Cation-Dependent Hierarchical Assembly of U60 Nanoclusters into Macro-Ion Assemblies Imaged via Cryogenic Transmission Electron Microscopy
Abstract not provided
Soltis, Jennifer A.↗
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Results for “Dynamic TEM”
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Layer size polydispersity in hydrated montmorillonite creates multiscale porosity networks
The aluminosilicate layers of the swelling clay mineral montmorillonite, and the saturated pores they delineate, control the mechanical properties and the transport of solutes in many natural and engineered environments. However, the structural basis of montmorillonite porosity remains poorly characterized due to the difficulty in visualizing hydrated samples in their native state. Here in this paper, we used cryogenic transmission electron microscopy (cryo-TEM) and cryo electron tomography (cryo-ET) to show that stacking defects within minimally altered, fully hydrated montmorillonite particles define multiscale porosity networks. Variations in layer lateral dimensions over tens to thousands of nanometers cause a range of topological and dynamic defects that generate pervasive curvature and introduce previously uncharacterized solute transport pathways. Observations of long-range rotational order between neighboring layers indicate that the layer-layer interactions that govern clay swelling involve three dimensional orienting forces that operate across nanoscale pores. These direct observations of the hierarchical structure of hydrated montmorillonite pore networks with nanoscale resolution reveal potentially general aspects of colloidal interactions in fluid-saturated clay minerals.
36 MATERIALS SCIENCE↗
Hydrodynamic Analysis of a Suspended Cylinder Under Regular Wave Loading Based on Computational Fluid Dynamics: Preprint
An investigation into the computation of hydrodynamic loads on a suspended cylinder in regular waves is presented. The primary goal was to perform a three-way-validation of the loads between experimental measurements and simulations from two computational methods. Experimental measurements of the longitudinal inline force on a cylinder suspended at a fixed po- sition were available from the Offshore Code Comparison Col- laboration, Continued, with Correlation (OC5) project, Phase Ia. These measurements were compared to Computational Fluid Dynamics (CFD) simulations based on the solution of Reynolds- averaged Navier-Stokes (RANS) equations, as implemented in STAR-CCM plus. The study encompassed a sensitivity analysis of the loads computed in STAR-CCM plus based on wave modeling, boundary conditions, turbulence modeling, and spatial and tem- poral discretization. The analysis was supplemented by results generated with the offshore wind turbine engineering software OpenFAST, based on a hybrid combination of second-order po- tential flow and viscous drag fromMorison's equation. The focus of the investigation was on the assessment of the accuracy of the computation of first- and higher-order hydrodynamic loads. Sub- stantial differences were observed in the numerical prediction of the second and third harmonic force contribution. Local flow field analysis with CFD was applied to study the physics of wave run-up and diffraction dynamics to identify the causes.
16 TIDAL AND WAVE POWER↗
Toward Computation-Guided Design of Tunable Organic-Inorganic CdS Quantum Dot Binary Superlattices
Combining the advantages of structural programmability in sequence-defined biomimetic molecules and the controllable packing geometry in nanoparticle superlattices, we demonstrate a self-assembled organic-inorganic superlattice whose structure can be altered with the slightest change in the sequence of the organic counterpart. Here, oleate-coated CdS quantum dots (QDs) form a square-packed superlattice with a 1:1 molar equivalence of a di-block amphiphilic peptoid (Nbrpe6Dig) in chloroform. In contrast, no apparent structure is observed in the organic solvent alone. Based on theoretical evidence, we show that the assembly is a binary superlattice where both the CdS QDs and the peptoids serve as building blocks and further predict a correlation between the superlattice structure and the peptoid sequence. The computationally guided prediction is validated by experiments where superlattice transformation is observed with modified peptoids. The mechanism identified in our work inspires new ways to control and tune organic-inorganic hybrid nanomaterial self-assembly.
Qi, Xin↗
Highly Conductive Multifunctional Graphene Polycarbonate Nanocomposites
Graphene nanosheet bisphenol A polycarbonate nanocomposites (0.027 2.2 vol %) prepared by both emulsion mixing and solution blending methods, followed by compression molding at 287 C, exhibited dc electrical percolation threshold of approx.0.14 and approx.0.38 vol %, respectively. The conductivities of 2.2 vol % graphene nanocomposites were 0.512 and 0.226 S/cm for emulsion and solution mixing. The 1.1 and 2.2 vol % graphene nanocomposites exhibited frequency-independent behavior. Inherent conductivity, extremely high aspect ratio, and nanostructure directed assembly of the graphene using PC nanospheres are the main factors for excellent electrical properties of the nanocomposites. Dynamic tensile moduli of nanocomposites increased with increasing graphene in the nanocomposite. The glass transition temperatures were decreased with increasing graphene for the emulsion series. High-resolution electron microscopy (HR-TEM) and small-angle neutron scattering (SANS) showed isolated graphene with no connectivity path for insulating nanocomposites and connected nanoparticles for the conductive nanocomposites. A stacked disk model was used to obtain the average particle radius, average number of graphene layers per stack, and stack spacing by simulation of the experimental SANS data. Morphology studies indicated the presence of well-dispersed graphene and small graphene stacking with infusion of polycarbonate within the stacks.
Yoonessi, Mitra↗
SAMS Acceleration Measurements on Mir (NASA Increment 4)
During NASA Increment 4 (January to May 1997), about 5 gigabytes of acceleration data were collected by the Space Acceleration Measurements System (SAMS) onboard the Russian Space Station, Mir. The data were recorded on 28 optical disks which were returned to Earth on STS-84. During this increment, SAMS data were collected in the Priroda module to support the Mir Structural Dynamics Experiment (MiSDE), the Binary Colloidal Alloy Tests (BCAT), Angular Liquid Bridge (ALB), Candle Flames in Microgravity (CFM), Diffusion Controlled Apparatus Module (DCAM), Enhanced Dynamic Load Sensors (EDLS), Forced Flow Flame Spreading Test (FFFr), Liquid Metal Diffusion (LMD), Protein Crystal Growth in Dewar (PCG/Dewar), Queen's University Experiments in Liquid Diffusion (QUELD), and Technical Evaluation of MIM (TEM). This report points out some of the salient features of the microgravity environment to which these experiments were exposed. Also documented are mission events of interest such as the docked phase of STS-84 operations, a Progress engine bum, Soyuz vehicle docking and undocking, and Progress vehicle docking. This report presents an overview of the SAMS acceleration measurements recorded by 10 Hz and 100 Hz sensor heads. The analyses included herein complement those presented in previous summary reports prepared by the Principal Investigator Microgravity Services (PIMS) group.
DeLombard, Richard↗
SAMS Acceleration Measurements on Mir From January to May 1997 (NASA Increment 4)
During NASA Increment 4 (January to May 1997), about 5 gigabytes of acceleration data were collected by the Space Acceleration Measurements System (SAMS) onboard the Russian Space Station, Mir. The data were recorded on 28 optical disks which were returned to Earth on STS-84. During this increment, SAMS data were collected in the Priroda module to support the Mir Structural Dynamics Experiment (MiSDE), the Binary Colloidal Alloy Tests (BCAT), Angular Liquid Bridge (ALB), Candle Flames in Microgravity (CFM), Diffusion Controlled Apparatus Module (DCAM), Enhanced Dynamic Load Sensors (EDLS), Forced Flow Flame Spreading Test (FFFT), Liquid Metal Diffusion (LMD), Protein Crystal Growth in Dewar (PCG/Dewar), Queen's University Experiments in Liquid Diffusion (QUELD), and Technical Evaluation of MIM (TEM). This report points out some of the salient features of the microgravity environment to which these experiments were exposed. Also documented are mission events of interest such as the docked phase of STS-84 operations, a Progress engine burn, Soyuz vehicle docking and undocking, and Progress vehicle docking. This report presents an overview of the SAMS acceleration measurements recorded by 10 Hz and 100 Hz sensor heads. The analyses included herein complement those presented in previous summary reports prepared by the Principal Investigator Microgravity Services (PIMS) group.
DeLombard, Richard↗
An Examination of Autumn Southern Polar Ozone Tendencies and the Residual Circulation in MERRA-2 Products
Changes in lower stratospheric ozone caused by dynamical transport can be difficult to characterize and thus are sometimes difficult to distinguish from chemical losses. Correlations between ozone changes and various dynamical proxies (e.g., the eddy heat flux) from year to year can be of interest, but they do little in themselves to explain the ozone transport mechanisms behind such correlations. In this study, we use products from the Modern-Era Retrospective analysis for Research and Applications Version 2 (MERRA-2) to calculate the ozone mass flux, integrating it in space and time over the upper tropospheric/lower stratospheric Southern polar cap during periods when little chemical loss is expected. The ozone mass flux is expressed in terms of components of the residual circulation of the Transformed Eulerian Mean (TEM, i.e., 𝑣𝑣̅ ∗and 𝑤𝑤(∗) as well as eddy mixing terms. We relate these terms to the local ozone mass tendency ("#! "$ ), similarly integrated, and we find that the interannual variability of the ozone changes are strongly related to the residual meridional circulation and the meridional eddy mixing terms. These directly calculated dynamical transport terms provide clearer ozone proxies. Removing these advective terms from a long-term ozone time series can more effectively reveal ozone variations and long-term trends, specifically those caused by photochemical production and losses (e.g., human-produced ozone depletion).
Ozone↗
New Thermoplastic Vulcanizate Based on Acetoacetoxy Functionalized Natural Rubber/Polyamide12 Blend Filled with Carbon Black
Thermoplastic vulcanizates (TPVs) based on blends of natural rubber (NR) grafted with poly(acetoacetoxyethyl methacrylate), NR-g-PAAEM, and polyamide12 (PA12) were prepared by the dynamic vulcanization technique. NR-g-PAAEM was first prepared and its surface free energy was evaluated by means of contact angles. Blends of NR-g-PAAEM and PA12 were then prepared at a 60/40 blend ratio (wt%) using a dynamic vulcanization technique. The results revealed that TPVs exhibited a dispersed-phase morphology. However, the TPVs filled with carbon black (CB) showed much smaller dispersed rubber particles when compared to the unfilled TPV. TEM analysis also revealed that the CB appeared to be mainly located within the NR-g-PAAEM phase. The presence of CB generally raised the melt viscosity and increased shear during melt-mixing, resulting in finer dispersion of the rubber particles. Additionally, a significant enhancement in the tensile properties of the TPV was also achieved by the incorporation of CB. The optimum tensile properties were attained by the addition 30 phr of CB. The results also showed that the incorporation of CB into the NR-g-PAAEM/PA12 TPVs improved their stress relaxation properties. Moreover, the effects of reprocessing on the mechanical properties of the TPV filled with CB were also investigated. Although the TPV filled with CB exhibited reprocessing capability, reprocessing at high temperature and shear forces was found to negatively affect its tensile properties, especially after the third reprocessing cycle.
36 MATERIALS SCIENCE↗
Impacts of surface spins and inter-particle interactions on the magnetism of hollow γ-Fe{sub 2}O{sub 3} nanoparticles
A comparative study of the static and dynamic magnetic properties of polycrystalline hollow γ-Fe{sub 2}O{sub 3} nanoparticles with two distinctly different sizes of 10.3 ± 1.3 nm and 14.8 ± 0.5 nm has been performed. High-resolution TEM images confirmed the crystalline structure and the presence of the shell thickness of 2.17 ± 0.28 nm and 3.25 ± 0.24 nm for the 10 nm and 15 nm particles, respectively. Quantitative fits of the frequency dependent ac susceptibility to the Vogel-Fulcher model, τ = τ{sub o} exp[E{sub a}/k(T − T{sub o})], show stronger inter-particle interactions in the 15 nm nanoparticles than in the 10 nm nanoparticles. A systematic analysis of the room-temperature magnetic loops using the modified Langevin function indicates a stronger effect of disordered surface spins in the 10 nm hollow particles as compared to the 15 nm hollow particles. Our study suggests that while the effect of disordered surface spins dominates the magnetic behavior of the 10 nm hollow particles, both the disordered surface spins and inter-particle interactions contribute to the magnetism of the 15 nm hollow particles.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Feasibility study of a high spatial and time resolution beam emission spectroscopy diagnostic for localized density fluctuation measurements in Lithium Tokamak eXperiment-β (LTX-β)
Trapped electron mode (TEM) is the main source of turbulence predicted for the unique operation regime of a flat temperature profile under low-recycling conditions in the LTX-β tokamak, while ion temperature gradient driven turbulence may also occur with gas fueling from the edge. To investigate mainly TEM scale density fluctuations, a high spatial and time resolution 2D beam emission spectroscopy (BES) diagnostic is being developed. Apart from spatially localized density turbulence measurement, BES can provide turbulence flow and flow shear dynamics. This BES system will be realized using an avalanche photodiode-based camera and narrow band interference filter. The system can acquire data at 2 MHz. Simulations with the Simulation of Spectra (SOS) code indicate that a high signal to noise ratio can be achieved with the proposed system. This will enable sampling the density fluctuations at this high time resolution. Finally, the design considerations and system optimization using the SOS code are presented.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
Formation and Growth of Stacking Fault Tetrahedra in Ni via Vacancy Aggregation Mechanism
Using molecular dynamics simulations, the formation and growth of stacking fault tetrahedra (SFT) are captured by vacancy cluster diffusion and aggregation mechanisms in Ni. The vacancytetrahedron acts as a nucleation point for SFT formation. Simulations show that perfect SFT can grow to the next size perfect SFT via a vacancy aggregation mechanism. The stopping and range of ions in matter (SRIM) calculations and transmission electron microscopy (TEM) observations reveal that SFT can form farther away from the initial cascade-event locations, indicating the operation of diffusion-based vacancy-aggregation mechanism.
74 ATOMIC AND MOLECULAR PHYSICS↗
Thermal annealing dynamics of carbon-coated LiFePO{sub 4} nanoparticles studied by in-situ analysis
The thermal behavior of core-shell carbon-coated lithium iron phosphate (LiFePO{sub 4}-C) nanoparticles made by flame spray pyrolysis (FSP) during annealing was investigated by in-situ transmission electron microscopy (TEM), in-situ X-ray powder diffraction (XRD) as well as ex-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Crystallization of the initially glassy LiFePO{sub 4}-C nanoparticles starts at quite low temperatures (T=400 °C), forming single crystals inside the confinement of the carbon shell. Upon increasing the temperature to T≥700 °C, LiFePO{sub 4} starts to diffuse through the carbon shell resulting in cavities inside the mostly intact carbon shell. By increasing the temperature further to T≥800 °C, the initial core-shell morphology converts into open carbon shells (flakes and cenospheres) and bulky LiFePO{sub 4} particles (diameter in the range 300–400 nm), in agreement with ex-situ experiments. - Graphical abstract: TEM images of a typical sample area recorded at room temperature and after heating in-situ heating reveal the growth of particles and the formation of empty carbon cages. - Highlights: • LiFePO{sub 4} coated by a carbon shell is produced by flame spray pyrolysis. • The amorphous LiFePO{sub 4} starts to crystallize at 400 °C as revealed by in-situ XRD. • Crystal growth was visualized by TEM heating experiments. • The formation of empty carbon cages starts at 700 °C.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Dynamics of Transformation from Platinum Icosahedral Nanoparticles to Larger FCC Crystal at Millisecond Time Resolution
Atomic motion at grain boundaries is essential to microstructure development, growth and stability of catalysts and other nanostructured materials. However, boundary atomic motion is often too fast to observe in a conventional transmission electron microscope (TEM) and too slow for ultrafast electron microscopy. Here, we report on the entire transformation process of strained Pt icosahedral nanoparticles (ICNPs) into larger FCC crystals, captured at 2.5 ms time resolution using a fast electron camera. Results show slow diffusive dislocation motion at nm/s inside ICNPs and fast surface transformation at μm/s. By characterizing nanoparticle strain, we show that the fast transformation is driven by inhomogeneous surface stress. And interaction with pre-existing defects led to the slowdown of the transformation front inside the nanoparticles. Particle coalescence, assisted by oxygen-induced surface migration at T ≥ 300°C, also played a critical role. Furthermore by studying transformation in the Pt ICNPs at high time and spatial resolution, we obtain critical insights into the transformation mechanisms in strained Pt nanoparticles.
36 MATERIALS SCIENCE↗
Experimental and theoretical investigation of a mesoporous K x WO 3 material having superior mechanical strength
Mesoporous materials with tailored properties hold great promise for energy harvesting and industrial applications. Here we have synthesized a novel tungsten bronze mesoporous material (K x WO 3 ; x ~ 0.07) having inverse FDU-12 type pore symmetry and a crystalline framework. In situ small angle X-ray scattering (SAXS) measurements of the mesoporous K 0.07 WO 3 show persistence of a highly ordered meso-scale pore structure to high pressure conditions (~18.5 GPa) and a material with remarkable mechanical strength despite having ~35% porosity. Pressure dependent in situ SAXS measurements reveal a bulk modulus κ = 44 ± 4 GPa for the mesoporous K x WO 3 which is comparable to the corresponding value for the bulk monoclinic WO 3 (γ-WO 3 ). Evidence from middle angle (MAXS) and wide angle X-ray scattering (WAXS), high-resolution transmission electron microscopy (HR-TEM) and Raman spectroscopy shows that the presence of potassium leads to the formation of a K-bearing orthorhombic tungsten bronze (OTB) phase within a monoclinic WO 3 host structure. Our ab initio molecular dynamics calculations show that the formation of the OTB phase provides superior strength to the mesoporous K 0.07 WO 3 .
36 MATERIALS SCIENCE↗
Energetic basis for the molecular-scale organization of bone
Here, the remarkable properties of bone derive from a highly organized arrangement of co-aligned nm-scale apatite platelets within a fibrillar collagen matrix. The origin of this arrangement is poorly understood and the crystal structures of hydroxyapatite (HAP) and the non-mineralized collagen fibrils alone do not provide an explanation. Moreover, little is known about collagen-apatite interaction energies, which should strongly influence both the molecular-scale organization and the resulting mechanical properties of the composite. We investigated collagen-mineral interactions by combining dynamic force spectroscopy (DFS) measurements of binding energies with molecular dynamics (MD) simulations of binding and AFM observations of collagen adsorption on single crystals of calcium phosphate for four mineral phases of potential importance in bone formation. In all cases, we observe a strong preferential orientation of collagen binding, but comparison between the observed orientations and TEM analyses native tissues shows only calcium-deficient apatite (CDAP) provides an interface with collagen that is consistent with both. MD simulations predict preferred collagen orientations that agree with observations and results from both MD and DFS reveal large values for the binding energy due to multiple binding sites. These findings reconcile apparent contradictions inherent in a hydroxyapatite or carbonated apatite (CAP) model of bone mineral and provide an energetic rationale for the molecular scale organization of bone.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Dynamic Nuclear Polarization Enhanced 113 Cd Solid-State Nuclear Magnetic Resonance Spectroscopy Reveals CdSe Nanocrystals with Triangular Two-Dimensional Projections are Terminated by {100} Facets
Surface structure plays an important role in particle growth and determining the chemical and photophysical properties of semiconductor nanocrystals (NCs). Therefore, there is a need for structural tools that can characterize and detect different surface facets. Here, we sought to investigate the structure of {111} CdSe facets by applying dynamic nuclear polarization (DNP) enhanced 113 Cd and 77 Se solid-state nuclear magnetic resonance (SSNMR) spectroscopy to zinc-blende CdSe NCs that exhibit triangular two-dimensional (2D) projections within transmission electron microscope (TEM) images. It was originally hypothesized in the literature that these CdSe NCs were tetrahedral in shape and terminated by facets from the {111} family of lattice planes of the zinc-blende structure. Surprisingly, we observe 113 Cd NMR spectra indicating that the primary facets are from the {100} family of lattice planes. We also obtained DNP-enhanced 113 Cd and 77 Se SSNMR spectra of recently reported right trigonal bipyramidal (rTriBP) CdSe NCs grown by seeded growth. The 113 Cd NMR spectra rTriBP CdSe NCs are consistent with {100} surface facets. TEM images show that rTriBP NCs may also exhibit triangular 2D projections that are similar to the so-called tetrahedral NCs. Based upon these results, we conclude that the so-called tetrahedral NCs are predominantly terminated by {100} surface facets and most likely have the same shape as rTriBP NCs. These results highlight the need for multiple complementary techniques when assigning the shape and surface termination of NCs.
Santhiran, Anuluxan [Ames Laboratory (AMES), Ames,↗
In Situ Probing Potassium-ion Intercalation-induced Amorphization in Crystalline Iron Phosphate Cathode Materials
Na-ion and K-ion batteries are promising alternatives for large-scale energy storage applications due to their abundance and low cost. Intercalation of these large ions could cause irreversible structural deformation and partial to complete amorphization in the crystalline electrodes. The designing of new amorphous electrodes is another route to develop electrodes to store these ions reversibly. Lack of understanding of dynamic changes in the amorphous nanostructures during battery operation is the bottleneck for further developments. Here, we report the utilization of in situ digital image correlation and in-operando X-ray diffraction (XRD) techniques to probe dynamic changes in the amorphous phase of iron phosphate during potassium intercalation. In-operando XRD demonstrates amorphization in the electrode’s nanostructure during the first charge/discharge cycle. Additionally, the ex-situ high-resolution transmission electron microscopy further confirms the amorphization after potassium insertion. In situ strain analysis detects the reversible deformation associated with redox reactions in the amorphous phases. Our approach offers new insights on the mechanisms of ion intercalation in the amorphous nanostructures which are highly potent for development of next-generation batteries.
Ozdogru, Bertan↗