Hydrophobic recovery of plasma-modified film surfaces of ethylene-co-tetrafluoroethylene co-polymer

Ethylene-co-tetrafluoroethylene copolymer (ETFE) films were modified by four plasmas: direct and remote H-2 plasmas and direct and remote O-2 plasmas; and the hydrophobic recovery process of these plasma-modified surfaces was investigated using water contact angle measurements and angular XPS. The water contact angle measurements showed important aspects for the hydrophobic recovery process. (1) All plasma-modified ETFE surfaces, regardless of the kind and mode of plasmas, showed increases in the contact angle with increasing aging time. The increase continued for 5 days after finishing the plasma modification, and stopped after 5 days. (2) The plasma-modified surfaces after the aging process never reverted back to the same level of the contact angle as for the unmodified (original ETFE) surfaces. (3) The contact angle after the aging process was strongly dependent on to what plasma the ETFE surfaces were exposed in the modification. (4) The aging temperature influenced the contact angle value after the aging process. The angular XPS measurements also provided a detailed description of the chemical composition of the topmost layer. (1) The chemical composition at the topmost layer of the surfaces altered during the aging process. (2) CH2-CH2-CHF, and CH2-CHF-CH2 and CH2-CH(OH)-CF2 groups disappeared from the topmost layer during the aging process; and CH2-CH2-CF2, and CH2-CH2-CF2 and CH2-CH(OH)-CHF groups appeared at the topmost layer. (3) Such disappearance and appearance occurred on all plasma-modified surfaces regardless of the kind (H-2 or O-2 plasma) or mode (direct or remote plasma) of plasmas used for the modification. This may be due to segmental mobility of CH2-CH2-CH2 sequences rather than of CF2-CF2-CF2 sequences.