Partial Molar Heat Research Articles

Phase Behavior and Heat Capacity of {DPnP + Water} Mixtures at the Temperature Range of 273.15–338.15 K

The differential scanning calorimetry method (DSC) was used to examine the miscibility in the{dipropylene glycol propyl ether (DPnP) + water}system. Based on recorded curves of differential heat flow on temperature, HF=f(T), the range (composition, temperature) of the occurrence of miscibility gap, the values of lower critical solution temperature (LCST), and critical concentration were determined. On the basis of the experimentally determined specific heat capacity data the partial molar heat capacities (Cp,2) of DPnP in the mixtures with water were calculated. Analyzing changes in the course ofCp,2=f(x2)function, the boundary of transition from a homogeneous solution was determined, in which the monomers of amphiphile dominate, to the region, in which aggregates of the cluster type appear.

Determination of the thermodynamic parameters of ionic liquid 1-hexyl-3-methylimidazolium tetrafluoroborate by inverse gas chromatography

Inverse gas chromatography (IGC) was used to characterize the thermodynamic properties of ionic liquid (IL) 1-hexyl-3-methylimidazolium tetrafluoroborate ([HMIM] BF4) in the temperature range from 343.15 K to 373. 15 K. A series of solvents with different chemical natures were used to determine the [HMIM] BF4-solvent interactions. The thermodynamic parameters including Flory-Huggins interaction parameter, partial molar heats of sorption, mixing and evaporation as well as the activity coefficient at infinite dilution were obtained to judge the interactions between [HMIM]BF4 and the selected solvents. In addition, the solubility parameters of [HMIM] BF4 at different temperatures were determined. The results showed that among the selected solvents, n-C6, n-C7, n-C8, n-C9, diethyl ether, tetrahydrofuran, benzene and cyclohexane were poor solvents for [HMIM] BF4, while toluene, m-xylene, methanol, ethanol, dichloromethane, tetrachloromethane, chloroform, acetone, ethyl acetate and methyl acetate were the favorite ones. The solubility parameter of [HMIM]BF4 at room temperature (298.15 K) was 23.70 (J x cm(-3)(0.5), which was obtained by the linear extrapolation method. The experiment proved that IGC is a simple and accurate method to obtain the thermodynamic properties of ionic liquids. The obtained thermodynamic parameters revealed the strength of the interactions between the selected solvents and the ionic liquid, which could be used as a reference to the further applications of the ionic liquid.

Heat capacity and density of potassium iodide solutions in mixed N-methylpyrrolidone-water solvent at 298.15 K

The heat capacity and density of potassium iodide solutions in a mixed N-methylpyrrolidone (MP)-water solvent with a low content of the organic component are measured via calorimetry and densimetry at 298.15 K. Standard partial molal heat capacities \(\bar C_{p,2}^ \circ \) and volumes \(\bar V_2^ \circ \) of potassium iodide in MP-water mixtures are calculated. Standard heat capacities \(\bar C_{p,i}^ \circ \) and volumes \(\bar V_i^ \circ \) of potassium and iodide ions are determined. The character of the changes in heat capacity and volume are discussed on the basis of calculating additivity coefficients δc and δv upon the mixing of isomolal binary solutions KI-MP and KI-water, depending on the composition of the MP-H2O mixture and the concentration of the electrolyte.

Heat capacity, configurational heat capacity and fragility of hydrous magmas

The glassy and liquid heat capacities of four series of dry and hydrous natural glasses and magma as a function of temperature and water content (up to 19.9mol%) were investigated using differential scanning calorimetry (DSC). The analyzed compositions are basalt, latite, trachyte and pantellerite. The results of this study indicate that the measured heat capacity of glasses (Cpg) is a linear function of composition and is well reproduced by the empirical model of Richet (1987). For the investigated glasses, the partial molar heat capacity of water can be considered as independent of composition, in agreement with Bouhifd et al. (2006). For hydrous liquids, the heat capacity (Cpliq) decreases nonlinearly with increasing water content. Previously published models, combined with the partial molar heat capacity of water from the literature, are not able to reproduce our experimental data in a satisfactory way. We estimated the partial molar heat capacity of water (CpH2O) in hydrous magma over a broad compositional range. The proposed value is 41±3Jmol−1K−1. Water strongly affects the configurational heat capacity at the glass transition temperature [Cpconf (Tg)]. An increases of Cpconf (Tg) with water content was measured for the polymerized liquids (trachyte and pantellerite), while the opposite behavior was observed for the most depolymerized liquids (basalt and latite). Structural and rheological implications of this behavior are discussed in light of the presented results.

Standard partial molar heat capacities and enthalpies of formation of aqueous aluminate under hydrothermal conditions from integral heat of solution measurements

Heats of solution of sodium aluminum oxide, NaAlO2(s), were measured in aqueous sodium hydroxide solutions using a Tian–Calvet heat-flow calorimeter (Setaram, Model C80) with high pressure “batch cells” made of hastelloy C-276, at five temperatures from (373.15 to 523.15)K, steam saturation pressure, and concentrations from (0.02 to 0.09)mol·kg−1. Standard molar enthalpies of solution, ΔsolnH∘, and relative standard molar enthalpies, [H∘(T)−H∘(298.15K)], of NaAl(OH)4(aq) were determined from the measured heats of solution. The results were fitted with the “density” model. The temperature dependence of ΔsolnH∘ from the model yielded the standard molar heat capacities of reaction, ΔsolnCp∘, from which standard partial molar heat capacities for aqueous aluminate, Cp∘[A1(OH)4−,aq], were calculated. Standard partial molar enthalpies of formation, ΔfH∘, and entropies, S∘, of A1(OH)4−(aq) were also determined. The values for Cp∘[A1(OH)4−,aq] agree with literature data determined up to T=413K from enthalpy of solution and heat capacity measurements to within the combined experimental uncertainties. They are consistent with differential heat capacity measurements up to T=573K from Schrödle et al. (2010) [29] using the same calorimeter, but this method has the advantage that measurements could be made at much lower concentrations in the presence of an excess concentration of ligand. To our knowledge, these are the first standard partial molar heat capacities measured under hydrothermal conditions by the integral heat of solution method in a commercial calorimeter to be reported in the literature.

Temperature dependence of limiting activity coefficients, Henry's law constants, and related infinite dilution properties of C4–C6 isomeric n-alkyl ethanoates/ethyl n-alkanoates in water. Measurement, critical compilation, correlation, and recommended data

Infinite dilution activity coefficients (γ1∞) of C4–C6 isomeric n-alkyl ethanoates/ethyl alkanoates, namely ethyl ethanoate, propyl ethanoate, ethyl propanoate, butyl ethanoate, ethyl butanoate in water were measured at several temperatures in the range from (273 to 361)K. Most measurements were carried out by the inert gas stripping method, although other three headspace gas chromatography techniques were also employed. A comprehensive critical review is further presented of literature data on γ1∞, infinite dilution partial molar excess enthalpies (H¯1E,∞) and heat capacities (C¯p,1E,∞) of these aqueous solutes. For each ester, the data measured in this work together with those reported previously in the literature were correlated with a suitable model equation providing adequate simultaneous description of the equilibrium measurements and the calorimetric information. As a result, a recommended temperature dependence of γ1∞ of superior accuracy was established. The consistency of recommended γ1∞(T) with literature data on mutual solubilities of esters and water was also demonstrated. Analogous recommendations were derived also for the temperature dependence of Henry's law constants (KH). The variation with temperature and ester molecular structure of γ1∞, KH, and related energetic functions of ester dissolution and hydration was overviewed and briefly discussed. Furthermore, the performance of five predictive approaches to estimate γ1∞(T) of the aqueous esters was tested.

Thermodynamics of poly(benzyl methacrylate)–probe interactions at different temperatures by using inverse gas chromatography

In this study, some thermodynamic properties of poly(benzyl methacrylate) (PBzMA) were studied by using the inverse gas chromatography (IGC) technique. The retention times (tr) of probes were determined from the interactions with PBzMA of four groups of solvents with different chemical natures and polarities. Then, specific volume (Vg0) values were determined for each probe molecules. The glass transition temperature (Tg) of PBzMA was found as 323K from inverse gas chromatography measurements. Under the glass transition temperatures adsorption heat (ΔHa) and above the glass transition molar heat (ΔH1S), free energies (ΔG1S) and entropies (ΔS1S) belonging to sorption for every probe were calculated from inverse gas chromatography measurements. The partial molar heat (ΔH1∞), partial molar free energy (ΔG1∞), Flory–Huggins interaction parameter (χ12∞) and weight fraction activity coefficient (a1/w1)∞, values for infinite dilute solutions were calculated for polymer–probe systems. The solubility parameter (δ2) of the polymer was obtained from the slope and intercepts of Flory–Huggins interaction parameter (χ12∞) graphs with solubility parameters (δ1) of probes.

Determination of thermodynamic interactions of poly(l-lactide) and biphasic calcium phosphate/poly(l-lactide) composite by inverse gas chromatography at infinite dilution

Inverse gas chromatography at infinite dilution was applied to determine the thermodynamic interactions of poly(l-lactide) (PLLA) and the composite of biphasic calcium phosphate and PLLA (BCP/PLLA). The specific retention volumes, $$ V_{\text{g}}^{0} $$ , of 11 organic compounds of different chemical nature and polarity (non-polar, donor or acceptor) were determined in the temperature range of 308–378 K for PLLA and 308–398 K for BCP/PLLA. The weight fraction activity coefficients of test sorbates, $$ \Omega_{1}^{\infty } $$ , and the Flory–Huggins interaction parameters, $$ \chi_{12}^{\infty } $$ , were estimated and discussed in terms of interactions of the sorbates with PLLA and BCP/PLLA. Also, the partial molar free energy, $$ \Delta G_{1}^{\infty } $$ , the partial molar heat of mixing, $$ \Delta H_{1}^{\infty } $$ , the sorption molar free energy, $$ \Delta G_{1}^{\text{S}} $$ , the sorption enthalpy, $$ \Delta H_{1}^{\text{S}} $$ , and the sorption entropy, $$ \Delta S_{1}^{\text{S}} $$ , were analyzed. A different chromatographic behavior of the two investigated samples, PLLA and BCP/PLLA, was observed. The values of $$ \Omega_{1}^{\infty } $$ indicated n-alkanes, diethyl ether, tetrahydrofurane (THF), cyclohexane, benzene, dioxane (except for 338 K), and ethyl acetate (EtAc) (except for 338 K) as non-solvents, and chloroform (CHCl3) as good solvent (except for 378 K) for PLLA. For BCP/PLLA, CHCl3, EtAc (for 378 K), dioxane (except for 378 K), and THF were indicated as good solvents.

Heat capacity of hydrous basaltic glasses and liquids

We determined the heat capacities of four series of glasses and liquids of basaltic and basaltic andesite compositions from remelted volcanic rock samples and Fe-free synthetic analogues. The samples are low-alkali, Ca- and Mg-rich aluminosilicates with non-bridging oxygen to tetrahedrally-coordinated cation ratios (NBO/T) ranging between 0.33 and 0.67. Differential scanning calorimetry measurements were performed at atmospheric pressure between room temperature and ~100K above the glass transition for hydrous samples and up to ~1800K for dry samples. The water contents investigated range up to 5.34wt.% (16.4mol%). Water does not measurably affect the heat capacity of glasses. We derived a new value of the partial molar heat capacity of water in silicate glasses of C¯P,H2Oglass=82.804+10−3T−48.274×10−5T−2 (J/molK) using our new data in combination with literature data on more and less polymerized compositions. The increase in heat capacity at the glass transition is of the order of ~30–40% and generally increases with increasing water content. The onset of the glass transition in hydrous samples occurs below the Dulong–Petit limit of 3R/g atom. The configurational heat capacity, i.e., the magnitude of the change in heat capacity observed at the glass transition, generally increases as polymerization decreases and as water content increases. We obtained a partial molar heat capacity of water in silicate liquids of basaltic composition of ~86J/molK. This value is comparable to the partial molar values for the major oxides which range from ~79 to 230J/molK. The partial molar heat capacity of water in silicate liquids appears to be compositionally-dependent, increasing as melt polymerization decreases. Such a dependence is certainly linked to the speciation and structural roles of water in complex silicate melts, however, a single value of ~93J/molK could reproduce the heat capacity of hydrous liquids of a wide range of NBO/T (0–1.51) at temperatures up to ~100K above the glass transition and water contents of 0–3.76wt.% with a root-mean square deviation of only 3.23J/molK.

Thermodynamic characteristics, structure, and interactions of L-proline in aqueous solutions of alcohols and urea

The enthalpies of dissolution of imino acid L-proline in aqueous solutions of methanol, 2-propanol, ethylene glycol, glycerin, and urea are measured by the calorimetric method at 313.15 K. Enthalpic parameters of the interaction of L-proline with nonaqueous components are calculated and compared with the data at 298.15 K. It is found that the sign of the heat capacity parameter of the pair and ternary interactions depends on whether the nonaqueous solvent component is a destroyer or stabilizer of the water structure. Partial molar heat capacities of proline in mixed solvents are obtained by the integral dissolution heat method. Temperature changes in the reduced enthalpy and entropy of the proline solution are determined at an increase in the temperature from 298 K to 313 K. It is shown that there is entropyenthalpy compensation at temperature changes in the characteristics during dissolution.

Enthalpies of solution, limiting solubilities, and partial molar heat capacities of n-alcohols in water and in trehalose crowded media

Abstract The enthalpies of solution of alcohols were determined by calorimetry in HEPES and (HEPES + trehalose) at 298.15 K. The used methodology and experiment’s design allowed us to extract from a single titration experiment the enthalpy of solution (Δsol H m), the limiting solubility of the alcohol in each aqueous media, and an estimation of the enthalpy of solution of water in the alcohol phase. From these values the changes in Gibbs energy (Δsol G m) and in entropy (Δsol S m) of solution were derived. A decrease in solubility for 1-butanol and 1-pentanol in the crowded media (HEPES + trehalose) was observed which is driven by a significant decrease in the favorable enthalpy of solution. The partial molar heat capacity, in each media was determined in our heat capacity drop calorimeter, also at 298.15 K. A significant decrease of the partial molar heat capacity was observed for both alcohols in (HEPES + trehalose), which together with the obtained decrease in favorable Δsol H m, is consistent with a decrease in hydrophobic solvation, as a result of a decrease in free solvent availability induced by the trehalose. Finally, we tentatively predict that in the aqueous media of the crowded solutions that characterize cells and biological fluids, solutes with low aqueous solubility will be more soluble, whereas the solubility of highly polar solutes will be reduced.

Determination of thermodynamic properties of poly (cyclohexyl methacrylate) by inverse gas chromatography.

In this work, some thermodynamic properties of poly (cyclohexyl methacrylate) were studied by inverse gas chromatography (IGC). For this purpose, the polymeric substance was coated on Chromosorb W and which was filled into a glass column. The retention times (t(r)) of the probes were determined from the interactions of poly (cyclohexyl methacrylate) with n-pentane, n-hexane, n-heptane, n-octane, n-decane, methanol, ethanol, 2-propanol, butanol, acetone, ethyl methyl ketone, benzene, toluene and o-xylene by IGC technique. Then, the specific volume (Vg(0)) was determined for each probe molecule. By using (1/T; lnVg(0)) graphics, the glass transition temperature of poly (cyclohexyl methacrylate) was found to be 373 K. The adsorption heat under the glass transition temperature (deltaH(a)), and partial molar heat of sorption above the glass transition (deltaH1(S)), partial molar free energy of sorption (deltaG1(S)) and partial molar entropy of sorption (deltaS1(S)) belonging to sorption for every probe were calculated. The partial molar heat of mixing at infinite dilution (deltaH1(infinity)), partial molar free energy of mixing at infinite dilution (deltaG1(infinity)), Flory-Huggins interaction parameter (chi12(infinity)) and weight fraction activity coefficient (a1/w1)(infinity) values of polymer-solute systems were calculated at different column temperatures. The solubility parameters (delta2) of the polymer were obtained by IGC technique.

Myths and verities in protein folding theories: From Frank and Evans iceberg-conjecture to explanation of the hydrophobic effect

Starting from the seminal article by Frank and Evans where the "iceberg formation" idea was first expressed, we follow the evolution of this idea to the explanation of the hydrophobic effect. We show that the idea of iceberg formation can provide an explanation to the entropy, and enthalpy of solvation of non-polar solutes in water, provided one first explains why a simple non-polar solute would form icebergs in the first place. Having done that, the questions regarding the outstanding large hydrophobic solvation Gibbs energy remains unexplained. This conclusion follows from the exact entropy-enthalpy-compensation pertaining to any structural changes induced in the solvent. We also comment on some misinterpretation of the partial molar heat capacity of non-polar solutes in water.

Ion-molecular interactions in solutions of potassium and cadmium thiocyanates in N-methylpyrrolidone at 298.15 k, according to calorimetry and densitometry data

The heat capacity and density of KNCS-N-methylpyrrolidone (MP), Cd(NCS)2-MP, and KNCS-Cd(NCS)2-MP solutions at 298.15 K are studied by means of calorimetry and densitometry. Standard partial molar heat capacities and volumes (\(\bar C^\circ _{p,2} \) and \(\bar V^\circ _2 \)) of the studied electrolytes in MP are calculated. Standard values of heat capacity \(\bar C^\circ _{p,i} \) and volume \(\bar V^\circ _i \) of NCS− ions in MP at 298.15 K are determined. Values of the heat capacity and volume changes upon the formation of the three-component system KNCS-Cd(NCS)2-MP from binary solutions are obtained and discussed.

Determination of the solubility parameter of ionic liquid 1-octyl-3-methylimidazolium hexafluorophosphate by inverse gas chromatography

The thermodynamic and physicochemical properties of 1-octyl-3-methylimidazolium hexafluorophosphate ([OMIM]PF6) were investigated by inverse gas chromatography from 343.15K to 373.15K. Two groups of solvents with different chemical natures and polarities were used to characterize [OMIM]PF6–solvent interactions. The specific retention volume, molar heat of sorption, weight fraction activity coefficient, partial molar heat of mixing, Flory–Huggins interaction parameter between [OMIM]PF6 and the tested solvents, as well as activity coefficients at infinite dilution were determined. The solubility parameters of [OMIM]PF6 were also determined by plotting the graph of δ12/(RT)−χ12∞/V1 versus the solubility parameter δ1 of the probes.

Heat capacity and density of solutions of calcium and cadmium nitrates in N-methylpyrrolidone at 298.15 K

The heat capacity and density of solutions of calcium and cadmium nitrates in N-methylpyrrolidone (MP) at 298.15 K are studied by calorimetry and densimetry. The obtained data are discussed in relation to certain features of solvation and complex formation in solutions of these salts. The standard partial molar heat capacities and volumes (\(\overline {C_{p^2 }^0 }\) and \(\overline {V_2^0 }\)) of the electrolytes in MP are calculated. The standard heat capacities \(\overline {C_{p^i }^0 }\) and volumes \(\overline {V_i^0 }\) of Ca2+ and Cd2+ ions in MP at 298.15 K were determined, along with the contribution from specific interactions to the values of \(\overline {C_{p^i }^0 }\) and \(\overline {V_i^0 }\) of Cd2+ ions in MP solution.

Determination of the solubility parameter of ionic liquid 1-allyl-3-methylimidazolium chloride by inverse gas chromatography

Some thermodynamic quantities were obtained for the interactions of ionic liquid 1-allyl-3-methylimidazolium chloride ([AMIM]Cl), with n-hexane (n-C6), n-heptane (n-C7), n-octane (n-C8), n-nonane (n-C9), chloroform, ethyl acetate, ether and acetone by the inverse gas chromatography (IGC) method in various temperatures. The thermodynamic parameters including the molar heat of sorption, weight fraction activity coefficient, Flory–Huggins interaction parameter and partial molar heat of mixing were calculated to judge the interactions between [AMIM]Cl and solvents at the studied temperatures. Also, the solubility parameter of [AMIM]Cl was found by plotting the graph of solubility parameters of probes. The results showed that the selected solvents n-C6, n-C7, n-C8, n-C9, ethyl acetate, ether and acetone were poor solvents for [AMIM]Cl, while chloroform was a favorite solvent for [AMIM]Cl. The solubility parameter of [AMIM]Cl was calculated to be 23.33 (J·cm−3)0.5 (343.15K), 22.57 (J·cm−3)0.5 (353.15K), 21.63 (J·cm−3)0.5 (363.15K), and 20.88 (J·cm−3)0.5 (373.15K) by IGC.

Determination of the Solubility Parameter of Epoxidized Soybean Oil by Inverse Gas Chromatography

The thermodynamic parameters of epoxidized soybean oil (ESO) were determined by means of inverse gas chromatography (IGC) in the temperature range of 303.15 K-343.15 K. Two groups of probe solvents with different chemical natures and polarities were used to obtain information about ESO. The thermodynamic parameters—such as molar heat of sorption, weight fraction activity coefficient, Flory–Huggins interaction parameter, and partial molar heat of mixing—were obtained to judge the interactions between ESO and solvents at the studied temperatures. Also, the solubility parameters of ESO were found by plotting the graph of δ1 2/(RT) – χ∞ 12/V1 vs. solubility parameters, δ1, of the probes. The results showed that the selected solvent ethyl acetate was a moderate solvent for ESO; n-hexane was a moderate (but close to a better) solvent; while the probes n-heptane, n-octane, n-nonane, and chloroform were excellent solvents. From the extrapolation to 298 K, the solubility parameter value of ESO was 16.70 (J/cm3)0.5.

Determination of the Solubility Parameter of Ionic Liquid 1-Hexyl-3-methylimidazolium Hexafluorophosphate by Inverse Gas Chromatography

In this study, physical and thermodynamic properties of 1-hexyl-3-methylimidazolium hexafluorophosphate ([HMIM]PF6) were investigated by using inverse gas chromatography (IGC). Two groups of solvents with different chemical natures and polarities were used to obtain information about [HMIM]PF6-solvent interactions: chloroform, ethyl acetate, ether, acetone and alkanes. The specific retention volume (Vg0), molar heat of sorption, weight fraction activity coefficient, activity coefficients at infinite dilution, partial molar heat of mixing and Flory–Huggins interaction parameter between [HMIM]PF6 and solvents were determined in the temperature range of 343.15–373.15 K. Also, the solubility parameters of [HMIM]PF6 at infinite dilution were found by plotting the graph of δ12/(RT) – χ1.2∞/V1 versus solubility parameters, δ1, of probes. The results showed that n-C6, n-C7, n-C8, n-C9, ether, and n-butyl alcohol were poor solvents for [HMIM]PF6; chloroform, acetone, and ethyl acetate were favorite ones, while ethanol was moderate solvent for [HMIM]PF6 (close to poor solvent). The solubility parameter of [HMIM]PF6 was determined as 23.28 (J/cm3)0.5 by the extrapolation at 298.15 K.

Heat capacities of hydrous silicate glasses and liquids

Differential scanning calorimetry measurements made at atmospheric pressure from 300K to about 100K above the glass transition temperature (Tg) are reported for two new series of hydrated aluminosilicate glasses and supercooled liquids for water contents between 0 and 7.3mol%. The compositions are synthetic iron-free analogs of tephrite and foidite lava compositions, and are depolymerized (NBO/T=0.8 and 1.5, respectively). In all cases, water exerts a marked depressing effect on Tg, in close agreement with the results of viscosity experiments on the same samples. For glasses, the partial molar heat capacity of water previously published for polymerized compositions (Bouhifd et al., 2006) reproduces the present data within the combined uncertainties of the experimental and model values. For the hydrous silicate glasses, the partial molar heat capacity of water can be thus considered as independent of composition, and insensitive to structural factors above room temperature. However, for hydrous liquids the existing data suggest two different coefficients for polymerized and depolymerized melts. In depolymerized liquids, the partial molar heat capacity of water C¯pH2O (is about 237±40J/molK, which is nearly three times higher than that previously determined for polymerized hydrous liquids C¯pH2O (≈85J/molK for three hydrous melts with 0<NBO/T<0.2; Bouhifd et al., 2006), and more than three times that of pure liquid water at ambient conditions. From speciation data, we found that the partial molar heat capacity for hydroxyl groups in depolymerized melts, C¯pOH−, is about 281±47J/molK, and that of molecular water, C¯pH2Omol, is about 30±15J/molK. The present study suggests that C¯pH2Omol is independent of composition, but, C¯pOH− for the depolymerized melts is close to double the value of 153±18J/molK previously obtained for the more polymerized melts. The present result suggests different structural roles of OH− in polymerized and depolymerized melts, and also the predominance of OH− species in depolymerized melts. This striking feature for water is discussed with reference to potential additional species in depolymerized melts, whose formation may have strong effects on hydrous melt properties.