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Systematic oxidation of polystyrene by ultraviolet-ozone,characterized by near edge x-ray absorption fine structure and contact angle

Published

Author(s)

Daniel A. Fischer, Robert Klein, Joseph~undefined~undefined~undefined~undefined~undefined Lenhart

Abstract

The process of implanting oxygen in polystyrene (PS) via exposure to ultraviolet-ozone (UV-O) was systematically investigated using the characterization technique of near edge x-ray absorption fine structure (NEXAFS). Samples of PS exposed to UV-O for 10s to 300 s and washed with isopropanol were analyzed using the carbon and oxygen K-edge NEXAFS partial electron yield, using various retarding bias voltages to depth-profile the oxygen penetration into the surface. Evaluation of reference polymers provided a scale to quantify the oxygen concentration implanted by UV-O treatment. We found that ozone initially reacts with the double bonds on the phenyl rings, forming carbonyl groups, but within 1 min of exposure the ratio of double to single oxygen bonds stabilizes at a lower value. Oxygen penetrates the film with relative ease, creating a fairly uniform distribution of oxygen within at least the first 4nm (the effective depth probed by NEXAFS here). Before oxygen accumulates in large concentrations, however, it preferentially degrades the uppermost layer of the film by removing oxygenated low-molecular-weight oligomers. The failure to accumulate high concentrations of oxygen is seen in the nearly constant carbon edge jump, the low concentration of oxygen even at 5 min exposure (58 % of that in poly(4-acetoxystyrene), the polymer with the most similarities to UV-O treated PS), and the relatively high contact angles. At 5 min exposure the oxygen concentration contains ca. 7 atomic % oxygen. The oxygen species that are implanted consist predominantly of single O-C bonds and double O=C bonds, but also include a small fraction of O-H. UV-O treatment leads a plateau after 2 min exposure in the water contact angle hysteresis, at a value of 67+2 degrees, due primarily to chemical heterogeneity. Annealing above Tg allows oxygenated species to move short distances away from the surface, but not diffuse further than 1-2 nm.
Citation
Langmuir
Volume
24
Issue
15

Keywords

NEXAFS, polystyrene, oxidation

Citation

Fischer, D. , Klein, R. and Lenhart, J. (2008), Systematic oxidation of polystyrene by ultraviolet-ozone,characterized by near edge x-ray absorption fine structure and contact angle, Langmuir, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=854034 (Accessed April 13, 2024)
Created August 5, 2008, Updated February 19, 2017