Abstract
We experimentally determined the inclination of microfibers, crystallinity, and the water wettability of columnar microfibrous thin-film substrates (mu FTFS) 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 chi(v), which is the angle between the direction of the collimated vapor and the wafer plane. The dependence of the microfiber inclination angle chi on chi(v) can be classified into four chi(v)-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 mu FTFS contain three crystal planes not evident in bulk Parylene-C films, the columnar mu FTFS are less crystalline than bulk Parylene-C films, and the crystallinity of the columnar mu FTFS reflects the four chi(v)-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 mu FTFS 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 chi(v). (C) 2015 Elsevier B.V. All rights reserved.