| A low-temperature, atmospheric pressure oxygen and helium plasma was used to treat the surfaces of high-density polyethylene (HDPE), polymethyl methacrylate (PMMA), polyethylene terephthalate, polyethylene naphthalate, polyetheretherketone (PEEK), polysulfone (PSU), polyethersulfone (PES), and polyphenylsulfone (PPS). The plasma physics and chemistry was investigated by numerical modeling. It was shown that for an electron density in the range of 3x1010 to 1x1012 cm-3, the concentration of O atoms and metastable oxygen molecules (1Delta g O2) in the afterglow varied from 6x1015 to 1x1017 cm-3, while the concentration of ozone remained constant at 3x1015 cm-3. The polymers were exposed to the plasma afterglow, and in less than 2.5 seconds of treatment, they were converted from a hydrophobic state with a water contact angle of 85+/-5° to a hydrophilic state with a water contact angle ranging between 10 and 40°. Plasma activation of the surface led to an increase in bond strength of the polymers to several different adhesives by as much as 16 times.;X-ray photoemission spectroscopy revealed that the aliphatic and aromatic carbon atoms on all the polymers were oxidized and converted into alcohols, aldehydes or ketones, and carboxylic acids. Attenuated total reflection infrared spectroscopy of high density polyethylene, polymethyl methacrylate, and polyethersulfone confirmed the presence of alcohols, aldehydes and carboxylic acid groups after plasma activation. In order to form the latter species, chain scission occurs on HDPE and PMMA, while on PES, the aromatic groups undergo ring-opening. The infrared measurements further showed that plasma activation is restricted to the first few layers of the polymer films. |
