44997-G10
Crystallization of N-Alkanes in Equilibrium and Under Shear
The aim of this project is to develop molecular simulations to understand the molecular mechanisms underlying crystal nucleation and growth of n-alkanes in equilibrium and under shear. In particular, we aim to elucidate the polymorph selection process, i.e. the process by which the system selects a specific crystalline structure (or polymorph). We have developed Molecular Dynamics as well as Hybrid Monte Carlo simulation methods to provide insight into the formation of a crystal nucleus of a critical size and to determine its structural evolution during the growth step. We also developed NonEquilibrium Molecular Dynamics methods, based on the transient-time correlation function formalism, to study systems subjected to experimentally accessible shear rates. We have applied these methods to study systems of increasing complexity. We started with a model system in which the interactions between particles are modelled with an inverse-power-law potential. We were able to propose a molecular mechanism for the crystallization process and to rationalize the choice of a specific polymorph during crystal growth. We then applied these methods to study the crystallization of a liquid metal, aluminum, modeled with a state-of-the-art many-body potential fitted to reproduce high-quality ab initio calculations on a wide range of Al nanoparticles. We were able to demonstrate that the crystallization mechanism of aluminum was markedly different from that observed for simpler fluids. More recently, we applied these methods to understand the nucleation and growth of nanoparticles of fullerene and to the nucleation and growth of n-alkanes. We showed in particular that the heterogeneous nucleation of one polymorph over another plays a pivotal role in the crystallization process. This work was carried out by a graduate student, Caroline Desgranges, who graduated in May 2008 and was partially supported by the PRF grant, and by the PI. Two peer-reviewed journal articles have been published (one in the Journal of Chemical Physics and another in the Journal of Physical Chemistry B) and two other manuscripts are currently under review. The award of the PRF grant played a key role in my first years as an independent researcher. It provided a great deal of encouragement and helped me develop a successful research effort on self-assembly on the nanoscale.
