Defect-induced carbon nanoscroll formation

Molecular dynamics simulations of the morphology transformations in unzipped carbon nanotubes

The diesel engine particulate which is one of the major sources of PM, affects the development of human health and production activities seriously. With the continuous strict of emission regulations, the diesel engine particles are subject to strict restriction in terms of quality and quantity. At present, the diesel particulate filter technology is an important technical measure to reduce the exhaust particulate matter of the diesel engine. And the efficient capture of particles is one of the key technologies for the diesel particulate filter. Diesel engine exhaust particles undergo nucleation, surface growth, agglomeration and other processes, in which the degree of agglomeration of exhaust particles will directly affect its number density, scale and the trapping efficiency of the filter and so on. The reason why particles can be agglomerated is mainly due to the interaction between the particles. Therefore, to explore the relationship between the force and the effect of particle agglomeration, it is necessary to carry out the study on the interaction between the exhaust particles of diesel engines. The interaction between particles will affect the process of particle agglomeration and related parameters significantly. The main forces include van der Waals force, electrostatic force and liquid bridge force. In this paper, theoretical models of Hamaker and some others are used to analyze the force between particles in the ideal state. The test methods of atomic force microscopy (AFM) and transmission electron microscopy (TEM) are used to investigate the total attraction force, adhesion force and adhesion energy between diesel exhaust particulates in dry environment (relative humidity RH≤20%), and measure the total attraction force, adhesion force and adhesion between particles, and explore the relationship between particle size and particle size. The results show that the particle size increases from 25 to 45 nm, the Van der Waals force increases about 4.6 times, the electrostatic force increases about 9.9 times, and the electrostatic force is smaller than the electrostatic force. The adhesion between particles and adhesion energy both increased about 1.8 times. The particles with the average particle size of 30, 37 and 46 nm are measured by AFM. With the increase of the particle size, the total attraction F at between the particle and the probe increases gradually, which is 1.04–1.38 nN. Van der Waals force F vdw is the main force of the F at, and Coulomb force is smaller. The attraction force F at and the adhesion energy W ad increase with the increase of particle size, F at increases from 3.21–3.75 nN, about 16.8%, while W ad increases from 2.03×10−16 J to 2.20×10−16 J, about 8.4%. The increase of F ad and W ad indicate that the adhesion as well as the energy barrier between the particles is increased, and the particle agglomeration is stable. With the increase of the average particle size, the particles agglomerate gradually and change from branch to cluster, showing a hill-like accumulation, and the particle density as well as the cluster size are increased, which indicates that there was a certain influence between the change of particle force and particle morphology.

This article reports a systematic study of local stress relaxation effects in thin Al films, deposited on silicon substrates by sputtering or electron beam evaporation. The stresses were induced thermally during an annealing cycle, as well as thermomechanically by micromechanical technique. The latter experiments were performed in situ in the vacuum chamber of a scanning electron microscope (SEM), which made it possible to monitor the reconstruction of the film surface as it happened, and simultaneously register applied forces, strains, and temperatures. Three fundamental, local stress relaxation phenomena were observed. Compressive film stresses were, at elevated temperature, relaxed by hillock formation. The in situ experiments in the SEM, combined with cross-sectional transmission electron microscopy of hillock structures, provided important information on the growth mechanism of hillocks. Tensional film stresses at elevated temperature were relaxed by two modes of local stress relief. One mode of tensional stress relief occurred in films of thickness 1 μm or more. Singular Al grains were observed to ‘‘collapse’’ and become wider and thinner than neighboring grains. Such grain collapses are scarcely reported by previous workers, and were in the present investigation seen to occur very suddenly, in a second or less, as the strain and the temperature reached critical levels. A collapse mechanism, based on local plastic yield and interfacial slip, is suggested. Films of submicron thickness relaxed by a second mode: hole formation. Essentially two types of holes were observed: small, circular holes and large branched-out holes. A hole formation mechanism, based on creep cavitation and interfacial slip, is suggested. The observed holes resemble the ‘‘voids’’ many other workers have reported in narrow, passivated Al lines. The present results show that passivation coatings and narrow geometries are not necessary prerequisites for holes in Al films; a high tensional film stress is enough.

Local ratcheting and stress relaxation at notch root of CP-Ti specimen under cyclic loading: Experiment and simulation

The possibility of the formation of glycine (Gly) from fundamental gas molecules in cold interstellar media was studied using quantum chemical methods, transition state theory and microcanonical molecular dynamics simulations with surface hopping dynamics (NVE-MDSH). This theoretical study emphasized five photochemical pathways in the lowest singlet-excited (S 1) state, thermochemical processes after non-radiative S 1→S 0 relaxations, and photo-to-thermal energy conversion in the NVE ensemble. The optimized reaction pathways suggested that to generate a reactive singlet dihydroxy carbene (HOCOH) intermediate, photochemical pathways involving the H2O…CO van der Waals and H2O-OC hydrogen bond precursors (Ch (1)_Step (1)) possess considerably lower energy barriers than the S 0 state pathways. The Gibbs free energy barriers (∆G ǂ ) calculated after the non-radiative S 1 →S 0 relaxations indicated higher spontaneous temperatures (T s) for the formation of the HOCOH intermediate (Ch (1)_Step (1)) than for Gly formation (Ch (1)_Step (2) and Ch (4)). Although the termolecular reaction in Ch (4) possesses a low energy barrier, and is thermodynamically favourable, the high exothermic S 1 →S 0 relaxation energy leads to the separation of the weakly associated H2O…CH2NH…CO complex into single molecules. The NVE-MDSH results also confirmed that the molecular processes after the S 1 →S 0 relaxations are thermally selective, and because the non-radiative S 1 →S 0 relaxation temperatures are exceedingly higher than T s, the formation of Gly on consecutive reaction pathways is non-synergistic with low yields and several side products. Based on the theoretical results, photo-to-thermal control strategies to promote desirable photochemical products are proposed. They could be used as guidelines for future theoretical and experimental research on photochemical reactions.

In this study, we investigate the stereoselective 1,2 migration reaction inside a carbon nanotube (CNT) using a combined quantum mechanics/molecular mechanics (QM/MM) approach. The steric and electronic effects of the CNT are found to significantly influence the stabilization of the guest molecule, highlighting the importance of nanotube diameter. By adjusting the nanotube diameter, it becomes possible to control the stereoselectivity of the migration reaction. Nanoreactors, such as CNTs, have emerged as promising tools for manipulating chemical reactions due to their versatile properties. We explore the impact of the nanotube environment on the migration mechanism and discuss the role of non-covalent interactions, such as van der Waals forces, in promoting stability and selectivity. Our computational results demonstrate that the presence of the CNT affects the reaction kinetics, energy barriers, and overall energetic outcomes. The choice of nanotube diameter is crucial to achieve optimal confinement of the guest molecule while maintaining stabilizing interactions. This study provides valuable insights into the potential of carbon nanotubes as nanoreactors for controlling stereochemistry in organic reactions, offering opportunities for tailored reaction design and synthesis.

Topological insulators represent a paradigm shift in surface physics. The most extensively studied Bi$_2$Se$_3$-type topological insulators exhibit layered structures, wherein neighboring layers are weakly bonded by van der Waals interactions. Using first principles density-functional theory calculations, we investigate the impact of the stacking sequence on the energetics and band structure properties of three polymorphs of Bi$_2$Se$_3$, Bi$_2$Te$_3$, and Sb$_2$Te$_3$. Considering their ultrathin films up to 6 nm as a function of its layer thickness, the overall dispersion of the band structure is found to be insensitive to the stacking sequence, while the band gap is highly sensitive, which may also affect the critical thickness for the onset of the topologically nontrivial phase. Our calculations are consistent with both experimental and theoretical results, where available. We further investigate tribological layer slippage, where we find a relatively low energy barrier between two of the considered structures. Both the stacking-dependent band gap and low slippage energy barriers, suggest that polymorphic stacking modification may offer an alternative route for controlling the properties of this new state of matter.

The trend to miniaturize silicon integrated circuits has brought with it a thermal stress-induced void formation problem in the aluminum conductor lines of these circuits. Here, local stress relaxation has been included quantitatively in the construction of a wedge-like void growth model. It is shown that under stress relaxation conditions, the stress-induced grain boundary diffusion equation transforms into the diffusion equation. With the use of appropriate boundary conditions and the initial conductor line stress profile, the diffusion equation is solved numerically. This solution yields the temporal history of void size and local stress. It is shown that two types of stress relaxation moderate and limit the growth of voids. From this analysis, a useful expression which relates final void size and initial stress is derived. With these results conservative estimates of the lifetime of aluminum conductor lines can be made. >

Electromechanical reshaping (EMR) involves reshaping cartilage by mechanical deformation and delivering electric current to the area around the bend axis, causing local stress relaxation and permanent shape change. The mechanism of EMR is currently unclear, although preliminary studies suggest that voltage and application time are directly related to the concentration and diffusion of acid-base products within the treated tissue with little heat generation. This study aims to characterize local tissue pH changes following EMR and to demonstrate that local tissue pH changes are correlated with tissue damage and shape change. Ex vivo animal study involving EMR of rabbit nasal septal cartilage and biochemical estimation of tissue pH changes. The magnitude and diffusion of acid-base chemical products in control (0V, 2 minutes), shape change (4V, 4 minutes; 6V, 1, 2, 4 minutes; 8V, 1, 2 minutes), and tissue damage (8V, 4, 5 minutes; 10V, 4, 5 minutes) parameters following EMR are approximated by analyzing local pH changes after pH indicator application. There is a direct relationship between total charge transfer and extent of acid-base product diffusion (P <0.05). A "pH transition zone" is seen surrounding the bend apex above 8V, 2 minutes. Colorimetric analysis suggests that small local pH changes (10(-8) hydrogen ions) are at least partly implicated in clinically efficacious EMR. These results provide additional insight into the translational applications of EMR, particularly the relationship among pH changes, shape change, and tissue injury, and are integral in optimizing this promising technology for clinical use.

Multiscale computational and experimental analysis of slip-GB reactions: In situ high-resolution electron backscattered diffraction and concurrent atomistic-continuum simulations

Electromechanical reshaping (EMR) is a promising surgical technique used to reshape cartilage by direct current and mechanical deformation. It causes local stress relaxation and permanent alterations in the shape of cartilage. The major advantages of EMR are its minimally invasive nature and nonthermal electrochemical mechanism of action. The purpose of this study is to validate that EMR does not cause thermal damage and to observe structural changes in post-EMR cartilage using several imaging modalities. Three imaging modality metrics were used to validate the performance of EMR by identifying structural deformation during cartilage reshaping: infrared thermography was used to sense the temperature of the flat cartilages (16.7°C at 6 V), optical coherence tomography (OCT) was used to examine the change in the cartilage by gauging deformation in the tissue matrix during EMR, and scanning electron microscopy (SEM) was used to show that EMR-treated cartilage is irregularly arranged and the thickness of collagen fibers varies, which affects the change in shape of the cartilage. In conclusion, the three imaging modalities reveal the nonthermal and electromechanical mechanisms of EMR and demonstrate that use of an EMR device is feasible for reshaping cartilage in a minimally invasive manner.

The aggregation phenomena of several metal oxide nanoparticles were analyzed and discussed based on the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory of colloidal stability. The attractive van der Waals (VDW) and the repulsive electrostatic double-layer (EDL) forces acting upon a pair of approaching particles are two kinds of the fundamental interaction forces that control their aggregation. The surface potential and the Debye length of the particles are also important factors. The particles that disperse in an aqueous solution were forced to aggregate under unstable dispersion conditions wherein the EDL interaction becomes much weaker than the VDW interaction between two particle surfaces. Under this condition, the agglomerated nanoparticles having a disorderly arranged structure, i.e. a lot of small pores, are created. In order to control the surface potential and the Debye length on the nanoparticles of the Ti-, Zn-, Al-, Sn- and Sb-oxides, the electrolyte (KBr) and acid/alkali were added into the colloidal solutions. Agglomerated their nanoparticles with pore structure were prepared after evaporating the solutions and removing KBr. In the case of the Ti- and Zn-oxides, a strong aggregate force was observed among the nanoparticles. The pore size and the pore volume of the agglomerated nanoparticles increased with decreasing energy barrier of the interaction energy among these particles. The other oxide nanoparticles also formed an agglomerate body in each pH-controlled (metal oxide/KBr) solution. However, the aggregate force was so weak that the particles could not keep the aggregate state in the removal stage of KBr, which resulted in the re-dispersion of the agglomerated particles into their primary particles. From the DLVO calculations of the experimental systems, it was confirmed that the dispersion/aggregation phenomena of the nanoparticles observed in each stage of the experiments are determined by the balance of the attractive and the repulsive interactions among them and their thermal kinetic energy.

Iso-octane aerosols in air have been ignited with a focused Nd:YAG laser at pressures and temperatures of 100 kPa and 270 K and imaged using schlieren photography. The aerosol was generated using the Wilson cloud chamber technique. The droplet diameter, gas phase equivalence ratio and droplet number density were determined. The input laser energy and overall equivalence ratio were varied. For 270 mJ pulse energies initial breakdown occurred at a number of sites along the laser beam axis. From measurements of the shock wave velocity it was found that energy was not deposited into the sites evenly. At pulse energies of 32 mJ a single ignition site was observed. Overall fuel lean flames were observed to locally extinguish, however both stoichiometric and fuel rich flames were ignited. The minimum ignition energy was found to depend on the likelihood of a droplet existing at the focus of the laser beam.

Molecular selection, ion exclusion, and water permeation are well known regulatory mechanisms in aquaporin. Water permeability was found to be diverse in different subgroups of plasma membrane intrinsic proteins (PIPs), even though the residues surrounding the water holes remained the same across the subgroups. Upon homology modeling and structural comparison, a conserved Ala/Ile(Val) residue difference was identified in helix 2 that affected the conformation of the NPA region and consequently influenced the water permeability. The residue difference was found to be conservative within the two subgroups of PIPs in rice as well as in other plants. Functional tests further confirmed the prediction via site-directed mutagenesis where replacement of Ala(103) or Ala(102) in respective OsPIP1;1 or OsPIP1;3 with Val yielded 7.0- and 2.2-fold increases in water transportation, and substitution of Ile(98) or Val(95) in respective OsPIP2;3 or OsPIP2;7 with Ala resulted in 73 or 52% reduction of water transportation. Based on structural analyses and molecular dynamics simulations, we proposed that the difference in water permeability was attributed to the orientation variations of helix 2 that modified water-water and water-protein interactions.

A Monte Carlo simulation of grafted poly(ethylene oxide) chains