In this work, we present a phase field dislocation dynamics formulation designed to treat a system comprised of two materials differing in moduli and lattice parameters that meet at a common interface. We apply the model to calculate the critical stress τ crit required to transmit a perfect dislocation across the bimaterial interface with a cubeon-cube orientation relationship. The calculation of τ crit accounts for the effects of: 1) the lattice mismatch (misfit or coherency stresses), 2) the elastic moduli mismatch (Koehler forces or image stresses), and 3) the formation of the residual dislocation in the interface. Our results show that the value of τ crit associated with the transmission of a dislocation from material 1 to 2 is not the same as that from material 2 to 1. Dislocation transmission from the material with the lower shear modulus and larger lattice parameter tends to be easier than the reverse and this apparent asymmetry in τ crit generally increases with increases in either lattice or moduli mismatch or both. In efforts to clarify the roles of lattice and moduli mismatch, we construct an analytical model for τ crit based on the formation energy of the residual dislocation. We show that path dependence in this energetic barrier can explain the asymmetry seen in the calculated τ crit values. Significantly, it reveals that τ crit scales with a (2) G (2) a (1) +a (2) a (1) a (2) − G (1) G (2) 2 , where G is the shear modulus, a is the lattice parameter, and the superscripts (1) and (2) indicate quantities for material 1 and material 2, respectively.

No abstract

electrical, [3] catalytic, [4] and magnetic [5] properties. To overcome the poor stability and severe aggregation in catalytic processes that remain major problems for UMNPs, MNPs have been immobilized onto/into various supports through postsynthetic and one-pot synthesis methods. [6] With either method, it is critical to control the interaction between the metal ions and supports and interactions between metal ions. Various functional groups have been selected and used to improve metal precursor impregnation rates and metal-support interactions to avoid metal leaching into the liquid phase and to control particle aggregation and growth; for example, P and N ligands constituted with bisphosphinoamino moieties, diphenylphosphinopyridine moieties, dendrimers, small organic molecules (amines, thiols, citrate, etc.), surfactants (hexadecyltrimethylammonium bromide), and silanization reagents (SH, NH 2 , and COOH) have been used. [7] However, these methods are not universally applicable to a large number of metals because of the limit of the coordination selectivity of ligands.DNA is one of the most attractive "building blocks" because of its double-stranded helical structure with well-defined minor and major grooves, well-regulated micrometer length, and a uniform diameter of ≈2 nm. More importantly, the unique chemical composition of DNA provides a variety of binding Supported ultrasmall metal/metal oxide nanoparticles (UMNPs) with sizes in the range of 1-5 nm exhibit unique properties in sensing, catalysis, biomedicine, etc. However, the metal-support and metal-metal precursor interactions were not as well controlled to stabilize the metal nanoparticles on/in the supports. Herein, DNA is chosen as a template and a ligand for the silica-supported UMNPs, taking full use of its binding ability to metal ions via either electrostatic or coordination interactions. UMNPs thus are highly dispersed in silica via self-assembly of DNA and DNA-metal ion interactions with the assistance of a co-structural directing agent (CSDA). A large number of metal ions are easily retained in the mesostructured DNA-silica materials, and their growth is controlled by the channels after calcination. Based on this directing concept, a material library, consisting of 50 mono-and 54 bicomponent UMNPs confined within silica and with narrow size distribution, is created. Theoretical calculation proves the indispensability of DNA with combination of several organics in the synthesis of ultrasmall metal nanoparticles. The Pt-silica and Pt/Ni-silica chosen from the library exhibit good catalytic performance for toluene combustion. This generalizable and straightforward synthesis strategy is expected to widen the corresponding applications of supported UMNPs.

Milling and micronization are commonly used to reduce the particle size of active pharmaceutical ingredients and excipients. During these processes the materials are subjected to extensive deformation that may result in defect nucleation, polymorphic transformations, and amorphization. Current amorphization models require parameters that demand extensive number of experiments. We present a multiscale framework to predict mechanically induced amorphization without experimental information. The model requires as input only the molecular structure and starts with molecular dynamics simulations to determine elastic constants, melting temperature, crystal-amorphous interface energy, and the energy density difference between the amorphous and crystalline phases. This information is used in a phase field model that includes defect nucleation and solid state amorphization. At each scale, the components of the model are validated by performing simulations of sucrose, lactose, acetaminophen, and gamma-indomethacin. The multiscale framework is exercised to predict the response of two pharmaceutical compounds F1 and F2, without any experimental information. The model indicates that F1 is resistant to disorder while F2 tends to be amorphized, in agreement with the experimental results.