## 3 Results and Discussion
The combination of the critical surface roughness of \(\sim\)0.70 \(\upmu\)m and presence of fluorinated species as confirmed by IRRAS analyses leads to the superhydrophobic properties with water roll-off properties. Figure 3: **(A)** Water contact angle variation, and **(B)** rms roughness as a function of number of layers coated using as-prepared (black) and dilute solution (red); **(C)** relationship between water contact angle and rms roughness as obtained on the coatings prepared using as-prepared solution on aluminum substrates; and **(D)** water contact angle variation with number of layers coated using dilute solution on different substrates, namely, aluminum (black), silicon (100) (red) and sodalime glass (blue). Inset shows transparency of our superhydrophobic coatings on glass substrates. The uniformity of the coating has been verified on various substrates as shown in Figure 3(D). In addition to aluminum substrates, the feasibility of the coatings were also tested on silicon (100) and sodalime glass substrates. Figure 3 (D) shows the water contact angle behavior for all the three substrates coated with diluted solution of fluorinated silica nanoparticles. The water contact values obtained on as-received flat substrates of Si(100) and glass are \(\sim\)60\({}^{\circ}\) and \(\sim\)30\({}^{\circ}\), respectively. In both cases, the water contact angle value increases with an increase in number of deposited layers. With just one layer of coating, the surface reaches the hydrophobic zone by providing water contact values greater than 90\({}^{\circ}\) in case of all the three substrates. Superhydrophobic properties are reached by increasing the number of deposited layers. The feasibility of obtaining superhydrophobicity on different substrate surfaces can have great potential in industrial use. As a potential for applications on glass windows or car wind-shields, we have provided images of glass substrates coated with one layer and nine layers of diluted solution in the inset of Figure 3(B). It is clear from these images that one layer or nine layers does not dramatically alter the transparency of the glass following coating visually, the only difference being that the one layer coating is hydrophobic while the nine layer coating is superhydrophobic. Such coatings also present promise for applications for aesthetic purposes when coated on opaque substrates. The combined effect of CA and CAH determine the self-cleaning properties [29]. A surface having CA more than 150\({}^{\circ}\) and CAH less than 5 degree shows self-cleaning properties. On the other hand, a surface showing CA more than 150\({}^{\circ}\) and CAH more than 10\({}^{\circ}\) does not show the self-cleaning properties [41]. In the view of claiming the self-cleaning properties of our superhydrophobic surfaces, we have performed both CA and CAH experiments. The CA results have been discussed in the previous section. In this section we describe the results of dynamic contact or CAH. Figure 4 shows the CAH data of the coatings prepared with fluorinated silica nanoparticles on flat aluminum substrates. One layer coating using both as-prepared as well as diluted solution provides CAH of  
Figure 4: Contact angle hysteresis (CAH) as a function of number of layers coated using as-prepared (black) and diluted solution (red). Inset image at the left shows high CAH of \(\sim\)15\({}^{\circ}\) for one layer coating and right shows low CAH of 2\({}^{\circ}\) for nine layers coating. \(14\pm 3^{\circ}\) and \(15\pm 3^{\circ}\), respectively. The CAH reduced to \(3\pm 1^{\circ}\) with three layers coatings of as-prepared solution. However, in the three layer coatings using diluted solution, the CAH was \(11\pm 4^{\circ}\). The CAH reduced to \(2\pm 1^{\circ}\) for the coatings obtained by seven layers using as-prepared solution. On the other hand, the seven layer coatings with the diluted solution provided a CAH of \(4\pm 1^{\circ}\). Finally, for both the solutions with nine layers of coatings, the CAH reduced to \(2\pm 1^{\circ}\).