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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 397 records · Page 22
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Rapid assessment of crystal orientation in semi-crystalline polymer films using rotational zone annealing and impact of orientation on mechanical properties

Crystal orientation in semi-crystalline polymers tends to enhance their performance, such as increased yield strength and modulus, along the orientation direction. Zone annealing (ZA) orients the crystal lamellae through a sharp temperature gradient that effectively directs the crystal growth, but the sweep rate (V ZA ) of this gradient significantly impacts the extent of crystal orientation. Here in this work, we demonstrate rotational zone annealing (RZA) as an efficient method to elucidate the influence of V ZA on the crystal morphology of thin films in a single experiment using isotactic poly(1-butene), PB-1, as a model semi-crystalline polymer. These RZA results are confirmed using standard, serial linear ZA to tune the structure from an almost unidirectional oriented morphology to weakly oriented spherulites. The overall crystallinity is only modestly changed in comparison to isothermal crystallization (maximum of 55% from ZA vs. 48% for isothermal crystallization). However, the average grain size increases and the spherulites become anisotropic from ZA. Due to these structural changes, the Young's modulus of the oriented films, both parallel and perpendicular to the spherulite orientation direction, is significantly increased by ZA. The modulus does become anisotropic after ZA due to the directionality in the crystal structure, with more than a threefold increase in the modulus parallel to the orientation direction for the highest oriented film in comparison to the modulus from isothermal crystallization. Lastly, RZA enables rapid identification of conditions to maximize orientation of crystals in thin polymer films, which could find utility in determining conditions to improve crystallinity and performance in organic electronics.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Towards 3D printed multifunctional immobilization for proton therapy: Initial materials characterization

Purpose: 3D printing technology is investigated for the purpose of patient immobilization during proton therapy. It potentially enables a merge of patient immobilization, bolus range shifting, and other functions into one single patient-specific structure. In this first step, a set of 3D printed materials is characterized in detail, in terms of structural and radiological properties, elemental composition, directional dependence, and structural changes induced by radiation damage. These data will serve as inputs for the design of 3D printed immobilization structure prototypes. Methods: Using four different 3D printing techniques, in total eight materials were subjected to testing. Samples with a nominal dimension of 20 × 20 × 80 mm{sup 3} were 3D printed. The geometrical printing accuracy of each test sample was measured with a dial gage. To assess the mechanical response of the samples, standardized compression tests were performed to determine the Young’s modulus. To investigate the effect of radiation on the mechanical response, the mechanical tests were performed both prior and after the administration of clinically relevant dose levels (70 Gy), multiplied with a safety factor of 1.4. Dual energy computed tomography (DECT) methods were used to calculate the relative electron density to water ρ{sub e}, the effective atomic number Z{sub eff}, and the proton stopping power ratio (SPR) to water SPR. In order to validate the DECT based calculation of radiological properties, beam measurements were performed on the 3D printed samples as well. Photon irradiations were performed to measure the photon linear attenuation coefficients, while proton irradiations were performed to measure the proton range shift of the samples. The directional dependence of these properties was investigated by performing the irradiations for different orientations of the samples. Results: The printed test objects showed reduced geometric printing accuracy for 2 materials (deviation > 0.25 mm). Compression tests yielded Young’s moduli ranging from 0.6 to 2940 MPa. No deterioration in the mechanical response was observed after exposure of the samples to 100 Gy in a therapeutic MV photon beam. The DECT-based characterization yielded Z{sub eff} ranging from 5.91 to 10.43. The SPR and ρ{sub e} both ranged from 0.6 to 1.22. The measured photon attenuation coefficients at clinical energies scaled linearly with ρ{sub e}. Good agreement was seen between the DECT estimated SPR and the measured range shift, except for the higher Z{sub eff}. As opposed to the photon attenuation, the proton range shifting appeared to be printing orientation dependent for certain materials. Conclusions: In this study, the first step toward 3D printed, multifunctional immobilization was performed, by going through a candidate clinical workflow for the first time: from the material printing to DECT characterization with a verification through beam measurements. Besides a proof of concept for beam modification, the mechanical response of printed materials was also investigated to assess their capabilities for positioning functionality. For the studied set of printing techniques and materials, a wide variety of mechanical and radiological properties can be selected from for the intended purpose. Moreover the elaborated hybrid DECT methods aid in performing in-house quality assurance of 3D printed components, as these methods enable the estimation of the radiological properties relevant for use in radiation therapy.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2013

Correlating Elastic Properties and Molecular Organization of an Ionic Organic Nanostructure

Mechanical and structural properties of ionically self-assembled nanostructures of meso-tetra(4-sulfonatophenyl)porphyrin (TSPP) and meso-tetra(4-pyridyl)porphyrin (TPyP) are presented. This is the first time that elastic modulus of an ionic porphyrin nanostructure has been reported. X-ray photoelectron spectroscopy (XPS), UV-visible spectra, and elemental analysis all support a stoichiometric 1 : 1 TSPP to TPyP composition. Atomic force microscopy (AFM) revealed that the porphyrin nanostructure is composed of stacked ribbons about 20 nm tall, 70 nm wide, and several microns in length. High resolution transmission electron microscopy (HRTEM) images showed clear lattice fringes 1.5 ± 0.2 nm in width aligned along the length of the nanorod. Selected area electron diffraction (SAED) and powder X-ray diffraction patterns of TSPP:TPyP are consistent with an orthorhombic system and space group Imm2 with lattice parameters a ¼ 26.71 °A, b ¼ 20.16 °A, and c ¼ 8.61 °A. Crystallographic data is consistent with an arrangement of alternating face-to-face TSPP and TPyP molecules forming ordered columns along the length of the nanorods. The structural integrity of the solid is attributed to combined noncovalent interactions that include ionic, hydrogen bonding, and p–p interactions. The values of Young’s modulus obtained for the crystalline TSPP:TPyP nanorods averaged 6.5 ± 1.3 GPa. This modulus is comparable to those reported for covalently bonded flexible polymeric systems. The robust bonding character of the TSPP:TPyP nanostructures combined with their mechanical properties makes them excellent candidates for flexible optoelectronic devices.

36 MATERIALS SCIENCE↗
NASA NTRS2002

Computational Nanomechanics of Carbon Nanotubes and Composites

Nanomechanics of individual carbon and boron-nitride nanotubes and their application as reinforcing fibers in polymer composites has been reviewed with interplay of theoretical modeling, computer simulations and experimental observations. The emphasis in this work is on elucidating the multi-length scales of the problems involved, and of different simulation techniques that are needed to address specific characteristics of individual nanotubes and nanotube polymer-matrix interfaces. Classical molecular dynamics simulations are shown to be sufficient to describe the generic behavior such as strength and stiffness modulus but are inadequate to describe elastic limit and nature of plastic buckling at large strength. Quantum molecular dynamics simulations are shown to bring out explicit atomic nature dependent behavior of these nanoscale materials objects that are not accessible either via continuum mechanics based descriptions or through classical molecular dynamics based simulations. As examples, we discus local plastic collapse of carbon nanotubes under axial compression and anisotropic plastic buckling of boron-nitride nanotubes. Dependence of the yield strain on the strain rate is addressed through temperature dependent simulations, a transition-state-theory based model of the strain as a function of strain rate and simulation temperature is presented, and in all cases extensive comparisons are made with experimental observations. Mechanical properties of nanotube-polymer composite materials are simulated with diverse nanotube-polymer interface structures (with van der Waals interaction). The atomistic mechanisms of the interface toughening for optimal load transfer through recycling, high-thermal expansion and diffusion coefficient composite formation above glass transition temperature, and enhancement of Young's modulus on addition of nanotubes to polymer are discussed and compared with experimental observations.

Srivastava, Deepak↗
DOE OSTI2014

Charge disproportionation in La{sub 1-x}Ca{sub x}FeO{sub 3−δ} (x = 0.4 and 0.5) investigated by mechanical spectroscopy

The nature of charge disproportionation in orthorhombic lanthanum orthoferrites La{sub 1-x}Ca{sub x}FeO{sub 3-δ} (x = 0.4 and 0.5) has been investigated by kilohertz mechanical spectroscopy. Contrast to rhombohedral La{sub 1-x}Sr{sub x}FeO{sub 3-δ} (x = 0.5), no elastic softening was observed in La{sub 1-x}Ca{sub x}FeO{sub 3-δ} above charge disproportionation. This different behavior of elastic modulus in La{sub 1-x}Ca{sub x}FeO{sub 3-δ} and La{sub 1-x}Sr{sub x}FeO{sub 3-δ} unveils the implicit orbital effect. Below charge disproportionation, an internal friction peak around 140 K was observed in La{sub 1-x}Ca{sub x}FeO{sub 3-δ}, which is similar to that in La{sub 1-x}Sr{sub x}FeO{sub 3-δ}. This peak is ascribed to an elastic manifestation of charge freezing and can be used as an indirect indication of CD in doped LaFeO{sub 3}.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Investigation of microstructure, micro-mechanical and optical properties of HfTiO{sub 4} thin films prepared by magnetron co-sputtering

Highlights: • HfTiO{sub 4} thin films were deposited by magnetron co-sputtering. • As-prepared and annealed at 800 °C thin films were nanocrystalline. • Optical properties and hardness were investigated in relation to thin films structure. • Hardness was 3-times higher in the case of as-deposited thin films. • HfTiO{sub 4} thin films are suitable for use as optical coatings with protective properties. - Abstract: Titania (TiO{sub 2}) and hafnium oxide (HfO{sub 2}) thin films are in the focus of interest to the microelectronics community from a dozen years. Because of their outstanding properties like, among the others, high stability, high refractive index, high electric permittivity, they found applications in many optical and electronics domains. In this work discussion on the hardness, microstructure and optical properties of as-deposited and annealed HfTiO{sub 4} thin films has been presented. Deposited films were prepared using magnetron co-sputtering method. Performed investigations revealed that as-deposited coatings were nanocrystalline with HfTiO{sub 4} structure. Deposited films were built from crystallites of ca. 4–12 nm in size and after additional annealing an increase in crystallites size up to 16 nm was observed. Micro-mechanical properties, i.e., hardness and elastic modulus were determined using conventional load-controlled nanoindentation testing. the annealed films had 3-times lower hardness as-compared to as-deposited ones (∼9 GPa). Based on optical investigations real and imaginary components of refractive index were calculated, both for as-deposited and annealed thin films. The real refractive index component increased after annealing from 2.03 to 2.16, while extinction coefficient increased by an order from 10{sup −4} to 10{sup −3}. Structure modification was analyzed together with optical energy band-gap, Urbach energy and using Wemple–DiDomenico model.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Recent advances in the mechanical characterization of shales at nano-to micro-scales: A review

Understanding geomechanical properties of shales, such as stiffness properties and fracture toughness, is important in different areas of petroleum industry-related activities. Nanoscale to microscale experiments on shale samples require a much smaller sample compared to macroscale experiments. This is a major advantage because irregularly-shaped drill cuttings from shales can be used for experimental analyses, such as nanoindentation or atomic force microscopy (AFM). However, characterization of mechanical properties at the nano- to micro-scale is a relatively new addition to classical geomechanical experiments on shales, and there is still a lack of both fundamental knowledge and standard procedures for conducting experiments at this scale. The theoretical principles of nanoindentation-based (Gridded Nanoindentation and Modulus Mapping) and AFM-based experimental methods (PeakForce QNMTM and AFM-IR), a review of the literature results and the major findings are explained in Sections 2 and 3, respectively. These experimental techniques are compared in Section 4. Overall, nanoindentation experiments reveal the anisotropy of organic matter (OM)-rich shales at the nanoscale, and it is shown that gridded nanoindentation is capable of characterizing different minerals with respect to their stiffness properties. The capability of AFM (PeakForce QNMTM) to differentiate between different minerals within OM-rich shales with distinct mechanical properties, in particular stiffness, is also demonstrated. It is shown that AFM-based methods are more straightforward than gridded-nanoindentation to characterize OM-rich shales based on the stiffness of different constituent minerals of OM-rich shales, but nanoindentation can apply higher loads than AFM-based methods. Therefore, they can measure creep properties and fracture toughness of OM-rich shales. Here, it is shown that the OM is the most compliant part of the OM-rich shales, but it is still unclear if thermal maturation has an impact on the stiffness of OM. It is necessary to investigate if there is a relationship between the OM type (kerogen, bitumen, etc.) and mechanical properties such as Young’s modulus and Creep rate.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Influence of temperature on the lattice misfit and elastic moduli of a Ni based single crystal superalloy with high volume fraction of γ′ phase

Highlights: • The variation of the lattice misfit with temperature in a Ni based single-crystal superalloy with high volume fraction of γ' phase was determined by high-temperature X-ray diffraction (HT-XRD) technique at temperatures between 25 °C and 1200 °C. • When the temperature was higher than 1100 °C, the γ' phase obviously dissolved, leading to a lower content of Mo and Re in the γ phase, and then resulted in a smaller absolute value of the lattice misfit. • The contribution of dissolution of γ′ phase to the reduction of the misfit increased with rising temperature and reached 29.5% at 1200 °C. • When the temperature exceeded 1100 °C, the difference of elastic moduli of γ and γ′ phases increased with rising temperature was attributed to the elastic modulus of γ phase decreased significantly. - Abstract: The variation of the lattice parameter with temperature in a Ni based single-crystal superalloy with high volume fraction of γ′ phase IC32 was determined by high-temperature X-ray diffraction (HT-XRD) technique at temperatures between 25 °C and 1200 °C. The effects of the temperature, especially the ultra-high temperature (beyond 1100 °C), on lattice misfit, elastic moduli, γ′ volume fraction and composition of γ, γ′ phases were investigated in this study. The results show that the absolute value of lattice misfit first increased and then decreased with increasing temperature and reached the maximum of 0.53% at 1100 °C. When the temperature was higher than 1100 °C, the γ′ precipitate obviously dissolved, leading to a lower content of Mo and Re in the γ phase, and then resulted in a smaller absolute value of lattice misfit. The contribution of dissolution of γ′ phase to the reduction of the misfit increased with rising temperature and reached 29.5% at 1200 °C. Moreover, when the temperature was above 1100 °C, the elastic moduli of the γ phase and alloy decreased significantly, while this phenomenon was not observed in the γ′ phase.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Impedance spectroscopy and conduction mechanism of LiAlP{sub 2}O{sub 7} material

Highlights: • X-ray diffraction analysis reveals the structure for LiAlP{sub 2}O{sub 7} compound. • Modulus study confirmed the grain relaxation. • The equivalent circuit consists of parallel combination of (R{sub g}//CPE{sub g}) series for region I and (R{sub g}//CPE{sub g}) series with CPE{sub e} for region II. • The conductivity is due to CBH model for region I and NSPT model for region II. - Abstract: LiAlP{sub 2}O{sub 7} compound has been obtained by standard solid-state reaction technique and found to crystallize in the monoclinic system with P2{sub 1/a} space group. The impedance plots are well fitted to two equivalent circuit models. The dc conductivity follows Arrhenius behavior with two different activation energies Ea(I) = 0.84 eV for T < 610 K and Ea(II) = 0.93 eV for T > 610 K. Actually, the values of activation energies obtained from the dc conductivity and the relaxation frequency are similar, and hence the transport in the titled compound can be described through a hopping mechanism, dominated by the motion of Li{sup +} ions. Besides, the frequency dependence of the conductivity is interpreted in terms of Jonscher’s law. The NSPT model and the CBH model is the most applicable conduction mechanism in region (I) and (II), respectively. The ion transport is due to the hopping of Li{sup +} ions along [100] tunnels direction. The conduction mechanism is studied with the help of Elliot’s theory, and the Elliot’s parameters are determined.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Fracture propagation in Indiana Limestone interpreted via linear softening cohesive fracture model

In this study, we examine the use of a linear softening cohesive fracture model (LCFM) to predict single-trace fracture growth in short-rod (SR) and notched 3-point-bend (N3PB) test configurations in Indiana Limestone. The broad goal of this work is to (a) understand the underlying assumptions of LCFM and (b) use experimental similarities and deviations from the LCFM to understand the role of loading paths of tensile fracture propagation. Cohesive fracture models are being applied in prediction of structural and subsurface fracture propagation in geomaterials. They lump the inelastic processes occurring during fracture propagation into a thin zone between elastic subdomains. LCFM assumes that the cohesive zone initially deforms elastically to a maximum tensile stress ( σ max ) and then softens linearly from the crack opening width at σ max to zero stress at a critical crack opening width w 1 . Using commercial finite element software, we developed LCFMs for the SR and N3PB configurations. After fixing σ max with results from cylinder splitting tests and finding an initial Young's modulus ( E ) with unconfined compressive strength tests, we manually calibrate E and w 1 in the SR model against an envelope of experimental data. We apply the calibrated LCFM parameters in the N3PB geometry and compare the model against an envelope of N3PB experiments. For accurate simulation of fracture propagation, simulated off-crack stresses are high enough to require inclusion of damage. Different elastic moduli are needed in tension and compression. We hypothesize that the timing and location of shear versus extensional micromechanical failures control the qualitative macroscopic force-versus-displacement response in different tests. For accurate prediction, the LCFM requires a constant style of failure, which the SR configuration maintains until very late in deformation. The N3PB configuration does not maintain this constancy. To be broadly applicable between geometries and failure styles, the LCFM would require additional physics, possibly including elastoplastic damage in the bulk material and more complicated cohesive softening models.

58 GEOSCIENCES↗
DOE OSTI2016

Direct observations of damage during unconfined brittle failure of Carrara marble

Abstract To observe and quantify the production of microfracturing from initial yield to failure, we deformed Carrara marble samples in uniaxial compression at 20, 105, and 180°C and continuously observed a region of about 1 mm 2 on an exposed face with a long‐working distance microscope. Using image processing and microscale strain‐mapping techniques, we measured local strains over a length scale of tens of micrometers. By treating the images with various filters, we identified linear damage features, as well as the magnitude of localized strain and the mode of deformation, i.e., shear versus normal deformation. In general, shear deformation is more prevalent after initial yielding, while tensile deformation dominates closer to peak stress. Independent measurements of both stress and microcrack density at different stages of each experiment provide a unique opportunity to explicitly compare the data with damage models. The model of Ashby and Sammis (1990) significantly underestimated the damage that the rock could sustain before peak stress, perhaps owing to the influence of weak grain boundaries on the damage production. In these samples, microcracks tended to form near boundaries before yield stress. During strain hardening, the damage parameters increased rapidly as longer microcracks grew along the boundaries and finally transected grains as loading neared peak stress. The microcrack density can be empirically related to the reduction of Young's modulus; stiffness ratios decay exponentially with increasing microcrack density for T ≤ 105°C.

Tal, Yuval↗
DOE OSTI2017

Field characterization of elastic properties across a fault zone reactivated by fluid injection

In this paper, we studied the elastic properties of a fault zone intersecting the Opalinus Clay formation at 300 m depth in the Mont Terri Underground Research Laboratory (Switzerland). Four controlled water injection experiments were performed in borehole straddle intervals set at successive locations across the fault zone. A three-component displacement sensor, which allowed capturing the borehole wall movements during injection, was used to estimate the elastic properties of representative locations across the fault zone, from the host rock to the damage zone to the fault core. Young's moduli were estimated by both an analytical approach and numerical finite difference modeling. Results show a decrease in Young's modulus from the host rock to the damage zone by a factor of 5 and from the damage zone to the fault core by a factor of 2. In the host rock, our results are in reasonable agreement with laboratory data showing a strong elastic anisotropy characterized by the direction of the plane of isotropy parallel to the laminar structure of the shale formation. In the fault zone, strong rotations of the direction of anisotropy can be observed. Finally, the plane of isotropy can be oriented either parallel to bedding (when few discontinuities are present), parallel to the direction of the main fracture family intersecting the zone, and possibly oriented parallel or perpendicular to the fractures critically oriented for shear reactivation (when repeated past rupture along this plane has created a zone).

58 GEOSCIENCES↗
DOE OSTI2018

Superstretchable, Self-Healing Polymeric Elastomers with Tunable Properties

Utilization of self-healing chemistry to develop synthetic polymer materials that can heal themselves with restored mechanical performance and functionality is of great interest. Self-healable polymer elastomers with tunable mechanical properties are especially attractive for a variety of applications. In this paper, a series of urea functionalized poly(dimethyl siloxane)-based elastomers (U-PDMS-Es) are reported with extremely high stretchability, self-healing mechanical properties, and recoverable gas-separation performance. Tailoring the molecular weights of poly(dimethyl siloxane) or weight ratio of elastic cross-linker offers tunable mechanical properties of the obtained U-PDMS-Es, such as ultimate elongation (from 984% to 5600%), Young's modulus, ultimate tensile strength, toughness, and elastic recovery. The U-PDMS-Es can serve as excellent acoustic and vibration damping materials over a broad range of temperature (over 100 °C). The strain-dependent elastic recovery behavior of U-PDMS-Es is also studied. After mechanical damage, the U-PDMS-Es can be healed in 120 min at ambient temperature or in 20 min at 40 °C with completely restored mechanical performance. Lastly, the U-PDMS-Es are also demonstrated to exhibit recoverable gas-separation functionality with retained permeability/selectivity after being damaged.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Mechanically Reinforced Pseudosolid Polyelectrolyte Membranes via Layer-by-Layer Assembly for High-Performing Lithium-Metal Batteries

Ionogels are emerging as high-potential pseudosolid electrolytes for lithium-metal batteries (LMBs), leveraging their intrinsic high ionic conductivity from entrapped ionic liquid (IL) electrolytes. However, their practical application is hindered by poor mechanical strength stemming from the confinement of ILs within a polymer matrix. To address this challenge, the formation of conformal polyion coatings with functional groups is reported to be relevant to LMBs’ application on ionogels, utilizing a layer-by-layer (LbL) assembly strategy. Here, this approach significantly enhances the mechanical strength (Young's modulus and tensile strength) and electrochemical performance of ionogels, owing to the tailored interface modifications introduced by functional groups’ specific conformal polyion coatings. The core of this methodology leverages the inherent ionic structure of ionogels to enable facile interface modification through Coulombic interactions between polyanions and polycations. These conformally coated interface functionalized membranes show improved electrochemical performance when integrated with cathode materials such as LiFePO 4 (LFP) and LiNi 0.8 Mn 0.1 Co 0.1 O 2 (NMC811) in an LMB configuration, underscoring their potential for robust, high-conductivity, pseudosolid membranes for LMB applications. These innovative pseudosolid membranes offer improved mechanical and electrochemical properties, leading to higher battery efficiency and safety, making them promising candidates for next-generation LMB technology.

25 ENERGY STORAGE↗
DOE OSTI2024

Self–Healing and Stretchable Molecular Ferroelectrics with High Expandability

The interplay between crystal ordering and stretchability is frequently encountered in contemporary materials science, particularly in the case of ferroelectrics. The inherent dilemma arises when these materials need to withstand repetitive mechanical deformations or stretching without sacrificing their crystal integrity, all while retaining their remarkable ferroelectric properties and even exhibiting self-healing capabilities. This complexity further presents a significant challenge in the design and engineering of mechanically rigid molecular ferroelectric crystals, particularly for applications where both precise crystalline structure and mechanical adaptability are crucial. In this study, the humidity-controlled expansion and contraction, dissolution, and recrystallization of a self-assembled molecular ferroelectric-in-hydrogel framework are reported. Self-healing ferroelectric-in-hydrogel networks exhibit a recyclable humidity-tailored ionic conductivity from 2.86 × 10 –6 to 1.36 × 10 –5 S cm –1 , facilitating the stretchable piezoelectric sensing. Additionally, the dynamic bond reforming interactions are observed, leading to the tailoring of Young's modulus from 452 to 170 MPa, maintaining ferroelectricity under a strain of 20% with a piezoelectric coefficient of 15.7 pC N –1 . Upon lattice contraction, the molecular contacts undergo reforming, leading to the restoration of stretchable ferroelectrics/piezoelectrics and paving the way for stretchable bioelectronics for full-body motion monitoring. The capabilities highlighted here open avenues for stretchable and self-healing ferroelectric-in-hydrogel bioelectronic technologies.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Strong Graphene 3D Assemblies with High Elastic Recovery and Hardness

The rational design and construction of 3D graphene assemblies is a crucial step to extend the graphene properties for practical applications. In this work, a novel interfacially reactive self-assembling process is reported to prepare well-organized 3D honeycomb-like graphene assemblies with unique polygonal nanopores interconnected by silicon-oxygen chemical bonds. The newly developed silicate-bridged graphene assembly (SGA) exhibits an exceptionally high hardness of 13.09 GPa, outperforming all existing 3D graphene materials, while maintains high Young’s modulus (162.96 GPa), elastic recovery (75.27%), and superb thermal stability (600 °C in air). The observed unusual merits are resulted from unique pore structure combining the mechanical stability of the trihedral-nanopore structure and the deformability of the other polygonal nanopores. As a filling material, a merely 0.05% (w/w) addition of SGA could double the impact resistance of unsaturated resins (e.g., polyester). While SGA is attractive for various applications, including body armors, wearable electronics, space elevators, and multifunctional reinforcement fibers for automobiles, and aerospace vehicles, the novel liquid sodium-water interfacial reactive self-assembling developed in this study could open avenues for further development of various well-defined 3D assemblies from graphene and many other materials.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Strain-Induced Structural Deformation Study of 2D Mo x W (1- x ) S 2

The potential ability of tuning properties and its possible applications in the fields of optoelectronics and/or flexible electronics, has increased the demand for 2D alloys in recent times. Understanding the mechanical performance of 2D materials under extreme conditions, such as strain, stress, and fracture is essential for the reliable electronic devices based on these structures. Here, combined molecular dynamics (MD) simulations and in situ Raman spectroscopic techniques are used to study the mechanical performance of a 2D alloy system, MoxW (1- x ) S 2 . It is determined that W substitution in MoS 2 causes solid-solution strengthening and increase in the Young's modulus values. Higher W content decreases failure strain for MoS 2 . Due to spatially resolved Raman spectroscopy and MD simulations results, a detailed model to explain failure mechanisms in MoxW (1- x ) S 2 alloys is proposed.

36 MATERIALS SCIENCE↗