Simulación computacional de fluidos nanoporosos

G. MELAUGH, N. GIRI, S. L. JAMES AND M. G. DEL PÓPOLO

Mendoza

Jornada; XXIII Jornadas de Investigación y V Jornadas de Posgrado de la Universidad Nacional de Cuyo; 2013

Standard nanoporous materials are crystalline solids that exhibit a regular array of cavities of uniform size and shape. In the liquid state interstitial cavities are transient and their concentration depends on the temperature and surface tension of the sample. Yet, a liquid system exhibiting intrinsic, permanent and controllable nano-porosity can be achieved if the appropriate cavities are built into the structure of the constituent molecules. We have synthesised a series liquids made of cage-like molecules and characterised their fluid properties, microscopic structure and sorption capabilities by computer simulation. Each cage is formed by a hollow tetrahedral core, whose vertices are decorated by hydrocarbon chains of varying length. Molecular dynamics simulations are employed to investigate the effect of the chain length and the size of terminal groups, on the distribution of intra- and inter-molecular cavity sizes. As some chain tips spontaneously penetrate into the core of neighbouring molecules, the thermodynamic work for displacing a tail-end into an empty cage has been computed along an appropriate reaction coordinate. The resulting free-energy profiles allow us to estimate the equilibrium fraction of occupied cages at a given temperature. Furthermore, Grand-Canonical Monte Carlo simulations are employed to investigate the absorption of small gas molecules into the fluid.