Nanoparticles, with sizes ranging between 1 and ∼102 nm, show dynamical properties distinctly different than those of bulk materials. Due to their large surface area to volume ratio, their properties often depend on length scales. We investigate the size and the collision velocity (vcoll) dependence of the coefficient of restitution (COR) for nanoparticles made of a face-centered cubic lattice of Lennard-Jones atoms via nonequilibrium molecular dynamics simulations. A sharp crossover between elastic collision and plastic collision occurs when vcoll=vY, where vY is the size-dependent yield velocity. For high-collision velocities the COR ∼vcoll-α, α∼1. This result is in agreement with recent small system simulations and with experiments and is distinct from the elasticity-theory-based result for COR for inelastic collisions which behaves as vcoll-α, with α=14. We find that the size-dependent critical vY approaches the theoretical constant value for macroscopic spheres as our particle sizes grow. Possible insights into the origins of α∼1 and the size dependence of the yield velocity are suggested. The work also suggests that sufficiently fast moving nanoparticles traveling through vacuum could be sticky and hence could be of potential interest in many applications.

The comprehension of the nonlinear effects provided by mixed alkali effect (MAE) in oxide glasses is useful to optimize glass compositions to achieve specific properties that depend on the mobility of ions, such as the chemical durability, glass transition temperature, viscosity and ionic conductivity. Although molecular dynamics (MD) simulations have already been applied to investigate the MAE on silicates, less effort has been devoted to study such phenomenon in mixed alkali aluminosilicate glasses where alkali cations can act both as modifiers, forming non-bridging oxygens and percolation channels, and as charge compensator of the Alo 4 − units present in the network. Moreover, the ionic conductivity has not been computed yet; thus, the accuracy of the atomistic simulations in reproducing the MAE on the property is still open to question. In this work, we have validated five major interatomic potentials for the classical MD simulations by modelling the structure, density, glass transition temperature and ionic conductivity for three aluminosilicate glasses, (25 − x)Na 2 o − x(K 2 O) − 10(Al 2 o 3) − 65(SiO 2) (x = 0, 12.5, 25). It was observed that only the core-shell (CS) polarizable force field well reproduces the experimentally measured MAe on T g and the ionic conductivity as well as the higher conductivity of single sodium aluminosilicate glass at low temperature and the higher conductivity of single potassium aluminosilicate glass at high temperature. The MAE is related to the suppression of jump events of the alkaline ions between dissimilar sites in the percolation channels consisting of both sodium and potassium ions as in the case of alkaline silicates. The superior reproducibility of the CS potential is originated from the larger and the flexible ring structures due to the smaller Si-O-Si inter-tetrahedra angle, creating appropriate percolation channels for ion conductivity. We also report detailed assessments for using the potential models including the CS potential for investigating MAE on aluminosilicates. Ionic conductivity in inorganic glasses is gaining a huge interest for the enormous number of applications that such materials are having in a number of major technological developments in the domains of energy conversion and storage (solid electrolytes in battery and fuel cells) or in the environmental monitoring (solid state ionic membranes for sensors) 1. Among the various ways to control ionic diffusion and thus ionic conductivity a possibility is that to exploit the so-called Mixed Alkali Effect (MAE) or more in general the Mixed Ion Effect (MIE) 2,3. This effect refers to a large non-linear deviation in glass properties observed when an alkali cation (or more in general a mobile ion) is gradually replaced by another alkali cation. The ionic conductivity of glasses exhibiting the MAE shows a deep minimum when half of the alkaline ions of type A are replaced by type B ions, meaning that cation mobility progressively reduces up to a substitution ratio equal to unity. The minimum is more pron...

In this report, we propose a novel framework for toughening brittle oxide glass originated from enhanced ductility by implanting a secondary material comprising different mechanical properties. To do so, copper-metal nanoparticles are implanted into the subsurface layer of commercial soda-lime silica glass by using the electrofloat method. The crack initiation load of the implanted glass is found to be comparable to the glass chemically strengthened in ordinary tempering conditions. By observing crack propagation and stress distribution from cross-section, it is found that the crack propagation stops within the metal nanoparticle implanted layer, due to the stress dissipation or relaxation. The copper-implanted glass shows improved toughness with decreased hardness. The toughening mechanism of the composite glass is theoretically studied using molecular dynamics calculations on an amorphous silica model with copper nanoparticles embedded, and Peridynamics fracture simulations for indentation on a glass sheet model whose surface was implicitly modeled as the copper-implanted oxide glass. The experimentally observed phenomena of intrinsic toughening were well explained by the series of the conducted simulations.

Kinetic energy fluctuations of a non-dissipative 1D granular chain held between perfectly reflecting walls with various precompressions are numerically investigated. The dynamics of the system is explored for three cases, i) for a weakly precompressed chain which admits only solitary waves that break down into secondary waves under wall collisions, which is consistent with other findings in the literature; ii) for a strongly precompressed chain which exhibits mostly acoustic waves; and iii) for a chain with intermediate precompression. Case iii) accommodates a nearly stable solitary wave that travels unaffected through the acoustic waves and bounces back and forth between the walls for extremely long times.

No abstract