# Investigating the Reliability and Dynamic Response of Fully 3D-Printed Thermistors
## 3 Results and Discussion
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Temperature Range**} & \multicolumn{2}{c}{**D1**} & \multicolumn{2}{c}{**D2**} \\ \cline{2-5}  & **Heating** & **Cooling** & **Heating** & **Cooling** \\ \hline
27–29 & 6.26 & 24.47 & 19.27 & 11.20 \\
29–31 & 5.81 & 21.88 & 4.71 & 13.08 \\
31–33 & 4.43 & 2.39 & 7.41 & 16.28 \\
33–35 & 3.18 & 2.02 & 6.20 & 9.13 \\
35–37 & 0.83 & 0.89 & 2.43 & 1.96 \\
37–39 & 1.54 & 0.94 & 1.00 & 0.70 \\
39–41 & 0.63 & 3.10 & 2.10 & 5.94 \\
41–43 & 0.14 & 3.07 & 1.29 & 2.76 \\
43–45 & 0.12 & 0.96 & 0.19 & 4.22 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: %Error of thermistors depending on their \(\beta\) values. Figure 5: Dynamic performance of **(a)** D1 and **(b)** D2 thermistors. According to Figure 5, both thermistors exhibited NTC behavior as evidenced by their inverse and parallel responses to the temperature changes within the environmental chamber. The dynamic performance of D1 and D2 thermistors was comparable, with normalized resistance variations ranging from 0.96 to 1. The consistent correlation between chamber temperature and resistance variations over time highlights the effectiveness of the proposed sensors for sensing applications. For D1 thermistors, the time required to complete a dynamic cycle was approximately 400 s, while the D2 thermistors completed the cycle slightly faster, in under 350 s. This variation is likely due to the shorter contact electrodes and smaller sensing area of the D2 thermistors, which facilitated faster response times and more rapid relaxation of the conductive particles during each cycle [8]. Notably, the thermistors demonstrated distinct behaviors during the dynamic cycles. Their response was relatively linear and rapid during heating but displayed significant fluctuations and slower recovery during cooling, which is likely due to the high heat capacitance of the substrate manufactured from PC material [44] since cooling is affected by how efficiently heat is dissipated. Similar observations have been reported in the literature for alternative substrates, including textiles [45]. Additionally, negligible deviations from the initial normalized resistance values were observed across the dynamic cycles, with the initial resistance value of subsequent cycles being slightly lower than that of the first. This behavior is likely attributed to the thermal degradation of the thermistors and their exposure to environmental humidity, as no insulation layer was incorporated during fabrication. Even so, the temperature data collected from the thermistors during both heating and cooling cycles showed good agreement with the environmental chamber results. The reliability of Ag films on PC substrates has been previously evaluated, demonstrating a high adhesion strength [9]. It is also well known that the adhesion of PEDOT:PSS films can pose challenges depending on the substrate [46]. Therefore, in this study, the mechanical reliability of PEDOT:PSS films on PC substrates and Ag films was of particular interest due to its direct contact within the thermistor structure. Consistent with this, the study findings indicated slight variations in the adhesion performance of PEDOT:PSS films based on the underlying substrate. The tested adhesion specimens are demonstrated in Figure 6.  
Figure 6: Adhesion tests of PEDOT:PSS. (**a**) On PC substrate and (**b**) and Ag film. According to visual evaluations in line with the reference pattern described in the ASTM D3359-17 standard classification table, PEDOT:PSS film deposited on the PC substrate exhibited very weak mechanical reliability, with an adhesion strength of 0B, as more than 65% of the film detached, as seen in Figure 6a. This is a likely result of the disparity between the surface energy of the substrate and the surface tension of the PEDOT:PSS solution [47].