Plasma polymer coatings were deposited from hexamethyldisiloxane on polyethylene terephthalate (PET) substrates while varying the operating conditions, such as the Ar and O(2) flow rates, at a fixed radio frequency power of 300 W. The water vapor transmission rate (WVTR) of the untreated PET was 54.56 g/m(2)/day and was decreased after depositing the silicon oxide (SiO(x)) coatings. The minimum WVTR, 0.47 g/m(2)/day, was observed at Ar and O(2) flow Fates of 4 and 20 sccm, respectively, with a coating thickness of 415.44 nm. The intensity of the peaks for the Si-O-Si bending at 800-820 cm(-1) and Si-O-Si Stretching at 1000-1150 cm(-1) varied depending on the Ar and O(2) flow rates. The contact angle of the SiO(x) coated PET increased as the Ar flow rate was increased from 2 to 8 sccm at a fixed O(2) flow rate of 20 sccm. It decreased gradually as the oxygen flow rate increased from 12 to 28 sccm at a fixed Ar carrier gas flow rate. The examination by atomic force microscopy revealed a correlation of the SiO(x) morphology and the water Vapor barrier performance with the At and O(2) flow rates. The toughness of the deposited coatings increased when either the O(2) or Ar flow rate was increased. (C) 2009 Elsevier B.V. All rights reserved.