title: Surface composition, chemistry, and structure of polystyrene modified by electron-beam-generated plasma.
abstract: Polystyrene (PS) surfaces were treated by electron-beam-generated plasmas in argon/oxygen, argon/nitrogen, and argon/sulfur hexafluoride environments. The resulting modifications of the polymer surface energy, morphology, and chemical composition were analyzed by a suite of complementary analytical techniques: contact angle goniometry, atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and reflection electron energy loss spectroscopy (REELS). The plasma treatments produced only minimal increases in the surface roughness while introducing the expected chemical modifications: oxygen-based after Ar/O(2) plasma, oxygen- and nitrogen-based after Ar/N(2) plasma, and fluorine-based after Ar/SF(6) plasma. Fluorinated PS surfaces became hydrophobic and did not significantly change their properties over time. In contrast, polymer treated in Ar/O(2) and Ar/N(2) plasmas initially became hydrophilic but underwent hydrophobic recovery after 28 days of aging. The aromatic carbon chemistry in the top 1 nm of these aged surfaces clearly indicated that the hydrophobic recovery was produced by reorientation/diffusion of undamaged aromatic polymer fragments from the bulk rather than by contamination. Nondestructive depth profiles of aged plasma-treated PS films were reconstructed from parallel angle-resolved XPS (ARXPS) measurements using a maximum-entropy algorithm. The salient features of reconstructed profiles were confirmed by sputter profiles obtained with 200 eV Ar ions. Both types of depth profiles showed that the electron-beam-generated plasma modifications are confined to the topmost 3-4 nm of the polymer surface, while valence band measurements and unsaturated carbon signatures in ARXPS and REELS data indicated that much of the PS structure was preserved below 9 nm.
authors.affiliation: Plasma Physics Division, Naval Research Laboratory, Washington, DC 20375, USA. evgeniya.lock@nrl.navy.mil
authors.forename: Evgeniya H
authors.initials: EH
authors.lastname: Lock
authors.forename: Dmitri Y
authors.initials: DY
authors.lastname: Petrovykh
authors.forename: Paul
authors.initials: P
authors.lastname: Mack
authors.forename: Tim
authors.initials: T
authors.lastname: Carney
authors.forename: Richard G
authors.initials: RG
authors.lastname: White
authors.forename: Scott G
authors.initials: SG
authors.lastname: Walton
authors.forename: Richard F
authors.initials: RF
authors.lastname: Fernsler
mesh_terms: D004583:Electrons; D018625:Microscopy, Atomic Force; D015394:Molecular Structure; D011137:Polystyrenes / Q000737:chemistry*; D013057:Spectrum Analysis / Q000379:methods; D013499:Surface Properties; D014965:X-Rays
chemical_list: D011137:Polystyrenes