## 4 Discussion  
This research explored the use of various flame parameters to create hydrophobic and superhydrophobic C-layers through a flame deposition process. This flame method is an inexpensive and rapid single step process that consistently creates a hydrophobic layer on an SS substrate while providing operators a significant amount of control over the deposited layer. The physical characteristics of the C-layer formed (degree of hydrophobicity, mass, thickness, and stability) can be controlled by fuel type of the flame, residence time of the substrate within the flame, insertion height of the substrate into the flame, and the amount of oxygen used during combustion. By adjusting the height at which the substrate is inserted into the CME/air flame volume, the mass, thickness, hydrophobicity, and surface structure of the C-layer was adjusted. To form a C-layer the substrate needed to be inserted into the flame above the pyrolysis zone, as within the pyrolysis zone a negligible amount of \"granular-like\" soot is deposited which does not promote hydrophobicity (Figure 3(a1,a2)). However, above the pyrolysis zone, specifically in the yellow luminous zone, hydrophobic films are readily formed. As substrate insertion height into the flame volume increased, the mass and thickness of the flame deposits also increased. Furthermore, the degree of hydrophobicity of the C-layer generally increased as well; C-layers at the lower region of the flame produced lower CAs compared to those formed in the upper region of the flame. This can partly be attributed to the change in structure of soot deposits between these two deposition regions. At the lower region (12 mm HAB), deposits appear to be much less densely packed and defined (Figure 3(b1,b2)) compared to the upper regions (\(\geq\)15 mm HAB) of the flame (Figure 3(c1,c2,d1,d2)). By changing the fuel type used in the flame (CME vs. CH\({}_{4}\)) it was possible to produce significant changes in the structure of deposited soot. At 50 mm HAB, the hydrophobic annular deposit has a unique microstructure unlike any formed within the CME flames. These were the only non-spherical soot deposits that displayed hydrophobic properties (Figure 3(e2,e3)). By adjusting insertion height of the substrate within the CH\({}_{4}\) flame, the structure of deposition was further altered. At an insertion height of 60 mm HAB a uniform hydrophobic C-layer was formed that shared similar structures to the CME/air flame. However, the particulates making up these weblike structures were finer than those of the CME/air flame (Figure 3(g2,g3)). The significant difference in structure of the soot deposits between insertion heights of 50 and 60 mm have large impacts on the hydrophobicity of the formed C-layers; the unique structures formed at the lower region of the flame were hydrophobic while the typical weblike structures formed in the upper region were superhydrophobic. It is important to recognize that by using a CH\({}_{4}\)/air flame it was possible to create hydrophobic C-layers with both similar (60 mm HAB) and drastically different (50 mm HAB) microstructures to those formed in the CME/air flame, demonstrating the importance of flame structure for hydrophobic soot deposition. Finally, by adjusting the amount of oxygen used in the CME flame there were dramatic changes in the flame structure, most significantly a reduction in flame size, which also impacts the rate of soot formation and growth. Under these conditions there were significant changes to deposited C-layer mass, degree of hydrophobicity, stability, and surface structure. Increasing the O\({}_{2}\) content from 21% O\({}_{2}\) to 35% O\({}_{2}\) showed changes in surface stability and morphology of the deposited film. At 35% O\({}_{2}\) the first instances of thermal stress and cracking were observed as well as highly compacted spherical soot deposits. The fracturing and compacting of deposited soot occurred on the perimeter of the deposition area, which correlates to the increased temperature region of the CME/35% O\({}_{2}\) flame.