Multitechnique surface spectroscopic studies of plasma-modified polymers II: H 2 O/Ar plasma-modified polymethylmethacry
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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 the x-ray photoelectron spectroscopy (XPS or ESCA), ion scattering spectroscopy (ISS or LEIS), and Fourier transform infrared spectrometry (FTIR) analyses are presented for unmodified and modified poly (methylmethacrylate)/poly (methacrylie acid) (PMMA/PMAA) copolymer films. Analyses of the unmodified PMMA/PMAA copolymer series, via ESCA, ISS, and FTIR, established the surface composition and functionality of the PMMA/PMAA copolymers before the H 2 O/Ar rf-plasma treatment was employed. The ESCA, ISS, and FTIR analysis of these modified PMMA/PMAA copolymers show that surface modification over a limited depth (50-200 A) has occurred. The composition, bonding, and functionality changes of the surfaces are discussed. A two-step modification mechanism (surface reduction of the PMMA/PMAA copolymer followed by H 2 O adsorption) is proposed to interpret the spectroscopic results.
I. INTRODUCTION In a previous paper1 the series of PMMA/PMAA random copolymers percent composition (100/0, 90/10, 80/20, 75/25) was investigated via angular-dependent x-ray photoelectron spectroscopy (ADXPS or ADESCA) and ion scattering spectroscopy (ISS). The unique ability of the ISS technique to differentiate the PMMA/PMAA copolymers on a basis of surface atomic C/O ratios was discussed. The ADESCA analysis of these PMMA/PMAA copolymers evaluated the surface functionality by curve fitting the carbon \s core level signal. The objective of the analyses was to correlate the data from the surface spectroscopic techniques and elucidate the surface microstructure of the PMMA/PMAA copolymers. The "multi-technique approach" has been described by Hercules2 and discussed by Gardella for various polymer systems.3'4 The preceeding paper contains a summary of the pertinant literature relating to this experimental approach.5 Reviews of pertinant literature on the modification and characterization of plasma-modified polymer films can also be found in the previous paper.5 Copolymerization of PMMA with PMAA in a random copolymer increases softness and changes the hydrophilic nature of the copolymers compared with PMMA. Andrade has taken this approach for PMMA by adding O-H containing monomers (hydroxyethylmethacrylate) in a copolymer process.6 These changes would be desirable for the surface region of the 132
J. Mater. Res. 2 (1), Jan/Feb 1987
PMMA. 5 However, these are bulk processes of copolymerization and alter the desired bulk properties of the PMMA polymer. The desire of the present study involving rf-plasma modification of these copolymers is to increase the softness and hydrophilic nature of the PMMA polymer with minimal copolymerization of PMAA in the bulk. The PMMA/PMAA copolymer series was investigated in a manner similiar to the tactic PMMA polymer series discussed in the preceeding paper.5 The ADESCA, ISS, and Fourier transform infrared spectrometry (FTIR) analyses are cor
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