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  • Short range order in disordered phases using neutron diffraction.  Open access

     Rovira Esteva, Muriel
    Department of Physics and Nuclear Engineering, Universitat Politècnica de Catalunya
    Theses

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    La difracció de neutrons és una tècnica molt potent que permet sondar l'estructura de fases desordenades en un ventall d'escales de longitud. Tanmateix, degut a la complexitat inherent d'aquestes fases desordenades, l'anàlisi de la informació quees desprèn de les dades experimentals no és evident.En aquest treball es presenten diversos mètodes alternatius que permeten treure el màxim profit de les mesures de difracció de neutrons, així com de les configuracions moleculars obtingudes en simulacions de dinàmica molecular o del modelatge de lesdades. Aquests mètodes consisteixen principalment en un enfocament bayesià en l'ajust de les estructures moleculars mesurades amb difracció de neutrons, i en una anàlisi multidimensional de les funcions de distribució de probabilitat de l'estructura molecular obtingudes en simulacions o tècniques de modelatge de dades, en comptes del mitjanat de diverses variables estàndard.Aquestes metodologies s'apliquen a la investigació de diversos sistemes desordenats per tal de resoldre una sèrie de qüestions obertes: l'origen de la transició líquid-líquid en el trans-1,2-dicloroetà (C2Cl2H2), l'extrema fragilitat del vidre orientacional del1,1,2,2-tetracloro-1,2-difluoroetà (F-112, C2Cl4F2), la paradoxa de la densitat local en el tetraclorur de carboni (CCl4), i els rols de les interaccions estèrica i electrostàtica en l'ordre de curt abast de líquids de molècules quasitetraèdriques, en particular el triclorobromometà (CBrCl3) i el dibromodiclorometà (CBr2Cl2).Addicionalment, també s'hi inclou un breu repàs del marc teòric de la difracció de neutrons en sistemes desordenats, així com dels aspectes pràctics de l'equip experimental i del tractament de dades necessari, per tal que els investigadors interessats disposin d'una visió general completa sobre tema.

    Neutron diffraction is a powerful technique that allows to probe the structure of disordered phases across a variety of length scales. However, due to the inherent complexity of these disordered hases, the analysis of the information contained in the experimental data is not obvious. In this work, a few alternative methods are presented that allow to make the most of the neutron diffraction measurements as well as the molecular configurations obtained from molecular dynamics simulations or data modelling. They mainly consist in a Bayesian approach to fit the molecular structures measured with neutron diffraction, and a multidimensional analysis of the molecular structure probability distribution functions obtained from simulations or data modelling techniques, instead of the standard averaging over many variables. These methodologies are then applied to the structural investigation of several disordered systems in order to answer a series of open questions: the origin of the liquid-liquid transition in trans-1,2-dichloroethene (C2Cl2H2), the extreme fragility of 1,1,2,2-tetrachloro-1,2-difluoroethane's orientational glass (F-112, C2Cl4F2), the local density paradox in carbon tetrachloride (CCl4), and the roles of steric and electrostatic interactions in the short range order of the liquids of quasitetrahedral molecules, particularly trichlorobromomethane (CBrCl3) and dibromodichloromethane (CBr2Cl2). Additionally, a concise summary of the theoretical framework for neutron diffraction of disordered systems, as well as the practicalities of the experimental setup and the necessary data treatment, are also included to provide interested researchers with a self-contained overview on the topic.

    La difracció de neutrons és una tècnica molt potent que permet sondar l'estructura de fases desordenades en un ventall d'escales de longitud. Tanmateix, degut a la complexitat inherent d'aquestes fases desordenades, l'anàlisi de la informació que es desprèn de les dades experimentals no és evident. En aquest treball es presenten diversos mètodes alternatius que permeten treure el màxim profit de les mesures de difracció de neutrons, així com de les configuracions moleculars obtingudes en simulacions de dinàmica molecular o del modelatge de les dades. Aquests mètodes consisteixen principalment en un enfocament bayesià en l'ajust de les estructures moleculars mesurades amb difracció de neutrons, i en una anàlisi multidimensional de les funcions de distribució de probabilitat de l'estructura molecular obtingudes en simulacions o tècniques de modelatge de dades, en comptes del mitjanat de diverses variables estàndard. Aquestes metodologies s'apliquen a la investigació de diversos sistemes desordenats per tal de resoldre una sèrie de qüestions obertes: l'origen de la transició líquid-líquid en el trans-1,2-dicloroetà (C2Cl2H2), l'extrema fragilitat del vidre orientacional del 1,1,2,2-tetracloro-1,2-difluoroetà (F-112, C2Cl4F2), la paradoxa de la densitat local en el tetraclorur de carboni (CCl4), i els rols de les interaccions estèrica i electrostàtica en l'ordre de curt abast de líquids de molècules quasitetraèdriques, en particular el triclorobromometà (CBrCl3) i el dibromodiclorometà (CBr2Cl2). Addicionalment, també s'hi inclou un breu repàs del marc teòric de la difracció de neutrons en sistemes desordenats, així com dels aspectes pràctics de l'equip experimental i del tractament de dades necessari, per tal que els investigadors interessats disposin d'una visió general completa sobre tema.

  • Transicions de fase, polimorfisme i dinàmica de la metastabilitat

     Crespo Artiaga, Daniel; Pradell Cara, Trinitat; Tamarit Mur, Jose Luis; Buti Papiol, Salvador; Del Barrio Casado, Maria; Pardo Soto, Luis Carlos; Pineda Soler, Eloy; Bruna Escuer, Pere; Salvado Cabre, Nativitat; Ruiz Martin, Maria Dolores; Macovez, Roberto; Rojas Gregorio, Jose Ignacio; Lloveras Muntane, Pol Marcel; Beltran Sanchidrian, Victòria; Ye, Jin; Liu, Chaoren; Madinehei, Seyed Milad; Mitsari, Efstratia; Molina Giralt, Gloria; Romanini, Michela; Rovira Esteva, Muriel; Tripathi, Pragya; Vispa, Alessandro; Vallés Sales, Araceli; Zachariah, Manesh; Zhai, Fuqiang
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  • Ultraslow dynamics of water in organic molecular solids

     Macovez, Roberto; Mitsari, Efstratia; Zachariah, Manesh; Romanini, Michela; Zygouri, Panagiota; Gournis, Dimitrios; Tamarit Mur, Jose Luis
    The journal of physical chemistry. Part C, nanomaterials and interfaces
    Vol. 118, num. 9, p. 4941-4950
    DOI: 10.1021/jp4097138
    Date of publication: 2014-03-06
    Journal article

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    The relaxation dynamics of water in hygroscopic molecular solids is probed by broadband dielectric spectroscopy in the temperature range from 200 to 450 K. Evidence is found for three types of dynamic processes. The intermediate process is common to all probed materials and is associated with the reorientation of bound water molecules that are attached directly onto organic molecules and counterions. A faster process is observed in rhodamine chloride and fullerol, which is the dynamic signature of water in higher hydration layers, either at grain boundaries (rhodamine) or in interstitial clusters (fullerol). All these processes are observed near room temperature and exhibit nonmonotonic temperature dependence and decreasing spectral strength upon heating. In fullerol a third, ultraslow relaxation is observed at high temperature, which may be due to the reorientation of water-fullerol complexes or to the diffusion of water vapor through intermolecular voids.

  • Polymorphism of 2-Adamantanone

     Negrier, Philippe; Del Barrio Casado, Maria; Romanini, Michela; Tamarit Mur, Jose Luis; Mondieig, Denise; Krivchikov, Alexander I; Kepinski, L.; Jezowski, Andrzej; Szewczyk, Daria
    Crystal growth and design
    Vol. 14, num. 5, p. 2626-2632
    DOI: 10.1021/cg500313m
    Date of publication: 2014-05-07
    Journal article

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    The polymorphism of 2-adamantanone (C10H14O) has been investigated by means of X-ray diffraction and high-pressure thermal analysis. The intricate behavior of the low-temperature crystalline phases has been disentangled. The stable phase has been found to be orthorhombic (Cmc2 1, Z = 4), fully ordered, with lattice parameters a = 6.8884(18) Å, b = 10.830(3) Å, c = 10.658(3) Å, and V/Z = 198.8(1) Å3. The metastable phase was determined to be monoclinic (P21/c, Z = 4) with lattice parameters a = 6.5920(17) Å, b = 11.118(3) Å, c = 12.589(3) Å, ß= 118.869(11) o, and V/Z = 202.0(1) Å3. The pressure-temperature phase diagram irrefutably shows the stability relation between both phases and, accordingly, the long-time unknown polymorphic behavior is now revealed and gives coherent physical explanation of the literature published so far.

  • Hopping conductivity and polarization effects in a fullerene derivative salt

     Macovez, Roberto; Zachariah, Manesh; Romanini, Michela; Zygouri, Panagiota; Gournis, Dimitrios; Tamarit Mur, Jose Luis
    The journal of physical chemistry. Part C, nanomaterials and interfaces
    Vol. 118, num. 23, p. 12170-12175
    DOI: 10.1021/jp503298e
    Date of publication: 2014-06-12
    Journal article

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    Impedance spectroscopy is employed to probe the frequency-dependent conductivity and dielectric response of the C60O24Na 24 fulleride. The conduction properties of this organic material match the so-called universal behavior of the ac conductivity in disordered media [Dyre, J. C.; Schroder, T. B. Rev. Mod. Phys. 2000, 72, 873-892]. In the whole temperature range studied, electrical conduction is due to intermolecular hopping processes of electronic charge carriers, characterized by an effective activation energy ranging between 0.7 eV at room temperature and 0.9 eV at 475 K. A single dielectric loss feature is observed, associated with the hopping of charge carriers surrounded by a polarization cloud. The polarizability of the material is mainly due to the distortion of the ionic O-Na bonds of the fullerene derivative, which are tight enough that no ionic contribution to the conductivity is observed up to the highest temperature probed (550 K). © 2014 American Chemical Society.

  • On the polymorphism of l -citrulline: Crystal structure and characterization of the orthorhombic d form

     Allouchi, Hassan; Nicolai, Beatrice; Del Barrio Casado, Maria; Céolin, René; Mahé, Nathalie; Tamarit Mur, Jose Luis; Do, Bernard; Rietveld, Ivo B.
    Crystal growth and design
    Vol. 14, num. 3, p. 1279-1286
    DOI: 10.1021/cg401801u
    Date of publication: 2014-03-01
    Journal article

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    Solid-state properties of active pharmaceutical compounds are closely related to their dissolution behavior and bioavailability, and understanding their phase behavior leads to better control in the drug formulation process. L-Citrulline is an amino acid, which is known to exhibit polymorphism; however, only the structure of the alpha form is reported in the literature. The structure of the form has been elusive due to lack of good quality single crystals. It has been found to be orthorhombic P2(1)2(1)2(1) with the cell parameters a, b, and c respectively 14.895(5) angstrom, 9.852(2) angstrom, and 5.353(2) angstrom. The unit cell contains four molecules, and its volume is 785.5(4) angstrom(3). Both the alpha form and the delta form possess uniaxial negative thermal expansion along the direction of the charge exchange of the L-citrulline zwitterions. In mixtures containing solid and saturated aqueous, solution, the alpha form quickly transforms in a dihydrate, whereas the delta phase persists for over three weeks. Although the evidence is not conclusive, the delta phase is most likely the more stable form and most suitable for storage.

  • Barocaloric and magnetocaloric effects in Fe49Rh51

     Stern Taulats, Enric; Planes Vila, Antoni; Lloveras Muntane, Pol Marcel; Del Barrio Casado, Maria; Tamarit Mur, Jose Luis; Pramanick, Sabyasachi; Majumdar, Subham; Frontera Beccaria, Carlos; Mañosa Carrera, Lluis
    Physical review. B, solid state
    Vol. 89, num. 21, p. 214105-1-214105-8
    DOI: 10.1103/PhysRevB.89.214105
    Date of publication: 2014-06-06
    Journal article

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    We report on calorimetry under applied hydrostatic pressure and magnetic field at the antiferromagnetic-ferromagnetic (AFM/FM) transition of Fe49Rh51. Results demonstrate the existence of a giant barocaloric effect in this alloy, a functional property that adds to the magnetocaloric and elastocaloric effects previously reported for this alloy. All caloric effects originate from the AFM/FM transition which encompasses changes in volume, magnetization, and entropy. The strong sensitivity of the transition temperatures to both hydrostatic pressure and magnetic field confers to this alloy outstanding values for the barocaloric and magnetocaloric strengths (vertical bar Delta S vertical bar/Delta p similar to 12 J kg(-1) K(-1)kbar(-1) and vertical bar Delta S vertical bar/mu(0)Delta H similar to 12 J kg(-1) K-1T-1). Both barocaloric and magnetocaloric effects have been found to be reproducible upon pressure and magnetic field cycling. Such a good reproducibility and the large caloric strengths make Fe-Rh alloys particularly appealing for solid-state cooling technologies at weak external stimuli.

    We report on calorimetry under applied hydrostatic pressure and magnetic field at the antiferromagnetic-ferromagnetic (AFM/FM) transition of Fe49Rh51. Results demonstrate the existence of a giant barocaloric effect in this alloy, a functional property that adds to the magnetocaloric and elastocaloric effects previously reported for this alloy. All caloric effects originate from the AFM/FM transition which encompasses changes in volume, magnetization, and entropy. The strong sensitivity of the transition temperatures to both hydrostatic pressure and magnetic field confers to this alloy outstanding values for the barocaloric and magnetocaloric strengths (|¿S|/¿p ~ 12 J kg-1K-1kbar-1 and |¿S|/µ0¿H~ 12 J kg-1K-1T-1). Both barocaloric and magnetocaloric effects have been found to be reproducible upon pressure and magnetic field cycling. Such a good reproducibility and the large caloric strengths make Fe-Rh alloys particularly appealing for solid-state cooling technologies at weak external stimuli.

  • Barocaloric effect in metamagnetic shape memory alloys

     Mañosa Carrera, Lluis; Stern Taulats, Enric; Planes Vila, Antoni; Lloveras Muntane, Pol Marcel; Del Barrio Casado, Maria; Tamarit Mur, Jose Luis; Emre, Baris; Yuce, Suheyla; Fabbrici, Simone; Albertini, Franca
    physical status solidi B
    p. 1-6
    DOI: 10.1002/pssb.201350371
    Date of publication: 2014-03-10
    Journal article

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  • Polymorphism of organic compounds as a function of temperature and pressure

     Tamarit Mur, Jose Luis; Céolin, René; Del Barrio Casado, Maria; Rietveld, Ivo B.
    Journées de Calorimétrie et d'Analyse Thermique
    p. INV2
    Presentation's date: 2014-05-21
    Presentation of work at congresses

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  • Much ado about nothing: Statistical occupational disorder and glassy features

     Tamarit Mur, Jose Luis; Bermejo, F. Javier; Del Barrio Casado, Maria; Pardo Soto, Luis Carlos; Krivchikov, Alexander I
    Reunión de la Sociedad Española de Técnicas Neutrónicas
    p. 17
    Presentation's date: 2014-06-23
    Presentation of work at congresses

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  • Polymorphism of 1,2-dibromo-ethane (C2Br2D4 and C2Br2H4)

     Negrier, Philippe; Del Barrio Casado, Maria; Tamarit Mur, Jose Luis; Mondieig, D.
    Journées d¿Etude des Equilibres entre Phases
    p. 74
    Presentation's date: 2014-03-26
    Presentation of work at congresses

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  • 2-Adamantanone (C10H14O): ordered and disordered phases, a complex case of polymorphism

     Negrier, Philippe; Del Barrio Casado, Maria; Tamarit Mur, Jose Luis; Romanini, Michela; Mondieig, D.
    Journées d¿Etude des Equilibres entre Phases
    p. 26
    Presentation's date: 2014-03-27
    Presentation of work at congresses

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  • Plastic phases under pressure, the case succinonitrile

     Rietveld, Ivo B.; Del Barrio Casado, Maria; Céolin, René; Tamarit Mur, Jose Luis
    Journées d¿Etude des Equilibres entre Phases
    p. 30
    Presentation's date: 2014-03-28
    Presentation of work at congresses

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  • The pressure-temperature phase relationships between benzocaine forms II, III, and its liquid

     Gana, Inès; Del Barrio Casado, Maria; Do, Bernard; Céolin, René; Tamarit Mur, Jose Luis; Rietveld, Ivo B.
    Journées d¿Etude des Equilibres entre Phases
    p. 122
    Presentation's date: 2014-03-26
    Presentation of work at congresses

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  • Ultra-slow dynamics of water in organic molecular solids

     Mitsari, Efstratia; Macovez, Roberto; Zachariah, Manesh; Tripathi, Pragya; Romanini, Michela; Zygouri, Panagiota; Gournis, Dimitrios; Tamarit Mur, Jose Luis
    WaterEurope
    p. 48
    Presentation's date: 2014-06-14
    Presentation of work at congresses

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  • The structure of water beyond the first coordination shell

     Pardo Soto, Luis Carlos; Henao Aristizábal, Andres; Guardia Manuel, Elvira; Tamarit Mur, Jose Luis
    WaterEurope
    p. 65
    Presentation's date: 2014-06-12
    Presentation of work at congresses

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  • Conformational polymorphism: The missing phase of 1,1,2,2-tetrachloroethane (Cl2HC-CHCl2)

     Del Barrio Casado, Maria; Tamarit Mur, Jose Luis; Mondieig, Denise; Zuriaga, Jose Mariano; Perez, Silvina C.; Negrier, Philippe
    Crystal growth and design
    Vol. 13, num. 5, p. 2143-2148
    DOI: 10.1021/cg400235b
    Date of publication: 2013-05
    Journal article

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    Halogenoethane derivatives are known to exhibit different polymorphs involving a different translational, orientational, and conformational order. The 1,1,2,2-tetrachloroethane (Cl2HC-CHCl2) exhibits a normal pressure orthorhombic phase beta (space group P2(1)2(1)2(1) with Z = 8 and Z' = 2), formed by molecules with one of the two gauche conformations. At high pressure, the stable polymorph is known to be monoclinic (space group P2(1)/c, with Z = 2 and Z' = 0.5), phase alpha, in which only the trans conformer appears. In this work, we demonstrate the existence of a normal pressure metastable polymorph, phase gamma, for which the two gauche conformers show up in the asymmetric unit of a monoclinic (space group P2(1)/c with Z = 8 and Z' = 2) structure. The new phase gamma is obtained by recrystallization upon heating the glass obtained after quench of the melt. It displays shorter type II Cl center dot center dot center dot Cl contacts than the high-pressure phase alpha due to attractive and directional interactions.

    Halogenoethane derivatives are known to exhibit different polymorphs involving a different translational, orientational, and conformational order. The 1,1,2,2- tetrachloroethane (Cl2HC−CHCl2) exhibits a normal pressure orthorhombic phase β (space group P212121 with Z = 8 and Z′ = 2), formed by molecules with one of the two gauche conformations. At high pressure, the stable polymorph is known to be monoclinic (space group P21/c, with Z = 2 and Z′ = 0.5), phase α, in which only the trans conformer appears. In this work, we demonstrate the existence of a normal pressure metastable polymorph, phase γ, for which the two gauche conformers show up in the asymmetric unit of a monoclinic (space group P21/c with Z = 8 and Z′ = 2) structure. The new phase γ is obtained by recrystallization upon heating the glass obtained after quench of the melt. It displays shorter type II Cl···Cl contacts than the high-pressure phase α due to attractive and directional interactions.

  • Solid-state properties and dehydration behavior of the active pharmaceutical ingredient potassium guaiacol-4-sulfonate

     Mahé, Nathalie; Nicolai, Beatrice; Del Barrio Casado, Maria; Perrin, Marc Antoine; Do, Bernard; Tamarit Mur, Jose Luis; Céolin, René; Rietveld, Ivo B.
    Crystal growth and design
    Vol. 13, num. 7, p. 3028-3035
    DOI: 10.1021/cg400427v
    Date of publication: 2013-05-20
    Journal article

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    Potassium guaiacolsulfonate is an active pharmaceutical ingredient that has been in use for more than a century, and it is still widely used in cough syrups. Nonetheless, no crystal structure has ever been determined to facilitate quality control. This is all the more surprising because two isomers are known to exist. A commercial sample has been studied by X-ray diffraction and thermogravimetric methods. It consists of potassium guaiacol-4-sulfonate, and it crystallizes in the monoclinic space group C2/c as a hemihydrate. The crystals exhibit uniaxial negative thermal expansion, and the electrostatic forces between the ions appear to be the major driving force of the observed displacements. Dehydration of the hemihydrate was observed above 380 K. The anhydrate has a structure similar to the hemihydrate with almost the same unit cell parameters. The dehydration kinetics points to a displacive mechanism; water molecules are located in channels, through which they leave the crystal. The structural readjustments that occur to accommodate the loss of water are driven by electrostatic interactions between the ions similar to the displacements observed for thermal expansion. Under ambient conditions (and humidity), the anhydrate is not stable and transforms into the hemihydrate.

    Potassium guaiacolsulfonate is an active pharmaceutical ingredient that has been in use for more than a century, and it is still widely used in cough syrups. Nonetheless, no crystal structure has ever been determined to facilitate quality control. This is all the more surprising because two isomers are known to exist. A commercial sample has been studied by X-ray diffraction and thermogravimetric methods. It consists of potassium guaiacol-4-sulfonate, and it crystallizes in the monoclinic space group C2/c as a hemihydrate. The crystals exhibit uniaxial negative thermal expansion, and the electrostatic forces between the ions appear to be the major driving force of the observed displacements. Dehydration of the hemihydrate was observed above 380 K. The anhydrate has a structure similar to the hemihydrate with almost the same unit cell parameters. The dehydration kinetics points to a displacive mechanism; water molecules are located in channels, through which they leave the crystal. The structural readjustments that occur to accommodate the loss of water are driven by electrostatic interactions between the ions similar to the displacements observed for thermal expansion. Under ambient conditions (and humidity), the anhydrate is not stable and transforms into the hemihydrate.

  • Liquid-liquid miscibility gaps in drug-water binary systems: crystal Structure and thermodynamic properties of prilocaine and the temperature-composition phase diagram of the prilocaine-water system

     Rietveld, Ivo B.; Perrin, Jean-Claude; Toscani, Siro; Del Barrio Casado, Maria; Nicolai, Beatrice; Tamarit Mur, Jose Luis; Céolin, René
    Molecular pharmaceutics
    Vol. 10, num. 4, p. 1332-1339
    DOI: 10.1021/mp300542k
    Date of publication: 2013-04
    Journal article

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    EMLA cream, a ¿eutectic mixture of local anesthetics¿, was developed in the early 1980s by Astra Pharmaceutical Production. The mixture of anesthetics containing lidocaine, prilocaine, and water is liquid at room temperature, which is partly due to the eutectic equilibrium between prilocaine and lidocaine at 293 K, as was clear from the start. However, the full thermodynamic background for the stability of the liquid and its emulsion-like appearance has never been elucidated. In the present study of the binary system prilocaine-water, a region of liquid-liquid demixing has been observed, linked to a monotectic equilibrium at 302.4 K. It results in a prilocaine-rich liquid containing approximately 0.7 mol fraction of anesthetic. Similar behavior has been reported for the binary system lidocaine-water (Ce´olin, R.; et al. J. Pharm. Sci. 2010, 99 (6), 2756-2765). In the ternary mixture, the combination of the monotectic equilibrium and the above-mentioned eutectic equilibrium between prilocaine and lidocaine results in an anesthetic-rich liquid that remains stable below room temperature. This liquid forms an emulsion-like mixture in the presence of an aqueous solution saturated with anesthetics. Physical properties and the crystal structure of prilocaine are also reported.

    EMLA cream, a “eutectic mixture of local anesthetics”, was developed in the early 1980s by Astra Pharmaceutical Production. The mixture of anesthetics containing lidocaine, prilocaine, and water is liquid at room temperature, which is partly due to the eutectic equilibrium between prilocaine and lidocaine at 293 K, as was clear from the start. However, the full thermodynamic background for the stability of the liquid and its emulsion-like appearance has never been elucidated. In the present study of the binary system prilocaine−water, a region of liquid−liquid demixing has been observed, linked to a monotectic equilibrium at 302.4 K. It results in a prilocaine-rich liquid containing approximately 0.7 mol fraction of anesthetic. Similar behavior has been reported for the binary system lidocaine−water (Céolin, R.; et al. J. Pharm. Sci. 2010, 99 (6), 2756−2765). In the ternary mixture, the combination of the monotectic equilibrium and the above-mentioned eutectic equilibrium between prilocaine and lidocaine results in an anesthetic-rich liquid that remains stable below room temperature. This liquid forms an emulsion-like mixture in the presence of an aqueous solution saturated with anesthetics. Physical properties and the crystal structure of prilocaine are also reported.

  • Dynamic heterogeneity in the glass-like monoclinic phases of some halogen methane compounds

     Zuriaga, Jose Mariano; Perez, Silvina C.; Pardo Soto, Luis Carlos; Tamarit Mur, Jose Luis
    American institute of physics inc. , Conf. AIP. Proc. (15517616, 0094243X)
    Vol. 1518, p. 59-66
    DOI: 10.1063/1.4794551
    Date of publication: 2013-02-25
    Journal article

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    In this work we study the heterogeneity of the dynamics on the low-temperature monoclinic phases of the simple molecular glassy systems , n = 0, 1, 2. In these systems the disorder comes exclusively from reorientational jumps mainly around the C3 molecular axes. The different time scales are determined by means of the analysis of the spin-lattice relaxation time obtained through Nuclear Quadrupole Resonance (NQR) technique. Results are compared with those obtained from dielectric spectroscopy, from which two a- and ß-relaxation times appear. NQR results enable us to ascribe with no doubt that the existence of two relaxations is due to dynamical heterogeneities which are the consequence of the different molecular surroundings of the molecules in the asymmetric unit cell of systems here studied. © 2013 American Institute of Physics Published online 25 febrero 2013

  • Crystal structure and solid-state properties of 3,4-diaminopyridine dihydrogen phosphate and their comparison with other diaminopyridine salts

     Mahe, Nathalie; Nicolaï, Béatrice; Allouchi, Hassan; Del Barrio Casado, Maria; Do, Bernard; Céolin, René; Tamarit Mur, Jose Luis; Rietveld, Ivo B.
    Crystal growth and design
    Vol. 13, num. 2, p. 708-715
    DOI: 10.1021/cg3014249
    Date of publication: 2013-02
    Journal article

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    3,4-Diaminopyridine is an active pharmaceutical ingredient for the treatment of Lambert-Eaton myasthenic syndrome (LEMS). It is 3,4-diaminopyridine dihydrogen phosphate that has become the active ingredient of choice. As part of a larger study for the development of this drug, solid-state studies have been carried out. At room temperature, the crystals are monoclinic (C2/c). Dihydrogen phosphate anions H2PO4 - form infinite chains parallel to the b axis, and these chains can be considered as macroanions (H2PO4)8. The organic cations form hydrogen bonds with the macroanions bridging them together. A negative thermal expansion is observed along the [103] direction in the crystal, which coincides with the direction of chains of interchanging anions and cations. The crystal packing shows similarities with the hydrogen tartrate salt as illustrated by a Hirshfeld surface analysis. This phosphate and this tartrate salt are also the two diaminopyridine salts that have been selected for therapeutic use because of their appropriate physical properties. © 2012 American Chemical Society.

    3,4-Diaminopyridine is an active pharmaceutical ingredient for the treatment of Lambert−Eaton myasthenic syndrome (LEMS). It is 3,4-diaminopyridine dihydrogen phosphate that has become the active ingredient of choice. As part of a larger study for the development of this drug, solid-state studies have been carried out. At room temperature, the crystals are monoclinic (C2/c). Dihydrogen phosphate anions H2PO4 − form infinite chains parallel to the b axis, and these chains can be considered as macroanions (H2PO4)∞. The organic cations form hydrogen bonds with the macroanions bridging them together. A negative thermal expansion is observed along the [103] direction in the crystal, which coincides with the direction of chains of interchanging anions and cations. The crystal packing shows similarities with the hydrogen tartrate salt as illustrated by a Hirshfeld surface analysis. This phosphate and this tartrate salt are also the two diaminopyridine salts that have been selected for therapeutic use because of their appropriate physical properties.

  • Comparison of the atomic level structure of the plastic crystalline and liquid phases of CBr2Cl2: Neutron diffraction and reverse Monte Carlo modelling

     Pothoczki, Szilvia; Temleitner, László; Pardo Soto, Luis Carlos; Cuello, Gabriel Julio; Rovira Esteva, Muriel; Tamarit Mur, Jose Luis
    Journal of physics: condensed matter
    Vol. 25, num. 45, p. 454216-454223
    DOI: 10.1088/0953-8984/25/45/454216
    Date of publication: 2013-10-18
    Journal article

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    Neutron diffraction results obtained for plastic crystalline dichlorodibromomethane (CBr2Cl2) have been modelled by means of the reverse Monte Carlo method. Comparison with its liquid phase is provided at several levels of the atomic structure (total scattering structure factors, partial radial distribution functions, orientational and dipole-dipole correlations). The results reveal that the relative orientation of neighbouring molecules largely depends on the steric effect. The small dipole moment does not have as strong an influence as the steric effect on the short-range order. Our observations fit well with earlier findings presented for the series CBr nCl4-n (n = 0, 1, 2, 4). © 2013 IOP Publishing Ltd.

  • Insights into the determination of molecular structure from diffraction data using a Bayesian algorithm

     Henao Aristizábal, Andres; Rovira Esteva, Muriel; Vispa, Alessandro; Tamarit Mur, Jose Luis; Guardia Manuel, Elvira; Pardo Soto, Luis Carlos
    Journal of physics: condensed matter
    Vol. 25, num. 45
    DOI: 10.1088/0953-8984/25/45/454217
    Date of publication: 2013-11-13
    Journal article

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    The determination of the molecular ordering in a liquid is still a controversial subject. There is no general consensus either on the methods to obtain reliable liquid structures or on the way to analyze them. Regardless of the method, it is very important to have a realistic molecular structure available that allows simulations to faithfully reproduce the sample features, and that minimizes the computing time in structure refinements. However, attention is not always paid to this point and molecular models coming from general force-fields are frequently used to undertake many of the analyses. We propose in this work to use a Bayesian scheme to fit the experimental data and produce reliable molecular models that can be used as the starting point of any simulation or refinement. The algorithm behind the proposed method is based on a Markov chain Monte Carlo procedure, as many other refinement programs such as reverse Monte Carlo or empirical potential structure refinement.

  • Benzocaine polymorphism: Pressure-temperature phase diagram involving forms II and III

     Gana, Inès; Del Barrio Casado, Maria; Do, Bernard; Tamarit Mur, Jose Luis; Céolin, René; Rietveld, Ivo B.
    International journal of pharmaceutics
    Vol. 456, num. 2, p. 480-488
    DOI: 10.1016/j.ijpharm.2013.08.031
    Date of publication: 2013-11-18
    Journal article

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    Understanding the phase behavior of an active pharmaceutical ingredient in a drug formulation is required to avoid the occurrence of sudden phase changes resulting in decrease of bioavailability in a marketed product. Benzocaine is known to possess three crystalline polymorphs, but their stability hierarchy has so far not been determined. A topological method and direct calorimetric measurements under pressure have been used to construct the topological pressure-temperature diagram of the phase relationships between the solid phases II and III, the liquid, and the vapor phase. In the process, the transition temperature between solid phases III and II and its enthalpy change have been determined. Solid phase II, which has the highest melting point, is the more stable phase under ambient conditions in this phase diagram. Surprisingly, solid phase I has not been observed during the study, even though the scarce literature data on its thermal behavior appear to indicate that it might be the most stable one of the three solid phases. © 2013 Elsevier B.V. All rights reserved.

    tUnderstanding the phase behavior of an active pharmaceutical ingredient in a drug formulation isrequired to avoid the occurrence of sudden phase changes resulting in decrease of bioavailability in amarketed product. Benzocaine is known to possess three crystalline polymorphs, but their stability hier-archy has so far not been determined. A topological method and direct calorimetric measurements underpressure have been used to construct the topological pressure–temperature diagram of the phase rela-tionships between the solid phases II and III, the liquid, and the vapor phase. In the process, the transitiontemperature between solid phases III and II and its enthalpy change have been determined. Solid phaseII, which has the highest melting point, is the more stable phase under ambient conditions in this phasediagram. Surprisingly, solid phase I has not been observed during the study, even though the scarce lit-erature data on its thermal behavior appear to indicate that it might be the most stable one of the threesolid phases.

  • Rimonabant dimorphism and its pressure¿temperature phasegiagram: A delicate case of overall monotropic behavior

     Perrin, Marc-Antoine; Bauer, Michel; Del Barrio Casado, Maria; Tamarit Mur, Jose Luis; Céolin, René; Rietveld, Ivo B.
    Journal of pharmaceutical sciences
    Vol. 102, num. 7, p. 2311-2321
    DOI: 10.1002/jps.23612
    Date of publication: 2013-05-20
    Journal article

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    Crystalline polymorphism occurs frequently in the solid state of active pharmaceutical ingredients, and this is problematic for the development of a suitable dose form. Rimonabant, an active pharmaceutical ingredient developed by Sanofi and discontinued because of side effects, exhibits dimorphism; both solid forms have nearly the same melting temperatures, melting enthalpies, and specific volumes. Although the problem may well be academic from an industrial point of view, the present case demonstrates the usefulness of constructing pressure¿temperature phase diagrams by direct measurement as well as by topological approach. The system is overall monotropic and form II is the more stable solid form. Interestingly, the more stable form does not possess any hydrogen bonds, whereas the less stable one does.

    Crystalline polymorphism occurs frequently in the solid state of active pharmaceutical ingredients, and this is problematic for the development of a suitable dose form. Rimonabant, an active pharmaceutical ingredient developed by Sanofi and discontinued because of side effects, exhibits dimorphism; both solid forms have nearly the same melting temperatures, melting enthalpies, and specific volumes. Although the problem may well be academic from an industrial point of view, the present case demonstrates the usefulness of constructing pressure–temperature phase diagrams by direct measurement as well as by topological approach. The system is overall monotropic and form II is the more stable solid form. Interestingly, the more stable form does not possess any hydrogen bonds, whereas the less stable one does.

  • Polymorphism in halogen-ethane derivatives: CCl3-CCl3 and ClF2C-CF2Cl

     Negrier, Philippe; Tamarit Mur, Jose Luis; Del Barrio Casado, Maria; Mondieig, Denise
    Crystal growth and design
    Vol. 13, num. 2, p. 782-791
    DOI: 10.1021/cg301498f
    Date of publication: 2013-02-06
    Journal article

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    The polymorphism of hexachloroethane, Cl3C−CCl3, has been reinvestigated by means of X-ray and neutron scattering. The long time unknown structure of the intermediate phase II of Cl3C−CCl3 has been determined as monoclinic C2/m, with lattice parameters a = 17.9835(21) Å, b = 10.3642(11) Å, c = 6.3014(8) Å, and β = 94.410(5)° at 323 K, Z = 6. The polymorphism of 1,2-dichloro-1,1,2,2-tetrafluoro-ethane, ClF2C−CF2Cl, has also been investigated, and the structure of the intermediate phase II has been found to be orthorhombic (Cmca, Z = 4) with lattice parameters a = 6.305(4) Å, b = 10.177(12) Å, c = 8.714 (7) Å. The high-temperature phase I of ClF2C− CF2Cl has been found to be isomorphous with the orientationally disordered phase I of Cl3C−CCl3 (body centered cubic, Im3̅m), a consequence of the pseudospherical molecular shape of halogeno-ethane C2X6−nYn (X = Cl, Y = F) molecular crystals. The similarities of the intricate disorder of the intermediate phases II of both Cl3C−CCl3 and ClF2C−CF2Cl compounds are analyzed, together with the influence of the conformational disorder appearing in the last compound.

  • Tricritical behavior of the nematic to smectic-A phase transition in the binary mixture of liquid crystal

     Mukherjee, Prabir K.; Tamarit Mur, Jose Luis
    Journal of chemical physics
    Vol. 138, num. 10, p. 104906-1-104906-6
    DOI: 10.1063/1.4794312
    Date of publication: 2013-03-14
    Journal article

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    We propose a phenomenological model to describe the tricritical behavior of the nematic to smectic-A (N-SmA) phase transition in liquid crystal mixture. To describe the mesophase transitions in binary mixture, nematic and smectic order parameters have been coupled with the concentration. We show that a tricritical point on the N-SmA phase transition line can be achieved under certain conditions. The predictive capability of the present model for determining the tricritical point of a binary mixture displaying the N-SmA transition has been demonstrated by testing with reported phase diagrams sharing both phases

    We propose a phenomenological model to describe the tricritical behavior of the nematic to smectic- A (N-SmA) phase transition in liquid crystal mixture. To describe the mesophase transitions in binary mixture, nematic and smectic order parameters have been coupled with the concentration. We show that a tricritical point on the N-SmA phase transition line can be achieved under certain conditions. The predictive capability of the present model for determining the tricritical point of a binary mixture displaying the N-SmA transition has been demonstrated by testing with reported phase diagrams sharing both phases

  • Pressure-temperature phase diagrams of drugs

     Del Barrio Casado, Maria; Rietveld, Ivo B.; Céolin, René; Tamarit Mur, Jose Luis
    Workshop on Stability of Amorphous Pharmaceuticals
    p. 20
    Presentation's date: 2013-10-18
    Presentation of work at congresses

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  • Determination of the short range order of molecular liquids: a general method

     Pardo Soto, Luis Carlos; Rovira Esteva, Muriel; Henao Aristizábal, Andres; Silva-Santisteban López, Alvaro; Murugan Natarajan, Arul; Cuello, Gabriel Julio; Gonzalez Lopez, Miguel Angel; Guardia Manuel, Elvira; Tamarit Mur, Jose Luis
    International Discussion Meeting on Relaxation in Complex Systems
    p. 197
    Presentation's date: 2013-07-26
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  • Secondary relaxations on a strong orientational glass

     Romanini, Michela; Del Barrio Casado, Maria; Capaccioli, Simone; Prevosto, Daniele; Tamarit Mur, Jose Luis
    International Discussion Meeting on Relaxation in Complex Systems
    p. 311
    Presentation's date: 2013-07-25
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  • Ultra-slow dynamics of water in hygroscopic molecular solids

     Macovez, Roberto; Mitsari, Efstratia; Zachariah, Manesh; Romanini, Michela; Capaccioli, Simone; Zygouri, Panagiota; Gournis, Dimitrios; Tamarit Mur, Jose Luis
    International Discussion Meeting on Relaxation in Complex Systems
    p. 383
    Presentation's date: 2013-07-22
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  • The microscopic structure behind the hydrogen bond in butanol

     González González, Miguel Angel; Silva-Santisteban López, Alvaro; Cuello, Gabriel Julio; Cristiglio, Viviana; Cabrillo García, Carlos; Ramos Ruiz, Miguel Angel; Shmyt'ko, Ivan; Tamarit Mur, Jose Luis; Pardo Soto, Luis Carlos
    International Discussion Meeting on Relaxation in Complex Systems
    p. 222-223
    Presentation's date: 2013-07-26
    Presentation of work at congresses

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    Aliphatic alcohols are the simplest molecular liquids possessing a polar hydroxyl group and a nonpolar alkyl tail, and may therefore be used as prototypes to explore how the molecular geometry and the length of the hydrophobic chain determine the structure of more complex substances. The structure of the smallest alcohols has been relatively well studied and the existence of a pre-peak before the main diffraction peak is well known from X-ray diffraction studies. It consists of a small side maximum that shifts to lower Q values with increasing chain length and is considered a signature of H-bonded association and related to the formation of clusters of mesoscopic size. We have recently found by means of X-ray and neutron diffraction that the height of the pre-peak associated with the formation of H-bonds increases with temperature. This behaviour is surprising, as one would expect that the influence of H-bonds in the structure should decrease with temperature. In order to unravel this counterintuitive effect, we have per formed in this work a series of Molecular Dynamics simulations. The standard analysis of the MD trajectories shows that the computed structure reproduces the experimental static structure factor reasonably well, including the position and intensity of thepre-peak as a function of temperature. We have then applied the new method developed by Pardo et al. to describe in detail the short range molecular ordering between neighbouring molecules and find out how H-bonding determines the structural features observed.

  • Dynamics as a function of temperature and pressure for an antiprotozoal drug

     Romanini, Michela; Capaccioli, Simone; Del Barrio Casado, Maria; Prevosto, Daniele; Tamarit Mur, Jose Luis
    International Discussion Meeting on Relaxation in Complex Systems
    p. 42
    Presentation's date: 2013-07-23
    Presentation of work at congresses

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  • Dynamics of an extremely fragile plastic crystal

     Tamarit Mur, Jose Luis; Romanini, Michela; Pardo Soto, Luis Carlos; Capaccioli, Simone; Vispa, Alessandro
    International Discussion Meeting on Relaxation in Complex Systems
    p. 202
    Presentation's date: 2013-07-25
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  • Well-ordered glasses: glassy features in long-range ordered systems

     Del Barrio Casado, Maria; Negrier, Philippe; Romanini, Michela; Capaccioli, Simone; Pardo Soto, Luis Carlos; Mondieig, Denise; Tamarit Mur, Jose Luis
    International Discussion Meeting on Relaxation in Complex Systems
    p. 358
    Presentation's date: 2013-07-25
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  • Low-temperature thermal conductivity of some simple molecular crystals for ordered and disordered phases

     Stachowiak, Piotr; Romanova, Tetiana; Jezowski, Andrzej; Krivchikov, Alexander I; Vdovichenko, Georgii A.; Tamarit Mur, Jose Luis; Bermejo, F. Javier
    International Discussion Meeting on Relaxation in Complex Systems
    p. 361
    Presentation's date: 2013-07-25
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  • New insights on stability of amorphous pharmaceutical systems from molecular dynamics investigation

     Capaccioli, Simone; Prevosto, D.; Labardi, M.; Tamarit Mur, Jose Luis; Romanini, Michela; Wang, Limin; Ngai, K.L.
    Workshop on Stability of Amorphous Pharmaceuticals
    p. 7-8
    Presentation's date: 2013-10-17
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  • Thermal conductivity of orientational glasses at low temperatures

     Vdovichenko, Georgii A.; Krivchikov, Alexander I; Korolyuk, O. A.; Pardo Soto, Luis Carlos; Tamarit Mur, Jose Luis; Bermejo Dominguez, Javier
    International Discussion Meeting on Relaxation in Complex Systems
    p. 355
    Presentation's date: 2013-07-25
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  • Detailed structural analysis of trans-1,2-dichloroethene liquids unravels the origin of its anomalies

     Rovira Esteva, Muriel; Murugan Natarajan, Arul; Pardo Soto, Luis Carlos; Busch, Sebastian; Tamarit Mur, Jose Luis; Cuello, Gabriel Julio; Bermejo Dominguez, Javier
    International Discussion Meeting on Relaxation in Complex Systems
    p. 201
    Presentation's date: 2013-07-26
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  • Boson peak and Ioffe-Regel frequency crossover on several orientational glasses

     Krivchikov, Alexander I; Vdovichenko, Georgii A.; Korolyuk, O. A.; Ramos Ruiz, Miguel Angel; Hassaine, M.; Kabtoul, B.; Bermejo, F. Javier; Tamarit Mur, Jose Luis
    International Discussion Meeting on Relaxation in Complex Systems
    p. 357
    Presentation's date: 2013-07-25
    Presentation of work at congresses

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  • A glacial state from a plastic molecular crystal

     Szewczyk, Daria; Jezowski, Andrzej; Krivchikov, Alexander I; Vdovichenko, Georgii A.; Del Barrio Casado, Maria; Tamarit Mur, Jose Luis
    International Discussion Meeting on Relaxation in Complex Systems
    p. 360
    Presentation's date: 2013-07-25
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  • Water-dependent conductivity of fullerene derivatives

     Zachariah, Manesh; Mitsari, Efstratia; Romanini, Michela; Tamarit Mur, Jose Luis; Zygouri, Panagiota; Gournis, Dimitrios; Macovez, Roberto
    International Discussion Meeting on Relaxation in Complex Systems
    p. 206
    Presentation's date: 2013-07-23
    Presentation of work at congresses

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  • Rimonabant dimorphism, much ado about almost nothing

     Perrin, Marc-Antoine; Bauer, M; Del Barrio Casado, Maria; Tamarit Mur, Jose Luis; Céolin, René; Rietveld, I.B.
    Joint European days on Equilibrium between Phases
    p. 65
    Presentation's date: 2013-03-21
    Presentation of work at congresses

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  • The conformational polymorphism of 1,1,2,2-tetrachloroehtane (C2 H2CI4)

     Negrier, Philippe; Del Barrio Casado, Maria; Zuriaga, Jose Mariano; Perez, Silvina C.; Tamarit Mur, Jose Luis; Mondieig, Denise
    Joint European days on Equilibrium between Phases
    p. 141
    Presentation's date: 2013-03-20
    Presentation of work at congresses

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    Halogenoethane derivatives are known to exhibit different polymorphs involving a different translational, orientational, and conformational order. The 1,1,2,2-tetrachloroethane (Cl2HC-CHCl2) exhibits a normal pressure orthorhombic phase (space group P212 121 with Z = 8 and Z = 2), formed by molecules with one of the two gauche conformations. At high pressure, the stable polymorph is known to be monoclinic (space group P21/c, with Z = 2 and Z = 0.5), phase , in which only the trans conformer appears. In this work, we demonstrate the existence of a normal pressure metastable polymorph, phase , for which the two gauche conformers show up in the asymmetric unit of a monoclinic (space group P21/c with Z = 8 and Z = 2) structure. The new phase is obtained by recrystallization upon heating the glass obtained after quench of the melt. It displays shorter type II ClCl contacts than the high-pressure phase due to attractive and directional interactions

  • Stable, metastable and unstable phases of halogen methane derivatives

     Tamarit Mur, Jose Luis
    Joint European days on Equilibrium between Phases
    p. 76
    Presentation's date: 2013-03-21
    Presentation of work at congresses

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  • Dinámica en sólidos desordenados

     Romanini, Michela; Macovez, Roberto; Ruiz Martin, Maria Dolores; Levit Valenzuela, Rafael; Pardo Soto, Luis Carlos; Del Barrio Casado, Maria; Vispa, Alessandro; Tamarit Mur, Jose Luis
    Competitive project

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    Emergence of glassy-like dynamics in an orientationally ordered phase  Open access

     Romanini, Michela; Negrier, Philippe; Tamarit Mur, Jose Luis; Capaccioli, Simone; Del Barrio Casado, Maria; Pardo Soto, Luis Carlos; Mondieig, Denise
    Physical review B: condensed matter and materials physics
    Vol. 85, num. 13, p. 134201-1-134201-7
    DOI: 10.1103/PhysRevB.85.134201
    Date of publication: 2012-04-04
    Journal article

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    The dynamics of a simple rigid pseudoglobular molecule (2-adamantanone) has been studied by means of dielectric spectroscopy and examined under the constraints imposed by the space group of the crystal structure determined by x-ray powder diffraction. The low-temperature monoclinic structure of 2-adamantanone, with one molecule per asymmetric unit (Z'= 1), displays a statistical intrinsic disorder, concerning the site occupancy of the oxygen atom along three different sites. Such a physically identifiable disorder gives rise to large-angle molecular rotations which inherently lead to time-average fluctuations of the molecular dipole, thus contributing to the dielectric susceptibility. The dielectric spectra for the low-temperature “ordered” phase displays a universal feature of glassy-like materials, i.e., coexistence of α- and β-relaxation processes. The former is clearly identified with the strongly restricted reorientational motions within the long-range “ordered” crystalline lattice. The latter, never observed before in fully translationally and highly orientationally ordered phases, displays all the properties of an original Johari-Goldstein β-relaxation, in spite of the strong character of this glass-like phase. These findings can be explained according to the coupling model, applied to such “ordered” phases.

  • Role of steric and electrostatic effects in the short-range order of quasitetrahedral molecular liquids

     Pothoczki, Sz.; Ottochian, A.; Rovira Esteva, Muriel; Pardo Soto, Luis Carlos; Tamarit Mur, Jose Luis; Cuello, G.J.
    Physical review B: condensed matter and materials physics
    Vol. 85, num. 1, p. 014202-1-014202-9
    DOI: 10.1103/PhysRevB.85.014202
    Date of publication: 2012-01-01
    Journal article

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    The study of how both steric and electrostatic interactions affect the structure of liquids formed by quasitetrahedral molecules has been undertaken in this work. We have studied trichlorobromomethane (CBrCl3) and dibromodichloromethane (CBr2Cl2), both displaying a dipole along their C3v and C2v molecular symmetry axes, respectively. The short-range order of the liquid state has been determined using neutron diffraction experiments that were modeled through the reverse Monte Carlo (RMC) technique. To study changes in steric effects due to the distortion of the tetrahedral symmetry, we have compared our results with a previous RMC modeling of carbon tetrachloride (CCl4). The subtle effects of the dipole in the structure of the liquid have been determined using a set of molecular dynamics simulations with and without atomic partial charges, being the force field validated via comparison with the diffraction data. In a first approximation, neither steric nor electrostatic interactions are able to modify the molecular ordering of a fully tetrahedral liquid such as CCl4. A more detailed analysis indicates that, although the interaction between dipoles does not have appreciable effects when aligned along the C3v molecular axes, as for the CBrCl3, it enhances the antiparallel orientation of dipoles when it is oriented along the C2v axes, as in the case of CBr2Cl2.

  • Polymorphism in halogen-ethane derivatives: CCl3-CF2Cl and CF3-CF2Cl

     Negrier, Philippe; Del Barrio Casado, Maria; Tamarit Mur, Jose Luis; Pardo Soto, Luis Carlos; Mondieig, Denise
    Crystal growth and design
    Vol. 12, num. 3, p. 1513-1519
    DOI: 10.1021/cg201575v
    Date of publication: 2012-01-03
    Journal article

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    Molecular crystals of halogen–ethane derivatives C2X6–nYn (X = Cl, Y = F) are known to display order–disorder phase transitions involving changes of the translational, orientational, and conformational order. The appearance of a high-temperature orientationally disordered phase with a high symmetry lattice is expected for this set of compounds in view of their “pseudospherical” molecular geometry. In this work, we present a study of polymorphism of the compounds 1,1,1,2-tetrachloro-2,2-difluoroethane (CCl3–CF2Cl) and 1-chloro-1,1,2,2,2-pentafluoroethane (CF3–CF2Cl), in which conformational disorder is not present, by combining neutron (D2B and D1B instruments at the Laue-Langevin Institute) and X-ray scattering experiments. We show that despite the close molecular shapes and molecular structures of both compounds, strong differences concerning the disorder appear in the low-temperature phase. The low-temperature phase for CF3–CF2Cl is found to be fully ordered, with a monoclinic P21/n structure (Z = 4), while that of CCl3–CF2Cl is found to be orthorhombic Pmna (Z = 4) with a disorder concerning one Cl and one F sites, each one with a fractional occupancy of 50%. Details related to the high-temperature orientationally disordered phases (both body-centered-cubic) are also given.

  • Differences in first neighbor orientation behind the anomalies in the low and high density trans-1,2-dichlorothene liquid

     Rovira Esteva, Muriel; Murugan, N.A.; Pardo Soto, Luis Carlos; Busch, Sebastian; Tamarit Mur, Jose Luis; Cuello, G. J.; Bermejo, F. Javier
    Journal of chemical physics
    Vol. 134, num. 12, p. 124514-1-124541-7
    DOI: 10.1063/1.3697849
    Date of publication: 2012-03-28
    Journal article

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