Decreased structure on dissolving methane in water

There is a widely held view that hydrophobic entities such as alkanes and alkyl head groups enhance the local structure of water (greater tetrahedrality) when dissolved in it. The idea stems from an early paper by Frank and Evans who speak about ice-like structures forming around hydrophobic entities in solution. Here, we probe directly for the first time the structure of water in a methane water solution using neutron diffraction with hydrogen isotope substitution. We find no evidence for enhanced water structure. If anything the structure is marginally less tetrahedral than in pure water at the same temperature and pressure. (c) 2005 Elsevier B.V. All rights reserved.