Amorphous Solid State Research Articles

Polyamorphism gets a magnetic boost

Four decades since the concept of polyamorphism was introduced by [L. S. Palatnik (1909–1994), Fiz. Nizk. Temp. 25, 400 (1909)], numerous investigations proved its presence in a broad variety of nonmagnetic short-range ordered materials, like structural, metallic, a-metallic, inorganic molecule, orientational, electron glasses, water, ice, carbons, and others. It was manifested by phase transitions between amorphous states as a function of the quench condition and under compression, mediated by long-wave fluctuations of an order parameter. There has been much recent discussion given to the phenomenon of polyamorphism where distinct, different states of amorphous liquids and solids are observed as a function of density. The outstanding contribution of the recently late [A. Sella, et al. (1956–2022), Nat. Mater. 21, 490 (2022)],2 in the field should be recognized here. Underlying this phenomenon is the possibility of a first-order liquid-liquid phase transition driven by the density and entropy differences between the two amorphous phases. Magnetic boost of multilayer graphene under pressure was also recently discovered. Their famous spin counterparts, such as spin liquid, spin ice, and spin glass have been less studied at this end despite numerous similarities, registered so far. Taking that in mind, for further polyamorphism platform development, we demonstrate the signatures of phase transition in spin glass, driven by a magnetic field, and eventually, a novel type of polyamorphism, the spin-glass one.

Colyophilized Sugar-Polymer Dispersions for Enhanced Processing and Storage Stability.

Sucrose and trehalose pharmaceutical excipients are employed to stabilize protein therapeutics in a dried state. The mechanism of therapeutic protein stabilization is dependent on the sugars being present in an amorphous solid-state. Colyophilization of sugars with high glass transition polymers, polyvinylpyrrolidone (PVP), and poly(vinylpyrrolidone vinyl acetate) (PVPVA), enhances amorphous sugar stability. This study investigates the stability of colyophilized sugar-polymer systems in the frozen solution state, dried state postlyophilization, and upon exposure to elevated humidity. Binary systems of sucrose or trehalose with PVP or PVPVA were lyophilized with sugar/polymer ratios ranging from 2:8 to 8:2. Frozen sugar-PVPVA solutions exhibited a higher glass transition temperature of the maximally freeze-concentrated amorphous phase (Tg') compared to sugar-PVP solutions, despite the glass transition temperature (Tg) of PVPVA being lower than PVP. Tg values of all colyophilized systems were in a similar temperature range irrespective of polymer type. Greater hydrogen bonding between sugars and PVP and the lower hygroscopicity of PVPVA influenced polymer antiplasticization effects and the plasticization effects of residual water. Plasticization due to water sorption was investigated in a dynamic vapor sorption humidity ramping experiment. Lyophilized sucrose systems exhibited increased amorphous stability compared to trehalose upon exposure to the humidity. Recrystallization of trehalose was observed and stabilized by polymer addition. Lower concentrations of PVP inhibited trehalose recrystallization compared to PVPVA. These stabilizing effects were attributed to the increased hydrogen bonding between trehalose and PVP compared to trehalose and PVPVA. Overall, the study demonstrated how differences in polymer hygroscopicity and hydrogen bonding with sugars influence the stability of colyophilized amorphous dispersions. These insights into excipient solid-state stability are relevant to the development of stabilized biopharmaceutical solid-state formulations.

Nanosilica from canary seed husk for corrosion protection of structural steel

AbstractAn alternative technique is presented for the corrosion protection of the A36 structural steel (A36SS) in acid medium (H2SO4) using silica obtained from canary seed husk (CSH). The silica was obtained in a solid amorphous state with a particle size of 10–22 nm. The anticorrosive properties of nanosilica (NS) were studied using potentiodynamic polarization (PDP), linear polarization resistance (LPR), and electrochemical impedance spectroscopy (EIS). Before carrying out the corrosion tests, the A36SS was subjected to a treatment with NaOH solution without and with the presence of NS. The A36SS treated with NS presented the lowest current density values and the noblest corrosion potential values, indicating that the corrosion rate decreased. The surface morphological study of the tested systems using SEM/EDS showed that the NS‐treated A36SS had a more efficient physical barrier against corrosive species.

Simulated phase state and viscosity of secondary organic aerosols over China

Abstract. Secondary organic aerosols (SOAs) can exist in liquid, semi-solid, or amorphous solid states. Chemical transport models (CTMs), however, usually assume that SOA particles are homogeneous and well-mixed liquids, with rapid establishment of gas–particle equilibrium for simulations of SOA formation and partitioning. Missing the information of SOA phase state and viscosity in CTMs impedes accurate representation of SOA formation and evolution, affecting the predictions of aerosol effects on air quality and climate. We have previously developed a parameterization to estimate the glass transition temperature (Tg) of an organic compound based on volatility and to predict viscosity of SOA. In this study, we apply this method to predict the phase state of SOA particles over China in summer of 2018 using the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem). The simulated Tg of dry SOA (Tg,org) agrees well with the value estimated from ambient volatility measurements at an urban site in Beijing. For the spatial distributions of Tg,org, simulations show that at the surface the values of Tg,org range from ∼287 to 305 K, with higher values in northwestern China, where SOA particles have larger mass fractions of low-volatility compounds. Considering water uptake by SOA particles, the SOA viscosity shows a prominent geospatial gradient in which highly viscous or solid SOA particles are mainly predicted in northwestern China. The lowest and highest SOA viscosity values both occur over the Qinghai–Tibet Plateau, where the solid phase state is predicted over dry and high-altitude areas and the liquid phase state is predicted mainly in the south of the plateau with high relative humidity during the summer monsoon season. Sensitivity simulations show that, including the formation of extremely low-volatility organic compounds, the percent time that a SOA particle is in the liquid phase state decreases by up to 12 % in southeastern China during the simulated period. With an assumption that the organic and inorganic compounds are internally mixed in one phase, we show that the water absorbed by inorganic species can significantly lower the simulated viscosity over southeastern China. This indicates that constraining the uncertainties in simulated SOA volatility distributions and the mixing state of the organic and inorganic compounds would improve prediction of viscosity in multicomponent particles in southeastern China. We also calculate the characteristic mixing timescale of organic molecules in 200 m SOA particles to evaluate kinetic limitations in SOA partitioning. Calculations show that during the simulated period the percent time of the mixing timescale longer than 1 h is >70 % at the surface and at 500 hPa in most areas of northern China, indicating that kinetic partitioning considering the bulk diffusion in viscous particles may be required for more accurate prediction of SOA mass concentrations and size distributions over these areas.

Influence of Zr aggregation on Li-ion conductivity of amorphous solid-state electrolyte Li-La-Zr-O.

In our study, we investigated the influence of the local structure of amorphous Li-La-Zr-O (a-LLZO) on Li-ion conductivity using abinitio molecular dynamics (AIMD). A-LLZO has shown promising properties in inhibiting the growth of lithium dendrites, making it a potential candidate for solid electrolytes in all-solid-state lithium batteries. The low Li-ion conductivity of a-LLZO is currently limiting its practical applications. Our findings revealed that the homogeneous distribution of Zr-O polyhedra within the pristine structure of a-LLZO contributes to enhanced Li-ion conductivity. By reducing the interconnections among Zr-O polyhedra, the AIMD-simulated a-LLZO sample achieved a Li-ion conductivity of 5.78 × 10-4 S/cm at room temperature, which is slightly lower than that of cubic LLZO (c-LLZO) with a Li-ion conductivity of 1.63 × 10-3 S/cm. Furthermore, we discovered that Li-ion conductivity can be influenced by adjusting the elemental ratios within a-LLZO. This suggests that fine-tuning the composition of a-LLZO can potentially further enhance its Li-ion conductivity and optimize its performance as a solid electrolyte in lithium batteries.

Liquid-like clusters in glassy solids as a unique state of matter: Dissipative but non-diffusive

The field of glassy studies has long speculated about the existence of liquid-like regions within solid amorphous states. However, limited evidence from indirect investigations has left the question of their presence unanswered. In this study, we propose a computational approach to analyze dissipation characteristics at the atomic level. Our findings reveal the actual existence of localized liquid-like dissipation clusters in the glassy state, demonstrating a damping factor similar to liquids and a vanishing shear modulus. Surprisingly, these clusters are only observed at low temperatures and do not involve diffusive motions, unlike typical liquids. This unique state of condensed matter is dissipative but non-diffusive. In metallic glasses, we show that these clusters are responsible for the recently discovered β' relaxation. Our results provide a solid basis for the longstanding concept of liquid-like region in glassy materials and provide a new perspective on establishing structure-property correlations.

Hydrogen bonding in glassy trehalose-water system: Insights from density functional theory and molecular dynamics simulations.

We report a detailed density functional theory and molecular dynamics study of hydrogen bonding between trehalose and water, with a special emphasis on interactions in the amorphous solid state. For comparison, water-water interactions in water dimers and tetramers are evaluated using quantum calculations. The results show that the hydrogen bonding energy is dependent not only on the geometry (bond length and angle) but also on the local environment of the hydrogen bond. This is seen in quantum calculations of complexes in vacuum as well as in amorphous solid states with periodic boundary conditions. The temperature-induced glass transition in the trehalose-water system was studied using molecular dynamics simulations with varying cooling and heating rates. The obtained parameters of the glass transition are in good agreement with the experiments. Moreover, the dehydration of trehalose in the glassy state was investigated through a gradual dehydration with multiple small steps under isothermal conditions. From these simulations, the values of water sorption energy at different temperatures were obtained. The partial molar enthalpy of mixing of water value of -18 kJ/mol found in calorimetric experiments was accurately reproduced in these simulations. These findings are discussed in light of the hydrogen bonding data in the system. We conclude that the observed exothermic effect is due to different responses of liquid and glassy matrices to perturbations associated with the addition or removal of water molecules.

Creating equilibrium glassy states via random particle bonding

Creating amorphous solid states by randomly bonding an ensemble of dense liquid monomers is a common procedure that is used to create a variety of materials, such as epoxy resins, colloidal gels, and vitrimers. However, the properties of the resulting solid do a priori strongly depend on the preparation history. This can lead to substantial aging of the material; for example, properties such as mechanical moduli and transport coefficients rely on the time elapsed since solidification, which can lead to a slow degradation of the material in technological applications. It is therefore important to understand under which conditions random monomer bonding can lead to stable solid states, that is, long-lived metastable states whose properties do not change over time. This work presents a theoretical and computational analysis of this problem and introduces a random bonding procedure that ensures the proper equilibration of the resulting amorphous states. Our procedure also provides a new route to investigate the fundamental properties of glassy energy landscapes by producing translationally invariant ultrastable glassy states in simple particle models.

Surface tension of metallic glass forming liquid nanoparticles

We report the surface tension γ of Cu64Zr36 metallic glass liquid nanoparticles calculated using molecular dynamics simulation. We carried out a systematic investigation to obtain the dependence of γ on particle size and temperature. The values of γ are between 0.85 and 1.25 N/m, with a negative coefficient of temperature dependence that covers both the liquid and (amorphous) solid state. The particle size dependence is extracted through the Tolman length δ, which takes the values between 0.53 and 0.83 Å. The surface tension is influenced by temperature, sphere size, and surface chemical segregation.

A Coformer Approach for Supramolecular Polymerization at High Concentrations.

Insolubility of functional molecules caused by polymorphism sometimes poses limitations for their solution-based processing. Such a situation can also occur in the preparation processes of supramolecular polymers formed in a solution. An effective strategy to address this issue is to prepare amorphous solid states by introducing a "coformer" molecule capable of inhibiting the formation of an insoluble polymorph through co-aggregation. Herein, inspired by the coformer approach, we demonstrated a solubility enhancement of a barbiturate π-conjugated compound that can supramolecularly polymerize through six-membered hydrogen-bonded rosettes. Our newly synthesized supramolecular coformer molecule features a sterically demanding methyl group in the π-conjugated unit of the parent molecule. Although the parent molecule exhibits low solubility in nonpolar solvents due to the formation of a crystalline polymorph comprising a tape-like hydrogen-bonded array prior to the supramolecular polymerization, mixing with the coformer compound enhanced the solubility by inhibiting mesoscopic organization of the tapes. The two monomers were then co-polymerized into desired helicoidal supramolecular polymers through the formation of heteromeric rosettes.

A Coformer Approach for Supramolecular Polymerization at High Concentrations

AbstractInsolubility of functional molecules caused by polymorphism sometimes poses limitations for their solution‐based processing. Such a situation can also occur in the preparation processes of supramolecular polymers formed in a solution. An effective strategy to address this issue is to prepare amorphous solid states by introducing a “coformer” molecule capable of inhibiting the formation of an insoluble polymorph through co‐aggregation. Herein, inspired by the coformer approach, we demonstrated a solubility enhancement of a barbiturate π‐conjugated compound that can supramolecularly polymerize through six‐membered hydrogen‐bonded rosettes. Our newly synthesized supramolecular coformer molecule features a sterically demanding methyl group in the π‐conjugated unit of the parent molecule. Although the parent molecule exhibits low solubility in nonpolar solvents due to the formation of a crystalline polymorph comprising a tape‐like hydrogen‐bonded array prior to the supramolecular polymerization, mixing with the coformer compound enhanced the solubility by inhibiting mesoscopic organization of the tapes. The two monomers were then co‐polymerized into desired helicoidal supramolecular polymers through the formation of heteromeric rosettes.

Integration of aggregation-induced emission and intramolecular charge transfer in a V-shaped organic donor-acceptor

Coumarin, an oxadiazole, and the V-shaped structural characteristic of a sulfone have been integrated to create a new symmetric compound, and the compound was characterized. The synthesized molecule was used as an emitter and an electron transporter in three different device configurations. The sulfone units induced a V-shaped structure that weakened the π-π stacking and thus limited aggregation-induced quenching. The molecule emitted strong fluorescence in the amorphous solid state, in a membrane, and in a non-polar solvent. From thermogravimetry and differential scanning calorimetry, the compound shows good thermal stability (381 °C) and glass-transition temperature (125 °C). The solvatochromism phenomenon and electrochemical properties were investigated in detail by fluorescence spectroscopy and cyclic voltammetry. Time-dependent density functional theory calculations were performed to understand the photophysical properties. This new type of compound exhibits tunable light emission in solution, making it a versatile emitter.

Mechanical Alloying in Zeolitic Imidazolate Framework for Enhanced Photocatalytic Dye Degradation.

A ball milling approach has been performed for isostructural ZnZIF-8 and CoZIF-8 in a 1:1 molar ratio to produce the amorphous (a) solid solution state (aZn0.5Co0.5ZIF-8). It further transformed to a crystalline (c) solid solution state (cZn0.5Co0.5ZIF-8) by exposing 95% relative humidity (RH) at 25 °C for 72 h. Unique heterometal solid solution structure and high catalytic active sites of aZn0.5Co0.5ZIF-8 showed excellent photocatalytic performance for the degradation of methylene blue dye under visible light source. The catalytic efficiency of aZn0.5Co0.5ZIF-8 (97.9%) is much higher than the pristine (p) as well as the amorphous state (a) of ZnZIF-8/CoZIF-8 and cZn0.5Co0.5ZIF-8.

Release of Arabidopsis seed dormancy by cold atmospheric plasma relies on cytoplasmic glass transition

When mature Arabidopsis thaliana seeds are dormant, their germination is prevented in apparently favorable conditions. This primary dormancy can be released during seed dry storage through a process called after-ripening whose duration can last several months. To reduce this delay, cold atmospheric plasmas (CAPs) can be used as sources of reactive oxygen species (ROS) capable of inducing heterogeneous chemical reactions. While CAP are known to stimulate the germination of various seed species, the relationship between CAP treatments and the amorphous solid state of dry seeds remains unexplored. Here, we demonstrate that seed dormancy can be alleviated using a cold plasma of ambient air and that this alleviation can be amplified for seeds with high water-content (typically 30%DW) or seeds heated at 60 °C during plasma treatment. Differential scanning micro-calorimetry shows that these characteristics control the glassy/rubbery state of the seed cytoplasm. This technique indicates also that a glass transition to the rubbery state strengthens the CAP effects to alleviate seed dormancy. We propose that lower cytoplasmic viscosity can promote the oxidative signaling induced by CAP which, in turn, improves the germination process.

Theory of rigidity and numerical analysis of density of states of two-dimensional amorphous solids with dispersed frictional grains in the linear response regime.

Using the Jacobian matrix, we obtain a theoretical expression of rigidity and the density of states of two-dimensional amorphous solids consisting of frictional grains in the linear response to an infinitesimal strain, in which we ignore the dynamical friction caused by the slip processes of contact points. The theoretical rigidity agrees with that obtained by molecular dynamics simulations. We confirm that the rigidity is smoothly connected to the value in the frictionless limit. We find that there are two modes in the density of states for sufficiently small k_{T}/k_{N}, which is the ratio of the tangential to normal stiffness. Rotational modes exist at low frequencies or small eigenvalues, whereas translational modes exist at high frequencies or large eigenvalues. The location of the rotational band shifts to the high-frequency region with an increase in k_{T}/k_{N} and becomes indistinguishable from the translational band for large k_{T}/k_{N}.

High-Entropy Alloy Films

High-entropy alloy films have the same excellent properties as high-entropy alloys and can better realize the practical applications of high-entropy alloys. This paper takes the high-entropy alloy films as the object of discussion. The preparation process, microstructure, hardness, wear resistance and corrosion resistance of high-entropy alloy films are mainly discussed and the influence of nitridation, sputtering power, substrate temperature, substrate bias and other factors on the phase structure of alloy films is analyzed. High-entropy alloy films can be prepared using magnetron sputtering, laser cladding, pulsed laser deposition, detonation spraying, electrochemical deposition and other processes. High-entropy alloy films tend to form a solid solution and amorphous state, and their hardness is far higher than that of traditional films. Among them, the hardness of high-entropy alloy nitride films can reach the standard of superhard films. Wear resistance is usually proportional to hardness. Due to the corrosion-resistant elements and amorphous structure, some high-entropy alloy films have better corrosion resistance than stainless steel. High-entropy alloy films have shown profound development prospects in the fields of wear-resistant coatings for tools, corrosion protection, diffusion barrier and photothermal conversion coatings.

Characterization of precursor sols for preparation of silica based nanofibers

Objective of this study was to prepare and characterize electrospun silica-based nanofibers. The goal of this research was to create amorphous to semicrystalline nanofiber mats, which are easily modifiable and usable in electrochemical applications such as separators or electrodes in amorphous glass solid state batteries. We investigated stability and workability of precursor TEOS based sols, effect of sol ageing on fibre morphology and effect of modification on sol workability and spinnability. Sol-gel reaction mechanism and speed was investigated by liquid state 29Si NMR spectroscopy.

Brittle yielding in supercooled liquids below the critical temperature of mode coupling theory.

Molecular dynamics computer simulations of a polydisperse soft-sphere model under shear are presented. The starting point for these simulations are deeply supercooled samples far below the critical temperature, Tc, of mode coupling theory. These samples are fully equilibrated with the aid of the swap Monte Carlo technique. For states below Tc, we identify a lifetime τlt that measures the time scale on which the system can be considered as an amorphous solid. The temperature dependence of τlt can be well described by an Arrhenius law. The existence of transient amorphous solid states below Tc is associated with the possibility of brittle yielding, as manifested by a sharp stress drop in the stress-strain relation and shear banding. We show that brittle yielding requires, on the one hand, low shear rates and, on the other hand, the time scale corresponding to the inverse shear rate has to be smaller or of the order of τlt. Both conditions can only be met for a large lifetime τlt, i.e., for states far below Tc.

Cage-Confinement Induced Emission Enhancement.

As a proof-of-concept study, Imi-cage and Phos-cage organic molecular cages (OMCs) containing the triphenylphosphine (TPP) moiety, a nonclassic AIE luminogen (AIEgen), have been designed to demonstrate the cage-confinement induced emission enhancement (CCIEE). Thanks to the confinement effect of OMCs, the rigid Imi-cage exhibits much higher photoluminescence (PL) quantum yield (ΦPL) than the open-shell Semicage and small molecule TPP in both solution and amorphous solid states. The emission of Phos-cage could be further enhanced in crystalline solid state with a remarkably high ΦPL of 97.6% (vs 3.47% of crystalline TPP) benefiting from AIE enabled by the highly ordered molecular packing. The novel strategy of CCIEE via confining an AIEgen into an OMC to achieve a significant emission enhancement will shed light on the development of solid-state highly fluorescent materials. The fluorescent nature of Imi-cage was further exploited for the ultrahighly sensitive detection of the explosive picric acid.

TSDC and DSC Investigation on the Molecular Mobility in the Amorphous Solid State and in the Glass Transformation Region of Two Benzodiazepine Derivatives: Diazepam and Nordazepam

In this work we study the molecular mobility in the amorphous solid state and in the glass transformation region of two compounds, diazepam and nordazepam; these are two benzodiazepines, a family of psychotropic drugs with sedative, anxiolytic and muscle-relaxing properties. The experimental techniques used are thermostimulated currents (TSC) and differential scanning calorimetry (DSC). TSC is a time-dependent technique recognized for its high resolving power; the use of this technique in the depolarization and polarization modes (TSDC and TSPC respectively), provides results that confirm and complement results of dielectric relaxation spectroscopy (DRS) published recently. On the other hand, the variation with the heating rate of the temperature position of the DSC glass transition signal also allowed the estimation of the activation energy at Tg and of the dynamic fragility of the two glass formers.