Investigation of the depth of preferential surface ordering in liquids: A photoelectron spectroscopic investigation of liquid mixtures

Angle resolved x-ray photoelectron spectroscopic studies of a series of liquid mixtures of a perfluoropolyether ~Krytox 16350! and a polyphenylether ~Santovac-5! show that the former spreads on the latter and the film thickness could even be smaller than the photoelectron mean free path. The molecular ordering in krytox remain as that of the free liquid which is manifested in the enhancement of the relative intensity of specific features in the photoelectron spectrum as the electron take-off angle is decreased. The preferential ordering is limited to the very top and an upper limit of this thickness is estimated to be about 8 Å. This observation is in accordance with molecular dynamics simulations of long chain hydrocarbon liquids. © 1997 American Institute of Physics. @S0021-9606~97!02502-6#