CONTROLLED MODIFICATION OF POLY(HYDROXYBUTYRATE) SURFACES BY A PERFLUOROHEXANE PLASMA - ESCA AND CONTACT-ANGLE STUDIES

Poly(hydroxybutyrate) films and inorganic glass slides were treated by cold plasma. The composition of the gas mixture of perfluorohexane and hydrogen was varied to obtain controlled surface coatings of different hydrophobicities. The analysis by weight variation, scanning electron microscopy (SEM), electron spectroscopy for chemical analysis (ESCA), and contact angle measurements were used to evaluate the influence of the flow rate, composition, and the plasma power on the surface structure after the plasma deposition. High-resolution ESCA spectra were used to determine quantitatively the amount of different fluorine-containing species present in the plasma-deposited layers. Molecular structures and surface energies of deposited layers on polymer substrates were compared with those on inorganic substrates. In both cases a strong correlation was found between the surface free energy and the fluorine/carbon ratio as well as the oxygen/carbon ratio. Furthermore, samples with high carbon/fluorine ratios showed a high content of CF2 and CF3 groups.