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Applications of sodium alginate (Alg) and polyacrylic acid (PAA) hydrogels in biomedicine are well-known. These are predefined by the strength and weakness of their properties, which in turn depend on the chemical structure and the architecture of their crosslinks. In this work, Alg biopolymer has been grafted to synthetic PAA that has been chemically crosslinked using N,N'-methylene-bisacrylamide (MBA) to produce a pH responsive hydrogel with adhesive property. The double crosslinking network, which combines MBA-mediated covalent crosslinks and ionic crosslinks in Alg domains, results in an elastic modulus that resembles that of highly anisotropic and viscoelastic human skin. After addressing the influence of the dual network onto the Alg-g-PAA hydrogel properties, a prospection of its potential as an adhesive has been made considering different surfaces (rubber, paper steel, porcine skin, etc). The bonding energy onto porcine skin, 32.6 ± 4.6 J/m2, revealed that the Alg-g-PAA hydrogel can be proposed in the biomedical field as tissue adhesive for wound healing applications. Finally, the hydrogel has been semi-interpenetrated with poly(hydroxymethyl-3,4-ethylenedioxythiophene) (PEDOT-MeOH) chains through a chemical oxidative polymerization process. The resulting hydrogel, Alg-g-PAA/PEDOT-MeOH, which is even more porous than Alg-g-PAA, in addition to being electro-responsive, maintains adhesive properties., Peer Reviewed, Postprint (published version)

We review experimental results obtained with broadband dielectric spectroscopy concerning the relaxation times and activation energies of intramolecular conformational relaxation processes in small-molecule glass-formers. Such processes are due to the interconversion between different conformers of relatively flexible molecules, and generally involve conformational changes of flexible chain or ring moieties, or else the rigid rotation of planar groups, such as conjugated phenyl rings. Comparative analysis of molecules possessing the same (type of) functional group is carried out in order to test the possibility of assigning the dynamic conformational isomerism of given families of organic compounds to the motion of specific molecular subunits. These range from terminal halomethyl and acetyl/acetoxy groups to both rigid and flexible ring structures, such as the planar halobenzene cycles or the buckled saccharide and diazepine rings. A short section on polyesters provides a generalisation of these findings to synthetic macromolecules., This work was supported by the MICINN project PID2020-112975GB-I00 (Spain) and by the DGU project 2021SGR-00343 (Catalonia). M.R. acknowledges financial support from MICINN under the Juan de la Cierva fellowship (IJC2019-040225-I)., Peer Reviewed, Objectius de Desenvolupament Sostenible::3 - Salut i Benestar, Postprint (published version)

In order to exploit the pharmacological potential of natural bioactive molecules with low water solubility, such as curcumin, it is necessary to develop formulations, such as amorphous polymer dispersions, which allow a constant release rate and at the same time avoid possible toxicity effects of the crystalline form of the molecule under scrutiny. In this study, polymer dispersions of curcumin were obtained in PADAS, a biodegradable semicrystalline copolymer based on 1,12-dodecanediol, sebacic acid and alanine. The dispersions were fully characterized by means of differential scanning calorimetry and broadband dielectric spectroscopy, and the drug release profile was measured in a simulated body fluid. Amorphous homogeneous binary dispersions were obtained for curcumin mass fraction between 30 and 50%. Curcumin has significantly higher glass transition temperature Tg (˜ 347 K) than the polymer matrix (˜274-277 K depending on the molecular weight), and dispersions displayed Tg’s intermediate between those of the pure amorphous components, implying that curcumin acts as an effective antiplasticizer for PADAS. Dielectric spectroscopy was employed to assess the relaxation dynamics of the binary dispersion with 30 wt% curcumin, as well as that of each (amorphous) component separately. The binary dispersion was characterized by a single structural relaxation, a single Johari-Goldstein process, and two local intramolecular processes, one for each component. Interestingly, the latter processes scaled with the Tg of the sample, indicating that they are viscosity-sensitive. In addition, both the pristine polymer and the dispersion exhibited an interfacial Maxwell-Wagner relaxation, likely due to spatial heterogeneities associated with phase disproportionation in this polymer. The release of curcumin from the dispersion in a simulated body fluid followed a Fickian diffusion profile, and 51% of the initial curcumin content was released in 48 h., Peer Reviewed, Postprint (published version)

The formation of coamorphous mixtures of pharmaceuticals is an interesting strategy to improve the solubility and bioavailability of drugs, while at the same time enhancing the kinetic stability of the resulting binary glass and allowing the simultaneous administration of two active principles. In this contribution, we describe kinetically stable amorphous binary mixtures of two commercial active pharmaceutical ingredients, diazepam and nordazepam, of which the latter, besides being administered as a drug on its own, is also the main active metabolite of the other in the human body. We report the eutectic equilibrium-phase diagram of the binary mixture, which is found to be characterized by an experimental eutectic composition of 0.18 molar fraction of nordazepam, with a eutectic melting point of Te = 395.4 ± 1.2 K. The two compounds are barely miscible in the crystalline phase. The mechanically obtained mixtures were melted and supercooled to study the glass-transition and molecular-relaxation dynamics of amorphous mixtures at the corresponding concentration. The glass-transition temperature was always higher than room temperature and varied linearly with composition. The Te was lower than the onset of thermal decomposition of either compound (pure nordazepam decomposes upon melting and pure diazepam well above its melting point), thus implying that the eutectic liquid and glass can be obtained without any degradation of the drugs. The eutectic glass was kinetically stable against crystallization for at least a few months. The relaxation processes of the amorphous mixtures were studied by dielectric spectroscopy, which provided evidence for a single structural (a) relaxation, a single Johari–Goldstein (ß) relaxation, and a ring-inversion conformational relaxation of the diazepinic ring, occurring on the same timescale in both drugs. We further characterized both the binary mixtures and pure compounds by FTIR spectroscopy and first-principles density functional theo, Peer Reviewed, Postprint (published version)

Amorphous molecule-macromolecule mixtures are ubiquitous in polymer technology and are one of the most studied routes for the development of amorphous drug formulations. For these applications it is crucial to understand how the preparation method affects the properties of the mixtures. Here, we employ differential scanning calorimetry and broadband dielectric spectroscopy to investigate dispersions of a small-molecule drug (the Nordazepam anxiolytic) in biodegradable polylactide, both in the form of solvent-cast films and electrospun microfibres. We show that the dispersion of the same small-molecule compound can have opposite (plasticizing or antiplasticizing) effects on the segmental mobility of a biopolymer depending on preparation method, temperature, and polymer enantiomerism. We compare two different chiral forms of the polymer, namely, the enantiomeric pure, semicrystalline L-polymer (PLLA), and a random, fully amorphous copolymer containing both L and D monomers (PDLLA), both of which have lower glass transition temperature (Tg) than the drug. While the drug has a weak antiplasticizing effect on the films, consistent with its higher Tg, we find that it actually acts as a plasticizer for the PLLA microfibres, reducing their Tg by as much as 14 K at 30%-weight drug loading, namely, to a value that is lower than the Tg of fully amorphous films. The structural relaxation time of the samples similarly depends on chemical composition and morphology. Most mixtures displayed a single structural relaxation, as expected for homogeneous samples. In the PLLA microfibres, the presence of crystalline domains increases the structural relaxation time of the amorphous fraction, while the presence of the drug lowers the structural relaxation time of the (partially stretched) chains in the microfibres, increasing chain mobility well above that of the fully amorphous polymer matrix. Even fully amorphous homogeneous mixtures exhibit two distinct Johari–Goldstein relaxation proc, Peer Reviewed, Postprint (author's final draft)

Aquest article presenta el desenvolupament i primers resultats d'ús d'un conjunt de cursos virtuals que pretenen proporcionar uns coneixements inicials bàsics de Matemàtiques, Física i !ímica als estudiants que accedeixen a estudis de grau a l'Escola d'Enginyeria de Barcelona Est (EEBE). Els cursos han estat desenvolupats sobre la plataforma Atenea (Moodle). El seu nucli el constitueixen un conjunt de materials per a autoaprenentatge que inclouen documents escrits, vídeos i tests d'autoavaluació. Els documents escrits i els vídeos corresponen tant a explicacions de teoria com a la resolució detallada d'exercicis. En el marc d'una prova pilot, els cursos, de seguiment voluntari durant el període transcorregut entre la matricula (mitjans de juliol) i l'inici de les classes (mitjans de setembre), van ser publicitats a tots els estudiants de nou accés del curs 2021-2022. Encara que la participació va ser més limitada del que s'esperava (únicament el 22% dels estudiants de nou accés es van inscriure), cal destacar que els estudiants que sí que van seguir els cursos van expressar majoritàriament una bona valoració dels mateixos (al respondre un qüestionari de satisfacció). Del desenvolupament dels cursos i de la realització de la prova pilot s'han obtingut unes quantes conclusions que també queden reflectides al final de l'article.

We employ differential scanning calorimetry, broadband dielectric spectroscopy and optical microscopy to investigate the glass transition, molecular relaxation dynamics, and isothermal recrystallization kinetics of amorphous mitotane, the only drug approved for the pharmacological treatment of adrenocortical carcinoma. Amorphous mitotane displays a glass transition at Tg = 243 ± 1 K, characterized by relatively low fragility index of 68 ± 2. Besides the structural and Johari-Goldstein relaxations, amorphous mitotane displays an intramolecular relaxation with activation energy of 25 ± 1 kJ mol-1. The same relaxation process, with virtually the same activation energy and relaxation times, is observed in the closely-related o,p’-dichlorobenzophenone compound, which allows identifying it as the rotation of the chlorobenzene ring with the chlorine closest to the central carbon. Such conformational relaxation is active at human body temperature, and may thus be potentially relevant for the mechanism of action of the drug. Our study shows that the comparative study of the relaxation map of related molecular species is a powerful tool to identify and classify secondary relaxation processes. The amorphous drug is found to be unstable against recrystallization at as well as slightly below room temperature, and to display-two-dimensional growth with only sporadic nucleation, characterized by an Avrami kinetic exponent of 2.05 ± 0.05. The kinetic stability of the amorphous form of mitotane, observed at room temperature in micellar formulations, is therefore limited to the nanoconfined sample and is not observed in the bulk compound., Peer Reviewed, Postprint (published version)

In glass-forming substances, the addition of water tends to produce the effect of lowering the glass transition temperature, T. In a previous work by some of us (Ruiz et al., Sci. Rep., 2017, 7, 7470) we reported on a rare anti-plasticizing effect of water on the molecular dynamics of a simple molecular system, the pharmaceutically active prilocaine molecule, for which the addition of water leads to an increase of T. In the present work, we study pure and hydrated prilocaine confined in 0.5 nm and 1 nm pore size molecular sieves, and carry out a comparison with the bulk compounds in order to gain a better understanding of the microscopic mechanisms that result in this rare effect. We find that the T of the drug under nanometric confinement can be lower than the bulk value by as much as 17 K. Through the concurrent use of differential scanning calorimetry and broadband dielectric spectroscopy we are able to observe the antiplasticizing effect of water in prilocaine also under nanometric confinement, finding an increase of T of up to almost 6 K upon hydration. The extension of our analysis to nanoconfined systems provides a plausible explanation for the very uncommon antiplasticizing effect, based on the formation of water-prilocaine molecular complexes. Moreover, this study deepens the understanding of the behavior of drugs under confinement, which is of relevance not only from a fundamental point of view, but also for practical applications such as drug delivery.

Melt electrospinning of polylactide (PLA) loaded with chloramphenicol (CAM) has been performed and characteristics of fibers, physical properties of scaffolds, CAM release behavior, antibacterial properties and biocompatibility have been evaluated. The interest of CAM loaded samples is nowadays enhanced for biomedical applications since this antibiotic has been demonstrated to be efficient for the treatment of cancer. Melt electrospinning has been selected as an ideal preparation process because it avoids the use of toxic solvents which are harmful to the environment and could be problematic for biomedical applications. The electrospinning process rendered fibers with a relatively large diameter (between 20 µm and 40 µm depending on the load) and minimum polymer degradation. Characteristics of melt electrospun scaffolds were also compared with those prepared by solution electrospinning. Differences consisted in a more sustained release and a higher biocompatibility for the melt processed samples. Bactericide effect was evaluated as an evidence of the maintenance of the CAM bioactivity after melt processing at high temperature and the slower release caused by the relatively high diameter of the constitutive fibers. Since pure CAM showed thermal degradation at temperatures relatively close to the PLA melting temperature, a complete analysis of the degradation process of pure CAM as well as of PLA samples loaded with CAM was performed. The Invariant Kinetic Parameters method allowed determining an initial decomposition step that followed an autoaccelatory Avrami model, and then an autocatalytic decomposition reaction took place for conversions higher than 50%. Dispersion in the PLA matrix enhances the thermal stability of the antibiotic, with an onset temperature of degradation that was higher by 16 ¿C in the meltelectrospun fibers than in the liquid state of pure CAM., Peer Reviewed, Postprint (author's final draft)

The structure of the metastable form II of 2-bromobenzophenone, obtained by crystallization from the melt, has been determined by powder X-ray diffraction. Form II has been solved in the centrosymmetric monoclinic space group P21/c with a = 8.4896(19) Å, b = 6.5438(8) Å, c = 20.253(1) Å; ß = 104.452(6)°, and Z = 4 (Z' = 1) at 200 K. Both form I and form II contain a multitude of aromatic interactions, and the strength and direction of these interactions could only be interpreted with the support of the thermal-expansion tensors. Both forms exhibit, unexpectedly, uniaxial negative thermal expansion, while hydrogen bonding does not play a significant role in either of these two structures. It appears to be the first time in the literature that uniaxial negative thermal expansion may be caused by aromatic interactions. Thermodynamic properties at normal and high pressure have been determined for the stable and metastable phases, and a pressure–temperature phase diagram has been constructed. While the metastable form behaves monotropically with respect to the stable form under ambient conditions, the phase relationship becomes enantiotropic at high pressure, providing a clear example of phase behavior in which the densest form is not the most stable form under ambient conditions., Peer Reviewed, Postprint (author's final draft)

Les vesícules lipídiques o liposomes serveixen com a un model simple per estudiar propietats bàsiques de membranes cel·lulars més complexes. En aquest projecte, produïm liposomes mitjançant dues metodologies diferents amb una composició lipídica que conté lípids saturats, lípids insaturats i colesterol. Utilitzem microscòpia de fluorescència per observar la coexistència de dues fase líquides: una fase líquida-desordenada i una fase líquida-ordenada. Les forces intermembranals mostren un comportament significativament diferent a ambdues fases, doncs només observem adhesió de les vesícules a través de la fase líquida-ordenada. Utilitzem tècniques d'aspiració amb micropipeta per investigar les propietats de cadascuna d'aquestes fases i intentar entendre la complexa interacció que hi ha entre composició lipídica, tensió de membrana i forces intermembranals., Las vesículas lipídicas o liposomas sirven como un modelo simple para estudiar propiedades básicas de membranas celulares más complejas. En este proyecto, producimos liposomas mediante dos metodologías distintas con una composición lipídica que contiene lípidos saturados, lípidos insaturados y colesterol. Usamos microscopia de fluorescencia para observar la coexistencia de dos fases líquidas en las membranas resultantes, una fase liquida-desordenada rica en lípido insaturado y una fase liquida-ordenada rica en lípido saturado y colesterol. Las fuerzas intermembranales muestran un comportamiento significativamente distinto en ambas fases, pues solo se observa la adhesión de vesículas a través de la fase líquida-ordenada. Usamos técnicas de aspiración con micropipeta para investigar las propiedades de cada una de estas fases e intentar entender la compleja interacción existente entre composición lipídica, tensión de membrana y fuerzas intermembranales., Lipid vesicles serve as a simple model to study basic properties of complex cell membranes. We produce synthetic lipid vesicles using two different methods with a membrane composition containing a ternary mixture saturated lipids, unsaturated lipids and cholesterol. We use fluorescent microscopy to observe two coexisting liquid phases on the resulting membranes, a liquid-disordered phase rich in the unsaturated lipid, and a liquid-ordered phase, rich in the saturated lipid and cholesterol. Intermembranal forces are observed to differ significantly between these two phases, as we only see vesicles adhere to each other on the liquid-ordered side. We use micropipette aspiration technique to further investigate the properties of each of the two liquid phases and try to understand the interplay between phase composition, membrane tension and intermembranal interactions., Outgoing

We employ temperature- and pressure-dependent dielectric spectroscopy, as well as differential scanning calorimetry, to characterize benzophenone and the singly-substituted ortho-bromobenzophenone derivative in the liquid and glass states, and analyze the results in terms of the molecular conformations reported for these molecules. Despite the significantly higher mass of the brominated derivative, its dynamic and calorimetric glass transition temperatures are only ten degrees higher than those of benzophenone. The kinetic fragility index of the halogenated molecule is lower than that of the parent compound, and is found to decrease with increasing pressure. By a detailed analysis of the dielectric loss spectra, we provide evidence for the existence of a Johari–Goldstein (JG) relaxation in both compounds, thus settling the controversy concerning the possible lack of a JG process in benzophenone and confirming the universality of this dielectric loss feature in molecular glass-formers. Both compounds also display an intramolecular relaxation, whose characteristic timescale appears to be correlated with that of the cooperative structural relaxation associated with the glass transition. The limited molecular flexibility of ortho-bromobenzophenone allows identifying the intramolecular relaxation as the inter-enantiomeric conversion between two isoenergetic conformers of opposite chirality, which only differ in the sign of the angle between the brominated aryl ring and the coplanar phenyl-ketone subunit. The observation by dielectric spectroscopy of a similar relaxation also in liquid benzophenone indicates that the inter-enantiomer conversion between the two isoenergetic helicoidal ground-state conformers of opposite chirality occurs via a transition state characterized by a coplanar phenyl-ketone moiety., Peer Reviewed, Postprint (published version)

Chemical derivatization and amorphization are two possible strategies to improve the solubility and bioavailability of drugs, which is a key issue for the pharmaceutical industry. In this contribution, we explore whether both strategies can be combined by studying how small differences in the molecular structure of three related pharmaceutical compounds affect their crystalline structure and melting point (Tm), the relaxation dynamics in the amorphous phase, and the glass transition temperature (Tg), as well as the tendency toward recrystallization. Three benzodiazepine derivatives of almost same molecular mass and structure (Diazepam, Nordazepam and Tetrazepam) were chosen as model compounds. Nordazepam is the only one that displays N–H···O hydrogen bonds both in crystalline and amorphous phases, which leads to a significantly higher Tm (by 70–80 K) and Tg (by 30–40 K) compared to those of Tetrazepam and Diazepam (which display similar values of characteristic temperatures). The relaxation dynamics in the amorphous phase, as determined experimentally using broadband dielectric spectroscopy, is dominated by a structural relaxation and a Johari–Goldstein secondary relaxation, both of which scale with the reduced temperature T/Tg. The kinetic fragility index is very low and virtually the same (mp ˜ 32) in all three compounds. Two more secondary relaxations are observed in the glass state: the slower of the two has virtually the same relaxation time and activation energy in all three compounds, and is assigned to the inter-enantiomer conversion dynamics of the flexible diazepine heterocycle between isoenergetic P and M conformations. We tentatively assign the fastest secondary relaxation, present only in Diazepam and Tetrazepam, to the rigid rotation of the fused diazepine–benzene double ring relative to the six-membered carbon ring. Such motion appears to be largely hindered in glassy Nordazepam, possibly due to the presence of the hydrogen bonds. Supercooled liquid T, Peer Reviewed, Postprint (author's final draft)

Transmission electron microscopy, temperature-modulated differential scanning calorimetry, and broadband dielectric spectroscopy were employed to characterize ternary nanocomposites consisting of carboxylated carbon nanotubes (CNT) dispersed in a blend of two immiscible polymers, poly(L,lactide) (PLLA) and thermoplastic polyurethane (TPU). The nanocomposite blends were obtained by melt-compounding of PLLA and TPU in the presence of 0.2 wt-% CNT, either in the presence or absence of a Joncryl® ADR chain extender for PLLA, leading to reactive and non-reactive melt mixed samples. In both cases, the binary PLLA/TPU blend is characterized by phase separation into submicron TPU droplets dispersed in the PLLA matrix, and displays two separate glass transition temperatures. The carbon nanotubes are present either inside the TPU phase (samples obtained without chain extender), or at their boundaries (reactive-melt mixed samples). The effect of the sub-micron confinement of the TPU component is to decrease the cooperativity length of the primary segmental relaxation of this polymer, which is accentuated by the presence of the CNT fillers. Depending on the type of sample, five or six distinct relaxations are observed by means of dielectric spectroscopy, which we are able to assign to different dielectric phenomena. Our dielectric data show that the CNT fillers do not contribute directly to the long-range charge transport in the nanocomposite blends, consistent with the nanocomposites morphology, but rather result in a shift of the Maxwell-Wagner-Sillars space-charge frequency associated with charge accumulation at the PLLA/TPU boundary. Such shift testifies to a selective conductivity enhancement of the TPU phase due to the filler., Peer Reviewed, Postprint (published version)

The amino acid lysine has been shown to prevent water crystallization at low temperatures in saturated aqueous solutions [S. Cerveny and J. Swenson, Phys. Chem. Chem. Phys., 2014, 16, 22382–22390]. Here, we investigate two ratios of water and lysine (5.4 water molecules per lysine (saturated) and 11 water molecules per lysine) by means of the complementary use of computer simulations and neutron diffraction. By performing a detailed structural analysis we have been able to explain the anti-freeze properties of lysine by the strong hydrogen bond interactions of interstitial water molecules with lysine that prevent them from forming crystalline seeds. Additional water molecules beyond the 1 : 5.4 proportion are no longer tightly bonded to lysine and therefore are free to form crystals.

The amino acid lysine has been shown to prevent water crystallization at low temperatures in saturated aqueous solutions [S. Cerveny and J. Swenson, Phys. Chem. Chem. Phys., 2014, 16, 22382–22390]. Here, we investigate two ratios of water and lysine (5.4 water molecules per lysine (saturated) and 11 water molecules per lysine) by means of the complementary use of computer simulations and neutron diffraction. By performing a detailed structural analysis we have been able to explain the anti-freeze properties of lysine by the strong hydrogen bond interactions of interstitial water molecules with lysine that prevent them from forming crystalline seeds. Additional water molecules beyond the 1 : 5.4 proportion are no longer tightly bonded to lysine and therefore are free to form crystals., Peer Reviewed, Postprint (author's final draft)

A facile, environment-friendly, versatile and reproducible approach to the successful oxidation of fullerenes (oxC60) and the formation of highly hydrophilic fullerene derivatives is introduced. This synthesis relies on the widely known Staudenmaier’s method for the oxidation of graphite, to produce both epoxy and hydroxy groups on the surface of fullerenes (C60) and thereby improve the solubility of the fullerene in polar solvents (e.g. water). The presence of epoxy groups allows for further functionalization via nucleophilic substitution reactions to generate new fullerene derivatives, which can potentially lead to a wealth of applications in the areas of medicine, biology, and composite materials. In order to justify the potential of oxidized C60 derivatives for bio-applications, we investigated their cytotoxicity in vitro as well as their utilization as support in biocatalysis applications, taking the immobilization of laccase for the decolorization of synthetic industrial dyes as a trial case., Peer Reviewed, Postprint (published version)

We study amorphous solid dispersions (ASDs) of the chloramphenicol antibiotic in two biodegradable polylactic acid polymers, namely a commercial sample of enantiomeric pure PLLA and a home-synthesized PDLLA copolymer, to study the effect of polylactic acid in stabilizing the amorphous form of the drug and controlling its release (e.g. for antitumoral purposes). We employ broadband dielectric spectroscopy and differential scanning calorimetry to study the homogeneity, glass transition temperature and relaxation dynamics of solvent-casted ASD membranes with different drug concentrations. We observe improved physical stability of the ASDs with respect to the pure drug, as well as a plasticizing effect of the antibiotic on the polymer, well described by the Gordon-Taylor equation. We study the release of the active pharmaceutical ingredient from the films in a simulated body fluid through UV/vis spectroscopy at two different drug concentrations (5 and 20% in weight), and find that the amount of released drug is proportional to the square root of time, with proportionality constant that is almost the same in both dispersions, despite the fact that the relaxation time and thus the viscosity of the two samples at body temperature differ by four orders of magnitude. The drug release kinetics does not display a significant dependence on the drug content in the carrier, and may thus be expected to remain roughly constant during longer release times., Peer Reviewed, Postprint (author's final draft)

We employ calorimetry, Rietveld refinement of X-ray powder diffraction, broadband dielectric spectroscopy and molecular dynamics simulations, to investigate the phase behavior, crystal structure, dc conductivity and dielectric response of the condensed phases of ethanolamine (EAM), an ethane derivative with two distinct hydrogen-bonding groups. EAM is found to exhibit, besides its stable crystal phase, a metastable crystalline phase obtained from the supercooled liquid phase. The metastable phase can only be maintained at low temperature; upon heating an irreversible exothermic transformation to the stable crystal structure takes place at 210 K, with a low transition enthalpy of ca. 2.4 J/g. The observed polymorphism is accompanied by differences in the molecular conformation and degree of structural order. Each EAM molecule participates in six H-bonds in both crystalline phases. While the stable phase is fully ordered, the metastable phase appears to be characterized by a statistical disorder in the position of the hydrogen atoms and thus of the intramolecular conformation and intermolecular hydrogen bonding. Our molecular dynamics simulations suggest that such disorder is dynamic in character, and allow analyzing the dynamic H-bonding motif of the metastable phase in terms of composition, length and energy of the H-bonds, and molecular conformations involved. Charge conduction is mainly ionic in both crystalline phases and exhibits the typical temperature dependence of disordered solid electrolytes, rather than crystalline ones. Dielectric characterization indicates that, upon crystallization of liquid EAM, a small fraction of the sample (approximately 5%) remains amorphous, a situation similar to that reported for other H-bonded systems such as glycerol and nbutanol., Postprint (author's final draft)

En este proyecto, se ha hecho un estudio del polimorfismo que presentan dos derivados de la benzofenona. El polimorfismo es la capacidad de una sustancia para cristalizar en más de una forma sólida. Para establecer los dominios de estabilidad de las diferentes formas, se ha determinado el diagrama de equilibrio presión-temperatura de ambos compuestos. Para la realización del estudio, se ha recurrido a la utilización de diferentes técnicas de análisis. Se ha utilizado la técnica de calorimetría diferencial de barrido, a fin de caracterizar térmicamente las transiciones entre fases que presentan cada uno de los compuestos; es decir, determinar la temperatura y la variación de entalpía asociadas a cada una de las transiciones. También se ha utilizado un sistema de análisis térmico diferencial en función de la presión, para obtener el diagrama presión-temperatura. Además, se ha empleado la difracción de rayos X, para caracterizar cristalográficamente las muestras y establecer la evolución del volumen específico con la temperatura. Durante el estudio, se han utilizado técnicas de purificación, como la cristalización por evaporación, y en algunos casos se ha tratado la muestra con N2. Los compuestos estudiados son dos, el 4-bromobenzofenona y el 2-bromobenzofenona. Ambos compuestos presentan dimorfismo a presión atmosférica. El compuesto 4-bromobenzofenona ha sido proporcionado por los laboratorios Aldrich con una pureza del 98%, mientras que el 2- bromobenzofenona ha sido proporcionado por el “B. Verkin Institute for Low Temperature Physics and Engineering” de Ucrania. Únicamente ha sido posible caracterizar completamente el 2-bromobenzofenona. Para el caso del 4- bromobenzofenona no se ha podido obtener el polimorfo metaestable y con ello ha sido imposible caracterizar por completo el compuesto.

We probe the dielectric response of the supercooled liquid phase of Morniflumate, a drug with anti-inflammatory and antipyretic properties, studying in particular the pressure and temperature dependence of the relaxation dynamics, glass transition temperature Tg, and recrystallization kinetics. Tg increases by roughly 20 K every 100 MPa at low applied pressure, where the ratio Tg/Tm has a constant value of ~0.8 (Tm = melting point). Liquid Morniflumate displays two dielectric relaxations: the structural a relaxation associated with the collective reorientational motions, which become arrested at Tg, and a secondary relaxation likely corresponding to an intramolecular dynamics. The relaxation times of both processes scale approximately with the inverse reduced temperature Tg/T. Near room temperature and under an applied pressure of 50 MPa, supercooled Morniflumate recrystallizes in a characteristic time of few hours, with an Avrami exponent of 1.15. Under these conditions, the recrystallization rate is a nonmonotonic function of temperature, displaying a maximum at around 298 K, which can be taken to be the optimum crystal growth temperature Tnose. The ß relaxation becomes kinetically frozen at ambient temperature under an applied hydrostatic pressure higher than 320 MPa, suggesting that the Morniflumate glass should be kinetically stable under these conditions., Peer Reviewed, Postprint (author's final draft)

We employ differential scanning calorimetry, IR spectroscopy, X-ray powder diffraction and dielectric spectroscopy to characterize binary mixtures of m-fluoroaniline (mFA), a rigid-molecule glass former, with two non-self-associating molecules containing benzene rings, namely m-xylene (mX) and a distyrene derivative (DS). The addition of mX suppresses the formation of H-bonded mFA clusters. While both mX and DS dilute the H-bond density of mFA, they have opposite effects on the glass transition temperature (Tg) and structural relaxation time of mFA, with mX acting as a plasticiser and DS as an antiplasticiser. While the mFA-DS mixtures can be studied in the supercooled liquid regime at DS molar mass fraction as high as 0.9 without undergoing phase separation, the mFA-mX mixtures remain homogeneous at low temperatures only up to a mX molar fraction of 0.5. All homogeneous mixtures display a structural relaxation which shifts according to the Tg of the mixture, and a secondary relaxation which remains virtually invariant with respect to that of pure mFA. For mX molar fraction higher than 0.5, the mixtures phase-separate into almost pure crystalline mX domains and a mFA-rich amorphous phase. Upon partial crystallization the structural relaxation time and Tg of the remaining amorphous fraction shift to larger values, consistent with the increased effective mFA concentration. At the same time, the secondary relaxation time undergoes a dramatic shift of more than two decades. These findings allow identifying the secondary relaxation in the rigid-molecule mFA glass former as a local reorientational motion of a m-fluoroaniline moiety around one of its H-bonds, a rotation that is strongly affected if the mobility of the H-bond sharing species is quenched by crystallization., Peer Reviewed, Postprint (author's final draft)