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Effect of an Interactive Surface on the Equilibrium Contact Angles in Bilayer Polymer Films

Summary: Effect of an Interactive Surface on the Equilibrium
Contact Angles in Bilayer Polymer Films
D. Slep,, J. Asselta, M. H. Rafailovich,*, J. Sokolov,*, D. A. Winesett,
A. P. Smith, H. Ade, and Simone Anders|
Hilord Chemical Corporation, Hauppauge, New York 11788, Department of Material Science,
State University of New York at Stony Brook, Stony Brook, New York 11974-2275,
Department of Physics, North Carolina State University, Raleigh, North Carolina 27596, and
Advanced Light Source, Ernest Orlando Lawrence Berkeley National Laboratory,
University of California, Berkeley, California 94720
Received January 12, 1999. In Final Form: November 2, 1999
Scanning transmission X-ray microscopy (STXM), atomic force microscopy (AFM), near-edge X-ray
absorption fine structure (NEXAFS) spectroscopy, and photoemission electron microscopy (PEEM) were
used to obtain the three-dimensional concentration profiles and the late-stage morphology of liquid bilayer
thin films of the two imiscible polymers polystyrene (PS) and (polybromostyrene) (PBrx)0.79S), where x )
fraction of monomers brominated) as a function of the lower PS film thickness. The results showed that
the apparent contact angle at the polymer/air interface decreases exponentially with increasing PS film
thickness with a constant that scales with the PS radius of gyration (Rg). In contrast, the Neuman angle,
as determined from the PBrS STXM images, increases with substrate thickness. NEXAFS and PEEM data
show that the droplets consist of a PBrS core fully encapsulated by PS for substrate thicknesses greater
than Rg. Only partial encapsulation is seen for substrates less than Rg. These results could not be explained


Source: Ade, Harald W.- Department of Physics, North Carolina State University


Collections: Physics