Deblurred observation of the molecular structure of an oil-water interface.
We simulated the interface between liquid water and a stationary phase of tethered n-C18 alkyl chains at a thermodynamic state of low pressure and water vapor-liquid coexistence. The interfacial water (oxygen atom) density profile so obtained is compared with a precisely defined proximal density of water molecules (oxygen atoms) conditional on the alkyl chain configurations. Though the conventional interfacial density profile takes a traditional monotonic form, the proximal radial distribution of oxygen atoms around a specific methyl (methylene) group closely resembles that for a solitary methane solute in liquid water. Moreover, this proximal radial distribution function is sufficient to accurately reconstruct the water oxygen density profile of the oil-water interface. These observations provide an alternative interpretation to collective drying or vaporization interpretations of commonly observed oil-water interfacial profiles for which water penetration into the interfacial region plays a role.
Ashbaugh
Henry S
HS
Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA.
Pratt
Lawrence R
LR
Paulaitis
Michael E
ME
Clohecy
Jason
J
Beck
Thomas L
TL
D002244:Carbon / Q000737:chemistry; D003102:Colloids; D057927:Hydrophobic and Hydrophilic Interactions; D008956:Models, Chemical; D009821:Oils / Q000737:chemistry*; D010100:Oxygen / Q000737:chemistry; D013499:Surface Properties; D014867:Water / Q000737:chemistry*
D003102:Colloids; D009821:Oils; D014867:Water; D002244:Carbon; D010100:Oxygen