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Article: Molecular dynamics and kinetic study of carbon coagulation in the release wave of detonation products
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ABSTRACT: We present a combined molecular dynamics and kinetic study of a carbon cluster aggregation process in thermodynamic conditions relevant for the detonation products of oxygen deficient explosives. Molecular dynamics simulations with the LCBOPII potential under gigapascal pressure and high temperatures indicate that (i) the cluster motion in the detonation gas is compatible with Brownian diffusion and (ii) the coalescence probability is 100% for two clusters entering the interaction cutoff distance. We used these results for a subsequent kinetic study with the Smoluchowski model, with realistic models applied for the physical parameters such as viscosity and cluster size. We found that purely aggregational kinetics yield too fast clustering, with moderate influence of the model parameters. In agreement with previous studies, the introduction of surface reactivity through a simple kinetic model is necessary to approach the clustering time scales suggested by experiments (1000 atoms after 100 ns, 10 000 atoms after 1 mu s). However, these models fail to reach all experimental criteria simultaneously and more complex modelling of the surface process seems desirable to go beyond these current limitations.The Journal of Chemical Physics 02/2012; 136(8):084506. · 3.33 Impact Factor -
Article: Least constraint approach to the extraction of internal motions from molecular dynamics trajectories of flexible macromolecules.
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ABSTRACT: We propose a rigorous method for removing rigid-body motions from a given molecular dynamics trajectory of a flexible macromolecule. The method becomes exact in the limit of an infinitesimally small sampling step for the input trajectory. In a recent paper [G. Kneller, J. Chem. Phys. 128, 194101 (2008)], one of us showed that virtual internal atomic displacements for small time increments can be derived from Gauss' principle of least constraint, which leads to a rotational superposition problem for the atomic coordinates in two consecutive time frames of the input trajectory. Here, we demonstrate that the accumulation of these displacements in a molecular-fixed frame, which evolves in time according to the virtual rigid-body motions, leads to the desired trajectory for internal motions. The atomic coordinates in the input and output trajectory are related by a roto-translation, which guarantees that the internal energy of the molecule is left invariant. We present a convenient implementation of our method, in which the accumulation of the internal displacements is performed implicitly. Two numerical examples illustrate the difference to the classical approach for removing macromolecular rigid-body motions, which consists of aligning its configurations in the input trajectory with a fixed reference structure.The Journal of chemical physics 08/2011; 135(8):084110. · 3.09 Impact Factor -
Article: Molecular dynamics simulations of nanocarbons at high pressure and temperature
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ABSTRACT: A molecular dynamics study of carbon nanoparticles; (980 and 10,034 atoms) under high temperature (1000-7000 K) and high pressure (2-45 GPa) has been made using the reactive LCBOPII potential. The most stable structure of the small cluster is onion-like (encapsulated fullerenic) on the whole pressure range, whereas a transition from onion-like to nanodiamond is observed for the big cluster as pressure increases from 2 to 45 GPa. The melting mechanism depends on the structure, initiated in the core in the case of an onion cluster and at the surface for the nanodiamond. A schematic phase diagram is proposed, that takes into account the finite size effects.Carbon 12/2009; 47(15):3392-3402. · 5.38 Impact Factor -
Article: Formation of multiwall fullerenes from nanodiamonds studied by atomistic simulations
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ABSTRACT: The high-temperature annealing of nanodiamonds with sizes typical of ultradisperse diamonds is studied with atomistic simulations using a recent and accurate classical reactive potential. At 3000 K, the complete transformation of the particles into carbon onions made of five to seven concentric fullerenes occurs according to a three-step mechanism: (i) formation of two to three graphitic shells at the surface, (ii) transformation of the diamond core into an amorphous sp(2) carbon, and (iii) reorganization of the core into concentric fullerene layers. At lower temperatures, the transformation stops at step (i) and the final structure is made of a diamond core surrounded by a few fullerene shells. The analysis of the internal pressure of the diamond core reveals that this state is metastable.Physical Review B 10/2009; 80(15):155420. · 3.69 Impact Factor -
Article: Molecular dynamics study of dicarbollide anions in nitrobenzene solution and at its aqueous interface. Synergistic effect in the Eu(III) assisted extraction.
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ABSTRACT: We report a molecular dynamics study of chlorinated cobalt bis(dicarbollide) anions [(B(9)C(2)H(8)Cl(3))(2)Co](-)"CCD(-)" in nitrobenzene and at the nitrobenzene-water interface, with the main aim to understand the solution state of these hydrophobic species and why they act as strong synergists in assisted liquid-liquid extraction of metallic cations. Neat nitrobenzene is found to well solubilize CCD(-), Cs(+) salts in the form of diluted pairs or oligomers, without displaying aggregation. In biphasic nitrobenzene-water systems, CCD(-) anions mainly partition to the organic phase, thus attracting Cs(+) or even more hydrophilic counterions like Eu(3+) into that phase. The remaining CCD(-) anions adsorb at the interface, but are less surface active than at the chloroform interface. Finally, we compare the interfacial behavior of the Eu(BTP)(3)(3+) complex in the absence and in the presence of CCD(-) anions and extractant molecules. It is found that in the absence of CCDs, the complex is trapped at the interface, while when the CCDs are concentrated enough, the complex is extracted to the nitrobenzene phase. These results are compared to those obtained with chloroform or octanol as organic phase and discussed in the context of synergistic effect of CCDs in liquid-liquid extraction, pointing to the importance of dual solvation properties of nitrobenzene or octanol to solubilize the CCD(-) salts as well as the extracted complex.Physical Chemistry Chemical Physics 12/2007; 9(44):5928-38. · 3.57 Impact Factor
