Molecular dynamics dispersion mechanisms

The earliest applications of the shell model, as with the Born model, were to analytical studies of phonon dispersion relations in solids.These early applications have been well reviewed elsewhere.In general, lattice dynamics applications of the shell model do not attempt to account for the dynamics of the nuclei and typically use analytical techniques to describe the statistical mechanics of the shells. Although the shell model continues to be used in this fashion, lattice dynamics applications are beyond the scope of this chapter. In recent decades, the shell model has come into widespread use as a model Hamiltonian for use in molecular dynamics simulations it is these applications of the shell model that are of interest to us here. 

Non-exponential phosphorescence decay is frequently observed for various aromatic chromophores molecularly dispersed in polymer matrices. Various possible mechanisms for non-exponential decay are reviewed, and a dynamic quenching mechanism by polymer matrices including the effect of a time-dependent transient term in the rate coefficient is discussed in some detail. The biphotonic triplet-triplet annihilation mechanism is also introduced for the non-exponential decay under high-intensity and/or repeated laser irradiation. 

With the aim of quantitatively predicting the orientational order of rigid solutes of small dimensions dissolved in the nematic liquid crystal solvent, 4-n-pentyl-4 cyanobiphenyl (5CB), an atomistic molecular dynamics (MD) computer simulation has been applied. It is found that for the cases examined the alignment mechanism is dominated by steric and van der Waals dispersive forces. A computer simulation of the deuterium NMR spectra of molecules in a thin nematic cell has been carried out and the director distribution in the cell has been studied. An experiment for the direct estimation of an element of the order matrix from H NMR spectra of strongly dipolar coupled spins that is based on the multiple quantum spin state selected detection of single quantum transitions has been proposed. The experiment also enables obtaining nearly accurate starting dipolar... 

Within the scope of physical-chemical mechanics, various approaches are used to describe the mechanical properties of various liquid-like and solid-like bodies and materials. These include the methods of macro- and microrheology, and molecular dynamic experiments, allowing one to approach the problem at the molecular dimension. The combination of these approaches provides one with the means to analyze the properties of real disperse systems and with methods for controlling them. Special attention is devoted to the Rehbinder effect, that is, to the adsorption-related influence of the dispersion medium on the mechanical properties of solids. 

The molecular dynamics of polyvinyl alcohol (PVA) and carboxymethyl cellulose (CMC) blends was investigated as a function of composition, temperature and frequency using DRS [44]. PVA and CMC were found to be compatible over the range of composition studied. When the dielectric permittivity, loss tangent and a. c. conductivity of all samples were studied as functions of temperature and frequency, the results showed that the dielectric dispersion consisted of both dipolar and interfacial polarization. The frequency dependence of the a.c. conductivity indicated that correlated barrier hopping (CBH) was the most suitable mechanism for conduction. 

Nanofluids or PCM slurries prepared from carrier fluids mixed with nanocapsules showed a significant increase in the capacity of heat transport values. In addition, nanocomposites made by nanomaterials with high thermal conductivity such as alumina and cupper nanoparticles, carbon nano-fibers, or and graphite nanoplatelets dispersed into paraffin can be used to enhance heat transfer and thermal properties [20]. Molecular dynamics simulations were performed by Rao et al. [20] to investigate the heat and mass transfer mechanism of nanoparticle-enhanced PCM and nano-encapsulated PCM. The nano-encapsulated PCM was studied using n-octadecane as core and SiO as shell material. Nanoparticle-enhanced PCM was studied by addition of Al nanoparticles with four different... 

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