AVS 47th International Symposium
    Surface Science Monday Sessions
       Session SS3-MoM

Paper SS3-MoM4
Determination of Molecular Structure at Polymer Interfaces by Sum-Frequency Generation

Monday, October 2, 2000, 9:20 am, Room 210

Session: Surface Science Opportunities and New Applications
Presenter: K.A. Briggman, National Institute of Standards and Technology
Authors: K.A. Briggman, National Institute of Standards and Technology
L.J. Richter, National Institute of Standards and Technology
J.C. Stephenson, National Institute of Standards and Technology
W.E. Wallace, National Institute of Standards and Technology
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The structure of polymer surfaces and interfaces can determine critical interfacial properties such as adhesion, molecular recognition and bonding in applications as diverse as optoelectronics and biomaterials. Linear vibrational spectroscopies (FTIR, ATIR, and Raman) are some of the most widely accepted and utilized diagnostics of bulk polymer systems but typically do not have sufficient specificity to probe interfaces. Vibrationally resolved sum-frequency generation (SFG), a non-linear optical technique, is uniquely interface specific as it is dipole forbidden in media with inversion symmetry. Additionally it has the ability to determine not only the alignment of molecular groups, but also their absolute orientation. We report vibrational SFG studies of the methylene and phenyl groups at the interfaces of thin, annealed polystyrene films. When applied to thin film systems, the contributions from multiple interfaces must be properly assigned. Multilayer systems are designed to separate the contribution of signals from the free surface and buried interface and to allow independent determinations of molecular orientation at each interface. The phenyl rings have polar order at the free surface and oriented away from the film. The degree of order is significantly weaker at the buried interface. We will present a detailed analysis of the orientational distibution of the rings.