nomena (11)(12)(13), details of the dynamic behavior of the The dynamic behavior of functional groups on polymer surfaces polar functional groups are still obscure.
was studied with regard to the effects of aging media on the work Recently, we have studied the changes in surface properof adhesion (W A ) and the surface free energy of the polymeric ties of polymeric solids during aging after the O 2 plasma solid ( g s ). Films of polystyrene (PS), polydimethylsiloxane treatment. In our previous study on polyethylene films, we (PDMS), and a cured phenol-formaldehyde resin (PFR) were found that the surface free energy (g s ) changed with aging exposed to oxygen plasma. The plasma-treated samples were time in different ways, depending on the aging medium ( 14).
washed with methanol to remove the low-molecular-weight com-
We concluded that the orientation of the polar groups ocponents from the surfaces and were aged in two environments, curred so as to optimize the combination of the component dry nitrogen gas and distilled water, at 25ะC for up to 500 h. The effects of changing the medium during aging were also studied. surface free energies of the film (the dispersion force compo-When the treated polymers were aged in nitrogen gas, the W A nent, g d s ; the polar component, g p s ; and the hydrogen bondvalue decreased with aging time. On the other hand, when the ing component, g h s ). We also suggested that the aging stabilpolymers were aged in water, the value of the surface free energy ity of the hydrophilicity of the polymer surface depends on approached that of water, 72.8 mJ/m 2 . In addition, in the case of the characteristics of the polymer (the crystallinity, the glass PS and PDMS, the W A values which decreased during aging in transition temperature, and so on) and that the stability is nitrogen increased after the medium was changed to water, and influenced by the low-molecular-weight components which vice versa. These results suggest that the functional groups introare formed by the plasma treatment (15).
duced by plasma treatment diffused from or to the polymer surface
In the present study, oxygen plasma treatment was carried and that their surface concentration was optimized to minimize out on three kinds of polymers with remarkably different the free energy of the interface between the polymer and the aging characteristics, i.e., thermoplastic polystyrene (PS), thermomedium.