Luis Romaní

University of Vigo, Vigo, Galicia, Spain

Are you Luis Romaní?

Claim your profile

Publications (106)157.34 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: The critical anomaly of the isobaric molar heat capacity for the liquid-liquid phase transition in binary nonionic mixtures is explained through a theory based on the general assumption that their partition function can be exactly mapped into that of the Ising three-dimensional model. Under this approximation, it is found that the heat capacity singularity is directly linked to molar excess enthalpy. In order to check this prediction and complete the available data for such systems, isobaric molar heat capacity and molar excess enthalpy near the liquid-liquid critical point were experimentally determined for a large set of binary liquid mixtures. Agreement between theory and experimental results-both from literature and from present work-is good for most cases. This fact opens a way for explaining and predicting the heat capacity divergence at the liquid-liquid critical point through basically the same microscopic arguments as for molar excess enthalpy, widely used in the frame of solution thermodynamics.
    Physical Review E 10/2013; 88(4-1):042107. · 2.31 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: In this work, the clusters residing in the {methanol + inert solvent} binary system have been characterized using a specific methodology in the framework of Monte Carlo molecular simulations. The cluster classification scheme considered distinguishes into five types: linear chains, cyclic clusters or isolated rings, branched linear chains, branched cyclic clusters, and composite rings. The procedure allows one to compute the next rich structural information: the fraction of molecules in the monomer or associated state, the fraction of each type of aggregate with a given size (and of molecules belonging to them), and the most probable and average cluster size for each type; likewise, the degree of branching in branched linear chains and the size distribution of the inner ring in branched cyclic clusters can be quantified. Specifically, all these properties were obtained for the {Optimized Potential for Liquid Simulation methanol + Lennard-Jones spheres} system at 298.15 K and 1 bar throughout the composition range. The results have provided a complete structural picture of this mixture describing comprehensively the effect of dilution into the hydrogen-bonded network of the pure associated fluid.
    The Journal of Chemical Physics 05/2013; 138(20):204505. · 3.12 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Mixtures containing associated substances show a singular thermodynamic behaviour that has attracted to scientific community during the last century. Particularly, binary systems composed of an associating fluid and an inert solvent, where association occurs only between molecules of the same kind, have been extensively studied. A number of theoretical approaches were used in order to gain insights into the effect of the association on the macroscopic behaviour, especially on the second-order thermodynamic derivatives (or response functions). Curiously, to our knowledge, molecular simulations have not been used to that end despite describing the molecules and their interactions in a more complete and realistic way than theoretical models. With this in mind, a simple methodology developed in the framework of Monte Carlo molecular simulation is used in this work to quantify the association contribution to a wide set of thermodynamic properties for the {methanol + Lennard Jones} specific system under room conditions and throughout the composition range. Special attention was paid to the response functions and their respective excess properties, for which a detailed comparison with selected previous works in the field has been established.
    The Journal of Chemical Physics 05/2013; 138(20):204506. · 3.12 Impact Factor
  • Source
    The Journal of Chemical Thermodynamics 05/2013; 65:131. · 2.30 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: A methodology for the determination of the oligomers residing in a pure associated fluid was developed in the framework of the molecular simulation technique. First, the number of hydrogen bonds between each pair of molecules of the fluid is computed by using a specific criterion to define the hydrogen bonding formation. Secondly, sets of molecules linked by hydrogen bonds are identified and classified as linear chains, cyclic aggregates, branched linear chains, branched cyclic aggregates, and the rest of clustering. The procedure is applied over all the configurations produced in usual Monte Carlo simulations and allows the computation of the following properties characterizing the structure of the fluid: the fraction of molecules in the monomer or associated state, the fraction of each type of aggregate with a given size (and of molecules belonging to them), and the most probable and the average cluster size for each type. In addition, the degree of branching in branched linear chains and the type of ring in branched cyclic clusters can be obtained. In this work, all these quantities were computed for OPLS methanol using NpT Monte Carlo simulations at atmospheric pressure for 298.15 K (room conditions) and from 800 K to 350 K (gas phase), and along several supercritical isobars: 25, 50, 100, 200, and 500 MPa from 250 K to 1000 K. An analysis of the results has provided a comprehensive structural picture of methanol over the whole thermodynamic state space.
    The Journal of Chemical Physics 01/2013; 138(4):044509. · 3.12 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: A simple methodology [P. Gómez-Álvarez, A. Dopazo-Paz, L. Romani, and D. González-Salgado, J. Chem. Phys. 134, 014512 (2011)] recently developed in the light of the Monte Carlo molecular simulation technique was used in this work to study the association effects on the response functions of methanol over the whole thermodynamic state space. It consists basically on evaluating the first order properties of the fluid (energy and volume) in terms of those for two hypothetical fluids living in the bulk composed by monomers and associated molecules, respectively. In this context, the second order thermodynamic derivatives can be expressed in a perturbative way as the sum of the monomer term (reference term) and the association contribution. Specifically, both contributions to the residual isobaric heat capacity, and to the pressure and temperature derivatives of the volume were determined for the optimized potential for liquid simulation (OPLS) of methanol through NPT Monte Carlo simulations from 250 K to 1000 K along the supercritical isobars 25, 100, 200, 500 MPa, and from 800 K to 350 K at 0.1 MPa. Results showed that both terms are relevant for the residual isobaric heat capacity and that their influence depends considerably on the thermodynamic conditions; however, the volumetric response functions were found mainly affected by the monomer contribution, especially the pressure derivative of the volume.
    The Journal of Chemical Physics 01/2013; 138(4):044510. · 3.12 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Isobaric heat capacity per unit volume, C(p), and excess molar enthalpy, h(E), were determined in the vicinity of the critical point for a set of binary systems formed by an ionic liquid and a molecular solvent. Moreover, and, since critical composition had to be accurately determined, liquid-liquid equilibrium curves were also obtained using a calorimetric method. The systems were selected with a view on representing, near room temperature, examples from clearly solvophobic to clearly coulombic behavior, which traditionally was related with the electric permittivity of the solvent. The chosen molecular compounds are: ethanol, 1-butanol, 1-hexanol, 1,3-dichloropropane, and diethylcarbonate, whereas ionic liquids are formed by imidazolium-based cations and tetrafluoroborate or bis-(trifluromethylsulfonyl)amide anions. The results reveal that solvophobic critical behavior-systems with molecular solvents of high dielectric permittivity-is very similar to that found for molecular binary systems. However, coulombic systems-those with low permittivity molecular solvents-show strong deviations from the results usually found for these magnitudes near the liquid-liquid phase transition. They present an extremely small critical anomaly in C(p)-several orders of magnitude lower than those typically obtained for binary mixtures-and extremely low h(E)-for one system even negative, fact not observed, up to date, for any liquid-liquid transition in the nearness of an upper critical solution temperature.
    The Journal of Chemical Physics 12/2011; 135(21):214507. · 3.12 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: En este trabajo se realiza un estudio de la evolución de corriente en función de la densidad de vórtices atrapados y se presenta una técnica para regular la corriente partiendo del valor crítico, en anillos superconductores de YBCO. Para generar una corriente persistente en los anillos se utiliza un método de tipo inductivo, denominado field cooling, que combinado con campos magnéticos en sentido contrario al inductor permite disminuir la densidad de vórtices atrapados y se logra también disminuir el decaimiento de corriente. Una vez que se ha inducido la corriente crítica en los anillos una zona muy localizada de éstos se calienta hasta que el superconductor alcanza el valor deseado de corriente, lo cual se comprueba mediante la medida de campo magnético con una sonda Hall.
    Boletín de la Sociedad Española de Cerámica y Vidrio, ISSN 0366-3175, Vol. 47, Nº. 2, 2008, pags. 105-109. 04/2011;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The temperature and pressure dependence of isobaric thermal expansivity, α(p), in liquids is discussed in this paper. Reported literature data allow general trends in this property that are consistent with experimental evidence to be established. Thus, a negative pressure dependence is to be expected except around the critical point. On the other hand, α(p) exhibits broad regions of negative and positive temperature dependence in the (T, p) plane depending on the nature of the particular liquid. These trends are rationalized here in terms of various molecular-based equations of state. The analysis of the Lennard-Jones, hard sphere square well and restricted primitive model equations allows understanding the differences in the α(p) behavior between liquids of diverse chemical nature (polar, nonpolar, and ionic): broader regions of negative temperature and positive pressure dependencies are obtained for liquids characterized by larger ranges of the interparticle potential. Also, using the statistical associating fluid theory (SAFT) allowed the behavior of more complex systems (basically, those potentially involving chain and association effects) to be described. The effect of chain length is rather simple: increasing it is apparently equivalent to raise the interaction range. By contrast, association presents a quite complex effect on α(p), which comes from a balance between the dispersive and associative parts of the interaction potential. Thus, if SAFT parameters are adjusted to obtain low association ability, α(p) is affected by each mechanism at clearly separate regions, one at low temperature, due to association, and the other to dispersive forces, which has its origin in fluctuations related with vapor-liquid transition.
    The Journal of Chemical Physics 03/2011; 134(9):094502. · 3.12 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Isobaric molar heat capacities at 288.15, 298.15, and 308.15 K and densities and speeds of sound at 288.15, 293.15, 298.15, and 308.15 K were determined for the dimethyl carbonate + benzene system over the whole composition range and at atmospheric pressure. In addition, speeds of sound at the same temperatures for the dimethyl carbonate + n-heptane system are reported. These experimental data were used to obtain molar volumes, isobaric thermal expansivities, isentropic and isothermal compressibilities, and isochoric molar heat capacities. Excess quantities of the above-mentioned properties were calculated using the Benson and Kiyohara criterion. The thermodynamic behaviour of the dimethyl carbonate + (n-heptane, cyclohexane, benzene, or toluene) systems is comparatively analyzed.Key words: binary mixtures, excess properties, dimethyl carbonate, benzene, hydrocarbon.
    Canadian Journal of Chemistry 02/2011; 80(4):370-378. · 0.96 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Excess molar volumes of mixtures of 2,5-dioxahexane + c-hexane, 2,5,8-trioxanonane + c-hexane, 2,5,8,11-tetraoxadodecane + c-hexane, and 2,5,8,11,14-pentaoxapentadecane + c-hexane were determined from density measurements at 283.15, 288.15, 298.15, and 308.15 K. These results allowed the following mixing quantities to be reported in the range of concentration: α, (δVE/δT)P, and (δHE/δP)T, at 298.15 K. The values obtained were then compared with the values calculated by using the Flory theory and the Nitta–Chao theory of liquid mixtures.
    Canadian Journal of Chemistry 02/2011; 72(2):454-462. · 0.96 Impact Factor
  • Source
    The Journal of Chemical Physics 02/2011; 134(5):059904. · 3.12 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: A simple methodology was developed to analyze association effects on the thermodynamic response functions for a pure self-associated fluid via Monte Carlo simulations. The procedure essentially involves expressing the residual energy and volume of the fluid in terms of these properties for two hypothetical fluids consisting of monomers and associated molecules, respectively. This allows the thermodynamic response functions to be expressed in a perturbative form as a combination of the values for the property in the monomeric fluid and the contribution of association (the perturbative term). The proposed methodology was used to determine both contributions to the isobaric heat capacity and to the temperature and pressure derivatives of the volume for OPLS methanol along the 50 MPa isobar from 220 to 1500 K. Based on the results, both terms exert a substantial influence on the isobaric heat capacity; by contrast, the association term for the volumetric properties is negligible. These results are consistent with those of a previous work involving simulations with the same model under identical thermodynamic conditions but a different approach. They are also compared with others previously reported in context. Moreover, a comprehensive study of the different types of clusters present in the fluid was performed and the results were related to thermodynamic properties. A strong correlation between the heat capacity of the monomeric fluid and this structural analysis was found.
    The Journal of Chemical Physics 01/2011; 134(1):014512. · 3.12 Impact Factor
  • Source
    Paloma Navia, Jacobo Troncoso, Luis Romaní
    The Journal of Chemical Thermodynamics 07/2010; 42(7):949. · 2.30 Impact Factor
  • Source
    Paloma Navia, Jacobo Troncoso, Luis Romaní
    Fluid Phase Equilibria 01/2010; 295(1):152-153. · 2.38 Impact Factor
  • Paloma Navia, Jacobo Troncoso, Luis Romaní
    [Show abstract] [Hide abstract]
    ABSTRACT: In order to study the influence of association on the isobaric thermal expansivity, this magnitude has been experimentally determined for a set of associating fluids within the temperature and pressure intervals (278.15 to 348.15) K and (5 to 55) MPa by means of calorimetric measurements. The 1-alcohol series, from methanol to 1-decanol, 2-pentanol, 3-pentanol, and 1-pentylamine were selected. With a view on checking the quality of the experimental data, they are compared with available literature values; good coherence was obtained for most of the studied liquids. The analysis of the experimental results reveals that the association capability presents a strong influence not only on the value of the isobaric thermal expansivity itself, but also on its behaviour against temperature and pressure.
    The Journal of Chemical Thermodynamics 01/2010; · 2.30 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: A specific calibration procedure that allows the accurate determination of densities of room temperature ionic liquids, RTILs, as a function of temperature and pressure using vibrating tube densimeters is presented. This methodology overcomes the problems of common calibration methods when they are used to determine the densities of high density and high viscosity fluids such as RTILs. The methodology is applied for the precise density determination of RTILs 1-ethyl-3-methylimidazolium tetrafluoroborate [Emim][BF4], 1-butyl-3-methylimidazolium tetrafluoroborate [Bmim][BF4], 1-hexyl-3-methylimidazolium tetrafluoroborate [Hmim][BF4], and 1-octyl-3-methylimidazolium tetrafluoroborate [Omim][BF4] in the temperature and pressure intervals (283.15 to 323.15)K and (0.1 to 60)MPa, respectively. The viscosities of these substances, needed for the estimation of the viscosity-induced errors, were estimated at the same conditions from the experimental measurements in the intervals (283.15 to 323.15)K and (0.1 to 14)MPa and from a specific extrapolation procedure. The uncertainty in the density measurements was estimated in ±0.30kg·m−3 which is an excellent value in the working intervals. The results of these RTILs have demonstrated that viscosity-induced errors are relevant and they must be taken into account for a precise density determination. Finally, an alternative tool for a simpler application of this procedure is presented.
    Journal of Chemical Thermodynamics - J CHEM THERMODYN. 01/2010; 42(4):553-563.
  • [Show abstract] [Hide abstract]
    ABSTRACT: The isobaric molar heat capacities as a function of temperature and pressure are, for the first time, reported for a set of imidazolium-based ionic liquids. The selected compounds belong to the 1-alkyl-3-methylimidazolium series, concretely, [Emim][BF4], [Bmim][BF4], [Hmim][BF4], and [Omim][BF4]. Isobaric heat capacity were determined in the temperature and pressure intervals of (283.15 to 323.15) K and (0.1 to 60) MPa using a micro DSCII calorimeter recently adapted to work at high pressure. The data at atmospheric pressure were compared with literature data; as a rule, good results were obtained for all liquids. Isobaric molar heat capacities for the studied ionic liquids show quite a different behavior than that obtained for usual organic solvents, which could be understood as these compounds behave like highly compressed molecular fluids. This is consistent with the behavior of other previously reported thermodynamic properties.
    Journal of Chemical and Engineering Data - J CHEM ENG DATA. 01/2010; 55(2):600-604.
  • [Show abstract] [Hide abstract]
    ABSTRACT: Isobaric thermal expansivity αp for a set of highly polar nitrogen compounds was experimentally determined by means of a calorimetric method in the temperature T and pressure p intervals (278.15 to 348.15) K and (5 to 55) MPa. The selected liquids were propionitrile, nitromethane, nitroethane, nitropropane, benzonitrile, and nitrobenzene. The experimental results were compared to available literature data, obtaining good results for most of the studied liquids. It was found that the αp trends against temperature highly depend on the studied pressure: αp increases at low pressure; however, as pressure is raised, the dependence on T becomes milder, and for some cases, it is obtained that αp clearly decreases against T at the highest pressures. The results are interpreted based on the phase-transition properties of the compounds, concretely, on vapor pressure and on distance of the experimental pressure and temperature from the critical coordinates.
    Journal of Chemical and Engineering Data - J CHEM ENG DATA. 12/2009; 55(4).
  • Paloma Navia, Jacobo Troncoso, Luís Romaní
    [Show abstract] [Hide abstract]
    ABSTRACT: Isobaric thermal expansivity for a set of nonpolar compounds is determined in the temperature and pressure intervals of (278.15 to 348.15) K and (0.6 to 55) MPa using a calorimetric method. The selected compounds are benzene, tetrachloromethane, and the alkane series, from nonane to pentadecane. These results are compared with literature data, with most of them obtained from density measurements. Temperature behavior is revealed to be highly dependent on the experimental pressure; at low pressure, isobaric thermal expansivity clearly increases with temperature. This dependence becomes milder as pressure is raised, and for some liquids at high pressure, it is undoubtedly observed that αp decreases against T. These results are rationalized by relating them with phase transition properties, concretely, vapor pressure and critical coordinates. Finally, well-known thermodynamic relations are used to obtain density and isobaric molar heat capacity as a function of temperature and pressure from isobaric thermal expansivity, density, and heat capacity at atmospheric pressure. The results thus obtained were compared with directly measured data.
    Journal of Chemical and Engineering Data - J CHEM ENG DATA. 11/2009; 55(6).

Publication Stats

443 Citations
157.34 Total Impact Points

Institutions

  • 1992–2013
    • University of Vigo
      • • Department of Applied Physics
      • • Faculty of Science
      Vigo, Galicia, Spain
  • 1985–1992
    • University of Santiago de Compostela
      • • Department of Applied Physics
      • • Faculty of Physics
      Santiago de Compostela, Galicia, Spain
  • 1989
    • University of Santiago, Chile
      • Departamento de Física
      Santiago, Region Metropolitana de Santiago, Chile