Séminaire - The inverted hydrophobic effect: squeezing oil into water under pressure - Victor Naden Robinson

Lundi 3 février 2020, 10 h 30

IMPMC - Sorbonne Université - 4 place Jussieu, 75005 Paris, tour 23, 4^e étage, couloir 22-23, salle 401

Victor Naden Robinson - ICTP

Abbstract

Molecular mixtures under pressure offer knowledge of how giant planets organize themselves as well as fundamental chemical interactions. After introducing recent work on ammonia and water mixtures up to 500 GPa, I will present new data on mixtures of methane and water. This work explores the hydrophobic effect as methane is squeezed into water, experimentally and computationally, under compression at 413 K. The molecular structure of dense homogeneous liquid water-methane mixtures was determined for the first time using high pressure neutron scattering techniques at 1.7 and 2.2 GPa. These studies reveal a pressure-induced mixing of methane and water as seen from the molecular structures obtained thereby reversing the hydrophobic effect. Ab initio molecular dynamics simulations are performed to unravel the microscopic mechanisms associated with this phenomena. These calculations reveal phase separation and mixing occurring at the expected pressures. Curiously, the mixed state does not involve any substantial disruption of the hydrogen water network as seen in several structural and topological properties. This is rooted in part by an enhancement of the mutual polarization of the methane and water under pressure, as seen by the dramatic increase in the dipole moment of methane and water molecules which essentially weakens the hydrophobic effect.