluated in the gaseous and crystalline phases, considering the calculated values of the standard Gibbs energies of formation, at 298.15 K. All these data, together with other physical and chemical properties, will be useful to predict the mobility and environmental distribution of these two compounds.     

纳米铁的低温热容和热力学性质研究

用扫描电子显微镜(SEM)测定了纳米铁试样的粒径, SEM结果表明Fe试样平均粒径d为25 nm. 在84～350 K温区, 用精密低温绝热量热计测定了该纳米铁试样的等压摩尔热容, 拟合出其等压摩尔热容与热力学温度的函数关系式: Cp=36.831+14.772x−5.4968x2−0.7099x3−1.3188x4, 其中x=(T−234)/156. 根据热容与热力学函数关系, 计算了以298.15 K为基准的纳米Fe(d=25 nm)热力学函数, 并与文献报导的粗晶Fe及粒径87 nm Fe的热容进行了比较, 从能量角度分析了不同粒径Fe热容曲线差别产生的原因.     

乙酸乙酯-水二元物系汽液平衡的研究

本文使用自行设计的带机械搅拌器的平衡釜,在760mmHg压力下,测定了乙酸乙酯-水二元部份互溶物系的汽、液平衡数据.经热力学检验,该数据符合热力学一致性.用NRTL等13个活度系数方程进行热力学关联和计算,获得了满意的结果,尤以McCann方程和NRTL方程拟合的精度最佳.     

Thermodynamic quantities for propane 3. The thermodynamic behaviour of saturated and compressed liquid propane

In an isochoric study the thermodynamic behaviour of liquid propane was experimentally investigated. Measurements were performed along six isochores with reduced densities from 2.0 to 2.5 at pressures up to 60 MPa. Additional measurements were carried out along the saturated-liquid curve. These results were critically examined and compared with results from the literature. The most reliable measurements were used to established a new equation of state for liquid propane of the Strobridge-type and new Wagner-type equations for vapour pressures and saturated-liquid densities, respectively. In addition isochoric and isobaric heat capacities were evaluated as well as ultrasonic speeds that agree with measurements from the literature to within their experimental uncertainty.