ISSN Online: 2377-424X
ISBN Print: 978-1-56700-421-2
International Heat Transfer Conference 15
Prediction of Anisotropic Crystal-Melt Interfacial Free Energy of Sugar Alcohols Through Molecular Simulations
摘要
Sugar alcohols have been recently under investigation for their use as phase change materials in long-term
heat storage systems. The thermal performances in such systems are strongly dominated by the nucleation
and crystal growth kinetics, which on their turn are linked to the crystal-melt interfacial free energy γSL. We report a novel technique using first principle calculations to accurately predict γSL of xylitol and β-D-mannitol,
as well as their anisotropy, from molecular modeling. The molecular model is based on a wellproven generalized AMBER force field, which can reliably reproduce the physics during the phase change. The calculation technique is generalized from a cleaving method which has been successfully implemented in monoatomic and rigid polyatomic molecular systems. This method essentially creates an artificial interface and gradually puts the crystal and melt phases into contact under the guidance of a cleaving potential. We
extended this method for the calculation of flexible polyatomic molecules. A specific cleaving potential is
designed for molecular systems with many degrees of freedoms. We made many efforts to achieve reliable
equilibrium Boltzmann sampling and reduction of hysteresis, including the selection of transition paths. The
samples of transition states are processed based on the Bennett Acceptance Ratio method. The predicted free
energies agree with available experimental estimations, and the large anisotropy in the interfacial free energy
is found which could be responsible for the dendritic growth of xylitol and D-mannitol systems as observed
in experiments.