Symposium CM02 : Structure---Property Relations in Non-Crystalline Materials

The continuous random network (CRN), introduced by Zachariasen for oxide glasses, became the paradigm for the structure of covalent, directionally bonded amorphous materials. Elemental amorphous Si and Ge, which form one of the simplest CRNs, have been studied for more than fifty years. We will review their structure, thermodynamic properties, phase transformations, flow and structural relaxation. We will revisit some striking features, such as their density being higher than that of the diamond cubic crystal, their negative activation volumes for crystallization, and the bimolecular kinetics of their structural relaxation.

To evaluate the damage resistance of glasses, instrumented indentation using sharp indenters is the method of choice, as it can mimic real-life damage incidents under controlled conditions. Furthermore, indentation provides a useful system to study crack initiation, as unstable crack propagation is prevented by the highly localized stress state. However, unravelling the nature of structural change under indentation is a formidable task in experiment because of the complexity that originates from the atomic-scale disorder of glass, and the experimental difficulties associated with the in-situ investigation at a local scale (tens of microns) under very high stresses. To this send, computer simulations can provide an important complement to experimental approaches. In this work, we carried out large scale molecular dynamics (MD) simulations to investigate the effect of quench pressuring during hot compression and chemical composition variation on the response of glass to nanoindentation. A rigid hollow Vickers indenter made of carbon atoms is used to indent the glass sample with a fixed loading rate, during which atoms in the indenter interact with the glass via a repulsive force field. To minimize the boundary condition effects in simulated nanoindentation tests, large samples of several hundred nm in lateral dimensions are used. The indenter angle is varied to study the effect of the indenter sharpness on the deformation of glasses, as what has been done in experiments. Short- and medium-range order of the plastically deformed glass are compared with those in the undeformed region. These simulated nanoindentation tests reveal how the stress field and glass structure evolve with the deformation underneath the indenter, which in turn shed light on the degree of densification and pile-up in different glasses.

Polymer glasses are frequently used in a form of additive manufacturing called fused filament fabrication (FFF). Melts are extruded onto previous layers and form a weld before the temperature drops below the glass transition temperature. Extrusion is typically fast enough to produce significant chain alignment that affects the welds formed by diffusion between layers and leads to a strongly anisotropic amorphous structure. Improved understanding of the structure property relations in printed parts is essential to optimizing FFF for structure-critical parts and FFF offers unique opportunities to create non-crystalline materials with continuously tunable local alignment and entanglement densities.

We have used molecular dynamics simulations of a generic polymer model to examine the relaxation of aligned melts, including the evolution of alignment and the entanglement density in bulk regions and at the interfacial weld. The mechanical properties of the resulting structures are then studied under tensile and shear loading. Local structure determines the initial yield stress while entanglements lead to strain hardening and crazing that strongly affects the total fracture energy. Alignment of chains along the deposition direction means that there are more weak van der Waals bonds in the perpendicular directions. This reduces the yield strength for shear and tensile failure perpendicular to the deposition axis. Alignment and changes in entanglement density also produce profound changes in the strain to failure and ultimate fracture energy. Welded regions are most affected by diffusion during cooling and may be stronger than adjacent bulk material which has higher entanglement density than the weld but is also strongly aligned.

Slowly strained solids deform via intermittent slips that exhibit a material-independent statistics and dynamics. We compare predictions of a simple model for the plastic deformation, the slip statistics and dynamics, and time series properties to experiments on slowly deformed bulk metallic glasses and granular materials. We highlight measures that can be used to differentiate between different systems and explain connections to other systems with avalanches. Predictions for future experiments will be discussed. The results are important for transferring results across scales and material structures.

This talk describes our recent success (F. Rao et al., Science 2017) in controlling the amorphous structure of chalcogenide Sc-Sb-Te glass to accelerate its crystallization, reaching an unprecedented operation speed for memory and switch applications. Specifically, we have designed a new phase-change memory alloy with drastically reduced crystal nucleation stochasticity from the parent amorphous phase. The ultrafast transition between the two metastable states accomplishes sub-nanosecond switching for cache-type phase-change random-access memory (PCRAM) technology. This is a milestone in memory materials, because operation speed is currently a key challenge in PCRAM technology, especially for achieving sub-nanosecond high-speed cache-memory (such as SRAM). The limiting factor in the commercialized PCRAM products is the writing speed (~currently several tens of nanoseconds), which originates from the stochastic crystal nucleation during the crystallization of the amorphous Ge2Sb2Te5 glass. Here we use alloying into the parent glass to speed up the crystallization kinetics by orders of magnitude. The newly designed chalcogenide Sc-Sb-Te alloy enables a record-setting writing speed (as short as ~700 picoseconds) in a conventional PCRAM device, with no requirement for pre-programming or additional device design. This ultrafast crystallization stems from the reduced stochasticity of nucleation via geometrically matched and robust chemical bonds that stabilize crystal precursors in the amorphous state, which are found via ab initio simulations to exhibit long life-times, shortening the incubation time for crystallization. This discovery is an example of physical metallurgy principles in action, using atomic-scale insight into glass structures (bonding configurations and sub-critical nuclei) to control properties. For details, see F. Rao et al., Science 358 (6369), 1423 (2017).

Application of mechanical stress to glass causes interesting changes in how it transmits light. This interplay is summarized by the elasto-optic tensor, the key metric for technological applications including zero stress-optic glass, and reduced stimulated Brillouin scattering glass. Fundamentally, these effects are controlled by the glass chemistry, and in particular the nature of the chemical bonds that make up the glass. We will summarize our approach to this problem, which is focused on both an empirical and ab initio approach to the structure-property relations governing the elasto-optic tensor. We will describe the control of the stress-optic response through judicious choice of glass chemistry, and also describe our current progress in understanding and developing glass with reduced stimulated Brillouin scattering. We will include discussion of both average properties and energy-dispersive effects. We will show how these effects may be computed ab initio, with a reasonable trade-off between accuracy and speed, and illustrate a bond-based model we are developing that attempts to put in simple terms the empirical relations we have discovered.

Lack of ductility is one of the major shortcomings of bulk metallic glasses which hamper their wide application as structural material. Ductility is a complex mechanical property which is difficult to characterize precisely. In a sense metallic glass is always microscopically ductile, because applied shear stress can locally liquefy glass. But it has no work-hardening, thus often local yielding results in catastrophic shear failure. In order to achieve macroscopic ductility glass must be able to relax local stress concentration before it starts macroscopic shear band or crack. In our view the key is the residual liquidity in glass. The structure of supercooled liquid is heterogeneous, and the frozen-in structure at the glass transition contains weak liquid-like and strong solid-like regions. It is difficult to assess such heterogeneity directly from the structure itself, but it is possible to characterize it through the structural response to applied stress. We determined the anisotropic pair-density function (PDF) of various metallic glass samples under uniaxial stress by high-energy x-ray diffraction using the spherical harmonics expansion of the structure function S(Q) and the PDF. The measured anisotropic PDF at large distances agrees with the one expected for affine (uniform) deformation which determines the long-range strain e_∞. However, at short distances it deviates from the affine deformation, and at the first neighbour the local strain, e₁, is smaller than e_∞. The deviation from the affine deformation occurs because of local liquid-like regions, so that the ratio G = e₀/e_∞ , or ΔG = 1 - G, characterizes the strength of residual liquidity in glass. We found that the ratio e₀/e_∞ is closely related to ductility. In particular, G_c = 0.77 is the threshold which separates brittle and ductile behaviors. If G > G_c the samples are brittle, whereas if G < G_c the samples are ductile. Thus we suggest that the percolation of the liquid-like regions results in ductile behaviour. This new parameter is compared to other criteria for ductility.

Borate, phosphate, and borophosphate glasses have been developed for a variety of technological applications, including fast ion conductors, optical substrates, and biomedical devices. For the latter, compositions are often tailored to control the rate at which physiologically significant ions are released to induce the desired biomedical response. These reaction rates depend on the hydrolysis of bonds that link neighboring glass forming polyhedra as well as the hydration of bonds associated with other metal cations that modify the glass forming network, and so detailed understanding of the glass structure connects composition to design performance. For borate and borophosphate glasses, the network hydrolysis rates decrease with increasing fractions of tetrahedral borate. For phosphate glasses, hydrolysis is not significant in neutral pH physiological conditions, but the hydration rates of metal cations are faster when they are linked to chain-forming P-tetrahedra than when they are linked to a chain-terminating tetrahedron. Quantitative and qualitative structural information about Na-Ca-borate, phosphate, and borophosphate glasses, obtained by techniques like nuclear magnetic resonance spectroscopy, Raman spectroscopy, and ion chromatography, will be described and used to explain their bio-functionality.

There is great interest in a developing understanding of the relationships between structures and
dynamics in liquid and glassy systems. Metallic liquids, which exhibit a degree of short and medium range ordering, are well suited to scattering probes, but there are many difficulties associated with selecting the proper furnaces for such studies. The Neutron Electrostatic Levitator (NESL) [1] at the Spallation Neutron Source is a containerless environment developed for challenging systems, including high temperature alloys and undercooled liquids. It provides a high vacuum, high purity, non-contact environment for fundamental studies of materials at wide temperature ranges. Combined with x-ray scattering data and isotopic substitution, the system is well suited to structural characterization of liquids via pair distribution function analysis, as has been successfully demonstrated at the Nanoscale Ordered Materials Diffractometer (NOMAD) [2,3].
A series of upgrades has improved the stability of the levitator and enabled new avenues of exploration. Recently, the system has been operated at the Wide Angular Range Chopper Spectrometer (ARCS) [4] and is currently being commissioned at the Cold Neutron Chopper Spectrometer (CNCS) [5] for high resolution inelastic and quasi-elastic scattering, enabling non-contact probes of excitations in glass forming liquids as well as high temperature self-diffusion measurements. The current capabilities and characteristics of the levitation furnace, progress in inelastic scattering measurements, and early results from the commissioning at CNCS will be discussed.
[1] Mauro, N. A., A. J. Vogt, K. S. Derendorf, M. L. Johnson, G. E. Rustan, D. G. Quirinale, A. Kreyssig et al. "Electrostatic levitation facility optimized for neutron diffraction studies of high temperature liquids at a spallation neutron source." Review of Scientific Instruments 87, no. 1 (2016): 013904.
[2] Neuefeind, Jörg, Mikhail Feygenson, John Carruth, Ron Hoffmann, and Kenneth K. Chipley. "The nanoscale ordered materials diffractometer NOMAD at the spallation neutron source SNS." Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms 287 (2012): 68-75.
[3] Johnson, M. L., M. E. Blodgett, K. A. Lokshin, N. A. Mauro, J. Neuefeind, C. Pueblo, D. G. Quirinale et al. "Measurements of structural and chemical order in Z r 80 P t 20 and Z r 77 R h 23 liquids." Physical Review B 93, no. 5 (2016): 054203.
[4] Abernathy, Douglas L., Matthew B. Stone, M. J. Loguillo, M. S. Lucas, O. Delaire, Xiaoli Tang, J. Y. Y. Lin, and B. Fultz. "Design and operation of the wide angular-range chopper spectrometer ARCS at the Spallation Neutron Source." Review of Scientific Instruments 83, no. 1 (2012): 015114.
[5] Ehlers, Georg, Andrey A. Podlesnyak, Jennifer L. Niedziela, Erik B. Iverson, and Paul E. Sokol. "The new cold neutron chopper spectrometer at the Spallation Neutron Source: design and performance." Review of Scientific Instruments 82, no. 8 (2011): 085108.

Modern drug delivery increasingly relies on micro- and nano-structures to achieve specific release rate and therapeutic target. The delivery systems modulate drug release via engineering control of the API domain and pore size. Other approaches involve the use of functional coating or performance-enabling excipients. The small-scale nature of pores, drug domains, and delivery vehicles demands higher resolution technique to characterize. High-resolution image-based characterization has been broadly utilized in drug product development for fundamental understanding on the process-property-performance interplay and optimizing formulation process and design. It finds applications in various novel drug release systems such as tailoring rate-limiting film coat thickness where the pore formation is critical to control drug release and interrogating the underlying mechanism of in-situ drug nanoparticle formation from amorphous solid dispersions in dissolution media for solubility enhancement. 3D micro-imaging can qualitatively visualize micro-structures, quantify their spatial and chemical distribution, and predict release behavior. In recent years, the emerging image-based numerical simulation has received significant traction and plays an important role on predicting drug release performance. Information-rich 3D images can be converted to characteristic drug transport parameters through intelligent analysis and applied to numerical simulation models to predict release performance. This image-based simulation approach represents a potential paradigm shift in drug design and evaluation, with significantly reduced evaluation time, improved release performance, and lowered in-vitro and in-vivo experiment cost.

Recently, bottlebrush polymers have attracted significant interest due to their potential applications in drug delivery and electronics. The tunability of their properties, stemming from the diversity of sidechains and their spatial arrangement, have emphasized their industrial potential as compared to the linear macromolecules. In this context, the structural information and organization of these systems play a major role in the rational design of functional bottlebrush polymers. Specifically, direct observation of the molecular organization can reveal inter-chain interaction phenomena and explain the fundamental physical properties of these systems. Here, we report a new method to analyze bulk macromolecular chain arrangement of bottlebrush polymers based on Helium Ion Microscopy (HIM). By using the HIM we were able to quantify structural nematic-type ordering in an amorphous polymer bottlebrush system. High-resolution imaging coupled with data analytics has proven to highlight the location and distribution of the polymer backbones, after oxygen plasma-generated height contrast; as well as map changes in the backbone spatial arrangement as a function of thermal annealing. Our experimental findings are corroborated by the coarse-grained molecular dynamics simulations. Overall, this approach can generate clear insights on the internal structure of amorphous materials and provides a complimentary information channel to scattering techniques and theoretical modelling.

This work was performed at the Center for Nanophase Materials Sciences, a US Department of Energy Office of Science User Facility. This research used resources of the Oak Ridge Leadership Computing Facility, which is a DOE Office of Science User Facility supported under Contract DE-AC05-00OR22725. The authors acknowledge Scott Retterer at the Center for Nanophase Materials Science at Oak Ridge National Laboratory for helpful input and discussion

We determine the nano-to-mesoscale structural heterogeneity in metallic glasses (MGs) using 4- dimensional (4D) nanodiffraction in scanning transmission electron microscopy (STEM). Structural heterogeneity in MGs has been suggested by both experiments and simulations previously. The heterogeneity must involve local structural ordering at the nanoscale, commonly known as medium range order (MRO), some of which has been studied using small electron probes in the past. However, the statistically reliable information on how such MRO constitutes the heterogeneity has remained difficult to determine. Our new approach to determine the MRO and structural heterogeneity involves 4D-STEM, which uses a new-generation pixelated fast STEM detector that allows for the continuous collection of the diffraction patterns from a large area of the MG sample. Using angular correlation and intensity variance analyses, the diffraction patterns can then be converted to real space maps of the local ordering, which we use to precisely determine the type, size, distribution, and volume fraction of MRO. We will present two cases of how the heterogeneity affects the important properties of MGs, one is the glass stability in Ti-based MGs, and the other is the ductility of Zr-based MGs. To connect the structural heterogeneity to ductility, we use a new mesoscale simulation that incorporates the experimentally determined heterogeneity, which can simulate realistic shear band formation and overall deformation that match the spatial and temporal scales of the deformation of real MGs.

It is well known that for a large number of glass forming liquids the static structure factor, S(Q), shows no or only subtle changes when passing from the liquid into the glass. In contrast the dynamic structure factor S(q,ω) of simple or more complex glass forming liquids evidences in the GHz - THz frequency range and close to the glass transition clear and common signatures which have been addressed by several theories over the last decades. In spite of large experimental and theoretical activity in this field the glass transition is still not fully understood. Quasielastic neutron scattering plays a vital role for the experimental investigation of dynamic properties of disordered materials, glasses and undercooled liquids. We will give a brief overview over typical experimental findings near the glass transition and over recent instrumental progress on neutron spectrometers before presenting some examples. We then focus on our recent investigations on simple organic, hydrogen bonded and ionic liquids for which we have probed the dynamics near the glass transition by simultaneous dielectric and neutron spectroscopy. For these simultaneous experiments we have controlled both temperature and pressure which did allow us to map lines in the (P,T)-diagram along which the dynamics is unchanged and therefore is isochronous over a wide time range.

We have used electron correlation microscopy (ECM) to image the nanometer scale heterogeneities in the relaxation dynamics of the supercooled liquid of a metallic glass forming alloy [1]. The length and time scales of the heterogeneous dynamics are central to the glass transition and influence nucleation and growth of crystals from the liquid. Electron correlation microscopy (ECM) experiments use time-resolved tilted dark field transmission electron microscopy with sub-nanometer resolution for direct measurement of those length and time scales. ECM data on Pt-based metallic glass nanowires above the glass transition temperature (T_g) reveal a relaxation time scale that varies from a few seconds to hundreds of seconds and a length scale that varies from 0.8 to 1.4 nm. They also demonstrate the existence of a ~1 nm thick near-surface layer with an order of magnitude shorter relaxation time than inside the bulk which may influence crystallization of the wires. Additional measurements of the surface layer relaxation time below the bulk T_g, and its connection to enhanced surface diffusion in metallic glasses and surface crystallization will be discussed.

[1] P. Zhang, J. J. Maldonis, Z. Liu, J. Schroers, P. M. Voyles, Nat. Commun. 9, 1129 (2018)

Metallic glass is a heterogeneous composite on the scale of a few nanometers; the structure of the glass on this scale governs its macroscopic thermo-mechanical response. This structure evolves in response to thermal and mechanical loading; this evolution is mediated by discrete kinetic events in which clusters of atoms locally rearrange themselves. We present a model of this structural evolution and mechanical response which consists of a thermodynamic state space, density of states, and models for relaxation and shear transformation events which move the glass through that state space. We implement this model in a homogenized statistical sense and compare to homogeneous relaxation and flow data previously in literature; we also implement it in a discrete mesoscale framework. We conclude with a discussion of gaps in the current understanding of the fundamental structure of metallic glass.

When subjected to external stimuli such as mechanical loading, atoms in disordered solids respond heterogeneously. Due to lack of representations to resolve the subtle packing difference around atom sites and approaches to deal with the long-range correlation involved, it is hard to quantitatively predict this heterogeneous, site-specific response solely from the structure. Here, by designing a robust hierarchical machine learning framework, we show that it is possible to predict the mechanical heterogeneity in disordered solids a priori, directly from the quenched structural state itself. We encyclopedically create a large pool of 810+ site descriptors, from 40+ sets of structural measures, spanning topological and chemical short- and medium-range order, and develop a novel hierarchical scheme to further extend the studied scale to an unprecedentedly long-range while still retaining good interpretability and generality. Impressive predictability is achieved in a fairly large strain regime, suggesting a long-lived inheritance of the quenched state until later obstructed by shear banding. The framework is robust over a range of compositions and processing conditions and can well detect the site environments tuned by these conditions. We also identify a bag of promising structural signatures unrevealed previously, with their predictability exhaustively benchmarked and discussed. This hierarchical learning framework is general and could potentially be applied to decode structural origin of any site-specific properties in the family of disordered materials.

In this work we use molecular dynamics (MD) simulations to investigate glass composites constituted by two brittle model glasses with different stiffness. We show that tuning the stiffness ratio (SR), shape, volume fraction and distribution of the two brittle glass constituent scan trigger a brittle to ductile (BTD) transition. Such composite glasses can exhibit high strength, remarkable toughness and some work hardening. The highest failure strain of 80% can be reached in composite glasses as compared to 7% in monolithic model glasses. We also found that mechanical properties of such glass composites will not be deteriorated by introduction of pre-notch. Excellent load redistribution capability introduced by structural heterogeneity is responsible for high ductility in our composite glasses. Through a systematic analysis, we unveil the design principles that lead to the aforementioned BTD transition. We believe the current approach could enhance ductility and broaden the application of glasses as enabling structural materials.

Glass is well known to be susceptible to stress corrosion cracking caused by chemicals in the environment, a phenomenon that can cause delayed failure of glasses due to growth of pre-existing surface defects in the presence of humidity. The complex macroscopic effects of stress corrosion, like fracture, occur due to microscopic interactions, which demand a study to replicate the microstructural interactions within a model, which should reproduce the macroscopic behaviors. The purpose of this research is to study the stress corrosion behavior of a model metallic glass system with a view towards representing the underlying atomic level mechanisms using a molecular dynamics approach.

This poster firstly introduces a new microfluidic method for preparing nanostructures of gallium-indium liquid alloy systems. Due to its smaller nanometer size (50-100nm diameter), good self-healing behavior, strong oxide layer formed by spontaneous oxidation, rich changeable nanomorphology driven by voltage variation and large undercooling range, the alloy system has become a good platform for studying amorphous structure transformation and internal structure of liquids using in-situ characterization technology under current conditions. We have successfully discovered the presence of secondary structures in this liquid metal system through in situ TEM lithiation experiments and subsequent nanomechanical and electrical experiments. By comparing the structural relaxation of the same kinetic fragility liquid with or without the oxide layer structure, we found that the oxide layer structure could guide the dynamic non-uniformity of the nano-amorphous system to some extent. At the same time, we are also actively exploring the future application of this alloy system in liquid metal self-healing electrodes, nano-heat pipes, nanoscale self-propelled robots and other industrial fields.

Forsterite glass exists as dust grains in interstellar molecular clouds and young stellar objects [1]. In interstellar molecular clouds, elements such as hydrogen, oxygen, carbon, and nitrogen deposit on dust grains, and form various molecules (e.g., H₂O, CO, CO₂, NH₃, CH₄, H₂CO, CH₃OH, and so on) [2]. These molecules undergo chemical evolutions to organic molecules through various processes on the surface of dust grains [2]. Dust grains are important materials governing the chemical and thermal evolutions in space. However, the transport coefficients of forsterite glass are less conclusive, because forsterite glass is easily to crystallize. To investigate the mechanism of self-diffusion of atoms in forsterite glass, molecular dynamics (MD) calculations were performed.

The MD calculations were performed using an atom-atom potential model with MXDORTO program [3]. The potential parameters were empirically determined by constraining the model to reproduce the experimental results of density, thermal expansion coefficient, and bulk modulus [4]. The transition point from glassy state of supercooled liquid state (T_g) for our potential model is 1567 K. A fundamental orthorhombic cell consisting of 160 Mg₂SiO₄ with three-dimensional periodic boundary conditions was used. The glass structure was prepared by quenching the liquid phase from 3000 K to 10 K with 0.4 K/ps in rate. The quenched glass was warmed to 3000 K with the same rate. The MD code was run with NTP ensemble. The pressure was kept at 0.1 MPa.

The self-diffusion coefficients of Mg, Si and O were calculated using mean-square displacement (MSD). To investigate the mechanisms of self-diffusion, the temporal variations of pair correlations functions for Mg were analyzed. The result shows that the jumping probability of Mg, which is located at a position with high Si and low Mg densities is high. Because of the strong Si–O bonds in the tetrahedral SiO₄ units, the jump of Mg atom (or MgO_x unit) was induced by structural distortion of the surrounded SiO₄ units. From analyses of spatial distribution of MSD, it was found that the MSD values of Mg are inhomogeneous at temperatures just below T_g. Because the self-diffusion coefficient of Si is significantly low at < T_g, the distribution of Si in forsterite glass is inhomogeneous. Therefore, the diffusivity of Mg depends on surrounded Si distribution.

Reference:
[1] J. P. Bradley, L. P. Keller, T. P. Snow, M. S. Hanner, G. J. Flynn, J. C. Gezo, S. J. Clemett, D. E. Brownlee, J. E. Bowey, Science, 285, 1716 (1999).
[2] N. Watanabe, A. Kouchi, Prog. Sur. Sci., 83, 439 (2008).
[3] K. Kawamura, MXDORTO, Japan Chemistry Program Exchange, #029 (1990).
[4] T. Ikeda-Fukazawa, J. Soc. Inorg. Mater. Jpn., 23, 130 (2016).

A plastic has a lower specific gravity than glass or metal and has many advantages such as lightweight and good mechanical properties.
These thermoplastics are rapidly replacing conventional glass and metal areas in fields such as electronic and automobile parts. Recently, as increasing need for environmentally friendly material, there is an increasing demand for plastic that can feel a metallic appearance similar to a metal without a spray process.
For the development of metal-feeling thermoplastics, it is well-known way to use metallic pigment. But because of difference in flowability between metal pigment and plastic, There is an appearance problem such as flow mark and weld-line. This is why metal-feeling plastic can’t be expanded. In order to solve these problems, much research have been studied to control the shape and aspect ratio of metallic pigment and to improve the surface coating of it. However, it is limited to improve the appearance problems such as aggregation and orientation.
In addition, there is no effective method for objectively estimating the appearance of the metallic feeling except for flop index. But the flop index can evaluate only the metallic brightness and the degree of defects such as flow mark and weld-line caused by the metallic pigment could not be evaluated. As a result, there is no method of evaluating the appearance that can represent the overall phenomenon caused by the metallic pigment as an objective numerical value. In this research, development of method for estimating appearance of metal-feeling plastic is studied. Through correction of flop index, new index named as ‘T/N_Flop_X’ was developed. Using this index, it is available to objective evaluation and comparison of metal-feeling. And using the CCD camera, it was studied that correlation of sparkle effect, metallic pigment’s orientation and weld-line.
Based on these studies, we found out sparkle index that could be explained about orientation and metal-feeling. Additionally we studied about control of metallic pigment for reduce an appearance problem. Orientation is important factor to determine weld-line degree and in a constant direction makes decrease it.
We found out factors that could control orientation especially additive having an affinity of polar and non-polar.

Marine biofouling is a highly complex process and a worldwide problem which involve a wide variety of species. The common techniques proposed inculde heavy metals (Cu₂O), or organic biocide, are bring potential harm to marine environment and ecosystem. Therefore, the nontoxic approaches, particularly silicone-included low-surface-energy Fouling Release Coatings (FRCs) may be the alternatives to chemically active coatings and more environmentally friendly AF strategies. In this study, a facile and versatile approach to the formation of amphiphilic marine antifouling is reported. The approach used boric acid (BA) to mediate the the plasma treated PDMS elastomer and subsequent immobilization of polyvinyl alcohol/poly (sulfobetaine methacrylate) (PVA/PSBMA) zwitterionic semi-interpenetrating hydrogel on solid substrates. PVA/PSBMA was immobilized on the PDMS surface via hydrogen bond and chemical bond. The resulting substrates were tested for the algae attachment test and protein adsorption assay, in which diatom and protein adhesion was significantly inhibited compared to PDMS. Advantageously, this approach allowed marine antifouling coatings to be prepared by a simple immersion process under environmentally friendly conditions.

This paper is funded by the International Exchange Program of Harbin Engineering University for Innovation-oriented Talents Cultivation.

Supramolecular polymer is comprised of oligomers or polymers that are held together by reversible non-covalent supramolecular interactions. It is capable of responding to damage or crack and restoring the polymer`s performance without affecting the initial materials properties. The healing property of supramolecular polymer network depends on two factors, that is, the first being the supramolecular interactions, and the second being the chain dynamics of the individual polymer chains. In this study, we synthesize the simple supramolecular network consisted of ureidopyrimidinone (UPy) ends functionalized 6-arm star poly(ε-caprolactone)s and investigate the effect of arm length on thermally induced self-healing behavior of the supramolecular star poly(ε-caprolactone) network. The resulting materials can be healed several times at 90C during 10 minutes, and even can be healed at 60C after 40 minutes. We find the compromise between number of tie points by supramolecular force and chain dynamics related to sufficient mobility of network. Both supramolecular end clustery crystal and main chain crystal might affect the mobility of network. For the efficient healing behavior, the crystalline domain of supramolecular polymer network should be collapsed. Thus, the sufficient thermally induced healing behavior can be achieved through the enhanced mobility of network.

As a pure element, bismuth is a semimetal which possesses several interesting physical properties, not all of them well understood. The recent discovery of superconductivity [1], as predicted by our group [2], and the increasing superconducting transition temperature as the pressure applied increases, are some examples of its particularities. Also, the fact that the amorphous phase is superconductive with a transition temperature several orders of magnitude larger than the crystalline at ambient pressure is unusual [2]. These phenomena have also motivated our predictions for the transition temperatures of Bi-bilayers [3] and the Bi-IV phase [4]. When mixed with other elements, bismuth seems to contribute to the superconducting character of the resulting material. Here we study the binary copper-bismuth amorphous system which is known to superconduct in diverse compositions [5]. Using ab initio molecular dynamics and the undermelt-quench method, we generate an amorphous structure for a 144-atom supercell corresponding to the Cu₈₈Bi₅₆ system. We shall report the calculated electronic and vibrational densities of states for this system and relate them to the superconducting properties of this alloy.

[1] O. Prakash, A. Kumar, A. Thamizhavel, S. Ramakrishnan. Evidence for bulk superconductivity in pure bismuth single crystals at ambient pressure. Science 355 (2017), pp. 52-55. DOI: 10.1126/science.aaf8227.
[2] Z. Mata-Pinzón, A. A. Valladares, R. M. Valladares, A. Valladares. Superconductivity in Bismuth. A New Look at an Old Problem. PLoS ONE 11 (2016), e0147645. DOI:10.1371/journal.pone.0147645.
[3] D. Hinojosa-Romero, I. Rodriguez, A. Valladares, R. M. Valladares, A. A. Valladares. Possible superconductivity in Bismuth (111) bilayers. Their electronic and vibrational properties from first principles. MRS Advances 3 (2018), pp. 313-319. DOI: 10.1557/adv.2018.119.
[4] A. A. Valladares, I. Rodríguez, D. Hinojosa-Romero, A. Valladares, R. M. Valladares. Possible superconductivity in the Bismuth IV solid phase under pressure. Scientific Reports 8 (2018) 5946 DOI:10.1038/s41598-018-24150-3.
[5] N. E. Alekseevskii, V. V. Bondar and Yu. M. Polukarov, Zh. Eksperim. i Teor. Fiz. 38 (1960), p. 294 [translation: Soviet Phys. - JETP 38 (1960), p. 213].

In the past decades the research community has explored diverse structures and new fabrication methods of non-crystalline solids. Glassy materials that belong to the semiconductor realm and to the metallic type are the most studied both experimentally and simulationally. The present work investigates common structural trends whenever they exist and different trends among different classes. Amorphous semiconductors display Pair Distribution Functions (PDF) that are very similar among themselves and this indicates that these network forming materials have properties that are alike ^[1]. Analogously metallic systems have comparable PDFs but different from the network forming materials, as it should be, since the properties between these two classes are very different ^[2][3].
Here we pay attention to the Short-Range Order (SRO) and Intermediate Range Order (IRO) of these two classes. In particular, the first peaks of the structures studied are contrasted, while the second peaks are shown to differ considerably. Whereas the semiconductor structures display a simple first and second peak with a near-zero value between them, the metallic systems have a very well defined non-zero value between the first and second peaks and they also display what we have come to identify as an “elephant” second peak ^[4]. To manifest the uncommonalities with amorphous semimetals we recall calculations carried out by our group for bismuth where the elephant peak does not appear but the non-zero behavior between the first and the second peak is present ^[5]. The Plane Angle Distribution (PAD) functions are also reported.

[1] A. A. Valladares, J. A. Díaz-Celaya, J. Galván-Colín, L. M. Mejía-Mendoza, J. A. Reyes-Retana, R. M. Valladares, A. Valladares, F. Alvarez-Ramirez, D. Qu and J. Shen, New Approaches to the Computer Simulation of Amorphous Alloys: A Review. Materials, 4, 716-781 (2011).
[2] C.U. Santiago-Cortés, Simulación de sistemas metálicos amorfos y porosos de elementos nobles, Thesis (PhD), Universidad Nacional Autónoma de México, México (2011).
[3] I. Rodríguez, R. M. Valladares, A. Valladares, A. A. Valladares, to be published (2018).
[4] A. de Saint-Exupéry, Le Petit Prince, Reynal & Hitchcock, pp 1-2 (1943).
[5] Z. Mata-Pinzón, A. A. Valladares, R. M. Valladares, A. Valladares, Superconductivity in Bismuth. A New Look at an Old Problem. PLOS ONE, 11(1): e0147645 (2016).

The mechanical properties of bulk metallic glasses are often tuned by annealing, which influences these properties by adjusting the relaxation or crystallization status of the glasses. Here, we studied the modulus of Pt_57.5Cu_14.7Ni_5.3P_22.5 bulk metallic glass (Pt-BMG) annealed at different temperatures in the metastable regime by nanoindentation, where the annealing gives the BMG different fictive temperature and fractions of crystallization. We find the modulus of the investigated BMG samples exhibits a “V trend”: As the annealing temperature increases, we first observe a decrease that is followed by an increase until saturation is reached. This phenomenon can be explained as a result of the combination of the glasses relaxation and the glasses crystallization: Relaxation caused by higher fictive temperatures lead first to higher free volumes, which leads to lower moduli, while past a specific temperature, crystallization generates new, denser phases with higher moduli. The latter finding is confirmed by nanoindentation measurements at which fully amorphous Pt-BMG samples with different fictive temperatures are compared with partially crystalline samples featuring the same fictive temperature.

Mass spectrometry (MS) has became an increasingly popular and useful in analyzing structures of proteins. Initially only information of low resolution and of the whole protein in general can be obtained. Many techniques that utilize property differences between parts of the protein to produce signature fragmentation patterns and products have been developed to gain more information on local geometry, such as collision induced dissociation (CID), electron transfer dissociation (ETD), electron capture dissociation (ECD) and ultraviolet photodissociation (UVPD). A new method called hydrogen elimination monitoring (HEM) was invented by Brodbelt et. al, to overcome disadvantage of other methods. For example, CID disrupts protein structure prior to fragmentation therefore higher order structural information is lost and ECD cannot differentiate highly ordered surface regions with internal buried regions. HEM aims finding out higher order structure anywhere in the protein by using hydrogen elimination information after fragmentation to determine the level of hydrogen binding prior to fragmentation, therefore determining local geometry. Experiments have demonstrated that hydrogen elimination correlates strongly to absence of backbone hydrogen bonding yet the underlying process and reason to this correlation is unknown. DFT studies of model peptides at ground state can help in illustrating the process and in providing theoretical support to HEM method.

In the computational study complementary to experimental findings, we used 3 structures of Ala₈ peptide models with increasing amount of hydrogen binding: an unstructured linear peptide, a hairpin turn and a helix, to study the thermodynamics as well as the kinetics of the fragmentation process, by finding out the enthalpy change of the fragmentation reaction and the minimum energy pathways (MEPs) for the processes. The thermodynamics show that fragmentation products without hydrogen elimination are much higher in energy compared to products with hydrogen elimination, and therefore extremely unfavorable. The MEPs revealed reasons why the thermodynamic favorable product may not always form. In the unstructured peptide, hydrogen elimination always take place at the same time as the C-C back bone is cleaved. In the hairpin turn and helix structure, however, the MEP show that C-C cleavage takes place first and produces spatial separation that could prevent hydrogen elimination. This finding shows the underlying principle of the correlation between hydrogen elimination and amount of hydrogen binding prior to fragmentation, and therefore supports HEM as an effective method for analyzing protein structure.

The deformation of materials in extreme dynamical environments such as high-velocity microparticle impact is a challenge to understand though important for many areas of science and technology from space exploration to sand erosion. While impact dynamics of macroscale projectiles have been studied in real time using high-speed imaging, investigations of microscale impact have been essentially limited to post-mortem analysis of impacted specimens. Here, we present real-time observations of supersonic microparticle impacts using multi-frame imaging. In a laser-induced projectile impact test, a microparticle is accelerated by laser ablation from a sacrificial gold layer on a glass substrate. These particles can be accelerated into free space with controllable speeds up to 1.0 km/s depending on laser pulse energy and particle characteristics. The particles are monitored in flight and during impact with an ultra-high-speed camera that can record up to 16 images with a minimum interframe time of 3 ns. We investigated the high-velocity impact deformation response of elastomers to further the fundamental understanding of the molecular influences on high strain rate elastomeric response. The types of materials that were synthesized and tested are glassy polymers, graft copolymers, and other materials. We show the dynamic stiffening response of various elastomers including poly(urea urethane) upon impact at strain rates of ~10⁸ s^-1 and demonstrate the significance of molecular constitution in the response. These results provide an impetus for modeling the molecular influence on high strain rate microscale impact responses in these polymeric materials.

Acrylonitrile butadiene styrene (ABS) has a similar matrix structure to the styrene acrylonitrile copolymer but has additional distribution of polybutadiene which strengthens it and allows ABS to surpass the properties of traditional commercial polymers. PLA is a 100% biodegradable polymer which can be regarded as a replacement to many current commercial plastics. However, it’s brittleness limited its application in the industrial processing. Commonly, binary blends including PLA and another polymer additives are created to enhance the mechanical properties of PLA, but this has been found to be ineffective due to the poor interfacial reaction between the polymers. Previous studies have determined that a 70:30 PLA: ABS ratio effectively balances the bio-based properties of PLA with the exceptional mechanical properties of ABS. Many have observed that the binary PLA/ABS blend actually has worse mechanical properties than just the PLA alone. Therefore, an efficient compatibilizer with good affinity with both PLA and ABS is a key factor to solve this problem. In our previous work, we have certified that PMMA is miscible with PLA and considering the structure of ABS, we hypothesis PMMA should be an excellent compatibilizer to the blend.

To create the ternary blends, the polymers were added to a C.W. Brabender and then molded into the tensile and impact test shapes using a Carver Hot Press. The blends were also run through an extruder to create filaments for 3D printing. A 286% increase for the molded sample in the impact test was observed when 4% by weight PMMA was used with the 70PLA/30ABS blend. Mechanical tests also showed that this ternary polymer material can maintain high mechanical properties even when 3D printing, as the mechanical properties of the 3D printed surpassed the pure PLA sample and PLA/ABS binary blend by 24.3% and 55.5% respectively. SEM and TEM imaging were used to verify the location of PMMA phase. And contact angle tests show that ABS has a higher affinity with PMMA than PLA.

The ternary blends reached their peak mechanical properties with less than 5% by weight of compatibilizer added, suggesting the economic efficiency of this blend for industrial use. For future study, interfacial properties in the ternary blends could be investigated using secondary ion mass spectrometry (SIMS) analysis to reveal interactions that contribute to mechanical strength.

We have designed and engineered ternary polymer blends with the mechanical properties comparable to high impact resistant conventional polymers under the guidance of the lattice self-consistent field model. Tow formulas were used to study the mechanical properties. In one system, poly (methyl methacrylate) (PMMA) was used as the compatibilizer for the widely studied biodegradable polymer blend, poly (lactic acid) (PLA)/Poly (butylene adipate-co-butylene terephthalate) (PBAT) blend. We characterized the compatibility of those components and found PMMA was miscible with PLA and partially compatible with PBAT, which allowed it to self-assemble to a nanoscale interfacial layer on the PLA/PBAT interface. This PMMA layer can significantly decrease the interfacial energy and strongly entangle with either PLA or PBAT, resulting in the strengthening of the interface and dramatically enhancement of the impact resistance of the ternary blend. The optimal mechanical performance was achieved when the total PMMA concentration was less than 10 wt %. Higher PMMA content embrittled the blend since the additional PMMA did not contribute to the minimization of the interfacial energy but remained in the PLA phase, increasing the glass transition temperature of the matrix. In the other system, as in our previous study, PMMA is miscible with PLA and PS is totally miscible with styrenic polymers such as HIPS and ABS, therefore, PLA/Styrene Acrylic Copolymers (SMMA) with different styrenic polymers were blended during the study. SMMA will self-assemble to become an interfacial layer on the PLA/PS (or HIPS or ABS) interface at very low concentration (SMMA concentration less than 2%), and enhance the impact resistance of the ternary blend up to 50% compared to the binary blend of PLA/styrenic polymers. Increasing the SMMA concentration will form a third phase domain in the polymer matrix which will embrittle the whole system.

The search for a simple and direct relationship between atomic scale arrangement and macroscopic properties of a material constitutes a principal task of the materials science. For example, the Bloch theorem establishes extended electronic wavefunctions and then a ballistic conduction if the atoms of a crystalline material are periodically ordered. At the other extreme, one- and two-dimensional amorphous solids with randomly arranged atoms possess only exponentially localized eigenstates [1]. Nowadays, the study of electronic transport in artificial structures is of great importance in condensed matter physics, because such structures introduce many new physical properties essential for technological applications of atomic-scale devices. In this work, we report a new convolution theorem developed for the Kubo-Greenwood formula in Labyrinth tiling by transforming the original two-dimensional lattice into a set of independent chains with rescaled Hamiltonians [2]. Such transformation leads to an analytical solution of the direct-current conductance spectra, where quantized steps with height of 2g₀ are found in Labyrinth tiling with periodic order along the applied electric field direction, in contrast to the step height of g₀ observed in the corresponding square lattices, being g₀ the conductance quantum. When this convolution theorem is combined with the real-space renormalization method [3], we can address in a non-perturbative way the electronic transport in macroscopic aperiodic Labyrinth tiling based on generalized Fibonacci chains [4]. Furthermore, we analytically demonstrate the existence of ballistic transport states in such aperiodic Labyrinth tiling. This finding suggests that the periodicity should not be a necessary condition for the single-electron ballistic transport even in multidimensional fully non-periodic lattices.

This work has been partially supported by UNAM-IN114916, UNAM-IN106317 and CONACyT-252943. Computations were performed at Miztli of DGTIC, UNAM.

[1] E. Abrahams, et al., Phys. Rev. Lett. 42, 673 (1979).
[2] F. Sánchez, V. Sánchez, C. Wang, Eur. Phys. J. B (2018) doi: 10.1140/epjb/e2018-90070-4.
[3] V. Sánchez and C. Wang, Phys. Rev. B 70, 144207 (2004).
[4] F. Sánchez, V. Sánchez, C. Wang, J. Non-Cryst. Solids 450, 194 (2016).

Ceramics are well used in various fields as functional materials and their property range is a way more expanded these days by adding new nanoscale properties. Even though a number of studies have been achieved for investigating electronic, magnetic, optic properties etc. at nanoscale, the fracture behavior is not reached to the same level of evaluation. It is in need of investigating the fundaments of fracture mechanics for nano-sized ceramic materials to guarantee the reliability of the systems adding to enjoy the newly enhanced nano-properties at the same time. Brittle failure of ceramics is usually mediated by a rapid crack propagation due to the lack of intrinsic crack tolerant mechanism which requires extremely high critical stress for its activation, usually never been reached before the total failure in bulk scale. However, in some theoretical studies, fracture of nanomaterials becomes insensitive to flaws when they shrink below a certain critical size and enables to reach almost theoretical strength of the material [1]. Getting ideas from this, here we present an unwonted roll of cracks at the nanoscale as an activator of a fracture resisting mechanism not as an enemy of brittle ceramics through nanoscale tensile experiments and finite element methods analysis. In situ SEM tensile fracture tests with different crack geometries were carried out. Diamond-like-carbon (DLC) was chosen to be conductive for SEM image quality, isotropic, and brittle material to eliminate any complicate material issues and to make the best focus on the mechanical analysis. Single-edge-notched-tension (SENT) and double-edge-notched-tension (DENT) samples with pre-notch size of 60 nm and thickness of 200 nm were fabricated in mushroom like shape with head size of ~2 μm using Focused Ion Beam (FIB) on DLC film of ~1.5 μm coated on Si wafer. The head part was grabbed and pulled by a self-produced claw-like tip. In short, we observed that the DENT samples were deviated from the expectations based on classical linear elastic fracture mechanics showing 150% higher fracture strength even with 60% of total crack length out of thickness. It is explained by the interaction between the two stress fields of each crack that activates additional fracture resisting mechanism in the neck region of the specimen preventing the whole sample from the failure.

[1] Gao, Huajian, et al. "Materials become insensitive to flaws at nanoscale: lessons from nature." Proceedings of the national Academy of Sciences 100.10 (2003): 5597-5600.

The photo-curing behaviors of acrylate monomers capable of urethane thermal reaction were investigated using time-resolved FTIR spectroscopy and photo-DSC (Differential Scanning Calorimetry). Faster photo-reaction and lower conversion of acrylate reactions were observed in the thermal-photo dual curing process compared to the photo-curing only process. In the case of the acrylate system with long chain oligomers, faster photo-reaction was also observed in the dual curing process although no difference was found in the degree of conversion of acrylates between two photo-curing processes. The photo-curing process of three acrylate monomers was investigated using ATR-FTIR spectroscopy with a deuterated acrylate compound. In the free-radical terpolymerization, the conversion of three acrylate monomers into terpolymer as a function of time was monitored by observing the characteristic FTIR peaks of each component. In order to identify the acrylate components involved in the free-radical terpolymerization, careful peak assignments were made for the acrylate terpolymer such that characteristic FTIR bands from different monomers chosen for quantitative analysis should not overlap with one another. The use of deuterium substituted acrylate monomer as an aid in the interpretation of the FTIR spectra of three component systems has been demonstrated in this study.

Carbon dots (C-dots) are a class of low-dimensional carbon-based particles which exhibit a signature photoluminescence (PL) consisting of a red-shifted emission when irradiated with uv-visible light. This Photoluminescence (PL) has been explained as either the effects of quantum confinement, or of energy traps on the particle surface. Recently, several groups have reported the synthesis of C-dots directly from the thermal treatment of aqueous solutions of simple sugars (e.g., glucose, sucrose) either in a conventional autoclave or in a microwave oven. These studies have looked exclusively a preparation from low concentration (less than 10 wt% sugar) solutions reacted at rather high temperatures (between 160 to 200 C). We report the synthesis of fluorescent carbon particles produced from viscous glucose solutions of a much higher concentration heated at much lower temperatures. Analysis by photon correlation spectroscopy (PCS) reveals the particles form immediately with a size (approximately 300 nm) that is nearly 100 times larger than the precursor clusters of sugar but which decrease slightly in size with additional heating. Despite their larger size, PL shows emission similar to that of smaller C-dots but with clear indications of fine structure suggesting a set of discrete surface energy levels likely associated with different functional groups attached to the particle's surface.

Chalkogenide phase change materials (PCM), such as those based on Ge-Sb-Te alloys, have been shown to have unique properties that have been used for a long time in optical memories (DVD), and, more recently, in non-volatile resistive memories [1, 2].
Nonetheless, several challenges must be overcome if PCM memory technology is to enter the market. The most critical of these challenges is that the resistance of the PCM amorphous phase increases with time (so-called "resistance drift phenomenon") due to the ageing of the material, and this drift has a negative effect on the storage of information.
The basic physical mechanisms underlying drift phenomena are still unclear and are currently the subject of intense discussion. Different and sometimes contradictory mechanisms have been proposed, such as [1]: increasing [3] or reducing [5, 4] disorder during drift; increase [6] or decrease [7] density of defect states during drift; impact [8] or no effect [9] of stress on drift.
Despite all the recent research efforts, we do not yet have a clear picture of the structural mechanism of relaxation occurring during the ageing of the amorphous PCM phase, and further research is needed.
Discussion and analysis of different mechanisms proposed for increasing of the resistivity of the chalcogenide based PCM amorphous phase with time is presented – taking into account recent reported results of measurements and concepts, eg: clustering of Ge atoms in the amorphous phase of GeTe during ageing [10]; thermal excitations of electrons trapped in defect states within the electronic gap [4]; correlation between drift coefficient and activation energy [15]; increasing of the band gap during ageing [11]; increase in the proportion of homopolar Ge-Ge bonds with ageing [10]; densification of the films during ageing [12]; localization of the gap states during ageing [13, 14]; formation of Ge-Ge bonds upon ageing in thin films [10].
Structural and quantum chemical analysis was carried out using modified procedures described eg in [16].
References:
[1]Noé P et al 2018, Semicond. Sci. Technol. 33, 013002]; [2] Kolobov AV et al 2017, Semicond. Sci. Technol. 32, 123003; [3] Fantini P et al 2012, Appl.Phys. Lett. 100 213506; [4] Ielmini D et al 2009, Microel. Eng. 86 1942; [5 ] Gopalakrishnan K et al 2010 Symp. on VLSI Tech. Dig. pp 205; [6 ] Pirovano A et al 2004, IEEE Trans. El. Dev. 51 714; [7 ] Ielmini D et al 2008, Appl.Phys. Lett. 92 193511; [8 ] Mitra M et al 2010, Appl.Phys. Lett. 96 222111; [9 ] Rizzi M et al 2011, Appl. Phys. Lett. 99 223513; [10] Noé P et al 2016, J. Phys. D: Appl.Phys. 49 035305; [11] Mitrofanov K V et al 2014, J. Appl. Phys. 115 173501; [12] Kalb J et al 2003, J. Appl. Phys. 94 4908; [13] Gabardi S et al. 2015, Phys. Rev. B 92 054201; [14] Sosso G et al 2012, Phys. Stat. Sol. B 249 1880; [15] Luckas J et al 2013, J. Appl. Phys. 113 023704; [16] Plucinski K J et al 2015, Mat. Sci. in Sem. Proc, 38, 184-187.

Although compounds exhibiting the perovskite structure, and particularly SrTiO₃, have been very well studied concerning their photoluminescence (PL) properties, to our knowledge, the effect of water purity used and the addition of aluminum substituting partially titanium atoms on the PL properties have not yet been studied. To complete the previous studies, samples of SrTi_1-xAl_xO₃ composition with x ranging from 0.005, 0.01, 0.03 and 0.05 were prepared by the modified polymer precursor method under different water purity. SrTi_1-xAlO₃ (STAO) composition samples with the amounts of aluminum equal to x = 0.005, 0.01, 0.03 and 0, 05 were synthesized by the modified polymer precursor method. The obtained resins were subsequently thermally treated at 250 °C at a heating rate of 10 °C/min for 4h under air atmosphere and subsequently ground to obtain fine black amorphous powders. Different temperatures of heat treatments between 450 ~ 500 ° C were selected as well as different calcination times between 2h and 8h. XANES spectra were collected at Ti K-edge using the transmission mode at the XAFS2 beam line of Brazilian storage ring. The pre-edge region of the XANES spectra on the Ti K-edge presents four transitions. They were attributed to a quadrupolar excitation of the 1s electron level to the octahedron t_2g orbitals; a transition of the 1s electron to unoccupied 3d level; transitions attributed to the dipole excitation of the 1s electron level to the t_2g and e_g orbitals of the neighboring octahedron. Significant differences in the intensity of the pre-edge transition for samples containing 3% and 5% of aluminum were observed indicating that in these samples the local symmetry around titanium presents a greater distortion or a greater degree of disorder. This distortion or disorder may originate from the existence of sites with titanium pentacoordinate (^[5]Ti) or hexacoordinated (^[6]Ti). The comparison of the intensity of the transition present in the pre-border region of the XANES spectra of the samples versus the value of the PL intensity area, in agreement with literature data, shows a clear evolution of PL emission with the relative proportions / amounts of pentacoordinate and hexacoordinated symmetries and also the PL decreasing with the beginning of the crystallization process.

Crystallization is a key issue in understanding glass and plays a fundamental role in the development of advanced glass-ceramics. In the absence of catalyzing agents, most supercooled liquids crystallize heterogeneously from the external surfaces; only a few systems crystallize homogeneously in the interior. , it is essential to follow the formation of the first nuclei. Is the whole local structure around the cations modified well before crystallization is completed? The precise role of nucleating agents in glass-ceramic formation will likely only be understood by investigating the very first stages of crystallization with a strictly local structural probe having atomic selectivity. The X-ray Absorption Fine Structure (XAFS) technique is quite appropriate to characterize the local structure of specific cations present in glassy samples from the earliest stage of crystal nucleation. In this work, partially crystallized and fully crystallized samples were obtained after treatment at temperatures and times defined in previous studies. The XANES and EXAFS spectra of selected cations ions in the BaO-SiO₂, Ba₂TiSi₂O₇, CaMgSi₂O₆ – 9 mol% Fe₂O₃, MgO-SiO₂, 1NaO-2CaO-3SiO₂ and 2NaO-1CaO-3SiO₂ glassy systems were collected at room temperature by using the transmission and total electron yield modes. A preliminary analysis of the data indeed showed modifications in the local order around some cations as the time of crystallization increased. The results will be fully discussed.

Metallic glass matrix (MGM) composites combine high-strength amorphous metals with ductile crystalline inclusions to overcome the inherent brittleness of metallic glasses. While the crystalline heterogeneities have been shown to influence the process of shear localization, the underlying mechanisms are not well understood especially since they seemingly operate at disparate length scales. To explore the role of crystalline inclusions in the process of strain delocalization, we employ instrumented nanoindentation, which is particularly suited to study the deformation physics of these composite materials due to its ability to detect individual shear band propagation events and its precise control over plastic zone size. Using nanoindentation, we focus on elucidating three specific phenomena including the onset of plasticity through the formation of shear bands, the propensity for shear localization and its dependence on indentation strain rate, and the nature of shear band propagation. In this presentation, we describe instrumented Hertzian contact experiments that provide quantitative evidence for enhanced shear band nucleation as the shear band trajectory evolves with indentation depth to encompass the crystalline phase. Additionally, by measuring the fraction of discrete plastic events deriving from shear band plasticity during loading, we outline a transition from discrete to continuous deformation with increasing indentation strain rate, which is consistent with the behavior of monolithic metallic glasses. Through comparison of the propensity for shear localization with microstructural length scales of the MGM composites, we show that the presence of amorphous-crystalline interfaces simultaneously limit shear band propagation and promote a more homogeneous response through the partitioning of shear strain to the crystalline phase.

We present an information-based total-energy optimization method to produce nearly defect-free structural models of amorphous silicon. Using geometrical, structural and topological information from tetrahedral networks, we have shown that it is possible to generate structural configurations of amorphous silicon, which are superior than the models obtained from conventional reverse Monte Carlo methods involving structural constraints and total-energy optimization. The new static (i.e. relaxation-based) approach presented here is capable of producing atomistic models with structural properties which are on a par with those obtained from the modified Wooten-Winer-Weaire (WWW) models of amorphous silicon. Structural, electronic, and vibrational properties of the hybrid models are compared with the best dynamical models obtained from using machine-intelligence-based algorithms and efficient molecular-dynamics simulations, reported in the recent literature. We have shown that, together with the WWW models, our hybrid models represent one of the best static models so far produced by total-energy-based Monte Carlo methods in conjunction with experimental diffraction data of amorphous silicon.

Hydrogenated amorphous silicon (a-Si:H) is known to exhibit light-induced metastable properties that are reversible upon annealing. Although these metastable properties suggest the existence of reversible optical properties of a-Si:H as well, very little is known about this effect. If indeed properly identified and characterized, such reversible optical properties may find application in the reversible programmable photonic integrated circuits (PICs) that can enable multiple functionalities on the same chip, similar to field-programmable gate arrays (FPGAs). However, the required reversible effective refractive index change due to light soaking and annealing has not been reported yet nor has it been thoroughly investigated. Therefore, the effects of prolonged high intensity light soaking and annealing on a-Si:H on the near infrared (NIR) optical properties are studied in this work. A thin-film interferometric technique was developed to detect minute changes probed using a NIR laser source (1465-1575 nm). Using this approach, an increase in refractive index resulted in a red shift of the sharp reflection minimum and a blue shift for the decrease in refractive index. To detect the changes in optical properties more precisely, double-layered thin films were used: a-Si:H was deposited by inductively coupled plasma-enhanced chemical vapour deposition (ICP-PECVD) on SiO2, which was in turn deposited by PECVD on a crystalline silicon substrate. The a-Si:H deposition temperature was set to 80 °C and 300 °C, such that significantly different structural properties, e.g. hydrogen content and density, could be achieved. An irreversible blue shift was observed during the first cycle of annealing and light soaking after the deposition. However, from the second cycle onwards, a red shift of the spectrum due to light soaking, i.e. reversal of the annealed state was observed. It appeared that the initial irreversible changes are inevitable and only after these changes reversibility is observable. The reversibility was sustained after further cycles of annealing and light soaking. The reversibility appears for both a-Si:H deposited at 80 °C and 300 °C. However, the magnitude of the reversibility for a-Si:H deposited at 80 °C is significantly larger when compared to a-Si:H deposited at 300 °C. This suggests a correlation of the metastable properties of a-Si:H on the hydrogen content and density of the material, i.e. porous films (deposited at 80 °C) are more susceptible to light-induced change than dense films (deposited at 300 °C). The magnitude of the reversibility in refractive index for a-Si:H deposited at 80 °C is estimated to be around 0.03%. Although small, this metastable change should be sufficient for an application in reversible programmable optical switch. These results therefore indicate that a-Si:H has potential in enabling reversible programmable PICs and work to implement this material in a photonic device is currently ongoing.

Ion implantation is an effective method for surface modification of materials, and that has been used in various fields such as the semiconductor and metal industries, and bio-technology.In general, a discharged plasma (gas) or liquid (e.g., liquid Ga for a focused ion beam) is used as the ion source so far. However, in these cases, side reactions (generation of radicals or various ions with different mass, e.g. in the case of H⁺ emission, H₂⁺ and H₃⁺ etc. are also generated) are unavoidable. Also, ion accelerators are huge and expensive.
On the other hand, ion emissions from high ion conducting solid electrolytes have also been investigated because in a good solid electrolyte the mobile ions can move almost as freely as those in a liquid. The emission of O⁻ions from O²⁻-ion-conducting yttria-stabilized zirconia (YSZ) was first reported in 1997. Similarly, continuous Ag⁺ion emissions for a few days were reported using Ag-ion-conducting (AgI)_0.5(AgPO₃)_0.5or RbAg₄I₅[8,9]. For 12CaO-7Al₂O₃(C12A7) clathrate crystals, it was found that not only electrons but also ions such as O⁻, H⁻, and F⁻ions can incorporate inside cages, and emissions of these anions from C12A7 pellets were also observed. In this ion emission method, a plasma is not required for ionization and the ion emission apparatus becomes simple.
We have studied ion emissions from various types of ion-conducting glasses [1-3]. One advantage of utilizing glass is its formability for tip sharpening because the electric field strength is proportional to the inverse of the curvature radius of the tip. Here we report Ag⁺ ion emission from a sharpened Ag⁺ ion conducting glasses. An aluminum phosphosilicate glasses Ag₂O-Al₂O₃-P₂O₅-SiO₂ show Ag⁺ ion conductivity of 3×10⁻³ S/cm at 300 °C, and an ionic current of Ag⁺ ion emission was successfully observed at 300 °C and 1×10⁻⁵ Pa. A good linear correlation is obtained between the log(current) and the square root of the acceleration voltage, suggesting the emission of Ag⁺ ion from the tip of glass fiber is expressed by Schottky model similar to a thermionic electron emission. On the other hand, in the case of AgI-B₂O₃-Ag₂O glasses known as a super-ion-conducting glass, an Ag⁺ ion conductivity was higher than 5×10⁻³ S cm⁻¹ at room temperature, and Ag⁺ ion emission was observed for the first time at room temperature and non-vacuum atmosphere. The relationship between the emission current and voltage is expressed by space-charge limited current model, in which the current is proportional to the (voltage)^3/2. Ag⁺ ion emission mechanisms are discussed in relation with these two models. We also tried a cell adhesion test using the palm-sized Ag⁺ion emission gun as a first step of an application for a bioengineering field.
[1] Y. Daiko et al., J. Sol-Gel. Sci. Technol.,83(2017) 252-258. [2] Y. Daiko et al., Solid State Ionics, 322(2018) 5-10. [3] Y. Daiko et al., Adv. Eng. Mater.,20(2018) 1800198.

Intermediate temperature fuel cells (IT-FCs) operating around 400-500 °C have attracted much attention as next-generation energy source owing to their high conversion efficiency and low fabrication cost. Our group successfully prepared a fast proton conducting phosphosilicate glass using conventional melting method, and we confirmed fuel cell operation using H₂ and O₂ at the intermediate temperature (~5 mW/cm²) [1,2]. Similar to typical oxide glasses, our glass has quite few H⁺ (OH groups) just after quenching the melt. However, based on originally developed in-situ FTIR measurement, we found a proton implantation into the phosphosilicate glass occurs under fuel cell operating condition [3]. We anticipated such proton implantation affects mechanical properties of glass. In this study, creep behavior of proton conducting glass in fuel cell atmosphere is reported.

A new electrochemical indentation apparatus was developed, in which we can control measuring conditions including atmosphere (H₂, N₂, air and relative humidity), temperature, and electrical field. A spherical Inconel 625 indenter was used as an electrode simultaneously, and we evaluated in-situ creep behavior under the proton implantation. Proton conducting glass was prepared by conventional melting method with composition of 7.5Na₂O･7.5K₂O･35P₂O₅･50SiO₂ (mol%). After polishing the glass with ~1 mm thickness, Pt ring-electrode was sputtered on a side of the glass plate. Atmosphere was controlled by flowing a humidified H₂gas (4%H₂-96% Ar), heating up to 200 ^oC, and applying DC 5 V between the Pt ring and Inconel electrodes. This condition is similar to the anode reaction of fuel cell (H₂ -> 2H⁺+ 2e^-), and proton implantation occurs. We conducted an indentation creep experiment under the reaction. We also carried out same experiments in N₂ atmosphere as comparison. Humidity effects were also investigated using humid gas (relative humidity ~1%).

The phosphosilicate glass showed typical creep behavior in N₂ atmosphere at 200 ^oC. Interestingly, the creep displacement increases remarkably in H₂ atmosphere, and we obtained a longer relaxation time for creep in H₂ atmosphere compared with that in N₂. These results suggest that proton implantation affects significantly for mechanical properties of glass. Results including Raman spectroscopy will be shown and discussed at the presentation.

[1] Y. Daiko, et al., Electrochem.SolidState Lett. 14, B63 (2011) [2] Y. Daiko, et al., Electrochemistry,82, 901 (2014) [3] Y. Daiko et al., J. Ceram. Soc. Jpn, 121, 539 (2013).

Zn-based metallic glasses (Zn₄₀Mg₁₁Ca_31+xYb_18-x, x=0-4) are strong glass forming alloys with low glass transition temperatures that enable metallic plastic behaviors. While the crystallization onset temperature is also low, the crystallization kinetics have not been examined and analyzed quantitatively. In this work, for one Zn-based metallic glass of Zn₄₀Mg₁₁Ca₃₁Yb₁₈, the thermodynamic properties and nucleation dynamics have been determined based on the application of the novel Flash DSC with ultrafast heating and cooling rate. The critical cooling rate range for glass formation was measured along with the critical heating rate for preventing crystallization and the kinetic fragility. A unique double-nose-shaped temperature-time-transformation (TTT) diagram between the glass transition temperature and the melting temperature was obtained by isothermal tests and it was verified to be induced by two different nucleation sites for the same crystallization products. To further investigate the properties of the two nucleation sites, a heterogeneous nucleation model was developed to simulate the experimental TTT diagram and reveal the novel nucleation pathway of Zn-based metallic glasses. This study provides a novel insight in the influence of spatial heterogeneity on crystallization dynamics in amorphous materials.

The stress-induced martensitic transformation of Cu₅₀Zr₅₀ at. % shape memory alloy was controlled through microalloying and co-microalloying and the performance compared at macro and nano scale. Nanoindentation (P/h)-h curves indicate that there is a change in deformation mode from dislocation slip to martensitic transformation during the loading. This change in mode is demonstrated from the change in slope at the initial stages of deformation. The maximum slope of 1.24 is attained for Cu₄₉Zr₅₀Ni₁ at. % compared to about 1.07 for the parent Cu₅₀Zr₅₀ alloy and 0.48 for Cu₄₉Zr₅₀Co₁ at. % thus suggesting that 1 at. % Ni promotes the martensitic transformation while 1 at. % Co decreases the effectiveness of the transformation compared to that of the parent alloy. For the co-microalloyed composition, Cu₄₉Zr₅₀Co_0.5Ni_0.5 at. %, the slope is about 0.88 and therefore intermediate. A similar trend is obtained by measuring the plasticity index values obtained from the ratio of plastic deformation area and total area under the P-h curves since it is minimum for the alloy with 1 at. % Ni (i.e., 0.49) and maximum for 1 at. % Co (i.e., 0.54) compared to that of Cu₅₀Zr₅₀ (i.e., 0.52). The effect of the microalloying elements on the twinning propensity of the parent alloy has also been assessed from measurements at macroscale from differential scanning calorimetry (measuring the shift of the transformation temperatures) and X-ray diffraction (relative intensity change of austenite and martensite peaks before and after pre-compression) studies.

We present a novel experimental design for high sensitivity measurements of the electrical resistance of samples at high pressures (0-6GPa) and high temperatures (0-1000K) in a ’Paris-Edinburgh’ type large volume press. Uniquely, the electrical measurements are carried out directly on a small sample, thus greatly increasing the sensitivity of the measurement. The sensitivity to even minor changes in electrical resistance can be used to clearly identify phase transitions in material samples. Electrical resistance measurements are relatively simple and rapid to execute and the efficacy of the present experimental design is demonstrated by measuring the electrical resistance of Pb, Sn and Bi across a wide domain of temperature-pressure phase space and employing it to identify the loci of phase transitions. Based on these results, the phase diagrams of these elements are reconstructed to high accuracy and found to be in excellent agreement with previous studies. In particular, by mapping the locations of several well-studied reference points in the phase diagram of Sn and Bi, it is demonstrated that a standard calibration exists for the temperature and pressure, thus eliminating the need for direct or indirect temperature and pressure measurements. The present technique will allow simple and accurate mapping of phase diagrams under extreme conditions and may be of particular importance in advancing studies of liquid state anomalies.

Ultra-high molecular weight polyethylene (UHMWPE) is of great interest as a next-generation body armor material due to its superior mechanical properties. However, such unique properties depend critically on its microscopic structure characteristics, including the degree of crystallinity, chain alignment and morphology. Here we present a highly aligned UHMWPE and of its composite sheets containing uniformly dispersed boron nitride (BN) nanosheets. The dispersion of BN nanosheets into the UHMWPE matrix increases its mechanical properties over a broad temperature range. Experiments and simulation confirm that the alignment of chain segments in the composite matrix increases with temperature, leading to an improvement in mechanical properties at high temperature. Together with the large thermal conductivity of UHMWPE and BN, our findings serve in expanding the application spectrum of highly aligned polymer nanocomposite materials for ballistic panels and body armor over a broad range of temperatures.

There is a need for tough PDMS that maintains its optical clarity and high temperature resistance. Fillers increase the modulus, toughness, and tear resistance of PDMS, but diminish optical clarity. Entanglements can be used to improve the mechanical properties of PDMS, without impacting desirable properties. By enhancing entanglements, we can further increase the modulus, toughness, and tear resistance of PDMS elastomers while maintaining optical clarity and high temperature resistance. Here we discuss our efforts to synthesize novel PDMS network architectures with entanglement promoted toughness.

During chemical reactions such as polymerizations, the physical as well as chemical properties of a material change. While the viscoelastic properties usually can be characterized with a rheometer, no chemical information is obtained by the mechanical testing. The interpretation of rheometric results often relies on empirical models and a more phenomenological approach. For directly relating the changes in rheological behavior to chemical changes, Raman spectroscopy is employed in-situ with rheology. Raman is a spectroscopic technique based on inelastic light scattering from the sample molecules. By measuring the presence and intensities of molecular vibrations, Raman spectroscopy provides information on the chemical composition and structure of the sample. Furthermore, the Raman spectrum reflects internal molecular parameters such as bond strengths and the structural arrangement of the molecules within the material.

The combination of both techniques enables the simultaneous correlation of the mechanical properties and the molecular structure to obtain a better understanding of the sample.

The Anton Paar MCRxx2 (Modular Compact Rheometer) series of rheometers can be easily combined with the Anton Paar Cora Raman spectrometers via an optical fiber probe. For the applications presented here, a high temperature probe with an extended working distance of 10 mm was used to obtain measurements through the lower measurement plate of the rheometer system. To demonstrate the possibilities of a combined Rheo-Raman system, we investigated resin hardening as well as the melting behavior of polyethylene. First, the hardening of an epoxy resin was monitored providing insight into the chemical and physical changes during the reaction. Specifically, the reaction induced changes in the flow characteristics over time were characterized. In the Raman spectrum, the chemical changes can be found in the decrease of vibrational bands belonging to the epoxy group of the reaction component. Secondly, the phase transition from the crystalline to amorphous state in HDPE (High Density Polyethylene) was monitored while the polymer was heated. This resulted in a higher viscosity as well as alteration of vibrational bands in the Raman spectrum reflecting the conversion from a crystalline to an amorphous structure.

Having both viscoelastic and spectroscopic information on a sample allows a more detailed characterization of the observed sample. As a result, sample behavior can be analyzed in all its facets for better quality control as well as optimizing the process properties of materials.

Use of a pixelated detector in scanning transmission electron microscopy (STEM) enables the simultaneous acquisition of both the conventional annular dark-field (ADF) signal and the coherent bright-field (BF) diffraction pattern at every probe position. By detecting the scattering angle of nearly all the primary electrons that interact with the specimen, this “4D-STEM” technique promises to provide much more information about the specimen than conventional STEM using only an ADF detector.

An acute challenge for acquisition of 4D-STEM data is the relatively slow speed of pixelated detectors for capturing the coherent BF signal. Slow acquisition of STEM data introduces deleterious artifacts from specimen drift and thus forces users to acquire a severely limited the field-of-view—a significant problem for non-crystalline specimens.

One strategy to improve the speed of these detectors, is to reduce the number of pixels in the pixel array. However, this strategy prevents acquisition of the low- and medium-angle DF signal on the pixelated detector and it may also undersample the BF diffraction pattern and reduce its usefulness for differential phase contrast (DPC) or ptychography. This is especially problematic for complex specimens, such as specimens containing light atoms.

To address this challenge, we have implemented a new compressive-sensing readout mode—called Arbitrary Kernel Row Addressing (AKRA)—on our DE-16 direct detection camera. In AKRA readout mode, the user can specify any arbitrary combination of kernel rows from the detector to readout; all other kernel rows are skipped. By reading out fewer pixels, the detector framerate can be increased, enabling STEM imaging of a larger field-of-view. But since the “missing” pixels are scattering across the detector, the pixelated detector still captures a large area of the BF diffraction pattern and surrounding DF signal, with the “missing” pixels reconstructed using compressive-sensing algorithms. Therefore, AKRA enables fast 4D-STEM acquisition with a large pixelated detector so that rich structural information can be collected for large regions-of-interest of complex specimens.

A number of oxides, when prepared in nano-scale crystallites, exhibit a larger than bulk lattice parameter. A couple of these nano-oxides also show decreasing thermal expansion as well as stiffness constants as crystal-size goes beyond 10nm. We will discuss the physics and the materials science behind such an extraordinary behavior and the implications for solid-state chemistry and physics in nanoscale.

Cavitation erosion is a common mode of propeller surface damage, which seriously affects the hydrodynamic performance of propeller. In industrial applications, it is a surface treatment technology can effectively improve the cavitation erosion resistance performance by spraying elastomer organic coating on hydraulic components. Fluorinated polyurethane is a good elastomer which not only has excellent mechanical properties, but also has good ability of anti-biofouling. Herein, hydrophobic fluorinated polyurethanes (FPU), which combination of cavitation erosion resistance and biological fouling resistance coating were prepared by using the method of introducing fluorine with perfluoroalkyl ethanol (TEOH-10) for modification of isophorone diisocyanate (IPDI) and controlling the IPDI adding dosage and time. The chemical structure of FPU was investigated by Fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance spectrum (NMR) and gel permeation chromatography (GPC). The bonding strength between top coating and metal interlayer is significantly excellent(>4 MPa). Cavitation erosion tests were performed on Ultrasonic bubble generator for 10h. The mass loss of different cavitation time was examined by balance analysis. Surface morphology of the specimens was observed by Contour GTX and scanning electron microscope (SEM), respectively. Six-months marine field test in the Yellow Sea revealed that the FPU coatings exhibited excellent antifouling/fouling release performance. (This paper is funded by the International Exchange Program of Harbin Engineering University for Innovation-oriented Talents Cultivation.)

The unique optical properties of solution-processed chalcogenide glasses have long been of interest for photonic devices; a common test system is arsenic (III) sulfide (As₂S₃) in amine solvents. It is widely accepted that As₂S₃ takes on nanoscale structures in solution, and our ability to control properties when processing for devices is limited by our lack of a full understanding of these structures and the factors that influence them. This, in turn, is limited by the difficulty of characterizing the material in its dissolved state. This is a challenge faced commonly in structural biology, where cryo-electron microscopy (cryo-EM) has become the method of choice for determining the structure of hydrated biological molecules. We adapt this novel characterization technique for the chalcogenide samples and employ it alongside liquid cell electron microscopy and other more traditional methods to explore the in-solution structure of As₂S₃ in n-propylamine. Our results provide the first visuals of a long hypothesized structure and begin to reveal its dependence on core processing parameters like solution concentration and solvent type.

Pure SiO₂ glass is generally considered to be brittle, yet it is known that it can be deformed plastically in indentation or scratch tests. Understanding this plastic deformation is important in the development of devices with improved resistance to mechanical failure, but very little is known about the atomic scale mechanisms that control plasticity. Most work in this area has depended on indentation experiments, where complex inhomogeneous stress state makes interpretation difficult. To study plastic deformation quantitatively, we have developed silica glass micropillars having highly ideal geometries and tested them in compression in-situ in a scanning electron microscope. We characterized yield behavior, strain hardening, and strain rate sensitivity. Many behaviors are evident that are not accessible in indentation tests, including strain softening. Extremely large plastic strains were observed. Plastic deformation mechanisms and the possible role of electron illumination in plasticity is elucidated.

The fracture toughness of eight glasses was measured by the surface crack in flexure (SCF) and single-edged precracked beam (SEPB) methods. These include four soda lime silicas including a common plate glass form, two low iron modern forms, and one ancient Roman glass, a fused silica, a borosilicate crown (BK-7) optical glass, and two other borosilicate glasses for armor applications. The historical soda lime silica glass was made in an ancient Roman glass factory that operated in Palestine until 383 AD. This glass was exposed to the environment for almost sixteen centuries. The two SCF and SEPB methods have different susceptibilities to environmentally-assisted slow crack growth, that can be a major interference in measuring fracture toughness in ambient testing environments. A new definition for fracture toughness of glasses is proposed.

The fracture surface energy (γ) and the fracture toughness (KIc) of glass were estimated from the nominal composition by means of a simple approach to the structure at the atomic scale. The theoretical values are compared with the experimental ones, as obtained by means of self-consistent methods such as the Single Edge Pre-crack Beam (SEPB) and Chevron Notch (CN) ones, when available. A remarkable agreement is observed for ionocovalent glasses. In comparison, indentation cracking methods are found to mostly overestimate KIc by up to 50 %. In the case of metallic glasses, the theoretical values are much smaller than the experimental ones, which supports the occurrence of crack tip plasticity and shielding effect. Toughness (or ductility) is chiefly governed by the average coordination number, the bond directionality, and the atomic packing density.

Glasses are usually brittle, seriously limiting their practical usages. Recently, the intrinsic ductility of glass was found to increase with the Poisson’s ratio (v), with a sharp brittle-to-ductile (BTD) transition at v_BTD=0.31-0.32. Such a correlation between far-from-equilibrium fracture and near-equilibrium elasticity is unexpected and not understood. Via force-field tuning technique, metallic glasses, amorphous silicon, silica glasses, and polymeric glasses have been investigated, showing BTD transition accompanied by an increase in their Poisson’s ratio. Interestingly, beyond monolithic glasses, the Poisson’s ratio of glassy composites embedded with crystallites also correlate to the intrinsic ductility. The Poisson’s ratio, although defined elastically, reflects the bonding covalency and structural disorder, as well as microstructure heterogeneity.

Micron-sized hard-sphere colloidal particles can be used to form dense amorphous packings. Due to the large size and slow dynamics of colloidal particles, confocal microscopy can be used to investigate the 3D structure and dynamics of these glasses at the particle level. Previous studies have directly visualized both the inhomogeneous particle level strains in deformed colloidal glasses (i.e. STZs), and surrounding continuum strain fields. Measuring the stress in colloidal glasses during deformation, however, is a significant challeng; due to the large size and thermal interaction energies, colloidal solids have very small elastic moduli, on the order to 10-100mPa. We introduce a new technique, traction force rheology, to directly measure the mechanical response of colloidal glasses while simultaneously visualizing the microstructure using a confocal microscope. The method consists of a bilayer of colloidal glass atop a well calibrated soft polymer gel of slightly greater shear modulus. The composite bilayer is sheared and the shear stresses are inferred from the displacement of embedded tracer particles in the calibrated polymer gel. Using these stress measurements, we show that under cyclic applied shear the colloidal glass goes through a sequence of reversible and irreversible microscopic rearrangements which are related to the spatially correlated heterogeneities in the stress field.

Mechanical testing of bulk materials at high strain rates is a well-established field of research over the past multiple decades. Recently in the past decade, the field of micromechanics has been established and it is now recognized that a reduction in sample dimensions to the micro- and nano- scale leads to enhanced material properties such as strength and ductility. Until now, the micromechanical experiments such as indentation and micropillar compression has been conducted only at quasi-static strain rates. This limitation of low strain rate testing (<~0.1/s) at the microscale arises primarily due to the lack of high strain rate testing platforms capable of simultaneous high-speed actuation and high-speed sensing of microscale displacements and millinewton loads. Thus, the micromechanical properties and the deformation mechanisms for almost every material at strain rates above 0.1/s remains largely unknown.
This presentation will report, for the first time, a piezo-based experimental methodology for conducting high strain rate in situ micropillar compression testing at rates upto ~1000/s inside a scanning electron microscope. The strain rate achieved in this study is an increase of approximately four orders of magnitude compared to the current state-of-the-art micromechanical testing. The advantages and unique challenges of conducting micromechanical testing at high strain rates, with a particular focus on wave phenomena, inertia and sample recovery capability at particular strain, will be compared against traditional macroscale high strain rate tests conducted using kolsky bars.
Subsequently, a case study on the high strain rate micromechanical characterization of amorphous silica or glass, a commercially relevant classic material, will be presented. The rate dependent mechanical properties of ~1µm diameter amorphous silica micropillars will be presented as a function of strain rate across eight orders of magnitude, from 0.0001/s to 1000/s. Remarkably, the amorphous silica micropillars undergo a unique ductile-brittle-ductile transition in failure mechanism as the strain rate is increased from quasi-static to 1000/s. The stress-strain curves become serrated at strain rates between 0.01 and 10/s, a typical mechanical response of amorphous materials. Using the extracted velocities of the load drops in the serrated stress-strain curves, analytical calculations based on adiabatic heating and atomistic simulations reported in literature, an explanation for the anomalous plasticity behavior of amorphous silica at different strain rates will be presented. Also, it will be shown, for the first time, that the yield stress increases as the strain rate is increased till 10/s and then saturates as the strain rates are increased further till 1000/s. Finally, a comparison between the macro-scale and micro-scale mechanical response of amorphous silica at high strain rates will be used to demonstrate their startling differences.

Brittleness of metallic glasses (MGs) is a major drawback for their structural use at bulk scale. It has been shown that when reduced to ~100nm, some metallic glasses undergo a brittle-to-ductile transition and become plastically deformable. To harness this ductility emergent only at nano-scale and proliferate it onto materials with macroscale dimensions, we produced hollow-tube octet-truss nanolattices made out of sputtered NiAlZr with median wall thicknesses of ~10 to ~100nm, which results in a relative density of ~5% and renders them to be 20x lighter than their bulk counterparts.
In-situ uniaxial compression experiments conducted inside an SEM reveal a transition from brittle, catastrophic failure in thicker-walled nanolattices (>60 nm) to deformable, gradual, layer-by-layer collapse in thinner-walled nanolattices (<40 nm). We explain the brittle-to-deformable transition as wall thickness decreases in terms of the "smaller is more deformable" material size effect that arises in nano-sized MGs. We further irradiated ZrNiAl nano-architectures with 12 MeV Ni⁴⁺ ions and found that the thickest-walled nanolattices (~88 nm) withstood irradiation; all other substantially shrunk and collapsed. In-situ nanomechanical experiments reveal significant improvement in mechanical response upon irradiation, with a ~36% increase in average yield strength and enhanced deformability. Irradiated nanolattices deformed via a layer-by-layer collapse in contrast to catastrophic failure in equivalent as-fabricated samples.
Shortage of literature on mechanical properties and structural analysis of sputtered MGs motivated fundamental study of NiAlZr. We measured as-sputtered thin film to have a Young’s modulus of 70 GPa and a yield strength of 1.8 GPa and discovered that room temperature aging for three years increased modulus by ~15% and yield strength by ~25%. In-situ tensile experiments on individual nano-samples uncovered their ductility to be larger than reported for other MGs, reaching >10% engineering strains, >150% true strains, and necking down to a point in relatively large, 150nm-wide, samples. Ductility was dependent on specimen size and annealing conditions, with highest ductility of ~150% true strain in ~90 nm wide samples; all annealed specimens of equivalent dimensions were substantially less ductile. We present molecular dynamics simulations, TEM microstructural analysis, and synchrotron XRD characterization to explain observed mechanical behavior in the framework of β-relaxation, free volume reduction and a concomitant increase in short- and medium- range order upon annealing and aging. These findings illustrate key role of the presence and distribution of free volume in governing mechanical deformation of MGs. Our work demonstrates the importance of sample dimensions, fabrication method (sputtering), post-processing conditions (annealing, aging, and irradiation), as well as nano-architecting, in tuning mechanical properties of MGs.