Breaking immiscibility : Dissolving large ratios of natural gas in water under extreme conditions
It has long been know the principle that "like dissolves like", meaning polar species readily mix with polar species and non-polar species with non-polar species. Specifically, the fact that water mixes in large ratios with other polar liquids but does not do so with apolar ones (like methane, hexane, etc.) is of crucial importance to chemistry (including large-scale industrial processes, such as production of stable water-in-oil or oil-in-water emulsions like vinaigrettes and milk), forms the basis of most processes molecular biology is concerned with and is also an important part of understanding the behaviour of the insides of planets like Uranus, Neptune and Venus, and some satellites, most notably Titan and Enceladus.
Despite the multitude of studies done of methane-water mixtures close to ambient conditions that provided a fairly exhaustive view of this system in that region of its phase diagram, the high-pressure and high-temperature behaviour of this binary mixture is still far from satisfactory. In our study, several samples consisting of water-methane mixture in different concentrations were loaded in Diamond Anvil Cells. Upon heating up and melting the samples, above a certain pressure the miscibility of methane in water was noticed to abruptly increase, up to 35(5) mole % at 2 GPa (and remained unchanged at least up to 3.2 GPa in the liquid phase). This suggests an unexpected increase in the hydrophobic hydration of methane, which is of crucial interest to planetary sciences as well as the food and energy industries and opens new possibilities for research as well as applications, enabling one to create finely-tuned environments in which chemical reactions can be studied.
This is a weekly series of informal talks given primarily by members of the soft condensed matter and statistical mechanics groups, but is also open to members of other groups and external visitors. The aim of the series is to promote discussion and learning of various topics at a level suitable to the broad background of the group. Everyone is welcome to attend..