## 3 Results and Discussion
The larger size in our case is attributed to the presence of an outer shell of fluorinated silane bonded around the silica nanospheres as a result of their functionalization using FAS-17 molecules as presented schematically in Figure 1(B). Water contact angle measurements were used to evaluate the wetting properties of the prepared surfaces. Increased contact angles are, partially, increased because of roughness, which increased air entrapment as stated by Cassie-Baxter equation. Figure 3 (A) shows the contact angles variation on the aluminum surfaces coated using the as-prepared fluorinated silica nanoparticles in the solution as well as the ones coated by diluting the same. In both cases, the water contact angle values were found to increase with the increase in the number of layers of the fluorinated silica nanoparticles deposited on the substrates until a critical number of layers was reached after which the water contact angle values remained similar on the surfaces coated using as-prepared solution. However, higher water contact angle values were obtained on surfaces coated using the as-prepared fluorinated silica nanoparticles solution. For example, on the aluminum surfaces coated with one layer of as-prepared solution, an increased water contact angle value of 137 \(\pm\) 1\({}^{\circ}\) was obtained, making these surfaces hydrophobic since a clean aluminum surface provides a water contact angle of only \(\sim\)70\({}^{\circ}\). The surface was rendered superhydrophobic when the number of layers was increased to three providing a higher water contact angle value of 152 \(\pm\) 1\({}^{\circ}\). This increase in water contact value is attributed to the rough micro-nanomorphological pattern obtained on these surfaces (Figure 2) as well as the presence of low surface energy fluorinated species present on these surfaces as confirmed by the IRRAS analyses (Figure 1(A)). This emphasizes the importance of the presence of both surface roughness as well as low surface energy, a phenomenon reported on lotus effect [4]. Further, the influence of surface roughness in leading to a large amount of air entrapment in the gaps of the rough structure to result in a composite structure of air and solid has been well elucidated by [PERSON] and [PERSON] [16]. With a further  
Figure 2: **(A)** SEM images of fluorinated silica nanoparticles of 119 \(\pm\) 12 nm diameter deposited on aluminum substrates in three layers by spin coating; Inset of Figure 2 (A) shows the image of a water drop placed on this surface exhibiting a very high water contact angle of \(\sim\)152\({}^{\circ}\), and (**B**) higher magnification image of (A). increase in the number of layers to five, the water contact angle values slightly increased to \(\sim\)153\({}^{\circ}\) and remained similar when coated with seven and nine layers. Therefore, three layers of coating may be considered as a critical parameter for obtaining superhydrophobic properties when the coating is made with the as-prepared solution. Similarly, an increasing tendency in water contact angle values was observed also in cases of coatings prepared with the dilute solution. However, the water contact angle reached lower values when the same number of layers was used as with the as-prepared solution. Such lower values may be attributed to the lower concentration of the fluorinated silica nanoparticles in the diluted solution, possibly resulting in morphologies with less surface roughness (Figure 3(B)). However, with the diluted solution, superhydrophobic properties were indeed obtained when the numbers of layers deposited on the surface was increased. For example, with only one layer coated with the dilute solution, the water contact angle increased to \(128\pm 2^{\circ}\) (although this is lower than on the same coating using as-prepared solution). With three layers, the contact angle reached \(135\pm 3^{\circ}\) which further increased to \(144\pm 1^{\circ}\) on deposition of five layers.