## 4 Results and Discussion
Hence, the amount of the PDMS indicated by the FTIR analysis and the contact angle measurement increases with an increase in polymer concentration in the solvent from 0.2% to 1.0%. However, when the concentration was elevated from 1.0% to 5.0%, the impact of the concentration increase was very small. Figure 6: The FTIR spectra of the fiberglass coated with PDMS for the range of the wavenumber: (**a**) 650–1550 cm\({}^{-1}\); (**b**) 2700–3100 cm\({}^{-1}\). Peaks related to characteristic chemical bonds in the PDMS were identified. Figure 7: The SEM images show layer I of fiberglass coated with PDMS from 5.0% solution at different magnifications (\(\sim\)6000\(\times\) on the left, and \(\sim\)16,000\(\times\) on the right). All afore-mentioned coatings were applied on the fiberglass media in the form of circular flat panels of the diameter 150 mm (the geometry suitable for the horizontal housing FH in Figure 3) and subject to experiments of the oil mist separation. As the reference for the effect of coating on the process, the experiment for the unmodified material was carried out. The results of the pressure drop and the efficiency versus time for the original material are presented in Figure 8. In this graph, the problem addressed in the research is easily noticeable at the end, when the filter media becomes saturated with the oil. The change in the pressure drop over time for the oleophilic unmodified material is shown in Figure 4:0 Characteristic variations of the dP were observed after the flow was interrupted and resumed. At the beginning, when not much liquid was held within the material, the monotonical increase of the pressure drop was not affected by the flow breaks. After that, when some amount of oil was accumulated in the material, a small decrease of the dP was visible (see Figure 8 between 60 and 180 min). However, when the saturation of the filter media approached the steady-state value (i.e., when a significant amount of oil was accumulated in the filter), each stoppage caused a significant step increase of the pressure drop. These different behaviors can be explained by the oil recombination driven by the capillary interaction. At low saturation, when the flow was interrupted, the oil was transported along the fibers so that it spread on their surface--the fibers became covered by oil film in a more uniform fashion, which created bigger passages for the flow of air. But when the saturation was high, much more oil from the downstream side of the filter was retracted back to the filter (imbibition caused by the capillary pressure), thus causing clogging of the porous media with the oil. Strong adhesion of oil to the fiber surface of the oleophilic material made it impossible to effectively push the liquid back to the outlet, hence the drift of the terminal value of the pressure drop was observed after each interrupting and resuming of the aerosol flow (see Figure 8--this issue started at time around 600 min, and above 720 min the increase was very high). Additionally, a decrease in separation efficiency was observed when the material became saturated with the oil. The reason for efficiency loss can be easily explained by analyzing the curve of fractional efficiency, which is presented in Figure 4:1  
Figure 4:2 The time-dependent profiles of the pressure drop and the separation efficiency for the unmodified filtration material. The fractional separation efficiency curve drops steeply for the size of droplets above 4 \(\upmu\)m (see Figure 9). The collecting and coalescing of the droplets of this size from the inlet aerosol is probably performed with nearly 100% efficiency, similarly for droplets 1-2 \(\upmu\)m, for which the collection mechanisms such as inertial impaction or interception are predominant. Thus, it can be deduced that the loss of efficiency for the droplets above 4 \(\upmu\)m is not due to their penetration, but they are formed due to the redispersion on the outlet, where most of the oil is accumulated.