Nanoscale materials modeling

With the advent of nanomaterials, different types of polymer-based composites developed as multiple scale analysis down to the nanoscale became a trend for development of new materials with new properties. Multiscale materials modeling continue to play a role in these endeavors as well. For example, Qian et al. [257] developed multiscale, multiphysics numerical tools to address simulations of carbon nanotubes and their associated effects in composites, including the mechanical properties of Young s modulus, bending stiffness, buckling, and strength. Maiti [258] also used multiscale modeling of carbon nanotubes for microelectronics applications. Friesecke and James [259] developed a concurrent numerical scheme to evaluate nanotubes and nanorods in a continuum. 

Much of the work to date on particle size effects on phase transformation kinetics has involved materials of technological interest (e.g., CdS and related materials, see Jacobs and Alivisatos, this volume) or other model compounds with characteristics that make them amenable to experimental studies. Jacobs and Alivisatos (this volume) tackle the question of pressure driven phase transformations where crystal size is largely invariant. In some ways, analysis of the kinetics of temperature-motivated phase transformations in nanoscale materials is more complex because crystal growth occurs simultaneously with polymorphic reactions. However, temperature is an important geological reality and is also a relevant parameter in design of materials for higher temperature applications. Thus, we consider the complicated problem of temperature-driven reaction kinetics in nanomaterials. 

The Center for Nanophase Materials Sciences at Oak Ridge National Laboratory (http //www.cnms.ornl.gov/) will concentrate on synthesis, characterization, theory/ modeling/simulation, and design of nanoscale materials. The NSF also funds several related facilities, such as the Cornell Uni-... 

Determined by their molecular nature, most CP nanoscale materials are either amorphous or polyerystalline. In the latter case, the size of the ordered crystalline grain/island is typically less than 10 nm [106]. This limits the electron and hole delocalization length to a similar scale. Therefore, based on this argument, unless the cross-seetion of a CP nanowire is comparable to the delocalization length, electron and hole transport in such a nanowire should follow their behavior in a 3-D bulk material. As we have discussed in the previous section, many nanowires and nanotubes prepared so far are indeed larger than the characteristic electronic localization length, and it is, in general, valid to treat these nanowires and nanotubes with the already established electronic-transport theories and models for 3-D CP materials. 

Expresso calculations and materials modeling at the nanoscale http //www. 

EPA, for example, in its White Paper on Nanotechnology, has openly expressed concern over this lack of data and has questioned the use of the very models it employs to predict movement of substances through the environment because these models are based on macro-scale substances. The reactivity and mobility associated with nanoscale materials could dramatically alter the models currently used. 

These examples also show that simulation is an important tool for many nanoscale materials problems. Although brute force simulation is not usually effective because the time scales are too long and the number of particles is too large, a combination of simulation in conjunction with analytical theory and simple models can be quite effective. 

Since the first systematic study of monolayers of amphiphilic molecules at the air-water interface published by Langmuir in 1917 [1], Langmuir monolayers have served mainly as model systems to mimic biological membranes. With the development of nanotechnology in the last two decades, the Langmuir monolayer technique has become an efficient tool to make nanoscale materials, especially as thin films for chemical and biosensor development [2-5]. 

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