Conditions for which the bulk fluid is anisotropic, or sideside interactions are stronger than face-face ones, can give the face-on orientation at the vapour interface. From our predictions based on the behaviour of a bulk isotropic fluid, the face-on orientation at the vapour interface is difficult to achieve, although it could be obtained by systems with stronger side-side than face-face interactions (e.g. by chemical functionalisation of the aromatic core of the OSC). The interface orientation of liquid crystal fluids has previously been shown to be much more variable. Under appropriate conditions, many OSCs form liquidcrystal phases, meaning the predictions of ref 37 based on the shape and interaction anisotropy can be applied to tune the orientation at the vapour interface.