Effects of the film thickness on the morphology, structure, and crystal orientation behavior of poly(chloro-p-xylylene) films



Poly(chloro-p-xylylene) (PPXC) films with a thickness range encompassing more than three orders of magnitude (from 102 nm to 102 μm) were prepared on Si substrates by the chemical vapor deposition method under the same conditions. The effect of the film thickness (d) on the morphology, crystal structure, and crystal orientation behavior of the PPXC films was studied. The average roughness of the root mean square (rms) of the films increased with increasing d according to a power law (rms ≈ dβ, where β is an exponent that depends on the film growth process over time and β = 0.240±0.005, as probed by atomic force microscopy), and the monomer diffusion and relaxation of polymer were suggested as the primary factors governing this morphological evolution. The X-ray diffraction results indicate that both the crystallinity and crystal size of PPXC increased with increasing d due to the surface confinement effect between the film and the substrate, which retarded the crystallization process. The X-ray pole figures suggested that the (020) fiber textures with the b axis parallel to the Si substrate normal existed in the PPXC films; these fiber textures, mainly composed of edge-on crystal lamellae, were thermodynamically favored. The Herman's orientation factor of the fiber textures increased gradually as d grew; this indicated that stronger (020) fiber textures with higher concentrations of edge-on lamellae existed in the thicker PPXC films. This thickness dependence of the crystal orientation behavior was interpreted to be caused by the strong adhesion between the polymer chains and the substrate. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41394.