# PpyNT/NR/NBR Composites with Excellent Microwave Absorbing Performance in X-Band
## 3 Results and Discussion
### MA Performance of PPyNT/NR/NBR Composites
#### 3.2.1 Optimization of PPyNT Content  
Different contents of PPyNT ranging from 3 to 12 phr are impregnated into NR/NBR (50/50). With this blend ratio, composites show a typical co-continuous phase structure, as shown in Figure S2 (see Supplementary Materials), where the bright and dark regions are NR and NBR phases, respectively [25]. Meanwhile, PPyNTs are selectively localized in the NR phase regardless of their content. Figure 1: (**a**) The schematic illustration of synthesis of PPyNT; (**b**,**c**) SEM images, (**d**,**e**) TEM images, (**f**) XRD pattern and (**g**) IR spectrum of typical PPyNT. The MA performance of an absorber highly relies on its complex permittivity (\(\epsilon_{\rm r}=\epsilon^{\prime}-\rm j\epsilon^{\prime\prime}\)) and permeability (\(\upmu_{\rm r}=\upmu^{\prime}-\rm j\upmu^{\prime\prime}\)). \(\epsilon^{\prime}\) and \(\upmu^{\prime}\) correlate with the capacity of the material in storing electrical and magnetic energy, respectively, while \(\epsilon^{\prime\prime}\) and \(\upmu^{\prime\prime}\) are related to its capability to dissipate electrical and magnetic energy, respectively [17]. Because of their non-magnetic nature, the \(\upmu^{\prime}\) and \(\upmu^{\prime\prime}\) values of all samples are almost 1 and 0, respectively. Therefore, only the complex permittivity is analyzed in detail here. As seen in Figure S3 (see Supplementary Materials), the \(\epsilon^{\prime}\) and \(\epsilon^{\prime\prime}\) of all samples show a typical frequency dispersion behavior, descending with an increase in frequency [26]. With increased PPyNT content, this frequency dispersion behavior is becoming more remarkable. At the same time, the values of \(\epsilon^{\prime}\) and \(\epsilon^{\prime\prime}\) increase clearly with the content of PPyNT rising, which confirms the effective medium theory [27]. On one hand, with the increase in PPyNT content, there are more mini-capacitors with PPyNT as the electrode and a very thin NR layer in between as dielectric [28] in the composites. On the other hand, a more interconnected PPyNT network tends to be formed in the composites with higher PPyNT content, as shown in Figure S2 (see Supplementary Materials), which is able to offer more paths to facilitate the electron migrating or hopping and in turn induce leakage current [22]. Consequently, the enhanced capability in storing and dissipating electromagnetic energy is observed simultaneously with increased PPyNT content. The reflection loss (\(RL\)) and effective absorption bandwidth (EAB) are employed to evaluate the MA performance of the composites. The values of \(RL\) are calculated by Equations (S1) and (S2) (see Supplementary Materials) based on the transmission line theory [12]. The criterion for the EAB is the value of \(RL\) less than \(-\)10 dB, meaning over 90% of energy is absorbed. The minimum \(RL\) (\(RL_{\rm min}\)) of the composite containing 3 phr PPyNT is only \(-\)9.8 dB at 11.2 GHz with a thickness of 3.4 mm (Figure 2a), indicating its weak absorbing capability. The composite with 6 phr PPyNT shows the best absorbing performance. Its \(RL_{\rm min}\) value can reach \(-\)37.94 dB at 8.3 GHz with a thickness of 3.4 mm (Figure 2b), and the corresponding EAB is 1.6 GHz (from 8.2-9.7 GHz) (Figure 2(b')). The thinner thickness of 2.8 mm can achieve the widest EAB of 3.4 GHz (from 8.8-12.1 GHz), covering 79% of the \(X\)-band (Figure 2(b')). Further increase in PPyNT content does not favor the improvement in MA performance. The \(RL_{\rm min}\) value of the composite with 9 phr PPyNT is \(-\)12.84 dB with a thickness of 2.2 mm (Figure 2c) and a corresponding EAB of 2.8 GHz (from 9.7-12.4 GHz) (Figure 2(c')). The composite with 12 phr PPyNT doesn't show effective absorption over the whole \(X\)-band, and its \(RL_{\rm min}\) value is only \(-\)7.84 dB at 9.7 GHz (Figure 2d).