## 4 Results and Discussion
It is also seen that the addition of GO enhanced the \(\beta\) phase nucleation due to the appearance of significantly strong \(\beta\) phase peaks along with the indistinctive peaks of \(\alpha\) phase. Thus, to understand the extent of polarization, the relative proportion of \(\beta\) phase using the FTIR spectra was calculated according to Equation (2) and the relative proportion of \(\beta\) phase was found to be increased as given: PVDF powder (0.23) \(<\) Pristine PNF (0.58) \(<\) PGRNF (0.61)  
PGANF (0.69). The obtained values for the relative proportion of \(\beta\) phase obtained from both XRD and FTIR (Figure S3 of SI) reveals that the proportion of \(\beta\) phase increased after the addition of GO into the PVDF. Moreover, the enhanced formation of \(\beta\) phase over \(\alpha\) phase was also strongly associated with the nanofiber alignment [39]. Thus, we strongly hypothesise that the PGANF will be an ideal candidate for piezoelectric sensors application. Before going into the piezoelectric sensor studies, we further analysed the effect of electrospinning on GO in combination polymeric chains of PVDF has been done using the Raman spectroscopy technique. The typical GO peaks around 1324 (D band) and 1592 cm\({}^{-1}\)(G band) [42] are clearly found in the Raman spectra of PGANF (Figure 2C), further confirming the presence of GO in the NF matrix. To further quantify the crystallinity, the differential scanning calorimetry studies were performed. The heating curve of the PGANF (Figure 2D) shows a peak melting temperature T\({}_{\rm m}\) of 162.42 \({}^{\circ}\)C. The crystallinity (\(\chi_{c}\)) of the sample was calculated according to Equation (3) and the crystallinity of PGANF was found to be 56.27%. Thus, according to the proportion of \(\beta\) phase obtained from XRD, FTIR and a DSC thermograph, we concluded that the PGANF can be used as a good material for biomechanical piezoelectric sensors. Figure 1: **(A)** Schematic illustration showing the electrospinningning setup, field emission scanning electron microscopy (FESEM) image showing the (**B**) pristine poly vinylidene fluoride (PVDF) random nanofiber (NF) (PNF), (**C**) pristine PVDF aligned NF, (**D**) PVDF-graphene oxide (GO) random NF (PCRNF), (**E**) PVDF-GO aligned NF (PGANF). The piezoelectric characteristics of the prepared samples were analysed by fabricating the NG as described earlier [43]. The optical image revealing the flexibility is given in Figure S4 of SI. The device is ready for piezoelectric characterisation. A further poling step is not required in the case of electrospun samples, as the electrospinning technique itself produce poling in the samples by the presence of electric field and the mechanical stretching [44,45]. Figure 3A shows the set up for the electrical characterisation of the FENG. The mechanical force is given by the help of a custom-made motor device and the mechanical force was controlled at different frequencies of vibrations. Figure 4 shows the piezoelectric response of the nanofiber samples prepared as part of the study. For that, the NG designs were made as described above and moderately high mechanical force with a frequency of 8 Hz with a uniform force of 12 N was applied across the PGANF, PGRNF and PVADF NFs FENGs respectively. The piezoelectric potential generated across the electrode was measured using an oscilloscope (Yokogawa, DL9040). As expected, PGANF exhibited maximum piezoelectric potential 2.1V compared to the PGRNF (1.5V) and PVDF NF (0.62V) FENGs. This can be attributed to the difference in the \(\beta\) phase nucleation in the different NF samples, which is directly related to the change in the piezoelectricity [46]. The d\({}_{33}\) value is calculated from output charge and applied mechanical force for the following samples: PVDF R, PVDF GO R, and PVDF GO A as 3.64, 8.75, and 12.25 pC/N, respectively. The results clearly confirm that the piezo potential of the sample increase with increasing polar \(\beta\) phase in the nanocomposite.