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.

Pradeep Thalappil

Department Of Chemistry

V. Bindu

Fulltext

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

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

Journal of Chemical Physics

Angle resolved X-ray photoelectron spectroscopic (XPS) studies of a series of perfluoropolyethers of general formula F[CF(CF3)CF2O]nCF2CF3, where n = 27, 65, and &gt;70, show that there is preferential ordering of-CF3 groups at the liquid surfaces. The C 1s intensity corresponding to the-CF3 groups increases with decrease in the electron take-off angle. No measurable change in the oxygen or fluorine intensity is observed upon varying the electron take-off angle. However, experiments show that no adsorption site exists at the surfaces, indicating that the ether oxygens are not available for any of the surface processes. Relative enhancement of the C 1s intensity of the-CF2/CF3 group with decreasing take-off angle is different for different liquids, with smaller chain length liquids showing a more rapid change. This is explained as due to an increase in helicity and tilt of molecular chains from the surface normal. Computational studies have been performed at the semiempirical level to understand the molecular structure. XPS data along with the computational studies suggest that at the liquid-air interface the molecular chains are ordered nearly perpendicular to the surface with a tilt which increases with chain length. The conclusions are in agreement with recent atomic and molecular beam scattering, ion/surface scattering and theoretical modelling studies. © 1998 Taylor &amp; Francis Group, LLC.

Molecular Physics

Tilted orientation of molecular chains at the surface of a series of perfluoropolyether liquids: An X-ray photoelectron spectroscopic investigation

Angle resolved X-ray photoelectron spectroscopy from a liquid perfluoropolyether shows that its surface is primarily composed of chain ends oriented nearly perpendicular to the surface. Indirect evidence suggests that the ether oxygens may not be available for any of the surface processes. The results are in agreement with recent atomic beam scattering experiments and molecular dynamics simulations. © 1995 Elsevier Science B.V. All rights reserved.

Journal	Data powered by TypesetJournal of Chemical Physics
Publisher	Data powered by TypesetAmerican Institute of Physics Inc.
ISSN	00219606
Open Access	No