Molecular dynamics of octane in a gas liquid solution

A gas/liquid solution was formed by applying up to 70 (MPa) of argon to n−octane. The molecular dynamics of octane in the solution were measured by NMR relaxation techniques. A relatively insoluble gas, helium, was also applied so that the effect of pressure could be contrasted with the effect of solution. The transport properties of octane compressed by argon possessed two distinguishing features. First, the behavior of its diffusion constant indicated that the viscosity of the fluid decreased with pressure as more argon dissolved into the liquid. Second, the pressure depencence of octane’s over−all rotational correlation time was much less than the estimated pressure dependence of the solution’s viscosity. This latter feature could be explained by a microviscosity theory which takes into account the effect of solvent size on the coupling between molecular rotation and viscosity.