arXiv subjects

Fernando Hevia

Publications and source records attributed to Fernando Hevia.

At least 19 recordsLinked to original sources

arXiv2026

Thermodynamics of 2-undecanone + n-alkane mixtures

Densities and excess molar volumes ($V_{\text{m}}^{\text{E}}$) at (293.15-303.15) K and excess molar enthalpies ($H_{\text{m}}^{\text{E}}$) at 298.15 K are reported for 2-undecanone + heptane, or + octane, or + decane, or + dodecane, or + tetradecane mixtures at 95 kPa. Densities and $H_{\text{m}}^{\text{E}}$ were measured using, respectively, a densitometer Anton Paar DMA 602 and a Tian-Calvet micro-calorimeter. $H_{\text{m}}^{\text{E}}$ results are positive, indicating that interactions between like molecules are dominant. Both $H_{\text{m}}^{\text{E}}$ and $V_{\text{m}}^{\text{E}}$ increase in line with $n$ (number of C atoms of the alkane), which reveals that the increase of $V_{\text{m}}^{\text{E}}$ can be ascribed to an increased interactional contribution. Nevertheless, systems with $n$ = 7,8 show negative $V_{\text{m}}^{\text{E}}$ values, which reveals that $V_{\text{m}}^{\text{E}}$ is determined mainly by structural effects. Isochoric excess molar internal energies ($U_{V\text{m}}^{\text{E}}$) at 298.15 K have been obtained from the present $H_{\text{m}}^{\text{E}}$ and $V_{\text{m}}^{\text{E}}$ data. At equimolar composition, $U_{V\text{m}}^{\text{E}}$is nearly constant for $n$ = 7-10, and then slightly increases. This has been explained in terms of a possible folding of 2-undecanone. From the comparison of $U_{V\text{m}}^{\text{E}}$ results for similar systems involving n-alkanoates, it is shown that folding is more likely in solutions with these compounds.

physics.chem-ph↗

arXiv2026

Excess molar enthalpies of (iodobenzene, or 1-iodonaphthalene + n-alkane) liquid mixtures at T = 298.15 K and p = 93 kPa

Excess molar enthalpies ($H_{\text{m}}^{\text{E}}$) for iodobenzene, or 1-iodonaphthalene + heptane, + decane, + dodecane, or + tetradecane mixtures at 298.15 K and 93 kPa have been measured using a Tian-Calvet micro-calorimeter. The values of $H_{\text{m}}^{\text{E}}$ are positive and indicate that interactions between like molecules are prevalent. In contrast, our previous results on excess molar volumes ($V_{\text{m}}^{\text{E}}$) are negative for the systems C$_6$H$_5$I + heptane, or 1-iodonaphthalene + n-alkane, which reveal the existence of large structural effects in such solutions. This set of measurements has been used to determine isochoric excess molar internal energies ($U_{V\text{m}}^{\text{E}}$). In the range of n-alkanes considered (n is the number of C atoms of the alkane), values of $U_{V\text{m}}^{\text{E}}$ at equimolar composition decrease from n = 7 to n = 10 and then slightly increase for systems with C$_6$H$_5$I, while decrease slowly for mixtures with 1-iodonaphthalene. These trends fit well with the patterns observed for other alkane mixtures containing cyclic molecules. Dispersive interactions are dominant and those between aromatic molecules with a given halogen atom become stronger when the size of this atom increases due to the corresponding increase of molecular polarizability. The mixtures were studied using the DISQUAC and Flory models. The latter was also applied to n-alkane solutions with C$_6$H$_5$F, or 1-methylnaphthalene. Both theories describe accurately the $H_{\text{m}}^{\text{E}}$ data. In terms of the Flory model, this means that the random mixing hypothesis is largely achieved. On the other hand, the theory overestimates the interactional contribution to $V_{\text{m}}^{\text{E}}$, particularly for systems with C$_6$H$_5$X (X = F, I).

physics.chem-ph↗

arXiv2025

Density and excess molar enthalpy of (2-propanol + glyme) liquid mixtures. Application of the Flory model

For glymes of general formula CH3O(CH2CH2O)uCH3, with u = 1, 2, 3, 4, the densities of the (2-propanol + glyme) systems at temperatures ranging from (293.15 to 303.15) K and at pressure 0.1 MPa were determined using a DSA 5000 densimeter (from Anton Paar). The corresponding excess molar volumes were calculated from these density measurements. In addition, excess molar enthalpies at 298.15 K and 0.1 MPa were measured using a Tian-Calvet micro-calorimeter. The results show that alkanol-ether interactions are strong but do not contribute significantly to the excess molar enthalpy, as the values are large and positive, and comparable to those of (glyme + n-heptane) systems. The excess molar volumes are small or even negative (in the case of the mixture with u = 4), indicating that they are mainly governed by structural effects. Mixtures with 1-propanol or 2-propanol behave similarly, although interactions between unlike molecules become slightly stronger when 1-propanol is involved. On the other hand, effects related to alcohol self-association play a decisive role in the thermodynamic properties when glymes are replaced by di-n-propyl ether. This is supported by the application of the Flory model, which shows that orientational effects are weak in the studied glyme-containing mixtures but become significantly stronger when di-n-propyl ether is considered.

physics.chem-ph↗

arXiv2025

Volumetric and viscosity data of 1-iodonaphthalene + n-alkanes mixture at (288.15-308.15) K

Density and viscosity measurements have been performed for the systems 1-iodonaphthalene + heptane, or + decane, or + dodecane, or + tetradecane over the temperature range (288.15-308.15) K and atmospheric pressure. At this end, a densitometer Anton-Paar DMA 602 and a Ubbelohde viscosimeter were used. Excess molar volumes are large and negative and decrease when the temperature is increased, which reveals that the main contribution to the excess molar volume arises from structural effects. The values of the deviations of dynamic viscosity from linear dependence on mole fraction are also large and negative, indicating that n-alkanes are good breakers of the interactions between 1-iodonaphthalene molecules. Different models were applied for describing viscosity data. McAllister's equation correlates well with kinematic viscosities. Results are similar when dynamic viscosities are correlated with the Grunberg-Nissan or Fang-He equations. This means that size effects are not relevant to the mentioned data. The adjustable parameter of the Grunberg-Nissan equation is negative for all the systems at any temperature, a typical feature of systems where dispersive interactions are dominant. This is in agreement with findings obtained in previous studies on similar n-alkane mixtures involving C$_6$H$_5$X (X = Cl, Br, I) or 1,2,4-trichlorobenzene or 1-chloronaphthalene. Free volume effects have little influence on the present dynamic viscosity results, well represented by the absolute rate model using residual molar Gibbs energies obtained from the DISQUAC model.

physics.chem-ph↗

arXiv2025

n-alkanoate + n-alkane mixtures: folding of hydrocarbon chains of n-alkanoates

The mixtures CH$_3$(CH$_2$)$_{u-1}$COO(CH$_2$)$_{v-1}$CH$_3$ ($u=5-13$, $v=1,2$; $u=1,2,3$, $v=3,4$; $u=1,2,4$, $v=5$) + n-alkane have been investigated using experimental data (viscosity and excess molar functions: enthalpy, $H_{\text{m}}^{\text{E}}$, volume, $V_{\text{m}}^{\text{E}}$, isobaric heat capacity, and isochoric internal energy, $U_{V\text{m}}^{\text{E}}$) and models (Flory, Grunberg-Nissan, Bloomfield-Dewan). They are characterized by weak orientational effects. Large structural effects are found in some systems, like those containing pentane. Some considerations from standard enthalpies of vaporization, cohesive energy densities and $V_{\text{m}}^{\text{E}}$ of heptane mixtures reveal the existence of structural changes in longer n-alkanoates, which lead to stronger interactions between them. The observed decrease of $H_{\text{m}}^{\text{E}}$ for systems with a given n-alkane seems to be more related to the steric hindrance of the COO group than to interactional effects. The $U_{V\text{m}}^{\text{E}}(n)$ function ($n=$ number of C atoms in the n-alkane) shows a minimum for systems with esters with ($u\geq4$, $v=1$); ($u\geq7$, $v=2$), or ($u\geq 1$, $v=4,5$). A similar dependence was found for n-alkane mixtures involving cyclic molecules (cyclohexane, benzene). This result suggests that certain n-alkanoates, in an alkane medium, can form quasi-cyclic structures. Viscosities are well described by means of free volume effects only. For systems with butyl ethanoate or methyl decanoate, the variation of $\Delta \eta (n)$ (deviation of dynamic viscosity) is consistent with that of $U_{V\text{m}}^{\text{E}}(n)$, which supports the existence of cyclic structures in these esters. The Flory model provides poor results on $H_{\text{m}}^{\text{E}}$ for systems with large structural effects. Results improve when the model is applied to $U_{V\text{m}}^{\text{E}}(n)$ data.

physics.chem-ph↗

arXiv2025

Liquid-liquid equilibria of systems containing 2-methoxyphenol or 2-ethoxyphenol and n-alkanes

Liquid-liquid equilibria phase diagrams have been determined for the systems: 2-methoxyphenol + n-decane, or + n-dodecane, or + n-tetradecane or + n-hexadecane and for 2-ethoxyphenol + n-octane, or + n-dodecane, or + n-tetradecane, or + n-hexadecane. The experimental method used is based on the observation, by means of a laser scattering technique, of the turbidity produced on cooling when a second phase appears. All the mixtures studied show an upper critical solution temperature, which increases with the n-alkane size. Dipolar interactions between like molecules become stronger in the sequence: 2-ethoxyphenol < 2-methoxyphenol < phenol. Data available in the literature suggest that this relative variation is also valid for n-alkane mixtures containing other substituted anilines, characterized by having a second polar group. The dependence of the upper critical solution temperature on the molecular structure of the polar aromatic compound involved is shortly discussed in terms of intramolecular and steric effects.

physics.chem-ph↗

arXiv2024

Thermodynamics of mixtures with strong negative deviations from Raoult's law. XVIII: Excess molar enthalpies for the (1-alkanol + cyclohexylamine) systems at 298.15 K and modelling

Excess molar enthalpies, $H_{\text{m}}^{\text{E}}$, have been measured using a Tian-Calvet microcalorimeter for the systems CH$_3$(CH$_2$)$_{u-1}$OH ($u$ = 1,2,3,4,7,10) + cyclohexylamine at 298.15 K and 0.1 MPa. The $H_{\text{m}}^{\text{E}}$ values are large and negative, indicating the existence of strong interactions between unlike molecules, which is consistent with the also large and negative excess molar volumes, $V_{\text{m}}^{\text{E}}$, of these solutions, previously measured by us. The contribution from the equation of state term to $H_{\text{m}}^{\text{E}}$ has been evaluated for the 1-alkanol + cyclohexylamine, or + 1-hexylamine, or + aniline mixtures, and the corresponding excess molar internal energies at constant volume, $U_{\text{m,}V}^{\text{E}}$, have been determined. It is shown that such contribution is particularly important for the methanol + aniline system, in such a way that the excess functions $H_{\text{m}}^{\text{E}}$ and $U_{\text{m,}V}^{\text{E}}$ have different sign at $x_1$ = 0.5. The DISQUAC and ERAS models have been applied to the cyclohexylamine systems, and the interaction parameters have been reported. DISQUAC improves ERAS results on $H_{\text{m}}^{\text{E}}$. The latter model describes correctly the $V_{\text{m}}^{\text{E}}$ curves. The variation of of CH$_3$(CH$_2$)$_{u-1}$OH + cyclohexylamine, or + 1-hexylamine, or + aniline mixtures with $u$ along a homologous series with a given amine, or with the amine in mixtures with a given 1-alkanol is discussed in terms of the different interactional contributions to $H_{\text{m}}^{\text{E}}$.

physics.chem-ph↗

arXiv2024

Thermodynamics of mixtures containing amines. XVII. Excess molar enthalpy and volume measurements for benzylamine + heptane or + 1-alkanol mixtures at 298.15 K. Application of the DISQUAC and ERAS models

Excess molar enthalpies, $H_{\text{m}}^{\text{E}}$, at 298.15 K and 0.1 MPa have been measured by means of a Tian-Calvet microcalorimeter for the systems benzylamine (phenylmethanamine) + heptane, or + methanol, or + 1-propanol, or + 1-pentanol, or + 1-heptanol, or + 1-decanol. In addition, excess molar volumes, $V_{\text{m}}^{\text{E}}$, at the same conditions have been also determined using a densimeter Anton Paar model DSA 5000 for the benzylamine + heptane mixture. The $H_{\text{m}}^{\text{E}}$ of this solution is large and positive since at 298.15 K the system temperature is close to its upper critical solution temperature. Thus, systems with n-alkanes show positive deviations from the Raoult's law. The measured $|V_{\text{m}}^{\text{E}}|$ values are low, indicating the existence of large structural effects. $H_{\text{m}}^{\text{E}}$ values of mixtures involving 1-alkanols are large and negative. That is, interactions between unlike molecules are dominant and the systems are characterized by negative deviations from Raoult's law. It is shown that the enthalpy of the hydrogen bonding between molecules of 1-alkanol and benzyalmine are more negative than those between 1-alkanol molecules. The $V_{\text{m}}^{\text{E}}$ values of the systems with 1-alkanols are also large and negative, and are determined mainly by interactional effects since they increase in line with $H_{\text{m}}^{\text{E}}$ and with the alcohol size. The different contributions to $H_{\text{m}}^{\text{E}}$ have been evaluated. The systems have been studied using the DISQUAC and ERAS models. ERAS describes correctly the $V_{\text{m}}^{\text{E}}$ function. DISQUAC largely improves ERAS results on $H_{\text{m}}^{\text{E}}$ or on excess molar heat capacities at constant pressure for the mixtures with 1-alkanols, which underlines that physical interactions are very relevant in such solutions.

physics.chem-ph↗

arXiv2024

Solid-Liquid Equilibria for the Binary Systems Naphthalene or Biphenyl + 1-Tetradecanol or + 1-Hexadecanol

A differential scanning calorimetric technique has been used to obtain solid-liquid equilibrium temperatures for the mixtures naphthalene or biphenyl + 1-tetradecanol, or + 1-hexadecanol. All the systems show a simple eutectic point, whose final composition was determined by means of the Tamman's plots using the needed values of the eutectic heat and of the heat of melting, which are also reported. DISQUAC interaction parameters for the OH/aromatic contacts in the selected systems are given. The present experimental SLE phase diagrams are similarly described by DISQUAC and UNIFAC (Dortmund) models. However, the comparison of DISQUAC and UNIFAC results for systems involving naphthalene and shorter 1-alkanols (methanol-1-octanol) reveals that the temperature dependence of the interaction parameters is more suitable in DISQUAC. The systems are also investigated in terms of the concentration-concentration structure factor. It is shown that the positive deviations from the Raoult's law of the studied solutions become weaker when the homocoordination decreases.

physics.chem-ph↗

arXiv2024

Thermodynamics of mixtures with strongly negative deviations from Raoult's law. XVII. Permittivities and refractive indices for alkan-1-ol + N,N-diethylethanamine systems at (293.15-303.15) K. Application of the Kirkwood-Fr\"ohlich model

Relative permittivities at 1 MHz, $\varepsilon_{\text{r}}$, at 0.1 MPa and (293.15-303.15) K and refractive indices, $n_{\text{D}}$, at similar conditions have been measured for the alkan-1-ol (methanol, propan-1-ol, butan-1-ol, pentan-1-ol or heptan-1-ol) + N,N-diethylethanamine (TEA) systems. Positive values of the excess permittivities, $\varepsilon_{\text{r}}^{\text{E}}$ , are encountered for the methanol system at high alcohol concentrations. The remaining mixtures are characterized by negative $\varepsilon_{\text{r}}^{\text{E}}$ values over the whole composition range. At ${\phi}_1$ (volume fraction) = 0.5, $\varepsilon_{\text{r}}^{\text{E}}$ changes in the order: methanol > propan-1-ol > butan-1-ol < pentan-1-ol < heptan-1-ol. Mixtures formed by alkan-1-ol and an isomeric amine, hexan-1-amine (HxA) or N-propylpropan-1-amine (DPA) or cyclohexylamine, behave similarly. This has been explained in terms of the lower and weaker self-association of longer alkan-1-ols. From the permittivity data, it is shown that: (i) (alkan-1-ol)-TEA interactions contribute positively to $\varepsilon_{\text{r}}^{\text{E}}$; (ii) TEA is an effective breaker of the network of the alkan-1-ols; (iii) structural effects, which are very important for the volumetric and calorimetric data of alkan-1-ol + TEA systems, are also relevant when evaluating dielectric data. This is confirmed by the comparison of $\varepsilon_{\text{r}}^{\text{E}}$ measurements for alkan-1-ol + aliphatic amine mixtures; (iv) the aromaticity effect (i.e., the replacement of TEA by pyridine in systems with a given alkan-1-ol) leads to an increase of the mixture polarization. Calculations conducted in the framework of the Kirkwood-Fr\"ohlich model are consistent with the previous statements.

physics.chem-ph↗

arXiv2024

Density, speed of sound, refractive index and relative permittivity of methanol, propan-1-ol or pentan-1-ol + benzylamine liquid mixtures. Application of the Kirkwood-Fr\"ohlich model

Densities ($\rho$), speeds of sound ($c$), relative permittivities at 1 MHz ($\varepsilon_{\text{r}}$) and refractive indices at the sodium D-line ($n_{\text{D}}$) at $T$ = (293.15 K to 303.15 K) and $p$ = 0.1 MPa are reported for binary liquid mixtures alkan-1-ol + benzylamine. Methanol, propan-1-ol and pentan-1-ol are the alkan-1-ols studied in this work. The values of the excess molar volume ($V_{\text{m}}^{\text{E}}$), excess isentropic compressibility ($\kappa_S^{\text{E}}$), excess speed of sound ($c^{\text{E}}$), excess refractive index ($n_{\text{D}}^{\text{E}}$), excess relative permittivity ($\varepsilon_{\text{r}}^{\text{E}}$) and its temperature derivative ${(\partial{\varepsilon_{\text{r}}}/\partial T)}_p$ are calculated, and they are adjusted to Redlich-Kister polynomials. The $V_{\text{m}}^{\text{E}}$ values are negative, indicating a predominance of the solvation between unlike molecules and structural effects. $\varepsilon_{\text{r}}^{\text{E}}$ values indicate a positive contribution from the creation of (alkan-1-ol)-benzylamine interactions, and the positive value for the methanol mixture emphasises the importance of solvation. Calculations on excess molar refractions point out to weaker dispersive interactions than in the ideal mixture, which may be explained by the mentioned solvation effects. The Kirkwood-Fr\"ohlich model has been applied to the mixtures, and the Kirkwood correlation factors suggest an important relative weight, especially in the methanol system, of linear-like molecules in the solutions, which is in accordance with the positive contribution of the formed multimers to $\varepsilon_{\text{r}}^{\text{E}}$ due to their good effective response to the electric field.

physics.chem-ph↗

arXiv2024

Thermodynamics of amine mixtures. Systems formed by alkyl-amine and ether, or N,N-dialkylamide, or ethanenitrile

Systems of the type linear primary or secondary amine + cyclohexane, or + polar compound (namely, linear or cyclic monoether, + 1,4-dioxane, + N,N-dialkylamide, or + ethanitrile) have been investigated using literature data, and by means of DISQUAC. Interaction parameters for the contacts amine/ether, amine/amide and amine/nitrile are provided. For a given contact, the QUAC interchange coefficients remain practically constant along each homologous series. A similar trend has been encountered in other many previous studies. DISQUAC correctly describes excess molar enthalpies, $H_{\text{m}}^{\text{E}}$, and vapour-liquid and solid-liquid equilibria of the studied mixtures and improves calculations on $H_{\text{m}}^{\text{E}}$ from the UNIFAC (Dortmund) model. The experimental data have been used to determine the enthalpy of the interactions between unlike molecules, which are stronger in systems with N,N-dialkylamides or ethanenitrile than in mixtures with ethers. On the other hand, it is shown that $H_{\text{m}}^{\text{E}}$ values of amine + C$_6$H$_{12}$ mixtures are closely related to the amine self-association, and that interactions between molecules of the polar compounds are determinant on $H_{\text{m}}^{\text{E}}$ results of the mixtures amine + fixed polar compound or of the systems fixed amine + polar compound (no linear monoether). Structural effects are relevant in the di-n-butylamine + linear ether systems. The application of the Flory model reveals that orientational effects are rather weak in the investigated solutions. This is in agreement with previous studies on this type of mixtures using the ERAS model.

physics.chem-ph↗

arXiv2024

Thermodynamics of amide+amine mixtures. 5. Excess molar enthalpies of N,N-dimethylformamide or N,N-dimethylacetamide+N-propylpropan-1-amine, +N-butylbutan-1-amine, +butan-1-amine, or +hexan-1-amine systems. ERAS results

Excess molar enthalpies, $H_{\text{m}}^{\text{E}}$, over the whole composition range have been determined for the liquid mixtures N,N-dimethylformamide (DMF) or N,N-dimethylacetamide (DMA) + butan-1-amine (BA), or + hexan-1-amine (HxA), or + N-propylpropan-1-amine (DPA), or N-butylbutan-1-amine (DBA) at 298.15 K and at 0.1 MPa using a BT2.15 calorimeter from Setaram adapted to work in dynamic mode at constant temperature and pressure. All the $H_{\text{m}}^{\text{E}}$ values are positive, indicating that interactions between like molecules are predominant. The replacement of DMF by DMA in systems with a given amine leads to lower $H_{\text{m}}^{\text{E}}$ results, which have been ascribed to stronger amide-amide interactions in DMF mixtures. The replacement of HxA by DPA in systems with a given amide leads to slightly higher $H_{\text{m}}^{\text{E}}$ values, as interactions between unlike molecules are weaker for the latter. Structural effects in the investigated solutions are also present, since the corresponding excess molar volumes ($V_{\text{m}}^{\text{E}}$), previously determined, are negative or slightly positive. The systems have been characterized in terms of the ERAS model reporting the interaction parameters. The model correctly describes both $H_{\text{m}}^{\text{E}}$ and $V_{\text{m}}^{\text{E}}$. The application of the model suggests that, in the systems under study, solvation effects are of minor importance and that physical interactions are dominant.

physics.chem-ph↗

arXiv2024

Thermodynamics of mixtures with strongly negative deviations from Raoult's law. XVI. Permittivities and refractive indices for 1-alkanol + di-n-propylamine systems at (293.15-303.15) K. Application of the Kirkwood-Fr\"ohlich model

Relative permittivities at 1 MHz, $\varepsilon_{\text{r}}$, and refractive indices at the sodium D-line, $n_{\text{D}}$, are reported at 0.1 MPa and at (293.15-303.15) K for the binary systems 1-alkanol + di-n-propylamine (DPA). Their corresponding excess functions are calculated and correlated. For the methanol mixture, positive values of the excess permittivities, $\varepsilon_{\text{r}}^{\text{E}}$, are found. Except at high concentrations of the alcohol in the 1-propanol mixture, the remaining systems show negative values of this property. This fact reveals that the creation of (1-alkanol)-DPA interactions contributes positively to $\varepsilon_{\text{r}}^{\text{E}}$, being this contribution dominant in the methanol mixture. At ${\phi}_1$ (volume fraction) = 0.5, $\varepsilon_{\text{r}}^{\text{E}}$ changes in the sequence: methanol > 1-propanol > 1-butanol > 1-pentanol < 1-heptanol. An analogous variation with the chain length of the 1-alkanol is observed in mixtures such as 1-alkanol + heptane, + cyclohexylamine or + n-hexylamine (HxA). Moreover, for a given 1-alkanol, $\varepsilon_{\text{r}}^{\text{E}}$ is larger for DPA than for HxA mixtures, suggesting that in DPA solutions multimers with parallel alignment of the molecular dipoles are favoured and cyclic multimers are disfavoured when compared to HxA mixtures. The ${(\partial{\varepsilon_{\text{r}}}/\partial T)}_p$ values are higher for the mixtures than for pure 1-alkanols, because (1-alkanol)-DPA interactions are stronger than those between 1-alkanol molecules. Molar refractions indicate that dispersive interactions in DPA systems increase with the chain length of the 1-alkanol and are practically identical to those in HxA solutions. The considered mixtures are treated by means of the Kirkwood-Fr\"ohlich model, reporting the Kirkwood correlation factors and their excess values.

physics.chem-ph↗

arXiv2024

Density, speed of sound, refractive index and relative permittivity of methanol, propan-1-ol or pentan-1-ol + aniline liquid mixtures. Application of the Kirkwood-Fr\"ohlich model

Densities and speeds of sound at a temperature $T$ = 298.15 K, relative permittivities at 1 MHz and refractive indices at the sodium D-line at $T$ = (293.15 K to 303.15 K), all at a pressure p = 0.1 MPa, are reported for liquid mixtures methanol, propan-1-ol or pentan-1-ol + aniline. Excess molar volume ($V_{\text{m}}^{\text{E}}$), excess isentropic compressibility, excess speed of sound, excess refractive index, excess relative permittivity ($\varepsilon_{\text{r}}^{\text{E}}$) and its temperature derivative are calculated and fitted to Redlich-Kister polynomials. The agreement among the reported data and other literature sources is analysed by comparing $V_{\text{m}}^{\text{E}}$, $n_{\text{D}}^{\text{E}}$, $\varepsilon_{\text{r}}^{\text{E}}$ and the deviation of the speed of sound from mole-fraction linearity. The positive excess molar internal energies at constant volume ($U_{\text{m,}V}^{\text{E}}$) show the dominance of the breaking of interactions between like molecules in the energy balance on mixing, particularly the breaking of strong dipolar interactions between aniline molecules. This contribution is also dominant for the $\varepsilon_{\text{r}}^{\text{E}}$ values, as they are negative and decrease with the length of the alkan-1-ol chain. Calculations on the concentration-concentration structure factor are consistent with these statements, revealing homocoordination in the studied systems. The $V_{\text{m}}^{\text{E}}$ are negative, which together with the positive $U_{\text{m,}V}^{\text{E}}$ indicate the existence of important structural effects in the studied mixtures. The application of the Kirkwood-Fr\"ohlich model shows that the average relative orientation of neighbouring dipoles is similar in the mixtures methanol + aniline or + pyridine, in spite of the different character of the predominant interactions in the latter mixture (heterocoordination).

physics.chem-ph↗

arXiv2024

Volumetric and Viscosimetric Measurements for Methanol + CH$_3$-O-(CH$_2$CH$_2$O)$_n$-CH$_3$ ($n$ = 2, 3, 4) Mixtures at (293.15-303.15) K and Atmospheric Pressure: Application of the ERAS Model

Densities, $\rho$, and kinematic viscosities, $\nu$, have been determined at atmospheric pressure and at (293.15-303.15) K for binary mixtures formed by methanol and one linear polyether of the type CH$_3$-O-(CH$_2$CH$_2$O)$_n$-CH$_3$ ($n$ = 2,3,4). The $\rho$ values are used to compute excess molar volumes, $V_{\text{m}}^{\text{E}}$, and, together with $\nu$ results, dynamic viscosities ($\eta$). Deviations from linear dependence on mole fraction for viscosity, $\Delta \eta$, are also provided. Different semi-empirical equations have been employed to correlate viscosity data. Particularly, the equations used are: Grunberg-Nissan, Hind, Frenkel, Katti-Chaudhri, McAllister and Heric. Calculations show that better results are obtained from the Hind equation. The $V_{\text{m}}^{\text{E}}$ values are large and negative and contrast with the positive excess molar enthalpies, $H_{\text{m}}^{\text{E}}$, available in the literature, for these systems. This indicates that structural effects are dominant. The $\Delta \eta$ results are positive and correlate well with the difference in volume of the mixture compounds confirming the importance of structural effects. The temperature dependences of $\eta$ and of the molar volume have been used to calculate enthalpies, entropies and Gibbs energies, $\Delta G^*$, of viscous flow. It is demonstrated that $\Delta G^*$ is essentially determined by enthalpic effects. Methanol + CH$_3$-O-(CH$_2$CH$_2$O)$_n$-CH$_3$ mixtures have been treated in the framework of the ERAS model. Results on $H_{\text{m}}^{\text{E}}$ are acceptable, while the composition dependence of the $V_{\text{m}}^{\text{E}}$ curves is poorly represented. This has been ascribed to the existence of strong dipolar and structural effects in the present solutions.

physics.chem-ph↗

arXiv2024

Thermodynamics of mixtures containing a very strongly polar compound. 12. Systems with nitrobenzene or 1-nitroalkane and hydrocarbons or 1-alkanols

Mixtures involving nitrobenzene and hydrocarbons, or 1-alkanols and 1-nitroalkane, or nitrobenzene have been investigated based on a whole set of thermophysical properties available in the literature: excess molar functions (enthalpies, entropies, isobaric heat capacities, and volumes), vapour-liquid and liquid-liquid equilibria, permittivities or dynamic viscosities. In addition, the mixtures have been studied by means of the DISQUAC, ERAS, and UNIFAC models, and the concentration-concentration structure factor. The corresponding DISQUAC and ERAS interaction parameters are reported. In alkane mixtures, dipolar interactions between 1-nitroalkane molecules are weakened when the size of the polar compound increases, accordingly with the relative variation of their effective dipolar moment. Dipolar interactions are stronger in nitrobenzene solutions than in those containing the smaller 1-nitropropane, although both nitroalkanes have very similar effective dipole moment (aromaticity effect). Systems with 1-alkanols are characterized by dipolar interactions between like molecules which sharply increases when the alkanol size increases. Simultaneously, interactions between unlike molecules become weaker, as the OH group is then more sterically hindered. Interactions between unlike molecules are stronger in systems with nitromethane than in nitrobenzene solutions. The replacement of nitromethane by nitroethane in systems with a given 1-alkanol leads to strengthen those effects related with the alcohol self-association. Permittivity data and results on Kirkwood correlation factors show that the addition of 1-alkanol to a nitroalkane leads to cooperative effects, which increase the dipolar polarization of the solution, in such way that the destruction of the existing structure in pure liquids is partially counterbalanced. This effect is less important when longer 1-alkanols are involved.

physics.chem-ph↗

arXiv2024

Characterization of 1-alkanol + strongly polar compound mixtures from thermophysical data and the application of the Kirkwood-Buff integrals and Kirkwood-Fr\"ohlich formalisms

Mixtures formed by 1-alkanol and one strongly polar compound (nitromethane (NM), ethanenitrile (EtN), dimethyl sulfoxide (DMSO), sulfolane (SULF), nitrobenzene (NTBz) or benzonitrile (BzCN)) have been investigated on the basis of a set of thermophysical data, which includes: excess molar functions (enthalpies, $H_{\text{m}}^{\text{E}}$, Gibbs energies, $G_{\text{m}}^{\text{E}}$, entropies, $T S_{\text{m}}^{\text{E}}$, isobaric heat capacities, $C_{p \text{m}}^{\text{E}}$, volumes, $V_{\text{m}}^{\text{E}}$); liquid-liquid equilibria (LLE), excess permittivities and deviations from the linearity of dynamic viscosities. In addition, calculations have been conducted to determine the Kirkwood-Buff integrals and the Kirkwood correlations factors, $g_{\text{K}}$, of the investigated mixtures. In the former case, DISQUAC has been employed for modeling the needed vapour-liquid equilibria data. Many systems under consideration are characterized by dipolar interactions between like molecules and have positive values of $H_{\text{m}}^{\text{E}}$, $C_{p \text{m}}^{\text{E}}$ and $T S_{\text{m}}^{\text{E}}$. On the other hand, alkanol-solvent interactions, for mixtures with a fixed 1-alkanol, become weakened in the sequence: DMSO $\approx$ SULF > EtN > NM > BzCN > NTBz. In systems with a given solvent, such interactions become also weaker when the chain length of the 1-alkanol is increased. Interestingly, the considered mixtures also show strong structural effects. Results on Kirkwood-Buff integrals reveal that nitriles are more preferred than nitroalkanes around a central alcohol molecule. Calculations on $g_{\text{K}}$ show that, in terms of the mixture polarization, the systems are rather unstructured, and that this trend becomes more important when the 1-alkanol size increases in solutions with a given solvent.

physics.chem-ph↗