# Electrically Conductive Nanocomposite Fibers for Flexible and Structural Electronics
## 3 Results and Discussion
### Electrical Properties  
DC resistivity measurements of the fabricated composite fibers were carried out using a four-probe method. For each fiber, the electrical resistivity of multiple 5 cm long sections was measured. Additionally, the average diameter of each fiber was calculated as the mean value of the diameters of the measured fragments. Due to the high elasticity of the  
Figure 1: M5 composite fibers extruded using different diameter nozzles—0.2 mm (**left**), 0.5 mm (**middle**), and 1 mm (**right**). tested materials, the diameter measurement was performed using an optical method. It should be noted that the sections with resistivity values above 200 M\(\Omega\) were considered as non-conductive. To calculate the resistivity of the samples, the relation  
\[\rho=\frac{\pi d^{2}R}{4l} \tag{1}\]  
was used, where \(\rho\) is a composite resistivity, \(d\) is the average diameter of the fibre, \(R\) is the average resistance of fiber, and \(l\) is the length of the measured fiber section. The calculated values of each composite fiber resistivity, depending on the diameter of the nozzle used during extrusion, were summarized in Table 2. It should be noted that the measurements were performed at a constant voltage value of 12 V.  
It can be observed that at a low concentration of filler, conductive carbon particles are isolated by the polymer matrix material and a conductive network cannot be formed. It was observed that the percolation threshold of the CNT filler is much lower than that of the graphite powder filler, which is in agreement with literature reports [13; 23; 24; 25; 26]. The main disadvantage of using CNTs in conductive polymer composites is the typical nature of conductivity in semiconducting materials, mainly based on the phenomenon of electron tunneling between individual conductive particles. This is evident in the non-linear current-voltage characteristics of such composites. Composites containing graphite powder do not show such properties and their conductivity character is more similar to metallic conductivity, according to [PERSON]'s law. In order to determine the dominant type of conductivity in the composites developed, especially those containing a dual functional phase, the current-voltage characteristics were determined. Composites G6, C2, C3, M3, M4, and M5, with a diameter of 0.5 mm, were tested for voltages ranging from 1-30 V. Other composites were excluded from the study due to too high resistivity, not meeting the initial criteria. Table 3 shows the average resistivity values of the respective composites, together with their minimum and maximum values and the coefficient of variation (\(V\)) determined according to Equation (2), in which \(s\) is the standard deviation and \(\underline{x}\) is the mean of measured resistivity values. \[V=\frac{s}{\underline{x}} \tag{2}\]  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline  & & \multicolumn{4}{c}{**Resistivity [\(\Omega\)m]**} \\ \cline{3-5}  & & \multicolumn{4}{c}{**Nozzle Diameter [mm]**} \\ \cline{3-5}  & & **0.2** & **0.5** & **1** \\ \hline \multirow{8}{*}{ \begin{tabular}{c} **C** \\ **C** \\ **C** \\ **C** \\ \end{tabular}