Multitechnique surface spectroscopic studies of plasma-modified polymers I: H 2 O/Ar plasma-modified polymethylmethacryl
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Lawrence Salvati, Jr. Perkin-Elmer Physical Electronics Laboratories, 5 Progress Street, Edison, New Jersey 08820 (Received 2 May 1986; accepted 19 November 1986) Results from x-ray photoelectron spectroscopy (XPS or ESCA), low-energy ion scattering spectrometry (LEIS or ISS), and Fourier transform infrared spectroscopy (FTIR) analyses are presented for unmodified and modified poly(methylmethacrylate) (PMMA) polymer films. Analysis of the unmodified PMMA polymers (isotactic, syndiotactic, and atactic) via ESCA, ISS, and FTIR, established the surface composition, bonding, and functionality before the modification was employed. An rf-plasma glow discharge created from an Ar/H 2 O gas mixture at different exposure times and power levels was used to treat the polymer surface. Subsequent ESCA, ISS, and FTIR analyses of these modified PMMA's show the effects of surface modification in terms of a model of structural differences, over a limited depth (50100 A). The composition and functionality changes of the resulting surfaces are discussed with respect to proposed mechanisms of the plasma reaction and differences in tacticity of the reactant. A two-step reaction mechanism involving reactive decarboxylation/reduction followed by H 2 O adsorption is proposed to understand the spectroscopic results.
I. INTRODUCTION The "multi-technique approach" for the spectroscopic analysis of surfaces has been described by Hercules1 and discussed by Gardella for various polymer systems.2'3 The use of several surface spectroscopic techniques presents a more comprehensive understanding of the surface composition, bonding, and functionality of the polymer system analyzed, because each technique provides complementary information. Microstructural models can be developed using methods with different sampling depths such as x-ray photoelectron spectroscopy (XPS or ESCA), low-energy ion scattering spectrometry (LEIS or ISS) and Fourier transform infrared spectroscopy (FTIR). We have used various combinations of these methods [and others, static secondary ion mass spectrometry (SIMS) ] to describe the surface structure of methacrylic polymers,2'4 highly ordered polymers,5 block copolymers,6'7 and blends.8 In this work the multi-technique approach is employed for the study of the plasma-modified polymer surfaces. In a previous paper9 isotactic, syndiotactic, and atactic poly(methylmethacrylate) (PMMA) were examined using ESCA and ISS. The unique ability of the ISS technique to differentiate the PMMA polymers on the basis of surface atomic C/O ratios was discussed in terms of molecular models of functional group arrangements that lead to different shielding and scattering probabilities for the incoming primary ion. The ESCA analysis of these tactic PMMA polymer films evaluated J. Mater. Res. 2 (1), Jan/Feb 1987
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the surface functionality via curve fitting the carbon \s core level signal and measuring the quantitative carbon/ oxygen ratio. No differences could be detected between the three polymers from the ESCA anal
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