# Graphene Deposition on Glass Fibers by Triboelectrification
## 3 Results and Discussion  
The physical appearances of glass fibers coated by the TE method are compared in Figure 3a-c. GO-coated fibers showed a light brown color, while rGO coated glass fibers assumed a darker color due to the chemical reduction process [43]. The darkening effect could be better seen on GF-coated fibers with higher GO concentrations, probably because of the higher amount of deposited nanomaterial. Apparently, the effect of triboelectrification of GF on the GO deposition is not so evident, as NEF, 1T, and 2T specimens obtained with the same GO concentration have a similar optical appearance. \begin{table}
\begin{tabular}{l c c} \hline \hline \multirow{2}{*}{**Sample Name**} & **Graphene Oxide** & \multirow{2}{*}{**Electrification Process**} \\  & **Concentration (\%)** & \\ \hline GF * & - & - \\
0.005 GO NEF/0.005 rGO NEF & 0.005 & NEF \\
0.005 GO 1T/0.005 rGO 1T & 0.005 & 1T \\
0.005 GO 2T/0.005 rGO 2T & 0.005 & 2T \\
0.05 GO NEF/0.05 rGO NEF & 0.05 & NEF \\
0.05 GO 1T/0.05 rGO 1T & 0.05 & 1T \\
0.05 GO 2T/0.05 rGO 2T & 0.05 & 2T \\
0.1 GO NEF/0.1 rGO NEF & 0.1 & NEF \\
0.1 GO 1T/0.1 rGO 1T & 0.1 & 1T \\
0.1 GO T/0.1 rGO T & 0.1 & 2T \\ \hline \hline \end{tabular}
* Glass fibers neither triboelectrified nor coated with graphene oxide.  
\end{table} 
Table 1: Uncoated and coated fibers designation. The amount of electrical charges accumulated onto the glass within 100 s of 0T, 1T, and 2T paths is summarized in Figure 4. For these preliminary charge measurements, the scrolling velocity was chosen arbitrarily equal to 2.8 rpm. The GF that followed the path, OT, showed a partially negative pre-existing surface electrification owing to the rubbing of fibers with other materials during their storage. The grounded electrodes allowed the fibers to be partially discharged. The use of efficiently grounded electrodes could be a valid possibility for improving the discharging of the fibers. Nevertheless, a completely discharged GF surface was not strictly necessary since the curve obtained from the 0T path accounted for the charge background. This was eventually subtracted from the curves obtained from 1T and 2T paths, allowing us to detect the neat triboelectrification effect on the GF surface. GF, as expected, assumed a positive surface charge when rubbed against the PTFE wheels, thus indicating that an effective triboelectrification process occurred. The increased number of contact points given by the contact with the second PTFE wheel allowed a furthermore intense surface charge electrification. Figure 4: GF electrification curves obtained from 0T, 1T, and 2T paths at a scrolling velocity equal to 2.8 rpm. Figure 3: Representative images of (**a**) 0.005 GO/rGO, (**b**) 0.05 GO/rGO, (**c**) 0.1 GO/rGO fibers (NEF, 1T, 2T). In Figure 5, the GF surface charge electrification curves obtained at three different scrolling velocities (i.e., 0.61 cm/s, 1.19 cm/s, and 4.05 cm/s), and following 1T path are reported. It can be seen that the higher the scrolling velocity, the greater the contact electrification. High scrolling velocity results in low contact time between fibers and PTFE wheels and thus in a high contact frequency. This means that the fibers were not discharged in air before being analyzed by the electrometer. Moreover, a high scrolling velocity induced an elevated contact pressure between the fibers and PTFE since the motor applied a higher tension on the fibers. High contact frequency and tension allowed to have a higher contact efficiency and thus a higher triboelectrification effect. However, an excessive scrolling velocity led to an unstable charge measurement due to the limitations on the maximum amount of charge measurable by the electrometer used (\(\pm\)2 \(\mu\)C). In fact, the curve obtained at the highest velocity (18.4 rpm) showed a rapid increment of the surface electrification up to 40 s, then the electrification stabilized showing a plateau approaching 2 \(\mu\)C. At about 80 s the measurement stopped since the detectable charge limit was reached.