Microfiber inclination, crystallinity, and water wettability of microfibrous thin-film substrates of Parylene C in relation to the direction of the monomer vapor during fabrication

• Published in: Applied surface science 2015-08, Vol.345, p.145-155
• Main Authors: Chindam, Chandraprakash, Wonderling, Nichole M., Lakhtakia, Akhlesh, Awadelkarim, Osama O., Orfali, Wasim
• Format: Article
• Language: English
• Subjects: Collimation; Contact-angle hysteresis; Crystallinity; Deposition; Hydrophobicity; Infrared spectroscopy; Microfibers; Microfibrous thin-film substrate; Monomers; Parylene C; Planes; Thin films; Water wettability; Wettability; X-ray diffraction
• ISSN: 0169-4332; 1873-5584
• DOI: 10.1016/j.apsusc.2015.03.165

•Columnar microfibrous thin-film substrates (μFTFS) of Parylene C were fabricated. The monomer deposition angle was varied.•The microfiber inclination angle can be classified with respect to the monomer deposition angle into four regimes of two different types.•Columnar μFTFS contain three crystal planes not evident in bulk Parylene-C films, but are less crystalline than bulk Parylene-C films.•Static hydrophobicity is anisotropic, but the upper and lower limits of static hydrophobicity are almost isotropic.•Both the static hydrophobicity as well as water adhesion can be maximized by a proper choice of monomer deposition angle. We experimentally determined the inclination of microfibers, crystallinity, and the water wettability of columnar microfibrous thin-film substrates (μFTFS) of Parylene C fabricated using a variant of conventional chemical vapor deposition, wherein a collimated vapor of reactive monomers is obliquely directed towards a planar wafer in a low-pressure chamber. The independent variable was the monomer deposition angle χv, which is the angle between the direction of the collimated vapor and the wafer plane. The dependence of the microfiber inclination angle χ on χv can be classified into four χv-regimes of two different types, and is reminiscent of the conversion of continuous rotation into intermittent rotary motion by a gear mechanism. X-ray diffraction (XRD) experiments indicate that the columnar μFTFS contain three crystal planes not evident in bulk Parylene-C films, the columnar μFTFS are less crystalline than bulk Parylene-C films, and the crystallinity of the columnar μFTFS reflects the four χv-regimes. Identical resonance frequencies in infrared absorbance spectra revealed that the atomic bonding is the same for all monomer deposition angles. The static hydrophobicity is more pronounced in the morphologically significant plane (MSP) of a columnar μFTFS than in the vertical plane orthogonal to the MSP, but the upper and lower limits of static hydrophobicity are almost isotropic. Both the static hydrophobicity as well as water adhesion can be maximized by a proper choice of χv.