Local Structural Deformation Research Articles

Surface Functionalization of Ti3C2Tx MXene with Highly Reliable Superhydrophobic Protection for Volatile Organic Compounds Sensing.

Two-dimensional (2D) transition-metal carbides (Ti3C2Tx MXene) have received a great deal of attention for potential use in gas sensing showing the highest sensitivity among 2D materials and good gas selectivity. However, one of the long-standing challenges of the MXenes is their poor stability against hydration and oxidation in a humid environment, limiting their long-term storage and applications. Integration of an effective protection layer with MXenes shows promise for overcoming this major drawback. Herein, we demonstrate a surface functionalization strategy for Ti3C2Tx with fluoroalkylsilane (FOTS) molecules through surface treatment, providing not only a superhydrophobic surface, mechanical/environmental stability but also enhanced sensing performance. The experimental results show that high sensitivity, good repeatability, long-term stability, and selectivity and faster response/recovery property were achieved by the FOTS-functionalized when Ti3C2Tx was integrated into chemoresistive sensors sensitive to oxygen-containing volatile organic compounds (ethanol, acetone). FOTS functionalization provided protection to sensing response when the dynamic response of the Ti3C2Tx-F sensor to 30 ppm of ethanol was measured over in the 5 to 80% relative humidity range. Density functional theory simulations suggested that the strong adsorption energy of ethanol on Ti3C2Tx-F and the local structure deformation induced by ethanol adsorption, contributing to the gas-sensing enhancement. This study offers a facile and practical solution for developing highly reliable MXene based gas-sensing devices with response that is stable in air and in the presence of water.

Pressure-induced decay of the Griffiths phase and accompanying exchange-bias collapse in Gd0.5Sr0.5CoO3−δ

The effect of pressure on both ferromagnetic (FM) cluster phase and the Griffiths phase (GP) was investigated in disordered cobaltite $\mathrm{G}{\mathrm{d}}_{0.5}\mathrm{S}{\mathrm{r}}_{0.5}\mathrm{Co}{\mathrm{O}}_{3\ensuremath{-}\ensuremath{\delta}}$, exhibiting low ${T}_{\mathrm{C}}=90\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, high Griffiths temperature ${T}_{\mathrm{G}}=220\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, and the exchange bias (EB) effect, which exists exotically inside GP. It was found that applied pressure leads to a decrease of ${T}_{\mathrm{C}}$ with a coefficient of $d{T}_{\mathrm{C}}/dP=\ensuremath{-}1\phantom{\rule{0.16em}{0ex}}\mathrm{K}/\mathrm{kbar}$ and dramatically suppresses GP, resulting in a rapid decrease in ${T}_{\mathrm{G}}$ at a rate of $d{T}_{\mathrm{G}}/dP=\ensuremath{-}3.6\phantom{\rule{0.16em}{0ex}}\mathrm{K}/\mathrm{kbar}$. Similarly, the EB field does not change significantly in the FM phase but it promptly collapses with pressure in GP, e.g., the EB field decreases four times under 10 kbar at 140 K. It appears that external pressure effectively eliminates local structure deformations that are responsible for magnetically ordered clusters existing above ${T}_{\mathrm{C}}$. It is suggested that the well-known pressure-induced transition from the high-spin $\mathrm{C}{\mathrm{o}}^{3+}$ state to the low-spin state is mainly responsible for the observed decay of the Griffiths phase and simultaneous EB collapse, as well as, for a decrease in ${T}_{\mathrm{C}}$ under pressure in $\mathrm{G}{\mathrm{d}}_{0.5}\mathrm{S}{\mathrm{r}}_{0.5}\mathrm{Co}{\mathrm{O}}_{3\ensuremath{-}\ensuremath{\delta}}$.

Microsecond molecular dynamics simulation of the adsorption and penetration of oil droplets on cellular membrane

The hazardous effects of petroleum contaminants in the soil and water environment are highly associated with their interactions with cellular membranes, but our understanding on the molecular-level mechanisms for the adsorption and penetration of heavy oil mixture on cellular membrane is very limited. In this study, microsecond molecular dynamics simulations were performed to gain insights into the morphological evolution and penetration dynamics of the multi-component and single-component oil droplets on the dipalmitoylphosphatidylcholine lipid membrane. Results highlighted the inhibition effect of the resins on the penetration of alkanes and aromatics, because they would form net structure making it difficult to release the latter two components from the oil droplet to the membrane. It also demonstrated the obviously different patterns of penetration between alkanes and aromatics. The overall steps for the toluene penetration included detachment from oil droplet, dispersion in water, adsorption on membrane surface, structure adjustment and penetration into membrane. By contrast, the step of dispersion in water was not necessary for the alkanes’ penetration. Instead, it relied on the adsorption of the whole oil droplet on the membrane surface which resulted in the formation of pores on the membrane surface by local structure deformation in the lipid head group regions.

Organic Cations Protect Methylammonium Lead Iodide Perovskites against Small Exciton-Polaron Formation.

Working organic-inorganic lead halide perovskite-based devices are notoriously sensitive to surface and interface effects. Using a combination of density functional theory (DFT) and time-dependent DFT methods, we report a comprehensive study of the changes (with respect to the bulk) in geometric and electronic structures going on at the (001) surface of a (tetragonal phase) methylammonium lead iodide perovskite slab, in the dark and upon photoexcitation. The formation of a hydrogen bonding pattern between the -NH3 groups of the organic cations and the iodine atoms of the outer inorganic layout is found to critically contribute to the relative thermodynamic stability of slabs with varying surface compositions and terminations. Most importantly, our results show that the hydrogen bond locking effects induced by the MA groups tend to protect the external two-dimensional lattice against large local structural deformations, i.e., the formation of a small exciton-polaron, at variance with purely inorganic lead halide perovskites.

Insights into Polymorphism of Lithium Manganese Oxide, Li0.95Mn2.05O4: A Comprehensive Survey of the High-Pressure Properties

Understanding the structural behavior of lithium manganese oxide (LMO) under high pressure, especially under nonhydrostatic pressure conditions, could provide more insights into control of the mechanochemical processes occurring during battery operation and allow predicting new applications for this type of oxides. Here, we report pressure-induced structural changes in Li0.95Mn2.05O4 at two temperatures, 300 and 380 K, investigated in situ through synchrotron X-ray powder diffraction up to 13 GPa in a diamond anvil cell. Compression-induced strain triggers a cascade of local structure deformations, which finally result in the structural phase transition to the high-pressure tetragonal phase. A comparison of bulk moduli at two temperatures reveal that due to the differences in the response of the structure to the strain, Li0.95Mn2.05O4 exhibits the rare property of “warm hardening”. Additionally, a direct correlation between hydrostaticity of the pressure-transmitting medium and structural transformations ...

Local and Global Responses of a Floating Bridge Under Ship–Girder Collisions

The Norwegian Public Roads Administration is running a project “Ferry Free Coastal Route E39” to replace existing ferry crossings by bridges across eight fjords in western Norway. Since most of the fjords are wide and deep, construction of traditional bridges with fixed foundations is not possible. Therefore, floating bridge concepts are proposed for the fjord-crossing project. Since the floating foundations of the bridges are close to the water surface, the concern of accidental ship collisions is raised. Considering the displacement and speed of the passing ships and the significant compliance of the bridge, interaction between the bridge and the ship can be significant should a collision occur. Many studies have been conducted on ship collision with bridge structures with a special focus on bridge piers. However, the research on ship collision with bridge girders is quite limited. The purpose of this study is to investigate the collision response of a floating bridge for ship–girder collision events. Both the local structural damage and the global dynamic response of the bridge are assessed. Local structural deformation and damage are first investigated by numerical simulations with detailed finite element (FE) models in ls-dyna. Subsequently, the bridge global response to the collision loads is analyzed in usfos using the force–deformation curves from the local analysis. By combining the local and global analysis results, a comprehensive overview of the bridge response during ship–girder collisions can be obtained.

Dual-type sensor placement optimization by fully utilizing structural modal information

Strain gauges and accelerometers are widely used in bridge structural health monitoring systems. Generally, the strain gauges are placed on the key locations to obtain local structural deformation information; the accelerometers are used to obtain the structural modal information. However, the modal information contained in the measured strains is not taken into account. In this article, to fully utilize the modal information contained in strains, a mode shape estimation method is proposed that the strain mode shapes of the strain locations are used to obtain the displacement mode shapes of some positions without accelerometers. At first, to simulate the practical situation, some positions with large structural deformations are selected as the strain gauge locations. Using the proposed mode shape estimation method, the displacement mode shapes of some locations without accelerometers are estimated by the strain mode shapes using the least squares method, and the locations with the smallest estimation error are finally determined as the estimated locations. Then, accelerometers are added to the existing sensor placement. Here, the modal assurance criterion is used to evaluate the distinguishability of the displacement mode shapes obtained from the strain gauges and accelerometers. The accelerometer locations that bring the smallest modal assurance criterion values are selected. In addition, a redundancy can be set to avoid the adjacent sensors containing similar modal information. Through the proposed sensor placement method, the deformation and modal information contained in the strain gauges is fully utilized; the modal information contained in the strain gauges and accelerometers is comprehensively utilized. Numerical experiments are carried out using a bridge benchmark structure to demonstrate the sensor placement method.

Structural and chemical insights into thermal transport for strained functionalised graphene: a molecular dynamics study

Aim of this article was to investigate the effect of chemical functionalisation on the thermal conductivity of graphene monolayer via reverse non-equilibrium molecular dynamics simulations. Separate simulations have been performed with hydroxyl and epoxide functional groups, which forms intrinsic part of graphene oxide nanostructure. Hydroxyl and epoxide functionalization of graphene has deteriorating effect on the thermal conductivity of graphene. Functionalisation of graphene alters the local structural deformation, phonon transmittance and vibrational frequency of the graphene lattice network. Spatial distribution of hydroxyl group in conjunction with tensile strain engineering plays a significant role in tailoring the thermal conductivity of functionalised graphene. Atomistic alterations such as stable flattening, formation of atomic chains network and epoxide-to-ether chemical transformation upon stretching resulted in an enhanced thermal conductivity. This improvement in thermal conductivity could enable graphene oxide as a promising candidate for thermoelectrics and thermal rectification applications.

Electronic band structure and magnetic properties of I vacancy and nonmetallic atoms doped single layer PbI2

We systematically explore the influence of I vacancy and a series of substitutional nonmetallic atoms, including F, Cl, Br, Si, P and S, on the stability, geometric structure, electronic structure and magnetic properties of single layer PbI2 using first-principles calculations. The results show that I vacancy and nonmetallic atoms X doped single layer PbI2 are stable at room temperature, although substitutional atom X and I vacancy lead to the local structure deformation. Moreover, substitutional F, Cl and Br dopants do not induce the magnetism in doped single layer PbI2 due to same number of valence electron of F, Cl, Br and I, while ground states of I vacancy, S, P and Si doped system are magnetic and the magnetic moments induced by one I vacancy, S, P and Si atom are 1.0, 1.0, 2.0 and 3.0 μB, respectively. It is found that the distribution of the magnetic moment induced by I vacancy and doping atom relate to the hybridization between doping atom and its neighboring Pb and I atoms or the hybridization between Pb and I atoms around vacancy. Remarkably, although the spin–orbit coupling (SOC) induce spin splitting of the electronic bands due to the absence of inversion symmetry in I vacancy and nonmetallic atoms X doped single layer PbI2, the SOC does not alter the electron occupation of the bands near the Fermi level. As a result, the magnetic moment induced by I vacancy, S, P and Si atoms are not changed and the magnetic moment of F, Cl and Br doped single layer PbI2 are still zero after the inclusion of SOC.

Rapid and phase pure synthesis of microporous copper silicate (CuSH–1Na) with 12-ring channel system

Phase pure sample of the microporous copper silicate CuSH–1Na has been obtained by simplified hydrothermal method without using additives (H2O2 and Na2HPO4). Ion exchange of Na+ by Cs+, Ca2+ and Sr2+ ions showed that the structure can suffer partial replacement of the charge compensating cations. Ion exchange with Cs+ resulted in distinct dehydration while the ion exchange with Sr2+ increased the total amount of water. Water content in the Ca-exchanged sample is comparable to the as-synthesized sodium phase. Raman spectroscopy revealed that the divalent cations as Ca2+ and Sr2+ induce stronger local structural deformations than the monovalent Cs+. These structural changes have been also followed by the refined lattice distortions. Magnetic analyses showed that CuSH–1Na presents a very weak ferromagnetic interaction along the Cu2+ chains with a nearly vanishing Curie–Weiss temperature. This magnetic coupling is associated with super-super-exchange interactions through Cu–Na–O–Na–Cu paths. Antiferromagnetic coupling, attributed to inter-chains super-super-exchange interactions, competes with the ferromagnetic one and prevails at the lowest temperature.

Drag reduction of slender blunt-based bodies using optimized rear cavities

We have investigated the use of the adjoint sensitivity formulation to design efficient passive control strategies aiming at reducing the drag coefficient of a slender blunt-based body with a straight rear cavity. In particular, two control techniques consisting in wake modifications generated by placing small control cylinders in the near wake and by geometry variations of the cavity respectively, have been evaluated numerically. Thus, we have computed the turbulent flow sensitivity of the drag coefficient to localized forcing for a two-dimensional body with a straight cavity at Re=ρU∞H∕μ=2000, where U∞ is the free-stream velocity, ρ and μ the fluid density and viscosity respectively and H the body height, showing that the highest values of sensitivity are obtained near the cavity edges. The effect of placing a pair of control cylinders around the most sensitive locations has been studied, obtaining a largest drag reduction of only 0.6%. Alternatively, a most efficient control strategy based on shape optimization has been thoroughly investigated. The drag shape sensitivity on the body surface (Othmer, 2014), computed using the former linear adjoint formulation, has been used in combination with a free-form deformation algorithm (Han et al., 2011), to guide the local structure deformations of the cavity, providing progressive drag reductions until the optimal, curved, shape is achieved. To deeply analyze the physical mechanisms behind the drag reduction provided by the optimal cavity, we have also performed more realistic three-dimensional numerical simulations using an IDDES model at two different Reynolds numbers, Re=2000 and 20000. The results corroborate the sensitivity analysis, obtaining a total drag reduction of 25.6% at Re=2000 and 43.9% at Re=20000, with respect to the original body without cavity, and 21.7% at Re=2000 and 29.6% at Re=20000 with respect to the body with a straight cavity. These reductions are mainly achieved by the inwards deflection of the flow upon detachment and a flow deceleration at the trailing edge due to an adverse pressure gradient introduced by the curved shape of the optimal cavity walls. Both combined effects reduce the size of the recirculation bubble formed behind the body, increasing the base pressure, and consequently, decreasing the drag. Furthermore, the addition of the optimized base cavity reduces the amplitude of the velocity fluctuations behind the body and stabilizes the wake, which becomes less chaotic and more two-dimensional.

Ru doping in iron-based pnictides: The “unfolded” dominant role of structural effects for superconductivity

We present an ab-initio study of Ru substitution in two different compounds, BaFe2As2 and LaFeAsO, pure and F-doped. Despite the many similarities among them, Ru substitution has very different effects on these compounds. By means of an unfolding technique, which allows us to trace back the electronic states into the primitive cell of the pure compounds, we are able to disentangle the effects brought by the local structural deformations and by the impurity potential to the states at the Fermi level. Our results are compared with available experiments and show: i) satisfying agreement of the calculated electronic properties with experiments, confirming the presence of a magnetic order on a short range scale; ii) Fermi surfaces strongly dependent on the internal structural parameters, more than on the impurity potential. These results enter a widely discussed field in the literature and provide a better understanding of the role of Ru in iron pnictides: although isovalent to Fe, the Ru-Fe substitution leads to changes in the band structure at the Fermi level mainly related to local structural modifications.

First-principles investigation of local structure deformation induced by x-ray irradiation in κ−(BEDT−TTF)2Cu[N(CN)2]Br

We investigated the local structure deformation induced by x-ray irradiation in an organic molecular conductor $\ensuremath{\kappa}\ensuremath{-}{(\mathrm{BEDT}\ensuremath{-}\mathrm{TTF})}_{2}\mathrm{Cu}[\mathrm{N}{(\mathrm{CN})}_{2}]\mathrm{Br}$ using density-functional-theory (DFT-) based first-principles calculations. Our results demonstrate that the structure change due to x-ray excitation can be predicted by introducing a core hole at specific light atoms of the anion molecules with an infinite lifetime. The formation of a bond-shifted structure triggered by a double excitation was expected as a possible irreversible molecular defect leading to permanent irradiation damage. The calculated change in molecular vibration spectra after irradiation was consistent with the experimental results, and some different vibration modes by further irradiation were also predicted. The calculated local density of states indicates that the bond-shifted structure in the anion layer causes local potential modulation to the carriers (holes) in the cation layer. The introduced potential disorder for the carriers could increase the resistivity due to a localization effect that has been observed experimentally so far.

Operando X-ray spectroscopic observations of modulations of local atomic and electronic structures of color switching smart film.

Smart windows, which change color in response to external stimuli, are extensively studied owing to their potential technological applications in sensors and their ability to reduce the energy consumed by buildings. Most related studies focus on the optical properties of smart color switching films that can control the transmission of light and that of heat independently. This study examines the vanadium pentoxide thin film as a model system of a color switchable window. A gasochromic thin film of V2O5 is fabricated using sol-gel spin coating. In operando soft X-ray absorption spectroscopy (XAS) at the V L-edge is used to determine the evolutions of the electronic and atomic structures of V2O5 thin film under gasochromic color switching. Analysis of the V K-edge with respect to crystalline structural symmetry and valence requires many reference samples, whereas the V L-edge, which involves V 3d orbitals of various symmetries, can provide information about the atomic/electronic structures without many reference samples. A new gas reaction in situ cell was developed to collect the total-electron-yield XAS. The total-electron-yield signal can provide more accurate information about atomic and electronic structures than can the fluorescence-yield signal, which typically exerts a saturation effect. Analytical results reveal that the gasochromic reaction changes the charge state and causes a local atomic structural deformation of the film. The suggestion has been made that in the reaction, the central vanadium atom within the octahedron moves closer to the basal plane such that the apical V-O bond becomes more symmetrical than the film before gasochromic coloration. Unlike the cell that is used for hard XAS, and for which only cation sites can be studied, this in situ gas cell enables the real-time studies of atomic/electronic structures at gas-solid interfaces from viewpoints of both cation and anion sites.

Structural analysis of dendrimers based on polyhedral oligomeric silsesquioxane and their assemblies in solution by small-angle neutron scattering: Fits to a modified two correlation lengths model

The small-angle neutron scattering (SANS) technique has been used to investigate the structure of dendrimers based on polyhedral oligomeric silsesquioxane (POSS) in solution. Three generations and two distinct terminal groups (either vinyl or polyethylene glycol (PEG) terminal groups) as well as four concentrations for each dendrimer have been measured in deuterated tetrahydrofuran. Two main scattering regimes, one with a length scale of nm and the other with a length scale of sub-micron, are found to contribute to the SANS signals. In order to fit the SANS data, a new modified two correlation lengths model has been developed. Fit parameters include scale factors, correlation lengths, Porod exponents and “particle” elongation parameters. Our fit results show that the local structure does not correspond to single dendrimer molecules, but rather to POSS-rich domains surrounded by POSS-poor domains. The large-scale structure represents the overall morphology of multi-dendrimer aggregates. The flexible PEG outer links help to enhance the stability of inorganic POSS cages, and allow the hybrid polymers to adjust their conformation in order to respond to their surroundings. With increasing concentration, the local structure becomes more compact as evidenced by the decrease of correlation length and concurrent increase of the Porod exponent. The deformation of local structure during the compaction process is also observed. The structure becomes elongated at intermediate concentrations whereas it tends to be more globular at low and high concentrations.

The mechanical property of single-walled carbon nanotube under combined electromechanical loading

ABSTRACTThe mechanical properties and failure process of single-walled carbon nanotube (SWCNT) under combined electric field and tensile loading are investigated using the semi-empirical quantum mechanical method. The local and global structural deformation and variation of mechanical properties of SWCNT under different directions and intensity of external electric field are discussed systematically. It is shown that the electric field induced deformation in the radial and axial directions of the SWCNT are strongly dependent on the direction of electric field. The analysis of mechanical properties shows that the structure stiffness, tensile strength and failure strain of the SWCNT all decrease with the increase of the field intensity, which is particularly evident under the longitudinal electric field. The Young's modulus of SWCNTs vary with the tube diameter and are affected by the electric field. The increase of the length of the tubes intensifies the charge concentration at the tube ends under the electric field and lead to the decrease of mechanical properties of SWCNTs. The failure process of SWCNTs under the coupling effect of electric field and tensile loading is found to be controlled by the field strength and also affected by the electric charge accumulation.

Quantitative microstructural imaging by scanning Laue x-ray micro- and nanodiffraction

Abstract

Combined particle-image velocimetry and force analysis of the three-dimensional fluid–structure interaction of a natural owl wing

Low-speed aerodynamics has gained increasing interest due to its relevance for the design process of small flying air vehicles. These small aircraft operate at similar aerodynamic conditions as, e.g. birds which therefore can serve as role models of how to overcome the well-known problems of low Reynolds number flight. The flight of the barn owl is characterized by a very low flight velocity in conjunction with a low noise emission and a high level of maneuverability at stable flight conditions. To investigate the complex three-dimensional flow field and the corresponding local structural deformation in combination with their influence on the resulting aerodynamic forces, time-resolved stereoscopic particle-image velocimetry and force and moment measurements are performed on a prepared natural barn owl wing. Several spanwise positions are measured via PIV in a range of angles of attack 6° and Reynolds numbers 40 000 120 000 based on the chord length. Additionally, the resulting forces and moments are recorded for −10° ≤ α ≤ 15° at the same Reynolds numbers. Depending on the spanwise position, the angle of attack, and the Reynolds number, the flow field on the wing’s pressure side is characterized by either a region of flow separation, causing large-scale vortical structures which lead to a time-dependent deflection of the flexible wing structure or wing regions showing no instantaneous deflection but a reduction of the time-averaged mean wing curvature. Based on the force measurements the three-dimensional fluid–structure interaction is assumed to considerably impact the aerodynamic forces acting on the wing leading to a strong mechanical loading of the interface between the wing and body. These time-depending loads which result from the flexibility of the wing should be taken into consideration for the design of future small flying air vehicles using flexible wing structures.

The electronic, structural and magnetic properties of La1−1/3Sr1/3MnO3 film with oxygen vacancy: a first principles investigation

We have systematically investigated the influence of oxygen vacancy defects on the structural, electronic and magnetic properties of La1−xSrxMnO3 (x = 1/3) film by means of ab initio calculations using bare GGA as well as GGA+U formalism, in the latter of which, the on-site Coulombic repulsion parameter U for Mn 3d orbital has been determined by the linear response theory. It is revealed that the introduction of the vacancy defects causes prominent structural changes including the distortion of MnO6 octahedra and local structural deformation surrounding the oxygen vacancy. The GGA+U formalism yields a significantly larger structural change than the bare GGA method, surprisingly in contrast with the general notion that the inclusion of Hubbard U parameter exerts little influence on structural properties. The distortion of MnO6 octahedra leads to a corresponding variation in the hybridization between Mn 3d and O 2p, which gets strengthened if the Mn-O distance becomes smaller and vice versa. The magnetic moments of the Mn atoms located in three typical sites of the vacancy-containing supercell are all larger than those in the pristine system. We have characterized the O-vacancy defect as a hole-type defect that forms a negative charge center, attracting electrons.

基于多点自由度约束的方向性保形拓扑优化设计方法

Shape preservation of aerodynamic surfaces and functional surfaces was an important aspect in aircraft stiffness design. An extended topology optimization method was presented with directional shape-preserving constraints, which suppressed the warping deformation of structural local domains in particular directions and generated required deformation patterns. On the one hand, artificial weak elements (AWEs) were established with respect to the finite control points in local shape-preserving domains. Multi-point constraints (MPCs) were further applied to transfer nodal displacements at the control points to nodes of the AWEs. Strain energy of the AWEs was then constrained to suppress the warping deformation. On the other hand, the MPCs were properly defined to transfer only the displacements of the specified degrees of freedom to be suppressed. Directional shape preservation was in turn achieved. The numerical examples and optimized designs prove the validity of the proposed method in maintaining directional shape preservation based on the stiffness maximization topology optimization. Compared with the existing shape-preserving topology optimization design method, the proposed directional shape-preserving one brings more flexibility in controlling the local structural deformation.