2024 AIChE Annual Meeting

(202b) Novel Melting and Freezing Behavior at High Pressure

Authors

Sadus, R. J. - Presenter, Swinburne Univ of Technology
Travis, K. P., Immobilisation Science Laboratory, University of Sheffield
Most commonly encountered substances have melting and freezing boundary curves over a small range of densities at which both solid and liquid phases coexist [1]. The temperature and pressure of solid-liquid equilibria extend to ever increasing values accompanied by a progressively more narrow range of densities. Whether or not the melting and freezing curves eventually coincide at extreme values of both temperature and pressure remains unresolved because measurements at pressures of many giga Pascals are very challenging [2]. Molecular simulation [3] provides an alternative to experiment and highly effective algorithms for solid-liquid equilibria have been devised [4]. Nonetheless, a solid-liquid equilibria closure has never been observed using physically realistic intermolecular potentials [2].

A common feature of many realistic intermolecular potentials is steep repulsion and long-range attractive interaction. Comparison [5] with ab initio data consistently indicates that the degree of repulsion is often over estimated, particularly at low intermolecular separation. We report [6] molecular simulations of solid-liquid equilibria using a relatively soft-repulsion, short attractive-ranged pair potential that demonstrate the closure of the freezing and melting lines at high pressures and temperature. The point of closure is accompanied a density inversion of the solid and liquid phases that is usually only observed for water.

[1] R.J. Sadus, High Pressure Phase Behavior of Multicomponent Fluid Mixtures, Elsevier, Amserdam 1992.

[2] R. Boehler, M. Ross, P. Söderlind, and D. B. Boercher, Phys. Rev. Lett. 86, 5731-5734 (2001).

[3] R.J. Sadus, Molecular Simulation of Fluids: Theory, Algorithms, Object-Orientation, and Parallel Computing, 2ndEd., Elsevier, Amsterdam, 2024 (https://www.elsevier.com/books-and-journals/book-companion/9780323853989).

[4] D. Kofke, J. Chem. Phys. 98, 4149-4162 (1993).

[5] U. K. Deiters and R. J. Sadus, J. Chem. Phys. 151, 034509 (2019).

[6] K. P. Travis and R. J. Sadus, J. Phys. Chem. B 128, 2922-2929 (2024).

[7] W. G. Hoover, Smooth Particle Applied Mechanics, World Scientific, Singapore, 2006.