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Plasma Surface Modification and Characterization of POSS-Based Nanocomposite Polymeric Thin Films
journal contribution
posted on 2007-04-10, 00:00 authored by Brian H. Augustine, Wm. Christopher Hughes, Kathryn J. Zimmermann, Ashley J. Figueiredo, Xiaowen Guo, Charles C. Chusuei, Jessica S. MaidmentThe effect of a remote oxygen plasma on nanocomposite hybrid polymer thin films of poly[(propylmethacryl-heptaisobutyl-polyhedral oligomeric silsequioxane)-co-(methylmethacrylate)] (POSS-MA) has been examined by
advancing contact angle, X-ray photoelectron spectroscopy (XPS), and variable-angle spectroscopic ellipsometry
(VASE). Exposure to a 25 W remote oxygen-containing plasma was found to convert the surface of POSS-MA films
from hydrophobic to hydrophilic within 20 s. The exposure time needed for this conversion to occur decreased as
the O2/N2 ratio in the plasma environment increased, indicating a positive correlation between the hydrophilicity and
the presence of oxygen in the plasma. Local bonding information inferred from high-resolution XPS data showed that
the isobutyl bonding to the POSS moiety is replaced with oxygen as a result of plasma exposure. Finally, VASE data
demonstrates that increasing the weight percent of POSS in the copolymer significantly impedes the oxygen plasma
degradation of POSS-MA films. On the basis of these results, a model is presented in which the oxygen plasma removes
isobutyl groups from the POSS cages and leaves a SiO2-like surface that is correspondingly more hydrophilic than
the surface of the untreated samples and is more resistant to oxidation by the plasma. The ability to modify surfaces
in this manner may impact the utility of this material for biomedical applications such as microfluidic devices in which
the ability to control surface chemistry is critical.