## 4 Results and Discussion  
Three modifications were carried out using three types of commercial solutions purchased from NanoX: EC1206, EC5208, and EC5029. The second group of surface treatments was the PDMS from its solutions in the hexane. The coatings were applied to the fiberglass filtration material and also to the wafers made of borosilicate glass following the same procedure. The results of the static contact angle with the oil and the water droplet are presented in Figure 4. For the porous filter media, it was possible to analyze the contact angle of the sessile droplet when no liquid penetration into the material occurred, i.e., for the values of contact angle above 90\({}^{\circ}\). This is why some of the measurement data with the oil shown in Figure 4b are missing. Figure 4: _Cont._  
Figure 3: Size distribution of the oil droplets upstream of the filter. The data presented in Figure 4a show that the glass is wettable well by both test liquids: the oil and the water. However, since some additives are typically included in the fiberglass material, usually resins for integrity and sometimes other quality chemicals, the fibrous fiberglass material appeared to be impregnated. As it turned out, some kind of modification was applied in the fibrous media because the water contact angle (WCA) was above 120\({}^{\circ}\) and no water penetration was observed, while for the clean, non-porous wafer made of the borosilicate glass, the WCA was around 14\({}^{\circ}\). Much more important values for the studied process were the contact angles with the oil (OCA) used in experiments. On the clean glass, the OCA values increased for all coatings--for EC1206, it was 43.7\({}^{\circ}\); for PDMS coatings, it increased with the increasing polymer concentration in the solution: 34\({}^{\circ}\), 49\({}^{\circ}\), and 50\({}^{\circ}\) for 0.2%, 1.0%, and 5.0%, respectively. For EC5028 and EC5029, the oil contact angles reached the highest values of around 82\({}^{\circ}\) and 100\({}^{\circ}\) on the flat glass, respectively. Although the oleophobic properties correspond to the OCA above 90\({}^{\circ}\), both coatings applied to the porous material caused that no oil imbibition was observed when the droplet was placed on the material (see Figure 5). Although the contact angle measurements refer to the material surface, the dip-coating process from organic solvents enables efficient penetration of the solution into the material. This was confirmed by SEM imaging that the coating material was present on the surface of all fibers in the entire volume of the porous filet structure. The FTIR-ATR analysis of the coated materials was performed. The results after subtracting the background signal for untreated material are presented in Figure 6. However,  
Figure 4: Contact angles on the surface of modified materials: (**a**) flat non-porous glass wafer, (**b**) fibrous filter media made of fiberglass. Figure 5: The oil droplet on the oleophobic fiberglass coated with EC5029: (**a**) a real photo; (**b**) an image from a goniometer. only spectra for the PDMS coatings provide a measurable absorption intensity; the PDMS formula is (CH\({}_{3}\))\({}_{3}\)-Si-[-O-(Si-CH\({}_{3}\))\({}_{2}\)-]\({}_{n}\)-O-Si-(CH\({}_{3}\))\({}_{3}\). The signal from other applied coatings was below a detection threshold of this technique; hence, these results are not included in Figure 6.  
Moreover, the SEM images shown in Figure 7 confirm that although in some regions a polymer film attached to adjacent fibers, especially at fiber intersections, is visible, the majority of material pores are not blocked for 5.0%, which is the highest concentration used in experiments. The results confirm the deposition of PDMS from the solution for all tested concentrations. The formation of the coating layer is due to the retaining of the solution in the pores of the filter material and its subsequent evaporation, which caused the formation of the polymer layer on the fibers.