Wettability, interface structure, and chemistry in functionalized poly(chloro-para-xylylene) films

Genetically hydrophobic polymer interfaces are functionalized by oxygen plasma and systematically analyzed using contact angle measurements, atomic force microscopy, and high resolution X-ray photoelectron spectroscopy. High resolution C 1s core level spectra indicate that approximately three of five hydrogen-abstracted carbon sites at the surface become terminated in equal weight by aldehyde and carboxylic acid. Without altering the global structure of the interface, the plasma treatments at E _RF > 100 J generate a network of small protuberances which grows with E _RF , and a wavelength selection with a characteristic length scale increasing with E _RF . While the polymer surface is continuously eroded in the rate of ∼4 nm/100 J, a delicate balance between the growth of the network of the local structure and the progression of the wavelength selection allows the polymer interface to maintain a relatively high level of the low molecular weight materials, which is responsible for the enhanced surface concentration of carbonyl group during the abrasive functionalization process above E _RF ∼ 100 J. The sharp increase in the wettability of the polymer interface upon the plasma treatment is closely related to the surface concentration of the total polar functional group containing oxygen rather than that of a specific functional group.