ABSTRACT
The liquid density across molecularly thin films is not uniform but has an oscillatory profile. The periodicity of the oscillations is close to the diameter of the liquid molecules3-9 and reflects the forced ordering of the liquid molecules into quasidiscrete layers between the two surfaces. The closer two surfaces approach each other the sharper these density oscillations become, and when only one layer remains between the two surfaces it can become difficult to distin guish its properties from that of a solid layer. This appears to be consistent with recent simulations which indicate that abrupt liquid-solid transitions may occur in thin liquid films at certain thicknesses,10-12 but the question as to whether these may be considered as true liquid or solid phases or whether the transitions are truly first-order (i.e., discontin
uous) has not been explored either experimentally or theo retically.
