Molecular Ordering in Thin Liquid Films of Polydimethylsiloxanes

X-ray reflectivity has been used for investigations of molecular ordering in thin liquid films of polydimethylsiloxanes (PDMS) of low molecular weights deposited on a polished silicon wafer. The liquid films we studied were ∼40−90 Å thick. Evidence of molecular layering induced by geometrical confin...

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Bibliographic Details
Published in:Langmuir 2001-06, Vol.17 (13), p.4021-4024
Main Authors: Evmenenko, G, Dugan, S. W, Kmetko, J, Dutta, P
Format: Article
Language:English
Subjects:
INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY
LIQUIDS
MOLECULAR STRUCTURE
NATIONAL SYNCHROTRON LIGHT SOURCE
SILOXANES
THIN FILMS
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Summary:X-ray reflectivity has been used for investigations of molecular ordering in thin liquid films of polydimethylsiloxanes (PDMS) of low molecular weights deposited on a polished silicon wafer. The liquid films we studied were ∼40−90 Å thick. Evidence of molecular layering induced by geometrical confinement by a hard wall is obtained for thin films of lowest molecular weight PDMS. The positions of the secondary maxima in the Patterson functions, P(z), for these samples reveal a periodicity of about 10 Å, consistent with the size of PDMS molecules. Further increasing the molecular weight leads to suppression of P(z) oscillations, causing the electron density profile to become more uniform. For higher molecular weight PDMS, a flatlike conformation of molecules absorbed on a solid surface is observed.
ISSN:0743-7463
1520-5827
DOI:10.1021/la0017734