# Automatic Transmission Fluids in Electrified Transmissions: Compatibility with Elastomers
## 3 Results and Discussion
### Results of Complementary Tests
The spectra of silicone (Figure 10) are reported as complete spectra (wavenumber between 600 to 4000 cm\({}^{-1}\)) and an amplified section between 2750 and 3050 cm\({}^{-1}\) in order to obtain a better understanding of the spectra peaks in this wavenumber interval. The FKM spectra (Figure 8) show the characteristic bands for this polymer, which are summarised in Table S1 in the Supplementary Material. The area of every peak was compared between the different FKM samples and considered different when the area failed a Grubb's test (\(p=0.01\), \(n=9\)). With this criterion, two main differences were found. First, the fresh sample showed a peak at 1735 cm\({}^{-1}\) which became lower in the rest of the samples. This peak is assignable to the stretching vibrations of the C=CF\({}_{2}\) bond [30], which seems to be at least partially damaged after aging. Furthermore, the sample aged in oil A for 168 h showed significant reductions at 3020, 1390, and 1350 cm\({}^{-1}\) which are assignable to asymmetric CH\({}_{2}\) stretching, -CH\({}_{2}\)- wagging vibration in -CH\({}_{2}\)F, and C-F stretching in C=CF\({}_{2}\), respectively [30], suggesting partial damage. However, understanding why the peaks were present after 672 h needs further study. On the other hand, the fresh sample showed a very broad peak around 3275 cm\({}^{-1}\), which could be interpreted as indicating \begin{table}
\begin{tabular}{c c c c} \hline \hline
**ATF** & **0 h** & **168 h** & **672 h** \\ \hline - & 65.50 & - & - \\ Oil A & - & 26.20 & 34.76 \\ Oil B & - & 23.47 & 34.51 \\ Oil C & & 18.73 & 17.35 \\ Oil D & - & 16.60 & 18.24 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Crystallinity percentage of the silicone samples for different aging times. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**ATF** & **0 h** & **168 h** & **672 h** \\ \hline - & 21.29 & - & - \\ Oil A & - & 13.47 & 13.50 \\ Oil B & - & 13.55 & 19.22 \\ Oil C & & 20.33 & 18.64 \\ Oil D & - & 13.96 & 12.45 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Crystallinity percentage of the FKM samples for different aging times. Regarding the EPDM samples, in addition to the bands at 2905 and 2840 cm\({}^{-1}\), assignable to -CH- stretching vibrations in alkanes [30], the band at 1450 cm\({}^{-1}\) is also very apparent in Figure 8 and coincides with the strongest band in the FTIR spectrum of CaCO\({}_{3}\)[30]. Calcium carbonate is a common inorganic additive in polymers, and its presence has also been confirmed by XRD (Figure 6). The different samples of silicone do not show significant differences in their basic structure. Thus, all samples maintain the characteristic Si-CH\({}_{3}\) peaks at 784 and 865 cm\({}^{-1}\) (stretching vibration) and 1257 cm\({}^{-1}\) (rocking vibration), as well as a broad band at 1004 cm\({}^{-1}\) that corresponds to the Si-O-Si asymmetric stretching. The band at 1411 cm\({}^{-1}\) reveals the presence of Si-CH=CH\({}_{2}\) in all the samples, too [31]. Likewise, two bands at 2890 and 2960 cm\({}^{-1}\), corresponding to the CH\({}_{3}\) symmetric and asymmetric stretching vibrations, respectively, are also present [30]. However, after coming into contact with each oil, and regardless of the contact time, VMQ samples showed two new bands at 2855 cm\({}^{-1}\) and 2925 cm\({}^{-1}\), which are very likely from -CH\({}_{2}\)- symmetric and asymmetric stretching vibrations, respectively (Figure 10) [30]. This result indicates the presence of new hydrocarbon chains in the material, which appeared after contact with the oil. This suggests the incorporation of the oil into the silicone material, which is reasonable, bearing in mind the increase in volume shown in Figure 1.  
Figures 11-13 show the thermogravimetric analysis for samples after aging for 168 h of FKM, EPDM, and silicone, respectively. Each figure shows both the percentage loss in weight with respect to the temperature (TGA), as well as the derivative of the aforementioned loss with time (DTGA).