# Graphene Deposition on Glass Fibers by Triboelectrification
## 3 Results and Discussion
Thus, for the coating process, a scrolling velocity equal to 5.4 rpm was selected since it represented a good compromise between the intensity of the surface electrification and the requirement to minimize the force applied on the fibers to preserve their mechanical properties. In Figure 6, a SEM image of a pristine GF specimen is shown. The surface appears to be smooth with no substantial defects except for the presence of the sizing agent since the GF was used without any pretreatment. The surface morphology of the fibers after the rGO deposition as a function of CE intensity and the GO solution concentration can be evaluated in Figure 7. It can be seen that for all GO solutions, the rGO nanosheets appear to be more homogeneously attached to the GF by increasing the intensity of the TE process (i.e., moving from NEF to 1T or 2T). This is due to the creation of an increasing amount of positive charges on the GF surface by TE, which electrostatically attracted the negatively charged grap  
Figure 5: GF electrification curves at different scrolling velocities obtained following 1T path. Figure 6: SEM image of GF. Qualitatively, SEM images confirm the increase of rGO deposition with the concentration of the GO solution. The same conclusions cannot be drawn considering the intensity of the TE process, since the difference of the rGO amount deposited passing from NEF to 2T is too small to be detected by SEM analysis. Further quantitative investigations, for example by using friction force microscopy (FFM) [27,44], could give more information on the effective quantity of the nanomaterial deposited upon the electrification. It can be, however, deduced that a physical interaction between GO nanosheets with charged GF takes place due to the creation of attractive surface charges on the latter. At a general level, it can be stated that the obtained homogeneity level of the deposited nanomaterial is a promising indication of an efficient deposition method. Representative load-displacement curves obtained from microdebonding tests on rGO coated glass fibers characterized by 2T electrification are reported in Figure 8 and compared with those of the uncoated GF sample. For each specimen, the obtained values of the pull-out force (F\({}_{\text{max}}\)) were used for the calculation of the interfacial shear strength (IFSS), as indicated in Equation (1). Figure 8: Comparison of load–displacement curves from microdebonding tests of uncoated GF and rGO coated GF, with electrification 2T. Figure 7: SEM images of rGO coated samples with varying graphene oxide (GO) concentrations and electrification process. A comparison of the average IFSS values of uncoated and rGO coated GF is shown in Figure 9. A decrease of IFSS values is observed by increasing the GO content in the solution, while a considerable increment of IFSS values from NEF to 2T can be registered in the case of 0.005 rGO coated fibers (+45% with respect to GF). It can be deduced that the TE-based coating under 2T conditions from the GO solution at the lowest concentration lead to the creation of an optimized rGO interphase that favored an enhancement of fiber/matrix interfacial adhesion. The positive effect of the electrification could be connected to the fact that the electrification promoted good compaction of the deposited coating since the GO sheets are electrostatically attracted by the opposite surface charges of the fibers. This may result in a lower relative sliding of the rGO sheets, thus favoring the adhesion of the matrix on the coated fibers. This compaction is probably partially lost, increasing the amount of nanomaterial deposited thus allowing an easier sliding between nanosheets and a decrease of the matrix/fiber adhesion. However, further analyses should be made to confirm this hypothesis.