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12 Surface Analysis of Thick Polymer Films by Infrared Spectroscopy Mark R . Adams, KiRyong H a , Jenifer Marchesi, Jiyue Yang, and Andrew Garton* Polymer Program and Department of Chemistry, University of Connecticut, Storrs, C T 06269-3136
Recent advances in the application of infrared internal reflection spectroscopy (IRIRS) are described for the surface analysis of thick polymer films. Examples are chosen to illustrate the nature of the information obtained for polymer surface modifications ranging from about 5 nm thickness (plasma-modified polypropylene), through about 100 nm (sodium-etched fluoropolymers), to several hundred nanometers thickness of the modified layer (polyolefin surfaces modified by "primers"). The IRIRS data are compared to data obtained by X-ray photoelectron spectroscopy. Particular emphasis is placed on the use of derivatization reactions, and the determination of concentration profiles in the modified surfaces.
^VIBRATIONAL SPECTROSCOPY IS CAPABLE OF SURFACE ANALYSIS (1,2) at sensiti vities corresponding to m o n o m o l e c u l a r layer coverage, using techniques such as r e f l e c t i o n - a b s o r p t i o n i n f r a r e d ( R A I R ) spectroscopy a n d surface-enhanced R a m a n spectroscopy ( S E R S ) . E v e n conventional transmission spectroscopy is a p o w e r f u l surface analysis technique i f the s p e c i m e n is adsorbed o n a h i g h surface area substrate such as a fine p o w d e r . H o w e v e r , most o f the n o m i n a l l y "surface-sensitive" techniques analyze t h i n films o n a n o n p o l y m e r i c substrate (e.g., a coating o n a metallic m i r r o r for R A I R o r material sorbed o n a r o u g h e n e d silver surface for S E R S ) rather than the surfaces o f thic k
films,
a n d many specimens o f scientific a n d technological interest are i n the f o r m o f thick films (i.e., greater that a few microns thick). T h e range of I R spectro* Corresponding author. 0065-2393/93/0236-0333$06.00/0 © 1993 American Chemical Society
In Structure-Property Relations in Polymers; Urban, M., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1993.
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S T R U C T U R E - P R O P E R T Y RELATIONS IN POLYMERS
scopic choices for surface analysis is then m u c h more l i m i t e d . F o r such applications, the i n f r a r e d internal reflection ( I R I R S ) technique [often called attenuated total reflectance ( A T R ) ] is often the only o p t i o n . T h e I R I R S technique is w e l l established a n d w i d e l y u s e d ( 3 - 5 ) , b u t is generally per ceived to be insufficiently surface sensitive to be useful for surface m o d i f i c a tions less than a f e w microns i n depth. T h i s chapter describes several applications that demonstrate that I R I R S can p e r f o r m surface analysis w i t h a sensitivity comparable to X - r a y photoelectron spectroscopy ( X P S ) , and, i f a p p l i e d w i t h ingenuity, can p r o v i d e i n f o r m a t i o n unobtainable w i t h other techniques. T h e applications are classified o n the basis o f the d e p t h o f the surface modification.
Surface Modification
