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Silane coupling is commonly used to connect organic polymers to inorganic substrates for surface modification and composite material fabrication. It is known that the covalent bonds that form betwe...

A nanocrystalline metal contains grains that are extremely small, with a high proportion of grain boundary (GB). For understanding of the mechanical properties of nanocrystalline metals, it is indispensable to elucidate the influence of GBs on plastic deformation. In this study, molecular dynamics simulations of uniaxial deformation tests on magnesium bicrystals with [ 1 ¯ 1 0 0 ] symmetric tilt GBs were performed in order to reveal the role of GBs during the plastic deformation of hexagonal close-packed metals. We found that not only the critical resolved shear stress but also the active deformation mode itself is sensitively dependent on both the misorientation angle between the grains and the loading direction. In particular, ease of nucleation of basal dislocations from the GB could be qualitatively explained by the dependence of the GB energy on the misorientation angle, where dislocation nucleation from the GB is regarded as a process by which GBs accommodate changes in misorientation angle caused by elastic deformation due to an applied load.

A quantitative evaluation of the deformation of metals is usually based on the critical resolved shear stress (CRSS), in which the influence of the normal stresses is not taken into account. Although it is plausible to use the CRSS for a quantitative evaluation of the deformation mode, some previous studies show that the CRSS depends on other stress components. In this work, atomistic simulations are performed to study the influence of the normal stresses on the nucleation of basal dislocations in a magnesium single crystal. We found that the activation free energy of dislocation nucleation decreases as the normal stress applied in the [ 1 1 2 ¯ 0 ] direction decreases, or that in the [ 0 0 0 1 ] direction increases. This tendency is consistent with the dependence of CRSS on the loading direction found in a previous work done by Barrett et al. (2012) on molecular dynamics simulations of tensile deformation tests of a magnesium single crystal.

A system of quinone molecules encapsulated in single-walled carbon nanotubes (SWCNTs) has been proposed as a next-generation cathode material for rechargeable batteries [Y. Ishii et al., Phys. Chem. Chem. Phys. 18 (2016) 10411–10418]. We use density functional theory (DFT) to theoretically investigate (i) the electronic and structural states of SWCNT-encapsulated quinone with or without Li and (ii) the Li insertion and extraction dynamics in the system. Substantial electron transfer from the quinone molecules to the SWCNT is thereby observed. This electron transfer stabilizes the positively charged quinone molecules in the negatively charged SWCNT through Coulomb attraction and decreases the electronic band gap for the SWCNT with semiconductor chirality. In the case of 9,10-phenanthrenequinone (PhQ), we observe that the cross-sectional shape of the SWCNT changes substantially in the relaxed state depending on the extent of Li insertion: the SWCNT exhibits a circular cylinder shape when no Li is present, whereas it is flattened upon sufficient Li insertion. These SWCNT shapes well reflect the aggregated shapes of PhQ molecules, which depend on the amount of Li inserted. As for the Li insertion and extraction dynamics, we find that the Li atoms can take either of two paths: one is along the SWCNT wall, and the other involves hopping on the PhQ molecules and/or the sites where the C atoms of the SWCNT and the O atoms of PhQ molecules contact each other. The Li-transfer rate on the SWCNT wall is large; hence, the hopping is the rate-limiting step.

The generalized Langevin equation (GLE) is considered with emphasis put on a mechanical random force , whose time evolution is not natural due to the presence of a projection operator in a propagator. We first derive the GLE for a set of dynamical variables of interest not by formal manipulation of the operator identity as is usually done, but by expressing the random force in terms of natural trajectory in the phase space. Based on this new derivation we observe two structural characteristics, (1) a linear functional interdependence between and and (2) a self-consistent structure (SCS) inherent in the GLE. The SCS gives an iterative procedure to determine and its time correlation function, i.e. a memory function K(t), once we have numerical data for supplied by computer experiments. This method generates and a memory function K(t), nicely for an exactly solvable many-body system after several iterations. Some merits of using the SCS are further discussed in connection with numerical methods to calculate the autocorrelation function of .