Ultrastable glasses : new perspectives for an old problem

Altres ajuts: the ICN2 was funded by the CERCA programme / Generalitat de Catalunya.Ultrastable glasses (mostly prepared from the vapor phase under optimized deposition conditions) represent a unique class of materials with low enthalpies and high kinetic stabilities. These highly stable and dense glasses show unique physicochemical properties, such as high thermal stability, improved mechanical properties or anomalous transitions into the supercooled liquid, offering unprecedented opportunities to understand many aspects of the glassy state. Their improved properties with respect to liquid-cooled glasses also open new prospects to their use in applications where liquid-cooled glasses failed or where not considered as usable materials. In this review article we summarize the state of the art of vapor-deposited (and other) ultrastable glasses with a focus on the mechanism of equilibration, the transformation to the liquid state and the low temperature properties. The review contains information on organic, metallic, polymeric and chalcogenide glasses and an updated list with relevant properties of all materials known today to form a stable glass

Acoustic-like dynamics of amorphous drugs in the THz regime

The high frequency dynamics of Indomethacin and Celecoxib glasses has been investigated by inelastic x-ray scattering, accessing a momentum-energy region still unexplored in amorphous pharmaceuticals. We find evidence of phonon-like acoustic dynamics, and determine the THz behavior of sound velocity and acoustic attenuation. Connections with ordinary sound propagation are discussed, along with the relation between fast and slow degrees of freedom as represented by non-ergodicity factor and kinetic fragility, respectively

Ultrastable glasses portray similar behaviour to ordinary glasses at high pressure

Pressure experiments provide a unique opportunity to unravel new insights into glass-forming liquids by exploring its effect on the dynamics of viscous liquids and on the evolution of the glass transition temperature. Here we compare the pressure dependence of the onset of devitrification, Ton, between two molecular glasses prepared from the same material but with extremely different ambient-pressure kinetic and thermodynamic stabilities. Our data clearly reveal that, while both glasses exhibit different dTon/dP values at low pressures, they evolve towards closer calorimetric devitrification temperature and pressure dependence as pressure increases. We tentatively interpret these results from the different densities of the starting materials at room temperature and pressure. Our data shows that at the probed pressures, the relaxation time of the glass into the supercooled liquid is determined by temperature and pressure similarly to the behaviour of liquids, but using stability-dependent parametersPostprint (published version

Relaxation dynamics of glasses along a wide stability and temperature range

While lots of measurements describe the relaxation dynamics of the liquid state, experimental data of the glass dynamics at high temperatures are much scarcer. We use ultrafast scanning calorimetry to expand the timescales of the glass to much shorter values than previously achieved. Our data show that the relaxation time of glasses follows a super-Arrhenius behaviour in the high-Temperature regime above the conventional devitrification temperature heating at 10 K/min. The liquid and glass states can be described by a common VFT-like expression that solely depends on temperature and limiting fictive temperature. We apply this common description to nearly-isotropic glasses of indomethacin, toluene and to recent data on metallic glasses. We also show that the dynamics of indomethacin glasses obey density scaling laws originally derived for the liquid. This work provides a strong connection between the dynamics of the equilibrium supercooled liquid and non-equilibrium glassy states

Calorimetric study of vapour deposited glasses : beyond conventional stability and temperature limits /

La deposición de capas a partir de la fase vapor se ha convertido recientemente en una herramienta muy potente de cara a la fabricación de vidrios de una estabilidad sin precedentes. Los vidrios depositados a partir de la fase vapor pueden tener propiedades seleccionadas a medida, simplemente ajustando las condiciones de deposición. En particular, los vidrios de máxima estabilidad se obtienen cuando la temperatura del substrato se encuentra alrededor de 0.85Tg. Por otra parte, la nanocalorimetría a altas velocidades de escaneo ha demostrado ser una herramienta muy útil para la caracterización térmica de la transición vítrea, a temperaturas muy superiores a las exploradas habitualmente. Es esta tesis presentamos un estudio detallado de diferentes aspectos de la transición vítrea en vidrios orgánicos de Indometacina y Celecoxib depositados a partir de la fase vapor. El estudio se ha realizado mediante el uso de diferentes técnicas calorimétricas, desde calorimetría convencional, a nanocalorimetría a alta velocidad de escaneo e incluyendo calorimetría a alta presión. Los vidrios estables producidos a partir de la fase vapor exhiben un mecanismo de transformación diferente a los vidrios obtenidos de forma convencional por enfriamiento rápido del líquido. Mientras que estos últimos se transforman de forma homogénea en todo el volumen, la transformación de los vidrios estables se produce a partir de un frente paralelo que comienza en la y se propaga hacia el interior de la muestra. A partir normalizar los datos considerando la superficie de la muestra ha sido posible identificar este mecanismo de transformación así como medir la velocidad del frente de propagación. Tanto la orientación molecular como la estabilidad termodinámica del vidrio parecen influir en la velocidad de transformación. Vidrios con destacada birefringencia y baja estabilidad presentan velocidades de transformación más altas. Una vez el frente de transformación ha avanzado una cierta distancia el mecanismo de transformación homogéneo se activa y pasa a dominar el ritmo al que se transforma el vidrio. El análisis de muestras más gruesas que esta distancia de cruce permite estudiar la dinámica de la transformación homogénea en volumen. Hemos visto que la evolución del tiempo de relajación en función de la temperatura sigue una dependencia de tipo super-Arrhenius. Esta nueva expresión describe de forma satisfactoria la dinámica del líquido sobreenfriado y de vidrios de diferente estabilidad de forma simultánea. Esta visión unificada de vidrios y líquido puede ayudar a entender la conexión entre las propiedades dinámicas y termodinámicas del vidrio. Hemos medido también la variación del inicio de la transformación en vidrios de diferente estabilidad en función de la presión hidrostática. Hemos visto que la temperatura de transformación tiende a un valor común, independientemente de la estabilidad del vidrio, mostrando un escenario en el que tanto el vidrio ultra estable como los vidrios convencionales se transformarían a la misma temperatura. Dado que la cristalización del sistema amorfo sigue siendo el mayor impedimento para la implementación completa de los vidrios en la industria farmacéutica, hemos analizado si la elevada estabilidad de los vidrios depositados en fase vapor podía ser relevante en este sentido. Hemos visto que los cristales crecen un 30% más lento en la superficie de los vidrios ultra estables. También hemos analizado la influencia de la estabilidad del vidrio en la absorción del agua, la cual puede inducir la cristalización del sistema, entre otros efectos no deseados. En este trabajo mostramos que la cantidad de agua absorbida por el vidrio depende de la estabilidad del mismo, alcanzando valores insignificantes en el caso de los vidrios ultra estables. El empaquetamiento compacto y la reducción de enlaces de hidrógeno disponibles en este tipo de vidrios podrían ser las causas de este comportamiento.Vapour deposition has emerged as a very powerful tool to produce glasses of unprecedented stability. By tuning the deposition conditions, one can tailor the properties of the deposited glass. In particular, at substrate temperatures around 0.85Tg, the maximum stability is reached. On the other hand, fast-scanning nanocalorimetry has proven to be an extremely useful technique to evaluate different characteristics of the mechanisms behind the glass transition at temperatures much above the typically explored low temperature range. In this thesis, we present a detailed study of different aspects of the glass transition on vapour deposited organic glasses of Indomethacin and Celecoxib, by combining a variety of calorimetric techniques, from conventional to fast-scanning calorimetry, including high pressure-calorimetry. Stable glasses produced from the vapour phase exhibit a different transformation mechanism with respect to glasses obtained by cooling the liquid. While the latter transform homogeneously throughout the volume of the sample, stable glasses initiate the transformation via a parallel transformation front that starts at the surface or interfaces and propagates into the bulk. By means of an ad-hoc surface normalization procedure we are able to identify transformation fronts and measure the front velocity. This velocity can be expressed as a function of the relaxation time of the liquid, v_gr=Cτ^(-0.79), where C depends on the deposition conditions of the sample and is not temperature dependent. This expression holds at least from Tg+10 K up to Tg+75 K. Both molecular orientation and thermodynamic stability, which are determined by deposition conditions, seem to play a role in the transformation rate. In particular, glasses with strong birefringence and low stability present faster front velocities. Eventually, once the front has advance a particular distance, called cross-over length, the homogeneous transformation is triggered and dominates the transformation. By analysing glassy films thicker than the crossover length, we can study the bulk transformation dynamics. From the onset of devitrication and the width of the transformation peaks we infer the relaxation time of the glass. We have seen that the evolution of relaxation time as a function of temperature follows a super-Arrhenius dependence, similar to the VFT expression for the equilibrium alpha relaxation time of the supercooled liquid. This expression satisfactorily describes the dynamics of supercooled liquid and glasses of different stability simultaneously. This unified view of glasses and liquids may help understating the connection between the dynamic and thermodynamic characteristics of a glass. Indeed, we have shown that glasses of different stability follow density scaling relationships that were conceived to describe uniquely equilibrium liquid states. In that sense, the dynamics of liquid and glasses are influenced, in the same manner, by temperature and density uniquely. We have also measured the variation of the onset temperature of devitrification of glasses with very different stability as a function of hydrostatic pressure, finding that the devitrification temperature tends to a unique Ton value, regardless of the stability of the glass, depicting a scenario in which both ultrastable and conventional glasses transform into the liquid at very similar temperatures. Being crystallization a major drawback for the use of glasses in the pharmaceutical industry, we consider if ultrastability would somehow have a significant impact. We see that crystals grow a 30% slower on ultrastable glass surfaces. We have also analysed the influence of stability on water absorption, which may induce glass crystallization, among other undesired effects. We show that the amount of absorbed water depends on the stability of the glass, reaching an almost negligible value in the case of ultrastable glasses. The improved packing and reduction of accessible hydrogen bonds in this type of glasses could explain this behaviour

Accelerated aging in ultrathin films of a molecular glass former

We report the thermodynamic measurement of the enthalpy released during the aging of supported films of a molecular glass former, toluene, at temperatures well below the glass transition temperature. By using microfabricated devices with very short equilibration times (below 1 s), we evidence a remarkable variation of the relaxation rate on decreasing film thickness from 100 nm down to a 7 nm thick film. Our results demonstrate that surface atoms are more efficient than bulk atoms in attaining low energy configurations within the potential energy landscape

Real-time microscopic view of the relaxation of a glass

The understanding of glassy dynamics above the devitrification temperature of a glass remains poorly understood. Here, we use real-time AFM imaging to build a spatio-temporal map of the relaxation dynamics of a highly stable glass into its supercooled liquid. This new methodology enables a direct visualization of the progression of the liquid phase and clarifies and quantifies the presence of localized fast mobility regions separated by giant length scales. Our data permit to establish a clear correlation between dynamic length and time scales in glasses. This approach may also be applicable to unveil the microscopic structure and dynamics of other glass forming systems with much shorter length and time scales, including liquid-cooled glasses

Differential cross section measurements for the production of a W boson in association with jets in proton–proton collisions at √s = 7 TeV

Measurements are reported of differential cross sections for the production of a W boson, which decays into a muon and a neutrino, in association with jets, as a function of several variables, including the transverse momenta (pT) and pseudorapidities of the four leading jets, the scalar sum of jet transverse momenta (HT), and the difference in azimuthal angle between the directions of each jet and the muon. The data sample of pp collisions at a centre-of-mass energy of 7 TeV was collected with the CMS detector at the LHC and corresponds to an integrated luminosity of 5.0 fb[superscript −1]. The measured cross sections are compared to predictions from Monte Carlo generators, MadGraph + pythia and sherpa, and to next-to-leading-order calculations from BlackHat + sherpa. The differential cross sections are found to be in agreement with the predictions, apart from the pT distributions of the leading jets at high pT values, the distributions of the HT at high-HT and low jet multiplicity, and the distribution of the difference in azimuthal angle between the leading jet and the muon at low values.United States. Dept. of EnergyNational Science Foundation (U.S.)Alfred P. Sloan Foundatio

Juxtaposing BTE and ATE – on the role of the European insurance industry in funding civil litigation

One of the ways in which legal services are financed, and indeed shaped, is through private insurance arrangement. Two contrasting types of legal expenses insurance contracts (LEI) seem to dominate in Europe: before the event (BTE) and after the event (ATE) legal expenses insurance. Notwithstanding institutional differences between different legal systems, BTE and ATE insurance arrangements may be instrumental if government policy is geared towards strengthening a market-oriented system of financing access to justice for individuals and business. At the same time, emphasizing the role of a private industry as a keeper of the gates to justice raises issues of accountability and transparency, not readily reconcilable with demands of competition. Moreover, multiple actors (clients, lawyers, courts, insurers) are involved, causing behavioural dynamics which are not easily predicted or influenced. Against this background, this paper looks into BTE and ATE arrangements by analysing the particularities of BTE and ATE arrangements currently available in some European jurisdictions and by painting a picture of their respective markets and legal contexts. This allows for some reflection on the performance of BTE and ATE providers as both financiers and keepers. Two issues emerge from the analysis that are worthy of some further reflection. Firstly, there is the problematic long-term sustainability of some ATE products. Secondly, the challenges faced by policymakers that would like to nudge consumers into voluntarily taking out BTE LEI