## 3 Results and Discussion  
The Turbiscan transmission profiles of the silica-MWCNTs/PDMS hybrid filler suspension are shown in Figure 1. Just after the synthesis, the transmission along the entire length of the flask was equal to zero because of the formation of an opaque, black product (the color comes from the carbon nanotubes). The increase in transmission at the top of the vessel over the time is due to the start of the gelling process and the phase separation--formation of a transparent solvent (alcohol) layer. To estimate the stability of the sample, the Turbiscan Stability Index (TSI) was calculated. This is a dimensionless indicator that allows one to compare the samples with each other and can vary in the range of 0-100. The value of the TSI is inversely proportional to the system stability [49]. The Turbiscan brochure states that up to the Turbiscan Stability Index equal to 1, the system is stable (referred to as Visually Excellent for TSI < 0.5 or Visually Good for TSI < 1.0). In this case, the TSI exceeded the value of 0.5 after 8 h 20 min. This means detecting the beginning of destabilization, but in a very early stage, this can be particles migration or size variation. The global TSI after 12 h is equal to 0.9, which allows to confirm the stability of the system during this time. It exceeded the value of 1.0 after 13 h 15 min, but the destabilization remains still invisible for the eye. The red curve shows the transmission profile for the system with complete gelling. The lowering of the upper meniscus of the sample is noteworthy. This confirms the formation of particle agglomerates and the reduction of their mobility, and thus the contraction of the system volume. As it can be observed in Figure 2, in the case of a composition for the dip-coating, the destabilization occurs faster. The TSI exceeded the value of 0.5 just after 6 min 28 s and 1.0 after 12 min 54 s. The value of 3.0 was reached after 38 min 32 s, which means that important stability destabilization occurs due to large sedimentation. In this stage, the destabilization may not be visible yet, but based on the transmission profiles in Figure 2, it can be concluded that the filler particles fall (sedimentation) to the bottom of the flask. If the composition is used for the spray coating, its stabilization should be considered. Figure 1: Transmission profiles of the silica–MWCNTs/PDMS hybrid filler suspension just after the synthesis. Figure 2: Transmission profiles of the coating composition just after the synthesis. The zeta potential (ZP) of the obtained filler (dried gel) suspension in the 32.5% ethanol solution was equal to \(-11.1\) mV. The negative value indicates the presence of negative charges on the nanoparticles surface. Therefore, it can be concluded that the surface silanol groups (Si-OH) take the form of the ionized Si-O' species. They can initiate a cross-linking reaction of the silanol groups, which will result in the formation of the oxygen bridging between the nanoparticles and could induce its agglomeration [50]. The ability to create bonds with nanoparticles of the filler is desirable in the synthesis of a coating composition. The information about the surface charge and its structure also allows for the stabilization of the filler nanoparticles suspension. The results of the thermal analysis of nonmodified multiwalled carbon nanotubes, PDMS, and the MWCNTs/PDMS composite are shown in Figure 3.  
The first step of weight loss of the PDMS starts from about 290 \({}^{\circ}\)C and corresponds to the depolymerization reaction resulting in the volatile cyclic oligomers. A significant weight loss in the second step from approximately 500 \({}^{\circ}\)C is caused by oxidation, which leads to the polymer residue decrease to even about 10% of its previous mass [51; 52]. The pristine MWCNTs are thermally stable up to about 400 \({}^{\circ}\)C, but above 500 \({}^{\circ}\)C, the decomposition process proceeds relatively fast.