# Electrically Conductive Nanocomposite Fibers for Flexible and Structural Electronics
## 3 Results and Discussion
### Electrical Properties
 } & G1 & - & - & - \\ \cline{1-1}  & G2 & - & - & - \\ \cline{1-1}  & G3 & - & 42.9 \(\pm\) 8.5 & 11.8 \(\pm\) 5.2 \\ \cline{1-1}  & G4 & - & 0.384 \(\pm\) 0.025 & 0.155 \(\pm\) 0.008 \\ \cline{1-1}  & G5 & 0.817 \(\pm\) 0.007 & 0.252 \(\pm\) 0.002 & 0.453 \(\pm\) 0.008 \\ \cline{1-1}  & G6 & 0.510 \(\pm\) 0.006 & 0.0412 \(\pm\) 0.0116 & 0.175 \(\pm\) 0.011 \\ \cline{1-1}  & C1 & - & - & - \\ \cline{1-1}  & C2 & 1.45 \(\pm\) 0.04 & 0.790 \(\pm\) 0.019 & 0.367 \(\pm\) 0.030 \\ \cline{1-1}  & C3 & - * & 0.00212 \(\pm\) 0.00056 & 0.0426 \(\pm\) 0.0089 \\ \cline{1-1}  & M1 & - & - & - \\ \cline{1-1}  & M2 & 1.57 \(\pm\) 0.06 & 0.479 \(\pm\) 0.026 & 2.96 \(\pm\) 0.02 \\ \cline{1-1}  & M3 & 0.337 \(\pm\) 0.015 & 0.271 \(\pm\) 0.007 & 0.581 \(\pm\) 0.029 \\ \cline{1-1}  & M4 & 0.233 \(\pm\) 0.004 & 0.0738 \(\pm\) 0 The obtained resistivity measurement results clearly indicate that the composites containing CNTs as a functional phase show a significant voltage dependence of the electrical conductivity. The C3 composite, despite its low resistivity, had a coefficient of variation equal to over 26%. In the case of the G6 composite, which had graphite powder as the functional phase, the coefficient was only 1.01%, which means that it had an almost constant value of resistivity regardless of the applied voltage. Composites containing a conductive phase in the form of a mixture of graphite and CNTs also showed a relatively constant resistivity value as a function of voltage. The M3, M4, and M5 composites studied had a constant CNT content of 5 vol. %. It was observed, however, that the M3 composite containing 5 vol. % of graphite in its composition was characterized by a slightly lower resistivity constant, similar to the C2 composite in which there was no graphite, compared to the M4 and M5 composites, in which the graphite addition was 10 vol. % and 15 vol. %, respectively. This means that the addition of graphite to the conductive composite containing CNTs allowed for an improvement in the linearity of the current-voltage characteristics. The graphite in the composite reduced the semiconducting character of the conductivity and allowed us to obtain a material with conductivity close to that of the metal. This was a significant advantage enabling a more comprehensive application of this type of conductive material in a wide voltage range. Figure 2 shows the ratio of the resistivity at voltages different to the resistivity at 12 V for each tested material. Composites C2 and C3 were observed to exhibit higher resistivity at lower voltages. The sudden decrease in resistivity is particularly evident for composite C3, which was due to the higher CNT content. A similar phenomenon of an increase in the dynamics of conductivity changes of composites with an applied voltage, depending on the CNT content, was presented in the literature in the examples of the polyaniline and epoxy matrix composites [27; 28]. The resistivity of the C3 composite decreased by almost 60% at 30 V compared to the resistivity at 12 V. Above a certain voltage, an exponential decrease in resistivity occurred. This phenomenon is due to two properties characteristic of CNTs: a negative temperature coefficient of resistivity (NTC effect) [29; 30] and electron tunneling [31; 32]. Firstly, an increase in voltage causes heat to be released in the material being tested, which reduces its resistivity. Secondly, in order to start electron tunneling between carbon nanotubes, it is necessary to apply a sufficiently high electrical potential. Once this is exceeded, a rapid flow of electrons occurs, which results in a significant increase in electrical conductivity. The G6 composite containing 50 vol. % of graphite showed a slight increase in resistivity with the increase in the applied voltage. Graphite, in contrast to the CNTs, had a positive temperature coefficient of resistivity. As the applied voltage increased, the power dissipated on the tested composite increased, which caused the temperature of the sample to rise, at the same time increasing its resistivity.