## 3 Results
### pH Test in Millimeter Channels  
In the investigation into the performance of the pH sensor films in the millireactor channels (Figure 5), the millireactors were tested by mixing solutions of different pH values at a constant flow rate of 500 \(\mu\)L/min. Solutions with pH values of 2 and 7, 7 and 11, and 2 and 11 were used to evaluate the response of the sensor films under varying flow conditions and assess their functionality across intricate channel designs. Figure 5: Millireactors made from (**a**) Anycubic Basic resin and (**b**) High Temp resin 300 s after the introduction of acid and base with marked points of analysis. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & \multicolumn{3}{c}{**\(\mathbf{\Theta\) (\({}^{\circ}\))**}} & \multicolumn{3}{c}{**OW (m) m\({}^{-}\)2)**} \\ \cline{2-6}  & **Water** & **Diiodomethane** & \(\gamma\) & \(\gamma^{\mathbf{d}}\) & \(\gamma^{\mathbf{P}}\) \\ \hline High Temp & 88.6 \(\pm\) 1.4 & 36.7 \(\pm\) 2.0 & 42.3 & 41.2 & 1.0 \\ \hline High Temp + sensor film & 60.1 \(\pm\) 1.4 & 24.8 \(\pm\) 1.3 & 56.4 & 46.2 & 10.2 \\ \hline Anycubic Basic & 72.3 \(\pm\) 1.0 & 37.0 \(\pm\) 2.8 & 48.0 & 41.1 & 6.9 \\ \hline Anycubic Basic + sensor film & 73.8 \(\pm\) 2.5 & 37.6 \(\pm\) 2.2 & 46.3 & 40.8 & 5.5 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Results of contact angle measurements and surface free energy calculations. After the preliminary research revealed that color change is most pronounced when using solutions with pH values 2 and 11, this combination of solutions was utilized during the cyclic assessments. During the cyclic experiments, solutions with pH 2 and 11 were brought into contact using varying flow rates, ensuring that one solution was in surplus during each cycle. The applied flow rates ranged from 50 \(\mu\)L/min to 500 \(\mu\)L/min, and a total of 20 cycles, each lasting 2 min, were conducted. The cycle duration was determined based on observations from the initial phase of the study, where color changes in the film were clearly visible after 60 s. The acid was introduced at inlet 1, while the base was introduced at inlet 2. All cycles were recorded, and color was monitored at the center of the millireactor, designated by points in Figure 5, through screen capture analysis using the Color Picker AR application. Screen captures were taken every 30 s. The first ones that were tested were the millireactors made from Anycubic Basic resin without the static mixers. The color change over time was tracked through screen capture analysis, and the corresponding H values were calculated based on the RGB values from the application. The H values were then plotted graphically to illustrate the dynamic processes occurring within the millireactors. The results shown in Figure 6 reveal that a sinusoidal curve is obtained by analyzing the color change in the film at the center of the millireactor. There is no mixing of the solutions, as the film's color is determined by the solution in excess; the film appears red when the acid is in excess, at which point the H values increase, and it appears purple when the base is in excess, at which point the H values decrease. The results in Figure 7 show that the curve takes on a sinusoidal shape during the examination of the color change. The film color alternates between red and purple depending on which solution is in excess, indicating that the solutions are mixed. However, improved mixing in the millireactor with the static mixers is reflected in the narrower range of \(H\) values observed at later times, which also suggests that the color of the pH film within the millireactor channels does not change as much during the change in the medium. Figure 6: Graphical representation of the dependence of the \(H\) values on time, with error bars, in the middle of the millireactor made of Anycubic Basic resin without static mixers in acid and base flow exchange cycles ((A)—acid flow is dominant, (B)—base flow is dominant).