## 4 Results and Discussion
### Influence of Plasma-Treated SiO\({}_{2}\) Nanofilers on Silicone-Rubber Nanocomite  
#### 4.2.1 Electrical Tree Parameters  
The tree initiation time (T\({}_{i}\)) of an electrical tree is the time at which small, observable trees initiate at the needle tip. Figure 6 shows the tree initiation time of the electrical trees of DMNC, STNC, and PTNC, with different nanofiller loadings of 1, 3, and 5 wt %. The error bar represents the maximum and minimum values of T\({}_{i}\), while the center box represents the corresponding average values. The average T\({}_{i}\) for unfilled SiR was 12.28 s, while the average T\({}_{i}\) for DMNC were 19.8, 55.0, and 66.0 s for 1, 3, and 5 wt %, respectively; the STNC showed a faster T\({}_{i}\) of 7.7, 30.7, and 72.6 s. In contrast, the PTNC possessed the slowest T\({}_{i}\), which were 34.6, 72.6, and 80.67 s for 1, 3, and 5 wt % nanocomposites, respectively. Results from statistical analysis, the one-way ANOVA (\(t\)-test), show that for the T\({}_{i}\), a significant difference exists between the three different treatment methods in 1% filler loading samples; while no significant difference in tree initiation times exists among the treatment methods for 3% and 5% filler loadings samples. The result shows that the tree initiation time of the nanocomposites depended on the condition of the treatment and nanofiller loading; in addition, the increase in filler concentration prolonged the initiation times. Nanocomposites with nanofiller took a long time to initiate compared to unfilled  
Figure 6: Tree initiation time for directly mixed nanocomposites (DMNC), silane-treated nanocomposites (STNC), and plasma-treated nanocomposites (PTNC). SiR. This result agrees with the result from [PERSON] et al. 's work [18]; they showed that even small amounts of added nanofiller led to significant improvements in tree initiation times. Our study has shown, however, that the STNC has a faster initiation time compared to DMNC and PTNC. This result agrees with the work of [PERSON] et al. [8] and [PERSON] et al. [7], who showed that silane coupling did not provide significant improvements in tree initiation time and resulted in slower propagation rates. In general, the improved bonding in nanocomposites due to plasma treatment played a role in prolonging tree initiation times, because the trapped charges needed higher energy to be extracted from the polymer; more time was thus required for the tree to initiate within the nanocomposites. Figure 7 shows the result of electrical tree performance for a sample of each of the SiR nanocomposites with different nanofiller treatments of 1%, 3%, and 5% wt filler loading for the three different treatment methods. The DMNC showed the fastest propagation rate, followed by STNC. PTNC exhibited the slowest propagation time. Similar results were observed for the rest of the samples. It can be seen from Figure 7 that the tree performances increased with an increase in nanofiller loadings. These results are in line with other studies that have been conducted in which higher filler concentrations led to densely packed structures for resisting electrical tree progression [19; 20]. The tree channels needed to propagate through the interfaces of the nanofiller in the packed structures of the polymer, which resulted in longer propagation times. From Figure 7, we can suggest that plasma treatment has a strong ability to slow electrical tree growth. This result agrees with [PERSON] et al. 's work [21], in which plasma-treated nanocomposites (plasma polymerization) exhibited slow tree propagation time, thus indicating that plasma treatment improved resistance against electrical treeing. To calculate the average growth rate, we plotted the best-fit line of the tree-propagation results. The growth rate was calculated using differences in tree length and time intervals. Figure 8 shows the average growth rate of electrical treeing for unfilled SiR with 1, 3, and 5 wt % of DMNC, STNC,  
Figure 7: Electrical tree performance (a) DMNC; (b) STNC; (c) PTNC. and PTNC.