## 1 Introduction  
Hydrophobic materials have the unique ability to repel water and are generally characterized by a low surface energy and rough topographical microstructure, nanostructure, or a hierarchical combination of the two. The hydrophobic properties of a material can be determined by the contact angle (CA) made by a water droplet placed on the material. The contact angle is defined as the angle made between the bottom of the droplet and the line tangent to the edge of the droplet at the surface liquid contact point. Materials that produce CAs greater than 90\({}^{\circ}\) are considered hydrophobic and materials with CAs exceeding 150\({}^{\circ}\) are considered superhydrophobic. It has been reported that the hydrophobicity of a material is influenced by its surface topography [1; 2; 3; 4]. Typically, hydrophobic materials are characterized by microscale roughness while superhydrophobic materials exhibit hierarchical roughness, where microscale surface structures contain finer nanoscale architectures. Through surface roughening and creating these hierarchical structures researchers have been able to transform a hydrophilic material into a hydrophobic one [2,4]. A significant portion of hydrophobic material research concentrates on the formation of micro and nanoscale roughness on materials. Hydrophobic surfaces can be further classified into one of two states: the Wenzel state (a wetting state) and the Cassie-Baxter state (a non-wetting state). In the Wenzel state, a wetting state, the water droplet's surface tension will be broken and wet the surface; this acts to adhere the water droplet in place and the droplet resists moving across the material [5, 6, 7]. In the Cassie-Baxter state, a non-wetting state, the water droplet's surface tension is unbroken. The water droplet rests upon the liquid/solid/air interface created by the water droplet, captured air pockets within the micro/nanostructure of the surface, and the surface itself. In the Cassie-Baxter state, the water droplet can freely and easily move across the material; this characteristic is utilized in many applications, such as self-cleaning materials, corrosion prevention, anti-fouling, microfluidic controls, aviation, etc. [8, 9, 10, 11, 12, 13, 14]. Due to the wide variety of applications for hydrophobic materials there is significant demand. There are many methods for creating hydrophobic surfaces, and all methods change the surface morphology of a material to make it rougher on the microscale, nanoscale, or some combination of the two (a hierarchical roughness). Common methods to create this micro/nanoscale roughness are through (i) plasma etching, which utilizes a low-pressure chamber where energized gas ions pelt a surface to roughen it. The ionic sputtering creates nanoscale imperfections in the surface that ultimately grant the substrate hydrophobic properties (Figure 1a) [15]. (ii) Electrospinning utilizes a DC voltage difference between a spinneret containing a polymer solution/molten polymer and a grounded substrate. The voltage difference allows for the easy collection of the material expelled from the spinneret (Figure 1b). The fine wires/strands expelled have nanoscale features and are ideal for creating a hydrophobic mesh on a substrate [16]. (iii) Chemical vapor deposition (CVD) creates a hydrophobic surface coating via sequential chemical processes (Figure 1c). The substrate is placed in the CVD chamber and a carrier gas transports gas phase precursors into the CVD chamber. Chemical reactions between the precursors and substrate create two products [17], a volatile product that is whisked away by the carrier gas as well as a film/coating on the substrate. (iv) Flame deposition involves placing a substrate within, or above, a flame volume and allowing soot deposits to form a thin continuous layer. Substrates of various material, geometries, and structure can be utilized. As shown in Figure 1d, a soft foil and a rigid plate can be easily coated.