The atomic force microscopy (AFM) was used to further observe the surface structures of the composite nanofibers. Scanning was carried out in tapping mode. All images were obtained at ambient conditions. Figure 1 confirms the isolation of the individual nanofiber synthesized by electrospinning, also revealed that the electrospun nanofiber is smooth with the absence of beads, proving that PEO was dissolved completely and the solution was homogenous enough to electrospinning. On the other hand, AFM image confirm that the electrospinning parameters used were suitable for generating smooth and highly aligned nanofibers.

Typical SEM image of G/PEO composite fiber is shown in Figure 2. No defects in the form of beads are observed in the fibers and their diameters range from 100 nm to 1.2 µm. SEM Image depict both good morphology and

good orientation due to the best choice of used parameters. It is difficult to confirm the presence of graphene sheets in the nanofibers from SEM and AFM images. In order to do that and check the dispersion of graphene, we have used high resolution optical microscopy.

The Optical Microscope was used to observe the alignment of the nanofibers to determine the optimum parameters and to further demonstrate the insertion of graphene nanosheets into polymer nanfibers by the appearence of black zones in fibers. Figure 3 shows images of such fibers. Here we observe black particles inside polymer matrix. These black particles are the graphene nanosheets which were found to be well dispersed and the fibers were relatively homogeneous in diameter. Further no beads formation is apparent, corfirming SEM results.

Using image analysis software, the diameters of the G/PEO nanofibers with 0, 1, 3, 5 and 7 wt% of graphene were 542.72, 602.84, 738.56, 817.57 and 913.76 nm, respectively. Graphene nanosheets had a clear effect on the formation of those nanofibers as reflects the average diameter of G/PEO nanofibers dependence on the amount of graphene sheets. We have found that this average increases with the loading of graphene nanosheets, and nanofibers in our samples have a minimum diameter of 100 nm and a maximum diameter of 1200 nm and the shorted measured length was 20 µm.

During graphite powder oxidation process in the concentrated acids using Hummer’s method, the original extended conjugated-orbital system of the graphite was destroyed and oxygen-containing functional groups were inserted into the carbon skeleton. After reduction with hydrazine, oxygen groups were then replaced with nitrogen ones. However, after a purification treatment, these functional groups derived from the intensive oxidation and hydrazine hydrate were eliminated, which may be proved by the existence of D, G and 2D bands only (Figure 4), reflecting the skeletal vibration of graphene sheets [15]. The G band that originates from in-plane vibration of sp² carbon atoms is doubly degenerate (TO and LO) phonon mode (E_2g symmetry) at the Brillouin zone center. The 2D band originates from a two phonon double resonance Raman process (Figure 4). The D band is attributed to defects in reduced graphene oxide nanosheets. On the other hand, relatively complex bands of typical polymeric materials were observed such as strong C-OH vibrations at 1150 cm⁻¹. As shown in the Raman spectra (Figure 5), there is no appearance of a new peaks or modification in the ratio of IG/ID intensities on the G/PEO nanofibers spectrum and the narrowing of PEO ray indicates a better alignment in the presence of graphene. These results indicate that the graphite oxide has been successfully exfoliated to graphene sheets, and also there are no interactions between graphene and PEO fibers. To confirm these results, we have also studied FTIR active vibrations.

FTIR spectrum of graphene solution is shown in Figure 4. The absence of graphite and graphene oxide peaks is a strong indication of the obtaining of graphene sheets. These peaks are: at 3400 cm⁻¹ (O-H stretching vibrations), at 1720 cm⁻¹ (stretching vibrations from C = O), at 1600 cm⁻¹ (skeletal vibrations from unoxidized graphitic domains), at 1220 cm⁻¹ (C-OH stretching vibrations), at 1060 cm⁻¹ (C-O stretching vibrations) [16], and stretching vibrations from C = O at 1720 cm⁻¹ due to the remaining of carboxyl groups even after hydrazine reduction the vibration modes of epoxide (C-O-C) (1230 - 1320 cm⁻¹, asymmetric stretching at 850 cm⁻¹, bending motion) [17]. The spectra in Figure 6 show a large broad band at 3320 cm⁻¹ due to PEO hydration. It was observed that the PEO is highly hydrophilic, thus it absorbs water and gets hydrated. Pure PEO shows many peaks, at 2924

cm⁻¹ corresponding to asymmetric CH₂, two CH₂ vibrational modes appear in PEO at 1460 cm⁻¹ which, correspond to asymmetric CH₂ bending (δ(CH₂)_a) and 1350 cm⁻¹ which, corresponds to symmetric CH₂ wagging and some C-C stretching (w(CH2)_s + ν(CC)) [18], at 1640 cm⁻¹ attributed to ν(C-O) band, the two bands at 1294 cm⁻¹ and 1250 cm⁻¹ are related to twisting vibration t(CH₂)_a also for stretching vibratio ν(C-O-C)_a [19] and at 107 cm⁻¹ that  corresponds to the ν(C-O-C)_a vibration mode. It has been reported in a previous study that the presence of a band at 942 cm⁻¹ is characteristic peak in supporting the gauche conformations of -CH₂-CH₂- groups, as needed for a pure PEO’s helical conformation [20]. The non serious modification of PEO FTIR spectrum after the inseration of graphene nanosheets confirms those derived from raman spectroscopy.

The TGA plot of composite fibers with different loading of graphene is shown in Figure 7. As expected, graphene was highly stable up to 600˚C. Reduced graphene showed an enhanced thermal stability due to the removal of oxygen-containing functional groups by reduction with hydrazine [21]. The major mass reduction started at ~350˚C leads to the decomposition of polymer in the samples which was completely decomposed at a temperature of ~425˚C. The weight percentage of the residue matches closely the graphene initial weight percentage during the preparation of the solution. The thermal stability of G/PEO was slightly improved by the presence of graphene, but this effect still negligible, which confirms again the absence of interactions between graphene and PEO.

Differential thermogravimetric (DTG) curves of these samples were shown in Figure 8. The temperature of the fastest weight loss rate (T_fl) of PEO were 396˚C, the T_fl of G/PEO (1%, wt/wt), G/PEO (3%, wt/wt), G/PEO (5%, wt/wt) and G/PEO (7%, wt/wt) were 400˚C, 401˚C, 409˚C and 412˚C, respectively. Obviously, this low shifting depending to rapheme loading may be attributed to the pressure of rapheme on PEO nanfibers and confirms the non functionalization of its nanosheets with PEO chains and absence of other interactions.