Anelasticity to plasticity transition in a model two-dimensional amorphous solid

Anelasticity, as an intrinsic property of amorphous solids, plays a significant role in understanding their relaxation and deformation mechanism. However, due to the lack of long-range order in amorphous solids, the structural origin of anelasticity and its distinction from plasticity remain elusive. In this work, using frozen matrix method, we study the transition from anelasticity to plasticity in a two-dimensional model glass. Three distinct mechanical behaviors, namely,elasticity, anelasticity, and plasticity, are identified with control parameters in the amorphous solid. Through the study of finite size effects on these mechanical behaviors, it is revealed that anelasticity can be distinguished from plasticity.Anelasticity serves as an intrinsic bridge connecting the elasticity and plasticity of amorphous solids. Additionally, it is observed that anelastic events are localized, while plastic events are subextensive. The transition from anelasticity to plasticity is found to resemble the entanglement of long-range interactions between element excitations. This study sheds light on the fundamental nature of anelasticity as a key property of element excitations in amorphous solids.

Advances in the development of amorphous solid dispersions:The role of polymeric carriers

Amorphous solid dispersion(ASD)is one of the most effective approaches for delivering poorly soluble drugs.In ASDs,polymeric materials serve as the carriers in which the drugs are dispersed at the molecular level.To prepare the solid dispersions,there are many polymers with various physicochemical and thermochemical characteristics available for use in ASD formulations.Polymer selection is of great importance because it influences the stability,solubility and dissolution rates,manufacturing process,and bioavailability of the ASD.This review article provides a comprehensive overview of ASDs from the perspectives of physicochemical characteristics of polymers,formulation designs and preparation methods.Furthermore,considerations of safety and regulatory requirements along with the studies recommended for characterizing and evaluating polymeric carriers are briefly discussed.

Analysis of Low-Frequency Vibrational Modes and Particle Rearrangements in Marginally Jammed Amorphous Solid under Quasi-Static Shear

We present the numerical simulation results of a model granular assembly formed by spherical particles with tIertzian interaction subjected to a simple shear in the athermal quasi-static limit. The stress-strain curve is shown to separate into smooth, elastic branches followed by a subsequent plastic event. Mode analysis shows that the lowest-frequency vibrational mode is more localized, and eigenvalues and participation ratios of low- frequency modes exhibit similar power-law behavior as the system approaches plastic instability, indicating that the nature of plastic events in the granular system is also a saddle node bifurcation. The analysis of projection and spatial structure shows that over 75% contributions to the non-affine displacement field at a plastic instability come from the lowest-frequency mode, and the lowest-frequency mode is strongly spatially correlated with local plastic rearrangements, inferring that the lowest-frequency mode could be used as a predictor for future plastic rearrangements in the disordered system jammed marginally.

An emerging terpolymeric nanoparticle pore former as an internal recrystallization inhibitor of celecoxib in controlled release amorphous solid dispersion beads:Experimental studies and molecular dynamics analysis

Solid oral controlled release formulations feature numerous clinical advantages for drug candidates with adequate solubility and dissolution rate.However,most new chemical entities exhibit poor water solubility,and hence are exempt from such benefits.Although combining drug amorphization with controlled release formulation is promising to elevate drug solubility,like other supersaturating systems,the problem of drug recrystallization has yet to be resolved,particularly within the dosage form.Here,we explored the potential of an emerging,non-leachable terpolymer nanoparticle(TPN)pore former as an internal recrystallization inhibitor within controlled release amorphous solid dispersion(CRASD)beads comprising a poorly soluble drug(celecoxib)reservoir and insoluble polymer(ethylcellulose)membrane.Compared to conventional pore former,polyvinylpyrrolidone(PVP),TPN-containing membranes exhibited superior structural integrity,less crystal formation at the CRASD bead surface,and greater extent of celecoxib release.All-atom molecular dynamics analyses revealed that in the presence of TPN,intra-molecular bonding,crystal formation tendency,diffusion coefficient,and molecular flexibility of celecoxib were reduced,while intermolecular H-bonding was increased as compared to PVP.This work suggests that selection of a pore former that promotes prolonged molecular separation within a nanoporous controlled release membrane structure may serve as an effective strategy to enhance amorphicity preservation inside CRASD.

Molecular dynamics simulations of the Li-ion diffusion in the amorphous solid electrolyte interphase

The solid electrolyte interphase(SEI),a passivation film covering the electrode surface,is crucial to the lifetime and efficiency of the lithium-ion(Li-ion)battery.Understanding the Li-ion diffusion mechanism within possible components in the mosaic-structured SEI is an essential step to improve the Li-ion conductivity and thus the battery performance.Here,we investigate the Li-ion diffusion mechanism within three amorphous SEI components(i.e.,the inorganic inner layer,organic outer layer,and their mixture with 1:1 molar ratio)via ab initio molecular dynamic(AIMD)simulations.Our simulations show that the Li-ion diffusion coefficient in the inorganic layer is two orders of magnitude faster than that in the organic layer.Therefore,the inorganic layer makes a major contribution to the Li-ion diffusion.Furthermore,we find that the Li-ion diffusivity in the organic layer decreases slightly with the increase of the carbon chain from the methyl to ethyl owing to the steric hindrance induced by large groups.Overall,our current work unravels the Li-ion diffusion mechanism,and provides an atomic-scale insight for the understanding of the Li-ion transport in the SEI components.

Pharmaceutical amorphous solid dispersion: A review of manufacturing strategies

Amorphous solid dispersions(ASDs)are popular for enhancing the solubility and bioavailability of poorly water-soluble drugs.Various approaches have been employed to produce ASDs and novel techniques are emerging.This review provides an updated overview of manufacturing techniques for preparing ASDs.As physical stability is a critical quality attribute for ASD,the impact of formulation,equipment,and process variables,together with the downstream processing on physical stability of ASDs have been discussed.Selection strategies are proposed to identify suitable manufacturing methods,which may aid in the development of ASDs with satisfactory physical stability.

Control of amorphous solid water target morphology induced by deposition on a charged surface

Microstructured targets demonstrate an enhanced coupling of high-intensity laser pulse to a target and play an important role in laser-induced ion acceleration.Here we demonstrate an approach that enables us to control the morphology of amorphous solid water(ASW)microstructured targets,by deposition of water vapor on a charged substrate,cooled down to 100 K.The morphology of the deposited ASW structures is controlled by varying the surface charge on the substrate and the pressure of water vapor.The obtained target is structured as multiple,dense spikes,confined by the charged area on the substrate,with increased aspect ratio of up to 5:1 and having a diameter comparable with the typical spot size of the laser focused onto the target.

Complex force network in marginally and deeply jammed solids

This paper studies the force network properties of marginally and deeply jammed packings of frictionless soft particlesfrom the perspective of complex network theory. We generate zero-temperature granular packings at different pressures by minimizing the inter-particle potential energy. The force networks are constructed as nodes representing particles and links representing normal forces between the particles. Deeply jammed solids show remarkably different behavior from marginally jammed solids in their degree distribution, strength distribution, degree correlation, and clustering coefficient. Bimodal and multi-modal distributions emerge when the system enters the deep jamming region. The results also show that small and large particles can show different correlation behavior in this simple system.

The Nanoscale Density Gradient as a Structural Stabilizer for Glass Formation

The rapid cooling of a metallic liquid(ML)results in short-range order(SRO)among the atomic arrangements and a disordered structure in the resulting metallic glass(MG).These phenomena cause various possible features in the microscopic structure of the MG,presenting a puzzle about the nature of the MGs’microscopic structure beyond SRO.In this study,the nanoscale density gradient(NDG)originating from a sequential arrangement of clusters with different atomic packing densities(APDs),representing the medium-range structural heterogeneity in Zr_(60)Cu_(30)Al_(10)MG,was characterized using electron tomography(ET)combined with image simulations based on structure modeling.The coarse polyhedrons with distinct facets identified in the three-dimensional images coincide with icosahedron-like clusters and represent the spatial positions of clusters with high APDs.Rearrangements of the different clusters according to descending APD order in the glass-forming process are responsible for the NDG that stabilizes both the supercooled ML and the amorphous states and acts as a hidden rule in the transition from ML to MG.

Generalization of the Hall-Petch and inverse Hall-Petch behaviors by tuning amorphous regions in 2D solids

The strengthσ_(y)(D)of a polycrystal can decrease or increase with the grain diameter D,i.e.,the famous Hall-Petch(HP)and inverse-Hall-Petch(IHP)behaviors,respectively.However,σ_(y)(D)under thick grain boundaries(GBs)(i.e.,GB thickness l>1 particle)andσ_(y)(l)have rarely been explored.Here we measure them by systematically varying D and l of two-dimensional glass-crystal composites in simulations.We demonstrate that increasing l and decreasing D have similar effects on reducing dislocation motions and promoting GB deformations.Consequently,the classical HP-IHP behaviors ofσ_(y)(D,l=1)and our generalized HP-IHP behaviors ofσ_(y)(D,l)share similar mechanisms and can be unified asσ_(y)(AGB/Atot),where AGB/Atot is the fraction of the amorphous region.The results reveal a way to exceed the maximum strength of normal polycrystals.The generalized HP-IHP behaviors ofσ_(y)(D,l)should be similar in 2D and 3D,except that the HP effect in 3D is stronger.

Jamming in confined geometry:Criticality of the jamming transition and implications of structural relaxation in confined supercooled liquids

In marginally jammed solids confined by walls,we calculate the particle and ensemble averaged value of an order parameter,Ψ(r),as a function of the distance to the wall,r.Being a microscopic indicator of structural disorder and particle mobility in solids,Ψis by definition the response of the mean square particle displacement to the increase of temperature in the harmonic approximation and can be directly calculated from the normal modes of vibration of the zerotemperature solids.We find that,in confined jammed solids,Ψ(r)curves at different pressures can collapse onto the same master curve following a scaling function,indicating the criticality of the jamming transition.The scaling collapse suggests a diverging length scale and marginal instability at the jamming transition,which should be accessible to sophisticatedly designed experiments.Moreover,Ψ(r)is found to be significantly suppressed when approaching the wall and anisotropic in directions perpendicular and parallel to the wall.This finding can be applied to understand the r-dependence and anisotropy of the structural relaxation in confined supercooled liquids,providing another example of understanding or predicting behaviors of supercooled liquids from the perspective of the zero-temperature amorphous solids.

Non-affinity:The emergence of networks from amorphous planar graphs

The primary research of physics is to reveal the underlying law of the physical world.However,for a complex system consisting of multiple components,even if we know every details of each component,we still cannot predict the collective behavior due to the emergence phenomenon.The amorphous networks of mass points hinged by springs belong to such a complex system.Owing to the non-affinity,one of the emergence phenomena of the network,the displacements field of the internal mass points under the external load tends to be chaotic,and there is no well-established theoretical framework to describe these points’collective behavior analytically.The non-affine mechanical responses of the amorphous networks are very common,whereas the affine response is rare and it occurs only in those lattices with one site per unit cell.The network’s non-affinity prevents us from further investigating the relationship between its intrinsic properties(such as the contact number,local structure,and topological characteristics)and the mechanical behaviors.As a result,it is very complicated and difficult to predict the responses of an amorphous network to an imposed strain.Interestingly,a sort of amorphous network derived from the jammed particles is reported to have almost perfect affine mechanical behavior,in a stark contrast with the general perception.These findings may shed light on uncovering the structural factors that affect the network’s affinity.This article will give a short review of the latest advances in this area.

Towards quantitative determination of atomic structures of amorphous materials in three dimensions

Amorphous materials such as glass,polymer and amorphous alloy have broad applications ranging from daily life to extreme conditions due to their unique properties in elasticity,strength and electrical resistivity.A better understanding of atomic structure of amorphous materials will provide invaluable information for their further engineering and applications.However,experimentally determining the three-dimensional(3D)atomic structure of amorphous materials has been a long-standing problem.Due to the disordered atomic arrangement,amorphous materials do not have any translational and rotational symmetry at long-range scale.Conventional characterization methods,such as the scattering and the microscopy imaging,can only provide the statistic structural information which is averaged over the macroscopic region.The knowledge of the 3D atomic structure of amorphous materials is limited.Recently atomic resolution electron tomography(AET)has proven an increasingly powerful tool for atomic scale structural characterization without any crystalline assumptions,which opens a door to determine the 3D structure of various amorphous materials.In this review,we summarize the state-of-art characterization methods for the exploration of atomic structures of amorphous materials in the past few decades,including X-ray/neutron diffraction,nano-beam and angstrom-beam electron diffraction,fluctuation electron microscopy,high-resolution scanning/transmission electron microscopy,and atom probe tomography.From experimental data and theoretical descriptions,3D structures of various amorphous materials have been built up.Particularly,we introduce the principles and recent progress of AET,and highlight the most recent groundbreaking feat accomplished by AET,i.e.,the first experimental determination of all 3D atomic positions in a multi-component glass-forming alloy and the 3D atomic packing in amorphous solids.We also discuss the new opportunities and challenges for characterizing the chemical and structural defects in amorphous materials.

Mechanical Alloying of Co and Al Powders

1.IntroductionMechanical alloying is one of the effec-tive methods to prepare amorphous alloys[1].This method was first used by Koch etal.to prepare the Ni;Nb;amorphous alloy[2].Since then many other amorphousbinary alloys have been prepared by the

Crosslinked hydrogels--a promising class of insoluble solid molecular dispersion carriers for enhancing the delivery of poorly soluble drugs

Water-insoluble materials containing amorphous solid dispersions(ASD)are an emerging category of drug carriers which can effectively improve dissolution kinetics and kinetic solubility of poorly soluble drugs.ASDs based on water-insoluble crosslinked hydrogels have unique features in contrast to those based on conventional water-soluble and water-insoluble carriers.For example,solid molecular dispersions of poorly soluble drugs in poly(2-hydroxyethyl methacrylate)(PHEMA)can maintain a high level of supersaturation over a prolonged period of time via a feedback-controlled diffusion mechanism thus avoiding the initial surge of supersaturation followed by a sharp decline in drug concentration typically encountered with ASDs based on water-soluble polymers.The creation of both immediate-and controlled-release ASD dosage forms is also achievable with the PHEMA based hydrogels.So far,ASD systems based on glassy PHEMA have been shown to be very effective in retarding precipitation of amorphous drugs in the solid state to achieve a robust physical stability.This review summarizes recent research efforts in investigating the potential of developing crosslinked PHEMA hydrogels as a promising alternative to conventional water-soluble ASD carriers,and a related finding that the rate of supersaturation generation does affect the kinetic solubility profiles implications to hydrogel based ASDs.

Multi-color luminescence in Eu^3＋/Tb^3＋ co-doped ZnAl amorphous materials and their annealed samples

Multi-color luminescence basing on amorphous Eu^3＋/Tb^3＋ co-doped Zn-A1 hydroxides and their annealed samples were studied in detail. Results suggest that excellent red emissions due to E^u3＋ and green emissions attributed to Tb^3＋ appear under the excitation of favorable wavelength for all the as- prepared amorphous samples. Moreover, the emission intensity depends on the Eu^3＋/Tb^3＋ molar ratio. The samples annealed at 300, 500, and 700 ℃ still exhibit amorphous state, and multi-color lumi- nescence kept in the samples annealed at 300 ℃, while luminescence quenched for the samples annealed at 500 and 700 ℃. However, a broad emission ranging from 450 to 650 nm occurs in some samples annealed at 900 ℃. Further, the fluorescence decay and lifetimes for the as-prepared samples and the samples annealed at 300℃ were investigated. It is found that all the decay curves of emissions due to Tb^3＋ and Eu^3＋ present characteristic double exponential function despite their different lifetimes. The present work may be a good example for developing new multi-color even white light emitting materials.

Role of disorder in determining the vibrational properties of mass-spring networks

By introducing four fundamental types of disorders into a two-dimensional triangular lattice separately, we determine the role of each type of disorder in the vibration of the resulting mass-spring networks. We are concerned mainly with the origin of the boson peak and the connection between the boson peak and the transverse Ioffe-Regel limit. For all types of disorders, we observe the emergence of the boson peak and Ioffe-Regel limits. With increasing disorder, the boson peak frequency ωBP, transverse Ioffe-Regel frequency ω^TIR, and longitudinal Ioffe-Regel frequency wLn all decrease. We find that there are two ways for the boson peak to form： developing from and coexisting with （but remaining independent of） the transverse van Hove singularity without and with local coordination number fluctuation. In the presence of a single type of disorder, ωTR 〉 wBp, and ωTIR≈BP only when the disorder is sufficiently strong and causes spatial fluctuation of the local coordination number. Moreover, if there is no positional disorder, ωTIR ≈ωLIR. Therefore, the argument that the boson peak is equivalent to the transverse Ioffe-Regel limit is not general. Our results suggest that both local coordination number and positional disorder are necessary for the argument to hold, which is actually the case for most disordered solids such as marginally jammed solids and structural glasses. We further combine two types of disorders to cause disorder in both the local coordination number and lattice site position. The density of vibrational states of the resulting networks resembles that of marginally jammed solids well. However, the relation between the boson peak and the transverse Ioffe-Regel limit is still indefinite and condition-dependent. Therefore, the interplay between different types of disorders is complicated, and more in-depth studies are required to sort it out.

Thermodynamic Characteristic and Phase Evolution in Immiscible Cr–Mo Binary Alloys

This paper systematically reports the thermodynamic characteristic and phase evolution of immiscible Cr–Mo binary alloy during mechanical alloying（MA） process. The Cr–35Mo（in at%） powder mixture was milled at 243 and258 K, respectively, for different time. For comparative study, Cr–15Mo and Cr–62Mo powder mixtures were milled at 243 K for 18 h. Solid solution Cr（Mo） with body-centered cubic（bcc） crystal structure and amorphous Cr（Mo） alloy was obtained during MA process caused by high-energy ball milling. Based on the Miedema＇s model, the free-energy change for forming either a solid solution or an amorphous in Cr–Mo alloy system is positive but small at a temperature range between 200 and 300 K. The thermodynamical barrier for forming alloy in Cr–Mo system can be overcome when MA occurs at 243 K, and the supersaturated solid solution crystal nuclei with bcc structure form continually, and three supersaturated solid solutions of Cr–62Mo, Cr–35Mo and Cr–15Mo formed. Milling the Cr–35Mo powder mixture at 258 K, the solid solution Cr（Mo） forms firstly, and then the solid solution Cr（Mo） transforms into the amorphous Cr（Mo）alloy with a few of nanocrystallines when milling is prolonged. At higher milling temperature, it is favorable for the formation of the amorphous phase, as indicated by the thermodynamical calculation for immiscible Cr–Mo alloy system.