Equilibration Mechanism Research Articles

Physical aging of selenium glass: Assessing the double mechanism of equilibration and the crystallization process

This work focuses on the study of the physical aging of a selenium glass by differential scanning calorimetry (DSC) and fast scanning calorimetry (FSC). Aged samples of 30 and 40 years old at room temperature were analysed by classical DSC, and their enthalpies of recovery were calculated, showing that the glass has reached its thermodynamic equilibrium and is stable over time. The study of accelerated physical aging by using FSC on a rejuvenated sample allows reproducing the way by which this glass has reached its thermodynamic equilibrium at the laboratory time scale. We evidence that the glass reaches its equilibrium state in one or two steps, depending on the gap between the aging temperature and the glass transition temperature, resulting from the difference in the mechanisms governing the relaxation process. Furthermore, a second phenomenon is evidenced, consisting in the crystallization of the glass once the equilibrium has been reached for aging temperatures close to the glass transition temperature.

Physical Aging Behavior of a Glassy Polyether.

The present work aims to provide insights on recent findings indicating the presence of multiple equilibration mechanisms in physical aging of glasses. To this aim, we have investigated a glass forming polyether, poly(1-4 cyclohexane di-methanol) (PCDM), by following the evolution of the enthalpic state during physical aging by fast scanning calorimetry (FSC). The main results of our study indicate that physical aging persists at temperatures way below the glass transition temperature and, in a narrow temperature range, is characterized by a two steps evolution of the enthalpic state. Altogether, our results indicate that the simple old-standing view of physical aging as triggered by the relaxation does not hold true when aging is carried out deep in the glassy state.

Using Deposition Rate and Substrate Temperature to Manipulate Liquid Crystal-Like Order in a Vapor-Deposited Hexagonal Columnar Glass.

We investigate vapor-deposited glasses of a phenanthroperylene ester, known to form an equilibrium hexagonal columnar phase, and show that liquid crystal-like order can be manipulated by the choice of deposition rate and substrate temperature during deposition. We find that rate-temperature superposition (RTS)-the equivalence of lowering the deposition rate and increasing the substrate temperature-can be used to predict and control the molecular orientation in vapor-deposited glasses over a wide range of substrate temperatures (0.75-1.0 Tg). This work extends RTS to a new structural motif, hexagonal columnar liquid crystal order, which is being explored for organic electronic applications. By several metrics, including the apparent average face-to-face nearest-neighbor distance, physical vapor deposition (PVD) glasses of the phenanthroperylene ester are as ordered as the glass prepared by cooling the equilibrium liquid crystal. By other measures, the PVD glasses are less ordered than the cooled liquid crystal. We explain the difference in the maximum attainable order with the existence of a gradient in molecular mobility at the free surface of a liquid crystal and its impact upon different mechanisms of structural rearrangement. This free surface equilibration mechanism explains the success of the RTS principle and provides guidance regarding the types of order most readily enhanced by vapor deposition. This work extends the applicability of RTS to include molecular systems with a diverse range of higher-order liquid-crystalline morphologies that could be useful for new organic electronic applications.

Self-discharge study of lignin/graphite hybrid material electrodes

Lignin has been proposed as electricity storage materials due to the redox activity of quinone (Q) and hydroquinone (QH2) groups, which can be formed in lignin. Scalable and low-cost lignosulfonate (LS)/graphite hybrid material electrodes have been developed. It is important to investigate the self-discharge mechanism for these electrodes since a high self-discharge rate was observed, which results in loss of energy density and power density. In this work, self-discharge measurements and models are applied to clarify the self-discharge mechanism of the LS/graphite electrodes. A combination of diffusion controlled, activation controlled and charge equilibration mechanisms are indicated during the self-discharge process at different charging voltages, due to the faradaic reactions of the Q/QH2 confined in the electrodes. Our work contributes deeper understanding of the structure and the self-discharge mechanisms of the biopolymer/graphite hybrid electrodes.

Physical aging of polystyrene blocks under three‐dimensional soft confinement in PS‐b‐poly(n‐butyl methacrylate) diblock copolymer: Two equilibrations on the way

AbstractPolystyrene‐block‐poly(n‐butyl methacrylate) (PS‐b‐PnBMA) was used to investigate three‐dimensional (3D) soft confinement effect on physical aging of the PS block therein. The soft confinement is constructed by phase‐separated PnBMA domains, as PnBMA is liquid on the aging temperatures of PS blocks due to its low glass transition temperature. In enthalpy recovery, aging response of PS blocks is represented by a low and broad heat capacity peak associated with an enhanced aging rate with respect to homo‐PS, when the aging temperature is relatively low. However, the aging response exhibits opposite characteristics at relatively high temperatures, compared with the results of homo‐PS. The phase‐separated morphology and thus the soft confinement on PS blocks was confirmed by atomic force microscope imaging using the Peak Force quantitative nanomechanical mapping (QNM) technique. Two local maximums of recovered enthalpy versus aging temperature indicate that two equilibration processes exist during aging of confined PS blocks, within a substantially shorter timescale to the bulk. The 3D soft confinement effect on aging of PS blocks is attributed to dual equilibration mechanisms: one dominates at higher aging temperatures, leading to a restrained aging rate, while the other plays a key role at lower aging temperatures, resulting in accelerated physical aging.

On the fate of impact-delivered metal in a terrestrial magma ocean

Impacts on Earth crucially influenced core formation and the subsequent evolution of Earth's mantle and may have contributed to late accretion of material. However, to what extent the present-day geochemical signature of Earth's mantle reflects the processes of core formation and late accretion, and how much of material delivered by giant impacts and by impacts of smaller projectiles during late accretion was incorporated into the core remains unclear. To improve the insight into these processes, it is of key importance to comprehend how impact-delivered metal droplets are dispersed and subsequently settle in a terrestrial magma ocean. Settling and mixing are potentially strongly influenced by the convective and rotational state of the magma ocean.Therefore, by means of numerical experiments in spherical geometry, we study how the convective state of the magma ocean and the potentially strong planetary rotation affect the settling of impact-delivered material in a deep global magma ocean. We reveal crucial differences in metal dispersion and in settling history depending on the impactor's target latitude. For an impact at either pole, the metal dispersion within the magma ocean is spatially limited while the metal droplets settle fast. Impacts at lower latitudes allow for a higher degree of dispersion, being accompanied by a slower metal settling. Consequently, metal-silicate equilibration may differ depending on the target latitude, being limited to certain localized domains of the magma ocean. We further demonstrate that the volume fraction undergoing metal-silicate equilibration seems to depend linearly on the impactor's diameter and may be largely underestimated in previous studies. Overall, we present a possible mechanism for heterogeneous metal-silicate equilibration and the generation of chemical heterogeneities and isotopic anomalies in Earth's mantle due to the influence of planetary rotation, potentially shaping the geochemical signatures that are observed today.

Plasma activation of N2, CH4 and CO2: an assessment of the vibrational non-equilibrium time window

Vibrational excitation potentially enhances the energy efficiency of plasma dissociation of stable molecules and may open new routes for energy storage and process electrification. Electron, vibrational and rotational temperatures were measured by in situ Thomson and Raman scattering in order to assess the opportunities and limitations of the essential vibration-translation non-equilibria in N2, CO2 and CH4 plasma. Electron temperatures of 1.1–2.8 eV were measured in N2 and CH4. These are used to confirm predominant energy transfer to vibrations after an initial phase of significant electronic excitation and ionization. The vibrational temperatures initially exceed rotational temperatures by almost 8000 K in N2, by 900 K in CO2, and by 300 K in CH4. Equilibration is observed at the 0.1 ms timescale. Based on the vibrational temperatures, the vibrational loss rates for different channels are estimated. In N2, vibrational quenching via N atoms is identified as the dominant equilibration mechanism. Atomic nitrogen population reaches a mole fraction of more than 1%, as inferred from the afterglow emission decay, and explains a gas heating rate of 25 K μs−1. CH4 equilibration at 1200 K is predominantly caused by vibrational-translational relaxation in CH4–CH4 collisions. As for CO2, vibrational-translational relaxation via parent molecules is responsible for a large fraction of the observed heating, whereas product-mediated VT relaxation is not significantly contributing. It is suggested that electronic excitation, followed by dissociation or quenching contributes to the remaining heat generation. In conclusion, the time window to profit from vibrational excitation under the present conditions is limiting practical application.

Diffusive scaling of the Kob–Andersen model in ${\mathbb{Z}}^{d}$

On considère le modèle de Kob–Andersen (KA), un modèle de particules sur réseau avec dynamique conservative et contraintes cinétiques. KA a été étudié en profondeur dans la literature physique en relation avec l’étude de la transition liquide/verre. On étudie le modèle dans une boite finie de taille $L$ avec un réservoir de particules aux bords. Notre résultat, qui est valable en toute dimension et qui améliore d’une façon très significative les résultats précédents, établit que pour toute densité de sites vides $q$ telle que $q>0$, le temps de relaxation du système, $T_{\mathrm{rel}}(q;L)$, est purement diffusif. De plus, on établit des bornes supérieures et inférieures pour $L^{-2}T_{\mathrm{rel}}(q;L)$ qui sont en accord avec l’heuristique des physiciens selon laquelle, quand $q\downarrow0$, le mécanisme dominant de relaxation est un mouvement coopératif de grandes et rares gouttelettes formées par des sites vides. Nos outils principaux mélangent : un ensemble de techniques et idées developpées pour établir les résultats d’universalité pour les modèles de spin avec contraintes cinétiques ; des méthodes developpeés en percolation bootstrap ; des méthodes developpées en percolation dirigée ; et la technique de chemins canoniques pour les chaînes de Markov.

Revealing the excitation energy transfer network of Light-Harvesting Complex II by a phenomenological analysis of two-dimensional electronic spectra at 77 K.

Energy equilibration in light-harvesting antenna systems normally occurs before energy is transferred to a reaction center. The equilibration mechanism is a characteristic of the excitation energy transfer (EET) network of the antenna. Characterizing this network is crucial in understanding the first step of photosynthesis. We present our phenomenology-based analysis procedure and results in obtaining the excitonic energy levels, spectral linewidths, and transfer-rate matrix of Light-Harvesting Complex II directly from its 2D electronic spectra recorded at 77 K with waiting times between 100 fs to 100 ps. Due to the restriction of the models and complexity of the system, a unique EET network cannot be constructed. Nevertheless, a recurring pattern of energy transfer with very similar overall time scales between spectral components (excitons) is consistently obtained. The models identify a "bottleneck" state in the 664-668 nm region although with a relatively shorter lifetime (∼4-6 ps) of this state compared to previous studies. The model also determines three terminal exciton states at 675, 677-678, and 680-681 nm that are weakly coupled to each other. The excitation energy equilibration between the three termini is found to be independent of the initial excitation conditions, which is a crucial design for the light-harvesting complexes to ensure the energy flow under different light conditions and avoid excitation trapping. We proposed two EET schemes with tentative pigment assignments based on the interpretation of the modeling results together with previous structure-based calculations and spectroscopic observables.

Charge regulation radically modifies electrostatics in membrane stacks.

Motivated by biological membrane-containing organelles in plants and photosynthetic bacteria, we study charge regulation in a model membrane stack. Considering (de)protonation as the simplest mechanism of charge equilibration between the membranes and with the bathing environment, we uncover a symmetry-broken charge state in the stack with a quasiperiodic effective charge sequence. In the case of a monovalent bathing salt solution our model predicts complex, inhomogeneous charge equilibria depending on the strength of the (de)protonation reaction, salt concentration, and membrane size. Our results shed light on the basic reorganization mechanism of thylakoid membrane stacks.

The First fm/c of Heavy-Ion Collisions

We present an introductory review of the early-time dynamics of high-energy heavy-ion collisions and the kinetics of high-temperature quantum chromodynamic matter. The equilibration mechanisms in the quark–gluon plasma uniquely reflect the nonabelian and ultrarelativistic character of the many-body system. Starting with a brief exposé of the key theoretical and experimental questions, we provide an overview of the theoretical tools employed in weak coupling studies of the early-time nonequilibrium dynamics. We highlight theoretical progress in understanding different thermalization mechanisms in weakly coupled nonabelian plasmas, and discuss their relevance in describing the approach to local thermal equilibrium during the first fm/ c of a heavy-ion collision. We also briefly discuss some important connections to the phenomenology of heavy-ion collisions.

Vapor deposition of a nonmesogen prepares highly structured organic glasses

We show that glasses with aligned smectic liquid crystal-like order can be produced by physical vapor deposition of a molecule without any equilibrium liquid crystal phases. Smectic-like order in vapor-deposited films was characterized by wide-angle X-ray scattering. A surface equilibration mechanism predicts the highly smectic-like vapor-deposited structure to be a result of significant vertical anchoring at the surface of the equilibrium liquid, and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy orientation analysis confirms this prediction. Understanding of the mechanism enables informed engineering of different levels of smectic order in vapor-deposited glasses to suit various applications. The preparation of a glass with orientational and translational order from a nonliquid crystal opens up an exciting paradigm for accessing extreme anisotropy in glassy solids.

Two Different Scenarios for the Equilibration of Polycation—Anionic Solutions at Water–Vapor Interfaces

The assembly in solution of the cationic polymer poly(diallyldimethylammonium chloride) (PDADMAC) and two different anionic surfactants, sodium lauryl ether sulfate (SLES) and sodium N-lauroyl-N-methyltaurate (SLMT), has been studied. Additionally, the adsorption of the formed complexes at the water–vapor interface have been measured to try to shed light on the complex physico-chemical behavior of these systems under conditions close to that used in commercial products. The results show that, independently of the type of surfactant, polyelectrolyte-surfactant interactions lead to the formation of kinetically trapped aggregates in solution. Such aggregates drive the solution to phase separation, even though the complexes should remain undercharged along the whole range of explored compositions. Despite the similarities in the bulk behavior, the equilibration of the interfacial layers formed upon adsorption of kinetically trapped aggregates at the water–vapor interface follows different mechanisms. This was pointed out by surface tension and interfacial dilational rheology measurements, which showed different equilibration mechanisms of the interfacial layer depending on the nature of the surfactant: (i) formation layers with intact aggregates in the PDADMAC-SLMT system, and (ii) dissociation and spreading of kinetically trapped aggregates after their incorporation at the fluid interface for the PDADMAC-SLES one. This evidences the critical impact of the chemical nature of the surfactant in the interfacial properties of these systems. It is expected that this work may contribute to the understanding of the complex interactions involved in this type of system to exploit its behavior for technological purposes.

Mechanism of macroscopic equilibration of isolated quantum systems

We discuss the approach toward equilibrium of an isolated quantum system. For a wide class of systems we argue that the time-averaged expectation value of a local operator in any initial state is bounded by the so-called deviation function, which characterizes maximal deviation from the equilibrium for all states with a given value of energy fluctuations. We provide numerical evidence that the bound is approximately saturated by the initial configurations with spatial inhomogeneities at macroscopic level. In this way the deviation function establishes an explicit connection between the macroscopically observed timescales associated with transport and properties of microscopic matrix elements. The form of the deviation function indicates that among the slowest states which saturate the bound there are also those with arbitrarily long equilibration times.

Cooperativity during Melting and Molecular Exchange in Micelles with Crystalline Cores.

Molecular exchange processes are important equilibration and transport mechanisms in both synthetic and biological self-assembled systems such as micelles, vesicles, and membranes. Still, these processes are not entirely understood, in particular the effect of crystallinity and the interplay between cooperative melting processes and chain exchange. Here we focus on a set of simple polymer micelles formed by binary mixtures of poly(ethylene oxide)-mono-n-alkyl-ethers (C_{n}-PEO5) which allows the melting point to be tuned over a wide range. We show that the melting transition is cooperative in the confined 4-5nm micellar core, whereas the exchange process is widely decoupled and unimeric in nature. As confirmed by differential scanning calorimetry, the total activation energy for ejecting a molecule out of the micellar core below the melting point is the sum of the enthalpy of fusion and the corresponding activation energy in the melt state. This suggests that a "local, single-chain melting process" preludes the molecular diffusion out of the micelle during chain exchange.

Dark matter amnesia in out-of-equilibrium scenarios

Models in which the dark matter is produced at extremely low rates from the annihilation of Standard Model particles in the early Universe allow us to explain the current dark matter relic density while easily evading the traditional experimental constraints. In scenarios where the dark matter interacts with the Standard Model via a new physics mediator, the early Universe dynamics of the dark sector can be particularly complex, as the dark matter and the mediator could be in thermal and chemical equilibrium with each other. This equilibration takes place via number-changing processes such as double Compton scattering and bremsstrahlung, whose amplitudes are cumbersome to calculate. In this paper, we show that in large regions of the parameter space, these equilibration mechanisms do not significantly affect the final dark matter relic density. In particular, for a model with a light dark photon mediator, the relic density can be reasonably estimated by considering that the dark matter is solely produced through the annihilation of Standard Model particles. This result considerably simplifies the treatment of a large class of dark matter theories, facilitating in particular the superimposition of the relic density constraints on the current and future experimental bounds.

Thermodynamic Ultrastability of a Polymer Glass Confined at the Micrometer Length Scale.

We employ fast scanning calorimetry to assess the thermodynamic state attained after a given cooling rate and the molecular mobility of glassy poly(4-tert-butylstyrene) confined at the micrometer length scale. We show that, for such a large confinement length scale, thermodynamic states with a fictive temperature (T_{f}) 80K below the polymer glass transition temperature (T_{g}) are attained, which allows to bypass the geological timescales required for bulk glasses. Access to such states is promoted by a fast mechanism of equilibration. Importantly, the tremendous T_{f} decrease takes place while the molecular mobility remains bulklike, indicating marked decoupling between vitrification kinetics and molecular mobility.

The Finite-Amplitude Evolution of Mixed Kelvin–Rossby Wave Instability and Equatorial Superrotation in a Shallow-Water Model and an Idealized GCM

Abstract An instability involving the resonant interaction of a Rossby wave and a Kelvin wave has been proposed to drive equatorial superrotation in planetary atmospheres with a substantially smaller radius or a smaller rotation rate than Earth, that is, with a large thermal Rossby number. To pursue this idea, this paper investigates the equilibration mechanism of Kelvin–Rossby instability by simulating the unforced initial-value problem in a shallow-water model and in a multilevel primitive equation model. Although the instability produces equatorward momentum fluxes in both models, only the multilevel model is found to superrotate. It is argued that the shortcoming of the shallow-water model is due to its difficulty in representing Kelvin wave breaking and dissipation, which is crucial for accelerating the flow in the tropics. In the absence of dissipation, the zonal momentum fluxed into the tropics is contained in the eddy contribution to the mass-weighted zonal wind rather than the zonal-mean zonal flow itself. In the shallow-water model, the zonal-mean zonal flow is only changed by the eddy potential vorticity flux, which is very small in our flow in the tropics and can only decelerate the flow in the absence of external vorticity stirring.

Bow Shock in Merging Cluster A520: The Edge of the Radio Halo and the Electron–Proton Equilibration Timescale

Abstract We studied the prominent bow shock in the merging galaxy cluster A520 using a deep Chandra X-ray observation and archival VLA radio data. This shock is a useful diagnostic tool, owing to its clear geometry and relatively high Mach number. At the “nose” of the shock, we measure a Mach number of . The shock becomes oblique away from the merger axis, with the Mach number falling to ≃1.6 around 30° from the nose. The electron temperature immediately behind the shock nose is consistent with that from the Rankine–Hugoniot adiabat, and is higher (at a 95% confidence) than expected for adiabatic compression of electrons followed by Coulomb electron–proton equilibration, indicating the presence of equilibration mechanisms faster than Coulomb collisions. This is similar to an earlier finding for the Bullet cluster. We also combined four archival VLA data sets to obtain a better image of the cluster’s giant radio halo at 1.4 GHz. An abrupt edge of the radio halo traces the shock front, and no emission is detected in the pre-shock region. If the radio edge were due only to adiabatic compression of relativistic electrons in pre-shock plasma, we would expect a pre-shock radio emission detectable in this radio data set; however, an interferometric artifact dominates the uncertainty, so we cannot rule this model out. Other interesting features of the radio halo include a peak at the remnant of the cool core, suggesting that the core used to have a radio minihalo, and a peak marking a possible region of high turbulence.

Mechanism of Fast Atmospheric Energetic Equilibration Following Radiative Forcing by CO2

AbstractIn energetic equilibrium, the atmosphere's net radiative divergence ( ) is balanced by sensible ( ) and latent ( ) heat fluxes, i.e., . Radiative forcing from increasing CO2 reduces , and the surface warming following an increase in CO2 is largely due to the reduction in atmospheric energy demand in and , with only a smaller surface radiative budget perturbation. With an idealized General Circulation Model, we show that the fast atmospheric adjustment at fixed surface temperature produces the required decrease in the sum of and through changes in the near‐surface temperature and specific humidity. In layers near the surface, the reduced radiative cooling forces a temperature increase that leads to a negative Planck radiative feedback and, because of the reduced surface‐atmosphere temperature difference, also to a reduction in sensible heat flux. In the free troposphere, the reduced radiative cooling leads to a weakening of the tropospheric circulation. Consequently, there is a decrease in the water flux exported from the layers near the surface, and as such in precipitation. By mass conservation, the near‐surface specific humidity increases and surface evaporation decreases until it balances the reduced export flux. Other processes can amplify or dampen the responses in and and change the partitioning between these two fluxes, but by themselves do not ensure .