## 3 Results and Discussion
### Results of Characterization of Materials
#### 3.1.2 Platinum-Based Functional Ink  
The boiling point of the solvent of formulated ink was measured at an air pressure of 750 mm Hg. The obtained value was equal to 119.6 \({}^{\circ}\)C. Figure 9 presents the results of the TG-DSC thermal analysis of the as-prepared ink. In the temperature range up to 170 \({}^{\circ}\)C, the loss of the ink mass was mostly due to the evaporation of the solvent components (water and ethylene glycol). A further increase in temperature resulted in the evaporation and oxidation of the plasticizer and the polymer, constituting the binder of the dry residue of the ink. The total mass loss at 750 \({}^{\circ}\)C was equal to 75.5 wt. %, so the residual 24.5 wt. % was accounted for by the platinum.  
Figure 8: SEM images of the sintered line, demonstrating the degree of sintering and the polycrystalline structure of the end material.  
Figure 7: Typical energy-dispersive X-ray spectroscopy (EDX) spectrum of the sintered material averaged over the area of 5 \(\times\) 5 \(\upmu\)m\({}^{2}\). The aluminum and oxygen lines were due to the contribution of the substrate.  
Figure 10 demonstrates the size distributions of the colloidal particles contained in two ink samples. The first one (green curve) is characteristic of the as-prepared ink, and the second one (red curve) is characteristic of the top layer of the ink after 5 days of its storage in a standard 2 mL Eppendorf safe-lock tube kept in a vertical position. The difference in the mean particle size characteristic of these samples, which is a measure of the sedimentation stability of the ink, was about 30%. According to the thermal analysis data, the concentration of platinum in the top layer of the ink after 5 days of storage decreased to 18.4 wt. % as a result of the evolution of the colloid toward the sedimentation-diffusion equilibrium in the gravitational field [30]. Further observations up to 15 days did not reveal changes both in the mean particle size and the concentration of platinum in the top layer within the measurement's accuracy. Gentle agitation of the aged ink (i.e., ink that was stored for several days with no movement) for tens of seconds was sufficient to bring it back to its initial (as-prepared) state. The surface tension of the agitated ink measured at 25 \({}^{\circ}\)C was equal to 43.9 mN/m. The viscosity of the ink was 11.4 mPa-s at 25 \({}^{\circ}\)C.  
Figure 11 presents the SEM images of the nanoparticles contained in the ink. The film under study was formed by annealing the printed ink in ambient air as follows: (1) heating up to 400 \({}^{\circ}\)C at a constant rate of 10 \({}^{\circ}\)C/min and (2) keeping 400 \({}^{\circ}\)C for 2 h. As a result of the heat treatment, the binder (polymer and plasticizer) was removed from the printed ink, and the obtained film represented an array of nanoparticles. It follows from Figure 11 that the film was characterized by a relatively high packing density of nanoparticles, which was important for attaining a high degree of sintering of the end material formed after the annealing at 750 \({}^{\circ}\)C.  
Figure 9: Results of the TG-DSC thermal analysis of the as-prepared ink. The green curve is the mass of the sample, and the blue curve is the heat flow per unit mass of the sample. The sample was heated at a rate of 10 \({}^{\circ}\)C/min in air supplied at a flow rate of 250 mL/min.