Pedro Morgado | Instituto Superior Técnico (original) (raw)
Papers by Pedro Morgado
Fluid Phase Equilibria, 2016
ABSTRACT The solubility of water in liquid alkanes and their mixtures is of vital importance to t... more ABSTRACT The solubility of water in liquid alkanes and their mixtures is of vital importance to the gas and petroleum industries. Preventing corrosion and hydrate crystal formation in subsea and terrestrial pipelines are examples of operating and safety problems, which require a precise knowledge of water content in hydrocarbons. Given the importance of the subject, a large number of results can be found in the literature. However, significant disagreement is found between these results, surely reflecting the difficulty of these measurements. On the other hand, the mutual (im)miscibility between water and perfluoroalkanes or perfluoroalkylalkanes (PFAA) has a very important role in their biomedical applications, and also in their use in biphasic synthesis and catalysis. Moreover, it has been demonstrated that the presence of water is fundamental for the processes of self-organization and nano-pattern formation in molecular films of PFAA. In this work, new experimental results for the solubility of water in liquid n-alkanes, perfluoroalkanes, in their mixtures and in perfluoroalkylalkanes, as a function of temperature, will be presented. The corresponding solution thermodynamic quantities are presented and discussed, and suggest a specific interaction between water and PFAA. The results were modeled using a version of the hetero-SAFT-VR equation that explicitly takes into account the presence of dipoles. The theoretical predictions quantitatively describe the experimental results, and confirm the importance of dipolar interactions in the behavior of water-PFAA systems.
ABSTRACT It is now well established that room temperature ionic liquids (RTILs) are highly struct... more ABSTRACT It is now well established that room temperature ionic liquids (RTILs) are highly structured fluids, displaying both polar and apolar domains that self-assemble forming bi-continuous phases, liquid crystals, etc. This structuration, confirmed by several experimental techniques such as X-ray and neutron diffraction studies, determines the macroscopic properties of the fluid and is also observed in molecular simulation studies. Due to its large electron cloud and high polarizability, the NMR active 129Xe atom is very sensitive to the local molecular environment around it. Depending only on the solvent, atomic Xe presents a range of chemical shifts larger than 250 ppm. Moreover, its small size as opposed to the usual molecular probes (e.g. fluorescence, solvatochromic, etc), assures little perturbation of the liquid structure. In this work, 129Xe chemical shifts have been obtained, as a function of temperature, for solutions of Xe in a wide range of ionic liquids, alkanes, perfluoroalkanes and perfluoroalkylalkanes (PFAA), providing insight into the structure of these liquids and helping to detect/confirm the presence of transitions to highly organized phases. For solutions of Xe in PFAA evidence has been obtained confirming the existence of mesophases below the melting point of some of the studied PFAA. In the case of ILs, these were chosen varying both the cation and anion families and the length of the alkyl side-chains. The experimental data show evidence for the change of liquid structure with the increase of the alkyl chain length along a given IL family, for the mobility of Xenon in both polar and apolar domains, and for its preferential interaction with the apolar regions. Molecular dynamics simulations were performed and help to elucidate the NMR results. Additionally, in the cases where the ILs displayed thermotropic liquid crystalline behaviour, 129Xe spectroscopy was able to identify the isotropic liquid to liquid crystal transition, and to provide insight on the differences between the molecular vicinity of Xenon in both phases. This work allows us to propose 129Xe NMR spectroscopy as a simple and accessible experimental link between the molecular structure of liquids and their macroscopic behaviour.
It is now well established that room temperature ionic liquids (RTILs) are highly structured flui... more It is now well established that room temperature ionic liquids (RTILs) are highly structured fluids, displaying both polar and apolar domains that self-assemble forming bi-continuous phases, liquid crystals, etc. This structuration, confirmed by several experimental techniques such as X-ray and neutron diffraction studies, determines the macroscopic properties of the fluid and is also observed in molecular simulation studies. Due to its large electron cloud and high polarizability, the NMR active 129Xe atom is very sensitive to the local molecular environment around it. Depending only on the solvent, atomic Xe presents a range of chemical shifts larger than 250 ppm. Moreover, its small size as opposed to the usual molecular probes (e.g. fluorescence, solvatochromic, etc), assures little perturbation of the liquid structure. In this work, 129Xe chemical shifts have been obtained, as a function of temperature, for solutions of Xe in a wide range of ionic liquids, alkanes, perfluoroalk...
Fluid Phase Equilibria, 2015
ABSTRACT Intra-diffusion coefficients of seven chlorophenols (2-chlorophenol, 3-chlorophenol, 4-c... more ABSTRACT Intra-diffusion coefficients of seven chlorophenols (2-chlorophenol, 3-chlorophenol, 4-chlorophenol, 2,4-dichlorophenol, 2,6-dichlorophenol, 2,4,6-dichlorophenol and pentachlorophenol) in water were determined by computer simulation (molecular dynamics) for dilute solutions at three different temperatures and the corresponding mutual diffusion coefficients estimated. The mutual diffusion coefficients of 2-chlorophenol in water agree with the available experimental results from the literature for all the temperatures studied. From the dependence of the diffusion coefficients on temperature, diffusion activation energies were estimated for all the solutes in water. Analyzing the radial distribution functions and spatial distribution functions of water around chlorophenols sites enable a discussion about intermolecular interactions (dominated by hydrogen bonding) between solute and solvent and its importance on the relative magnitude of diffusion coefficients. Finally the mutual diffusion coefficients obtained by simulation were correlated by the well-known Wilke–Chang equation.
The Journal of Physical Chemistry B, 2015
The vapor pressure of four liquid perfluoroalkylalkanes (CF3(CF2)n(CH2)mCH3; n = 3, m = 4,5,7; n ... more The vapor pressure of four liquid perfluoroalkylalkanes (CF3(CF2)n(CH2)mCH3; n = 3, m = 4,5,7; n = 5, m = 5) was measured as a function of temperature between 278 and 328 K. Molar enthalpies of vaporization were calculated from the experimental data, and the results were compared with data from the literature for the corresponding alkanes and perfluoroalkanes. The heterosegmented statistical associating fluid theory was used to interpret the results at the molecular level both with and without the explicit inclusion of the dipolar nature of the molecules. Additionally, ab initio calculations were performed for all perfluoroalkylalkanes studied to determine the dipole moment to be used in the theoretical calculations. We demonstrate that the inclusion of a dipolar term is essential for describing the vapor-liquid equilibria of perfluoroalkylalkanes. It is also shown that vapor-liquid equilibria in these compounds result from a subtle balance between dipolar interactions, which decrease the vapor pressure, and the relatively weak dispersive interactions between the hydrogenated and fluorinated segments.
Journal of Chemical & Engineering Data, 2014
ABSTRACT Intradiffusion coefficients of 2,2,2-trifluoroethanol in water have been measured by the... more ABSTRACT Intradiffusion coefficients of 2,2,2-trifluoroethanol in water have been measured by the pulsed field gradient (PFG)-NMR spin-echo technique as a function of temperature and composition on the dilute alcohol region. The measurements extend the range of compositions already studied in the literature and, for the first time, include the study of the temperature dependence. At the same time, intradiffusion coefficients of 2,2,2-trifluoroethanol, 2,2,3,3,3-pentafluoropropan-1-ol, and 2,2,3,3,4,4,4-heptafluorobutan-1-ol in water were obtained by computer simulation (molecular dynamics) as a function of composition and temperature. The intradiffusion coefficients of 2,2,2-trifluoroethanol in water obtained by simulation agree with the experimental results, while those of 2,2,3,3,3-pentafluoropropan-1-ol and 2,2,3,3,4,4,4-heptafluorobutan-1-ol are the first estimation of this property for those systems. The molecular dynamics simulations were also used to calculate the intradiffusion coefficients of perfluorooctanesulfonic acid and perfluorooctanoic acid in water at infinite dilution as a function of temperature, which are very difficult to obtain experimentally because of the very low solubility of these substances. From the dependence of the intradiffusion coefficients on temperature, diffusion activation energies were estimated for all the solutes in water.
![Research paper thumbnail of Fluid-Phase Behavior of {1Hexyl3-methylimidazolium Bis(trifluoromethylsulfonyl) Imide, [C 6 mim][NTf 2 ], + C 2 −C 8 n Alcohol} Mixtures: Liquid−Liquid Equilibrium and Excess Volumes ‡](https://attachments.academia-assets.com/47079518/thumbnails/1.jpg)
](Journal of Chemical and Engineering Data, 2006
In the frame of the IUPAC Project entitled Thermodynamics of ionic liquids, ionic liquid mixtures... more In the frame of the IUPAC Project entitled Thermodynamics of ionic liquids, ionic liquid mixtures, and the deVelopment of standarized systems, 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide, [C 6 mim]-[NTf 2 ], was selected as the "model" ionic liquid to perform round-robin measurements on a series of ionic liquid properties. In this work, the temperature-composition liquid-liquid equilibria of this ionic liquid with linear alkan-1-ols, C n H (2n+1) OH, with n ) 4, 5, 6, and 8, were determined at a nominal pressure of 0.1 MPa and up to 50 MPa for n ) 4, 5, and 6. Excess molar volumes, V E , of mixtures of this same ionic liquid with linear alkan-1-ols, C n H 2n+1 OH, with n ranging from 2 to 5, were measured at a nominal pressure of 0.1 MPa. The consistency between the two sets of experimental data (phase diagrams and V E ) was analyzed from a theoretical perspective; we noticed that as the alkyl chain length, n, of the linear alcohol varies both the pressure dependence of the phase diagrams and the critical excess molar volume change sign. ‡ Work performed in the frame of the IUPAC Project 2002-005-1-100 entitled Thermodynamics of ionic liquids, ionic liquid mixtures, and the deVelopment of standardized systems (http://www.iupac.org/projects/2002/ 2002-005-1-100.html).
The Journal of Physical Chemistry B
Langmuir, 2014
Aiming at providing a comprehensive study of the influence of the cation symmetry and alkyl side ... more Aiming at providing a comprehensive study of the influence of the cation symmetry and alkyl side chain length on the surface tension and surface organization of ionic liquids (ILs), this work addresses the experimental measurements of the surface tension of two extended series of ILs, namely R,R′-dialkylimidazolium bis-[(trifluoromethyl)sulfonyl]imide ([C n C n im][NTf 2 ]) and R-alkyl-3methylimidazolium bis[(trifluoromethyl)sulfonyl]imide ([C n C 1 im]-[NTf 2 ]), and their dependence with temperature (from 298 to 343 K). For both series of ILs the surface tension decreases with an increase in the cation side alkyl chain length up to aliphatic chains no longer than hexyl, here labeled as critical alkyl chain length (CACL). For ILs with aliphatic moieties longer than CACL the surface tension displays an almost constant value up to [C 12 C 12 im][NTf 2 ] or [C 16 C 1 im][NTf 2 ]. These constant values further converge to the surface tension of long chain n-alkanes, indicating that, for sufficiently long alkyl side chains, the surface ordering is strongly dominated by the aliphatic tails present in the IL. The enthalpies and entropies of surface were also derived and the critical temperatures were estimated from the experimental data. The trend of the derived thermodynamic properties highlights the effect of the structural organization of the IL at the surface with visible trend shifts occurring at a well-defined CACL in both symmetric and asymmetric series of ILs. Finally, the structure of a long-alkyl side chain IL at the vacuum-liquid interface was also explored using Molecular Dynamics simulations. In general, it was found that for the symmetric series of ILs, at the outermost polar layers, more cations point one of their aliphatic tails outward and the other inward, relative to the surface, than cations pointing both tails outward. The number of the former, while being the preferred conformation, exceeds the latter by around 75%.
Journal of Physical Chemistry B, 2006
The phase behavior of nitrogen + n-alkanes is studied within the framework of the statistical ass... more The phase behavior of nitrogen + n-alkanes is studied within the framework of the statistical associating fluid theory for potentials of variable range (SAFT-VR). The effect of the quadrupole moment of nitrogen on the phase behavior is considered through an extension of the SAFT-VR equation that includes an additional contribution to the Helmholtz free energy due to quadrupolar interactions. A significant improvement in the description of the phase diagram of the binary mixtures of nitrogen with different n-alkanes is obtained with the new approach when compared to predictions from the original SAFT-VR EOS (i.e., without the quadrupolar term). The experimental value for the quadrupole moment of nitrogen is used in the new equation; thus, no additional parameters are employed. Given the nonideal nature of the binary mixtures, a binary interaction parameter is needed to describe the full-phase diagram and high-pressure critical lines of these systems; however, this can be fitted to a single system and successfully used to predict the phase behavior of other binary mixtures without additional fitting. Furthermore, only a single, transferable, cross-energy parameter is required when the quadrupolar term is considered, whereas a cross-range parameter is also needed with the original SAFT-VR approach. The inclusion of the quadrupolar term in the equation of state therefore reduces the need to use effective parameters by explicitly including at the molecular level interactions due to the quadrupole moment.
The Journal of Physical Chemistry B, 2014
The mutual solubilities of [C 2 C 1 im][Ntf 2 ] ionic liquid and aromatic molecules (benzene and ... more The mutual solubilities of [C 2 C 1 im][Ntf 2 ] ionic liquid and aromatic molecules (benzene and its fluorinated derivatives) can be correlated to the dipolar and quadrupolar moments of the latter molecules. This fact can be interpreted as a consequence of the charge-induced structuration of the IL ions around the aromatic molecules. In this paper we demonstrate that we can follow the above-mentioned structural changes in the mixtures using different NMRbased techniques, namely 1D 1 H and 13 C NMR and 2D 1 H− 1 H NOESY NMR spectroscopy. These have been complemented by more detailed structural analyses of the different (IL plus aromatic solute) mixtures using MD simulations. Such systematic studies included eight systems, namely mixtures of the 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ionic liquid with benzene,
The Journal of Physical Chemistry B, 2011
The Journal of Physical Chemistry B, 2006
The phase behavior of nitrogen + n-alkanes is studied within the framework of the statistical ass... more The phase behavior of nitrogen + n-alkanes is studied within the framework of the statistical associating fluid theory for potentials of variable range (SAFT-VR). The effect of the quadrupole moment of nitrogen on the phase behavior is considered through an extension of the SAFT-VR equation that includes an additional contribution to the Helmholtz free energy due to quadrupolar interactions. A significant improvement in the description of the phase diagram of the binary mixtures of nitrogen with different n-alkanes is obtained with the new approach when compared to predictions from the original SAFT-VR EOS (i.e., without the quadrupolar term). The experimental value for the quadrupole moment of nitrogen is used in the new equation; thus, no additional parameters are employed. Given the nonideal nature of the binary mixtures, a binary interaction parameter is needed to describe the full-phase diagram and high-pressure critical lines of these systems; however, this can be fitted to a single system and successfully used to predict the phase behavior of other binary mixtures without additional fitting. Furthermore, only a single, transferable, cross-energy parameter is required when the quadrupolar term is considered, whereas a cross-range parameter is also needed with the original SAFT-VR approach. The inclusion of the quadrupolar term in the equation of state therefore reduces the need to use effective parameters by explicitly including at the molecular level interactions due to the quadrupole moment.
The Journal of Physical Chemistry B, 2013
The liquid organization of linear, branched, and cyclic alkanes was studied using atomic 129 Xe a... more The liquid organization of linear, branched, and cyclic alkanes was studied using atomic 129 Xe as a NMR probe. 129 Xe chemical shifts have been experimentally determined for xenon dissolved in a total of 21 alkanes. In order to allow the comparison of the different solvents at similar thermodynamic conditions, the measurements were performed over a wide range of temperatures, from the melting point of the solvent up to 350 K. The results were rationalized in terms of the density, nature, and organization of the chemical groups within xenon's coordination sphere. Additionally, molecular dynamics simulations were performed using established atomistic force fields to interpret and clarify the conclusions suggested by the experimental results. The analysis is able to interpret previous results in the literature for ethane and propane at very different experimental conditions.
The Journal of Physical Chemistry B, 2011
The Journal of Physical Chemistry Letters, 2013
The mesoscopic structure of 30 distinct ionic liquids was probed by 129 Xe NMR spectroscopy. The ... more The mesoscopic structure of 30 distinct ionic liquids was probed by 129 Xe NMR spectroscopy. The interpretation of the experimental data was complemented using molecular dynamics results. The results clearly show that xenon can effectively probe the various environments characteristic of different ionic liquids (ILs) and is thus able to distinguish between distinct ionic liquid families, including different types of interactions with diverse types of anion/polar networks. A finer analysis of the NMR data also confirmed that the xenon probes can also provide information on how the complex structure of an IL evolves along a homologous series.
Fluid Phase Equilibria, 2013
Fluid Phase Equilibria, 2005
The phase and volumetric behaviour of binary mixtures of n-alkanes and n-perfluoroalkanes at subc... more The phase and volumetric behaviour of binary mixtures of n-alkanes and n-perfluoroalkanes at subcritical conditions have been studied using the SAFT-VR equation of state. In previous work [C. McCabe, A. Galindo, A. Gil-Villegas, G. Jackson, Predicting the high-pressure phase equilibria of binary mixtures of perfluoro-n-alkanes plus n-alkanes using the SAFT-VR approach, J. Phys. Chem. B 102 (1998) 8060-8069] the SAFT-VR equation was successfully used to predict the phase behaviour of binary mixtures of low molecular weight n-perfluoroalkanes + n-alkanes. A transferable binary interaction parameter was proposed which enabled the accurate prediction of the critical lines for all the systems studied. In this work we focus on the low pressure liquid-liquid immiscibility displayed by binary mixtures of longer chains (C 5 C 8 ). New transferable binary interaction parameters for these mixtures are proposed, based on the reproduction of the UCST and excess volumes for the n-hexane + n-perfluorohexane system. With these parameters, predictions are then made for the vapour-liquid equilibria (VLE), liquid-liquid equilibria (LLE) and excess volumes of other binary mixtures without any additional fitting to experimental data. The resulting predictions from the SAFT-VR equation are in good agreement with the available experimental data.
Fluid Phase Equilibria, 2016
ABSTRACT The solubility of water in liquid alkanes and their mixtures is of vital importance to t... more ABSTRACT The solubility of water in liquid alkanes and their mixtures is of vital importance to the gas and petroleum industries. Preventing corrosion and hydrate crystal formation in subsea and terrestrial pipelines are examples of operating and safety problems, which require a precise knowledge of water content in hydrocarbons. Given the importance of the subject, a large number of results can be found in the literature. However, significant disagreement is found between these results, surely reflecting the difficulty of these measurements. On the other hand, the mutual (im)miscibility between water and perfluoroalkanes or perfluoroalkylalkanes (PFAA) has a very important role in their biomedical applications, and also in their use in biphasic synthesis and catalysis. Moreover, it has been demonstrated that the presence of water is fundamental for the processes of self-organization and nano-pattern formation in molecular films of PFAA. In this work, new experimental results for the solubility of water in liquid n-alkanes, perfluoroalkanes, in their mixtures and in perfluoroalkylalkanes, as a function of temperature, will be presented. The corresponding solution thermodynamic quantities are presented and discussed, and suggest a specific interaction between water and PFAA. The results were modeled using a version of the hetero-SAFT-VR equation that explicitly takes into account the presence of dipoles. The theoretical predictions quantitatively describe the experimental results, and confirm the importance of dipolar interactions in the behavior of water-PFAA systems.
ABSTRACT It is now well established that room temperature ionic liquids (RTILs) are highly struct... more ABSTRACT It is now well established that room temperature ionic liquids (RTILs) are highly structured fluids, displaying both polar and apolar domains that self-assemble forming bi-continuous phases, liquid crystals, etc. This structuration, confirmed by several experimental techniques such as X-ray and neutron diffraction studies, determines the macroscopic properties of the fluid and is also observed in molecular simulation studies. Due to its large electron cloud and high polarizability, the NMR active 129Xe atom is very sensitive to the local molecular environment around it. Depending only on the solvent, atomic Xe presents a range of chemical shifts larger than 250 ppm. Moreover, its small size as opposed to the usual molecular probes (e.g. fluorescence, solvatochromic, etc), assures little perturbation of the liquid structure. In this work, 129Xe chemical shifts have been obtained, as a function of temperature, for solutions of Xe in a wide range of ionic liquids, alkanes, perfluoroalkanes and perfluoroalkylalkanes (PFAA), providing insight into the structure of these liquids and helping to detect/confirm the presence of transitions to highly organized phases. For solutions of Xe in PFAA evidence has been obtained confirming the existence of mesophases below the melting point of some of the studied PFAA. In the case of ILs, these were chosen varying both the cation and anion families and the length of the alkyl side-chains. The experimental data show evidence for the change of liquid structure with the increase of the alkyl chain length along a given IL family, for the mobility of Xenon in both polar and apolar domains, and for its preferential interaction with the apolar regions. Molecular dynamics simulations were performed and help to elucidate the NMR results. Additionally, in the cases where the ILs displayed thermotropic liquid crystalline behaviour, 129Xe spectroscopy was able to identify the isotropic liquid to liquid crystal transition, and to provide insight on the differences between the molecular vicinity of Xenon in both phases. This work allows us to propose 129Xe NMR spectroscopy as a simple and accessible experimental link between the molecular structure of liquids and their macroscopic behaviour.
It is now well established that room temperature ionic liquids (RTILs) are highly structured flui... more It is now well established that room temperature ionic liquids (RTILs) are highly structured fluids, displaying both polar and apolar domains that self-assemble forming bi-continuous phases, liquid crystals, etc. This structuration, confirmed by several experimental techniques such as X-ray and neutron diffraction studies, determines the macroscopic properties of the fluid and is also observed in molecular simulation studies. Due to its large electron cloud and high polarizability, the NMR active 129Xe atom is very sensitive to the local molecular environment around it. Depending only on the solvent, atomic Xe presents a range of chemical shifts larger than 250 ppm. Moreover, its small size as opposed to the usual molecular probes (e.g. fluorescence, solvatochromic, etc), assures little perturbation of the liquid structure. In this work, 129Xe chemical shifts have been obtained, as a function of temperature, for solutions of Xe in a wide range of ionic liquids, alkanes, perfluoroalk...
Fluid Phase Equilibria, 2015
ABSTRACT Intra-diffusion coefficients of seven chlorophenols (2-chlorophenol, 3-chlorophenol, 4-c... more ABSTRACT Intra-diffusion coefficients of seven chlorophenols (2-chlorophenol, 3-chlorophenol, 4-chlorophenol, 2,4-dichlorophenol, 2,6-dichlorophenol, 2,4,6-dichlorophenol and pentachlorophenol) in water were determined by computer simulation (molecular dynamics) for dilute solutions at three different temperatures and the corresponding mutual diffusion coefficients estimated. The mutual diffusion coefficients of 2-chlorophenol in water agree with the available experimental results from the literature for all the temperatures studied. From the dependence of the diffusion coefficients on temperature, diffusion activation energies were estimated for all the solutes in water. Analyzing the radial distribution functions and spatial distribution functions of water around chlorophenols sites enable a discussion about intermolecular interactions (dominated by hydrogen bonding) between solute and solvent and its importance on the relative magnitude of diffusion coefficients. Finally the mutual diffusion coefficients obtained by simulation were correlated by the well-known Wilke–Chang equation.
The Journal of Physical Chemistry B, 2015
The vapor pressure of four liquid perfluoroalkylalkanes (CF3(CF2)n(CH2)mCH3; n = 3, m = 4,5,7; n ... more The vapor pressure of four liquid perfluoroalkylalkanes (CF3(CF2)n(CH2)mCH3; n = 3, m = 4,5,7; n = 5, m = 5) was measured as a function of temperature between 278 and 328 K. Molar enthalpies of vaporization were calculated from the experimental data, and the results were compared with data from the literature for the corresponding alkanes and perfluoroalkanes. The heterosegmented statistical associating fluid theory was used to interpret the results at the molecular level both with and without the explicit inclusion of the dipolar nature of the molecules. Additionally, ab initio calculations were performed for all perfluoroalkylalkanes studied to determine the dipole moment to be used in the theoretical calculations. We demonstrate that the inclusion of a dipolar term is essential for describing the vapor-liquid equilibria of perfluoroalkylalkanes. It is also shown that vapor-liquid equilibria in these compounds result from a subtle balance between dipolar interactions, which decrease the vapor pressure, and the relatively weak dispersive interactions between the hydrogenated and fluorinated segments.
Journal of Chemical & Engineering Data, 2014
ABSTRACT Intradiffusion coefficients of 2,2,2-trifluoroethanol in water have been measured by the... more ABSTRACT Intradiffusion coefficients of 2,2,2-trifluoroethanol in water have been measured by the pulsed field gradient (PFG)-NMR spin-echo technique as a function of temperature and composition on the dilute alcohol region. The measurements extend the range of compositions already studied in the literature and, for the first time, include the study of the temperature dependence. At the same time, intradiffusion coefficients of 2,2,2-trifluoroethanol, 2,2,3,3,3-pentafluoropropan-1-ol, and 2,2,3,3,4,4,4-heptafluorobutan-1-ol in water were obtained by computer simulation (molecular dynamics) as a function of composition and temperature. The intradiffusion coefficients of 2,2,2-trifluoroethanol in water obtained by simulation agree with the experimental results, while those of 2,2,3,3,3-pentafluoropropan-1-ol and 2,2,3,3,4,4,4-heptafluorobutan-1-ol are the first estimation of this property for those systems. The molecular dynamics simulations were also used to calculate the intradiffusion coefficients of perfluorooctanesulfonic acid and perfluorooctanoic acid in water at infinite dilution as a function of temperature, which are very difficult to obtain experimentally because of the very low solubility of these substances. From the dependence of the intradiffusion coefficients on temperature, diffusion activation energies were estimated for all the solutes in water.
Journal of Chemical and Engineering Data, 2006
In the frame of the IUPAC Project entitled Thermodynamics of ionic liquids, ionic liquid mixtures... more In the frame of the IUPAC Project entitled Thermodynamics of ionic liquids, ionic liquid mixtures, and the deVelopment of standarized systems, 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide, [C 6 mim]-[NTf 2 ], was selected as the "model" ionic liquid to perform round-robin measurements on a series of ionic liquid properties. In this work, the temperature-composition liquid-liquid equilibria of this ionic liquid with linear alkan-1-ols, C n H (2n+1) OH, with n ) 4, 5, 6, and 8, were determined at a nominal pressure of 0.1 MPa and up to 50 MPa for n ) 4, 5, and 6. Excess molar volumes, V E , of mixtures of this same ionic liquid with linear alkan-1-ols, C n H 2n+1 OH, with n ranging from 2 to 5, were measured at a nominal pressure of 0.1 MPa. The consistency between the two sets of experimental data (phase diagrams and V E ) was analyzed from a theoretical perspective; we noticed that as the alkyl chain length, n, of the linear alcohol varies both the pressure dependence of the phase diagrams and the critical excess molar volume change sign. ‡ Work performed in the frame of the IUPAC Project 2002-005-1-100 entitled Thermodynamics of ionic liquids, ionic liquid mixtures, and the deVelopment of standardized systems (http://www.iupac.org/projects/2002/ 2002-005-1-100.html).
The Journal of Physical Chemistry B
Langmuir, 2014
Aiming at providing a comprehensive study of the influence of the cation symmetry and alkyl side ... more Aiming at providing a comprehensive study of the influence of the cation symmetry and alkyl side chain length on the surface tension and surface organization of ionic liquids (ILs), this work addresses the experimental measurements of the surface tension of two extended series of ILs, namely R,R′-dialkylimidazolium bis-[(trifluoromethyl)sulfonyl]imide ([C n C n im][NTf 2 ]) and R-alkyl-3methylimidazolium bis[(trifluoromethyl)sulfonyl]imide ([C n C 1 im]-[NTf 2 ]), and their dependence with temperature (from 298 to 343 K). For both series of ILs the surface tension decreases with an increase in the cation side alkyl chain length up to aliphatic chains no longer than hexyl, here labeled as critical alkyl chain length (CACL). For ILs with aliphatic moieties longer than CACL the surface tension displays an almost constant value up to [C 12 C 12 im][NTf 2 ] or [C 16 C 1 im][NTf 2 ]. These constant values further converge to the surface tension of long chain n-alkanes, indicating that, for sufficiently long alkyl side chains, the surface ordering is strongly dominated by the aliphatic tails present in the IL. The enthalpies and entropies of surface were also derived and the critical temperatures were estimated from the experimental data. The trend of the derived thermodynamic properties highlights the effect of the structural organization of the IL at the surface with visible trend shifts occurring at a well-defined CACL in both symmetric and asymmetric series of ILs. Finally, the structure of a long-alkyl side chain IL at the vacuum-liquid interface was also explored using Molecular Dynamics simulations. In general, it was found that for the symmetric series of ILs, at the outermost polar layers, more cations point one of their aliphatic tails outward and the other inward, relative to the surface, than cations pointing both tails outward. The number of the former, while being the preferred conformation, exceeds the latter by around 75%.
Journal of Physical Chemistry B, 2006
The phase behavior of nitrogen + n-alkanes is studied within the framework of the statistical ass... more The phase behavior of nitrogen + n-alkanes is studied within the framework of the statistical associating fluid theory for potentials of variable range (SAFT-VR). The effect of the quadrupole moment of nitrogen on the phase behavior is considered through an extension of the SAFT-VR equation that includes an additional contribution to the Helmholtz free energy due to quadrupolar interactions. A significant improvement in the description of the phase diagram of the binary mixtures of nitrogen with different n-alkanes is obtained with the new approach when compared to predictions from the original SAFT-VR EOS (i.e., without the quadrupolar term). The experimental value for the quadrupole moment of nitrogen is used in the new equation; thus, no additional parameters are employed. Given the nonideal nature of the binary mixtures, a binary interaction parameter is needed to describe the full-phase diagram and high-pressure critical lines of these systems; however, this can be fitted to a single system and successfully used to predict the phase behavior of other binary mixtures without additional fitting. Furthermore, only a single, transferable, cross-energy parameter is required when the quadrupolar term is considered, whereas a cross-range parameter is also needed with the original SAFT-VR approach. The inclusion of the quadrupolar term in the equation of state therefore reduces the need to use effective parameters by explicitly including at the molecular level interactions due to the quadrupole moment.
The Journal of Physical Chemistry B, 2014
The mutual solubilities of [C 2 C 1 im][Ntf 2 ] ionic liquid and aromatic molecules (benzene and ... more The mutual solubilities of [C 2 C 1 im][Ntf 2 ] ionic liquid and aromatic molecules (benzene and its fluorinated derivatives) can be correlated to the dipolar and quadrupolar moments of the latter molecules. This fact can be interpreted as a consequence of the charge-induced structuration of the IL ions around the aromatic molecules. In this paper we demonstrate that we can follow the above-mentioned structural changes in the mixtures using different NMRbased techniques, namely 1D 1 H and 13 C NMR and 2D 1 H− 1 H NOESY NMR spectroscopy. These have been complemented by more detailed structural analyses of the different (IL plus aromatic solute) mixtures using MD simulations. Such systematic studies included eight systems, namely mixtures of the 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ionic liquid with benzene,
The Journal of Physical Chemistry B, 2011
The Journal of Physical Chemistry B, 2006
The phase behavior of nitrogen + n-alkanes is studied within the framework of the statistical ass... more The phase behavior of nitrogen + n-alkanes is studied within the framework of the statistical associating fluid theory for potentials of variable range (SAFT-VR). The effect of the quadrupole moment of nitrogen on the phase behavior is considered through an extension of the SAFT-VR equation that includes an additional contribution to the Helmholtz free energy due to quadrupolar interactions. A significant improvement in the description of the phase diagram of the binary mixtures of nitrogen with different n-alkanes is obtained with the new approach when compared to predictions from the original SAFT-VR EOS (i.e., without the quadrupolar term). The experimental value for the quadrupole moment of nitrogen is used in the new equation; thus, no additional parameters are employed. Given the nonideal nature of the binary mixtures, a binary interaction parameter is needed to describe the full-phase diagram and high-pressure critical lines of these systems; however, this can be fitted to a single system and successfully used to predict the phase behavior of other binary mixtures without additional fitting. Furthermore, only a single, transferable, cross-energy parameter is required when the quadrupolar term is considered, whereas a cross-range parameter is also needed with the original SAFT-VR approach. The inclusion of the quadrupolar term in the equation of state therefore reduces the need to use effective parameters by explicitly including at the molecular level interactions due to the quadrupole moment.
The Journal of Physical Chemistry B, 2013
The liquid organization of linear, branched, and cyclic alkanes was studied using atomic 129 Xe a... more The liquid organization of linear, branched, and cyclic alkanes was studied using atomic 129 Xe as a NMR probe. 129 Xe chemical shifts have been experimentally determined for xenon dissolved in a total of 21 alkanes. In order to allow the comparison of the different solvents at similar thermodynamic conditions, the measurements were performed over a wide range of temperatures, from the melting point of the solvent up to 350 K. The results were rationalized in terms of the density, nature, and organization of the chemical groups within xenon's coordination sphere. Additionally, molecular dynamics simulations were performed using established atomistic force fields to interpret and clarify the conclusions suggested by the experimental results. The analysis is able to interpret previous results in the literature for ethane and propane at very different experimental conditions.
The Journal of Physical Chemistry B, 2011
The Journal of Physical Chemistry Letters, 2013
The mesoscopic structure of 30 distinct ionic liquids was probed by 129 Xe NMR spectroscopy. The ... more The mesoscopic structure of 30 distinct ionic liquids was probed by 129 Xe NMR spectroscopy. The interpretation of the experimental data was complemented using molecular dynamics results. The results clearly show that xenon can effectively probe the various environments characteristic of different ionic liquids (ILs) and is thus able to distinguish between distinct ionic liquid families, including different types of interactions with diverse types of anion/polar networks. A finer analysis of the NMR data also confirmed that the xenon probes can also provide information on how the complex structure of an IL evolves along a homologous series.
Fluid Phase Equilibria, 2013
Fluid Phase Equilibria, 2005
The phase and volumetric behaviour of binary mixtures of n-alkanes and n-perfluoroalkanes at subc... more The phase and volumetric behaviour of binary mixtures of n-alkanes and n-perfluoroalkanes at subcritical conditions have been studied using the SAFT-VR equation of state. In previous work [C. McCabe, A. Galindo, A. Gil-Villegas, G. Jackson, Predicting the high-pressure phase equilibria of binary mixtures of perfluoro-n-alkanes plus n-alkanes using the SAFT-VR approach, J. Phys. Chem. B 102 (1998) 8060-8069] the SAFT-VR equation was successfully used to predict the phase behaviour of binary mixtures of low molecular weight n-perfluoroalkanes + n-alkanes. A transferable binary interaction parameter was proposed which enabled the accurate prediction of the critical lines for all the systems studied. In this work we focus on the low pressure liquid-liquid immiscibility displayed by binary mixtures of longer chains (C 5 C 8 ). New transferable binary interaction parameters for these mixtures are proposed, based on the reproduction of the UCST and excess volumes for the n-hexane + n-perfluorohexane system. With these parameters, predictions are then made for the vapour-liquid equilibria (VLE), liquid-liquid equilibria (LLE) and excess volumes of other binary mixtures without any additional fitting to experimental data. The resulting predictions from the SAFT-VR equation are in good agreement with the available experimental data.