The wetting behaviour and associated pressure effect of water in single-walled carbon nanotubes (SWCNTs) are investigated through molecular dynamics (MD) simulations. It is found that water molecules ...can enter SWCNTs via surface diffusion, and the effective infiltration rate increases with pressure. The effect of pressure on infiltration rate is highly non-linear, exhibiting characteristics of both hydrophilic and hydrophobic surfaces. There exists a nominal infiltration pressure that is dependent on the SWCNT size, above which the water flux is significantly increased.
The fracture behavior of graphene monolayer with the substrate binding effect can be investigated by the indentation response of graphene/poly-dimethylsiloxane (PDMS) nanocomposite (graphene ...monolayer mounted on super-soft substrate-PDMS) performed by atomic force microscopy (AFM). The nonlinear elastic constant of graphene is predicted by the reverse analysis of the experimental results using finite element method (FEM), based on which the intrinsic strength of graphene monolayer is evaluated as 37.6 N/m (corresponding to 112 GPa) and the corresponding strain is ∼0.23. It is found that the fracture stress of graphene is essentially not sensitive to the substrate binding effect (∼10% lower than their free-standing counterpart). On the basis of FEM, the deformation of graphene in graphene/PDMS under indentation is very similar to that of graphene in free-standing indentation, and the main strain of graphene is not transferred by the graphene/substrate interface but directly applied by the indentation load, which creates a very low deformation mismatch across the interface (or a very low interface stress). Therefore, there is no sliding/debonding occurrence for the graphene/PDMS interface in the indentation tests till the failure of graphene. The present work actually provides an alternative way to measure the fracture behavior of graphene with substrate sticking effect.
Indentation behavior of two-dimensional (2D) materials mounted on the substrates with varying stiffness is investigated using finite element method (FEM). The primary objective of present work is to ...understand the effect of the ratio of the elastic modulus of 2D-material to that of the substrate (λ) on the indentation deformation of the composite structure (2D-material/substrate). It is found that with the increase of λ, the deformations of both 2D-material and substrate become less localized; the contact area rapidly decreases with λ, which cannot be properly predicted by the classic indentation models. Therefore, for a large value of λ (e.g., λ > 104), the existing indentation models are not able to properly describe the indentation response of 2D-material/substrate. In addition, due to an ultra-low thickness of 2D-material, the indentation behavior of 2D-material/substrate is mainly controlled by the substrate properties when λ is lower than 103; whereas the ratio of the strain energy of 2D-maerial to that of the overall strain energy rapidly increases with λ, which will reach the peak value of 1/3 at λ = 106. Therefore, for a high λ, it is possible to determine the elastic modulus of 2D-material from the overall indentation response of 2D-material/substrate by the inverse analysis with the help of FEM.
Display omitted For a small the elastic moduli ratio of 2D materials to their substrate (λ)(e.g., λ ≤ 100), the overall indentation response can be effectively described by the classic indentation model; whereas for a large λ (e.g., λ≥ 103), the indentation response begins to deviate from the behavior predicted by the classic indentation model.
Membrane capacitive deionization (MCDI) has emerged as a promising technique for desalination due to the merits of high capacity, low energy consumption, and high energy efficiency. However, normal ...free-standing ion-exchange membranes are used in MCDI, and they usually have the drawbacks of high thickness and cost, limiting their large-scale application in industrial promotion. Here, we report a scalable, continuous processing strategy to produce MCDI electrodes for enhancing capacitive desalination capacity and electrode stability, in which the carbon electrodes are coated using poly(arylene alkylene)-based ion-exchange polymers. The MCDI based on integrated ion-exchange polymer-coated membrane electrodes (C-MCDI) delivered a high salt adsorption capacity of up to 23.7 mg g–1 and an excellent charge efficiency of up to 98%, far higher than that of membrane-free CDI with bare carbon electrodes and MCDI with free-standing membrane-based carbon electrodes (FS-MCDI). The COMSOL simulation demonstrated that the coated ion-exchange membrane in C-MCDI was more effective for reducing the interface contact resistance between the carbon and ion-exchange membrane and enhancing the ion transportation. Furthermore, the C-MCDI device showed a long lifespan with a stable desalination capacity of around 18.6 mg g–1 after 500 cycles; instead, the capacity continuously attenuated to near zero in CDI with bare carbon electrodes. Hence, this work proposed two novel polymer-based ion-exchange materials for scalable fabrication of high-performance MCDI electrodes via an environmentally friendly, cost-effective, and process-integrated method.
Using finite element modeling, the mechanical properties of biological cells are investigated based on the power-law rheology (PLR) model under atomic force microscopy (AFM) indentation testing. ...Three different loading modes, including relaxation tests, quasi-static indentation and dynamic indentation are considered. After correcting the effects of the Hertz contact radius and substrate stiffening, the parameters of E sub(0) and alpha in the PLR model can be accurately determined from all three loading modes under AFM indentation. In addition, for all the three indentation loading modes, the aforementioned two effects are not sensitive to the material model used for the cell (e.g., the values of alpha and E sub(0)) but only depend upon the ratio of the indentation depth to the cell thickness. Because the parameters determined from various loading modes can be validated among each other, the AFM indentation will be a very effective route to accurately determine the cell mechanical properties based on the PLR model.
Nanoindentation is a promising technique for deducing the elastic property of carbon nanotubes (CNTs). The paper presents an atomistic study on the nanoindentation mechanisms of single-walled and ...multiwalled CNTs and CNT clusters, through which the deformation characteristics are linked with CNT elastic stiffness. The assembly of individual single-walled CNTs (SWCNTs) into multiwalled CNTs (MWCNTs) and CNT clusters would significantly increase the buckling resistance in terms of withstanding the indentation load. Reverse analysis algorithms are proposed to extract the CNT stiffness by utilizing the indentation force-depth data measured from the prebuckling regimes. The numerical studies carried out in this paper may be used to guide the nanoindentation experiments, explain and extract useful data from the test, as well as stimulate new experiments.
The elastic properties of ZnO nanofilms with different film thickness, surface orientations and loading directions are investigated by using molecular mechanics (MM) method. The size dependence of ...elastic properties is relevant to both the film surface crystallographic orientation and loading direction. Both atomic structure analysis and energy calculation are employed to identify the mechanisms of the size-dependent elastic properties, under different loading directions and surface orientations. Upon small axial deformation, the relationship between intralayer and interlayer bond length variation and film elastic stiffness is established; it is found that the atomic layers with larger bond length variation have higher elastic stiffness. The strain energies of atomic layers of ZnO nanofilm and bulk are decoupled, from which the stiffness of film surface, intralayers, and interlayers are derived and compared with their bulk counterparts. The surface stiffness is found to be much lower than that of the interior layers and bulk counterpart, and with the decrease of film thickness, the residual tension-stiffened interior atomic layers are the main contributions of the increased elastic modulus of ZnO nanofilms.
The thermodynamics, solidification behavior, and as-cast microstructure in the multi-alloyed superalloy GH2150A preparation process have been investigated. The precipitation order of the main phases ...in the GH2150A alloy during the solidification process is
γ
matrix (FCC) → MC ((Nb, C) Ti) phase →
γ
′ Ni
3
(Al, Ti) phase →
μ
phase → Laves phase. The
γ
matrix is in the form of a dendrite. The MC ((Nb, C) Ti) phase exists at the dendrite arm, which leads to an alloy with weak plasticity during hot working. The
γ
′ Ni
3
(Al, Ti) phase is in the gaps between the dendrite, which can effectively enhance the strength of the GH2150A alloy during processing. The heat treatment results show that the
γ
′Ni
3
(Al, Ti) phase begins to melt and agglomerate at 920°C, and that all the
γ
′ phase particles melt at 1030°C. The content of the MC ((Nb, C) Ti) phase decreased with increasing temperature, and all the MC phase was solute at 1180°C.
The effect of the nucleus on the cell mechanical behavior was investigated based on the dynamic indentation response of cells under a spherical tip. A “two-component” cell model (including cytoplasm ...and nucleus) is used, and the dynamic indentation behavior is studied by a semiempirical method, which is established based on fitting the numerical simulation results of the quasi-static indentation response of cells. We found that the “
routine analysis
” (based on the Hertz’s contact solution of homogeneous model) significantly overestimated the nucleus effect on the overall cell indentation response due to the effects of the Hertz contact radius and the substrate stiffening. These effects are significantly stronger in the “two-component” cell model than in the homogeneous model. The inaccuracy created by the “
routine analysis
” slightly increases with the modulus ratio of nucleus to cytoplasm and the volume fraction of nucleus. Finally, the error sensitivity to the geometrical parameters used in the model is discussed, which shows the indentation analysis is not very sensitive to these parameters, and the reasonable assumptions for these parameters are effective. This systematic analysis can provide a useful guideline to understanding the mechanical behavior of cells and nuclei.
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