On mechanical characteristics of nanocrystals

The dependence of the elastic moduli of a nanocrystal on its size is investigated theoretically with reference to a two-dimensional single-crystal strip. It is shown that the uncertainty (of a fundamental nature) in the size of a nanocrystal causes the determination of many of its mechanical characteristics to be ambiguous. It is found that the Cauchy-Green relations are modified and the elastic-constant tensor ceases to be symmetric; the size and shape of a nanocrystal render its mechanical properties more anisotropic. For a single-crystal strip, the Poisson ratio decreases and the Young modulus increases with decreasing thickness of the strip; in the case of a very thin crystal film (two atomic layers thick), these elastic moduli can differ from their macroscopic values by a factor of two. The size effects which make the continuum elasticity theory inapplicable to nanocrystals are estimated. The size effects that occur when the molecular dynamics method is applied for modeling macroscopic objects are also discussed.     

Anionic Liposomes in Contact with Cationic Chitosan Particles

Russian Journal of General Chemistry - Nanoparticles of ionically cross-linked chitosan have been prepared from the linear polymer with weight-average molecular mass Mw of 30000, 63000, or 300000...     

Molecular Dynamics Simulation of Impact Fracture in Polycrystalline Materials

Technique for creation of polycrystalline computer materials is presented. The method considered allows for the obtaining of not only polycrystalline particle packings with various grains sizes but also the creating of materials with the preset value of porosity. Plate impact experiments were performed to compare strength properties of mono- and polycrystalline computer materials and also to investigate influence of the material porosity on the shock wave penetration and spallation processes. The experiments show significant differences in the impact fracture processes between mono- and polycrystalline materials. Smearing the shock waves due to heterogeneity of the granular structure of the polycrystals decreases localization effects, and the fracture occupies larger areas but with the smaller level of injury. Porosity adds significant resistance due to the strong plastic deformation during the pore collapsing. This effect can strongly decrease the penetration distance of the shock wave and even prevent the spallation.     

Biodegradable liposome–chitosan complexes: enzyme-mediated release of encapsulated substances

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