(342h) Excluded Volume Monte Carlo Simulations for Anisotropic Fluid Structure Predictions

High-flux neutron scattering is recently being used to determine the multidimensional structures of polyatomic and anisotropic molecules, providing novel insights into the structural patterns of local fluid structure. The experimental outcomes indicate complex molecular organization and behavior change with thermodynamic conditions. We have recently investigated two hydrocarbon fluids (benzene and 1-methylnaphthalene) adopting wide-angle neutron scattering of isotopically substituted molecules to experimentally determine local fluid structure. We observed that face-to-face structural motifs tend to show increased order (1-methylnaphthalene) or remain unchanged (benzene) when the temperature is increased. We attributed this apparently contradictory behavior as entropically-driven induced by the shape of the molecule, widely observed in hard-particles and colloidal systems. We developed a stochastic Monte-Carlo-based simulation tool to portray this entropically-driven ordering by simply estimating the free-volume, eliminating the molecular modeling high-computational costs and complexity associated with many-electron systems and consequent limitations to represent the emergent many-body entropic properties. The tool enabled predicting the structural motifs susceptible to increased (or unchanged) order with the temperature representing an emergent entropic effect in the system. The motifs with the highest free volume were observed to show enhanced ordering from neutron scattering results. The developed simple technique can be an ideal tool to predict entropically-driven ordering for other complex molecules (e.g., liquid crystals, organic photovoltaics, petroleum derivatives), specifically for systems difficult to test experimentally.