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

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.