## 4 Discussion
Furthermore, a noticeable hysteresis occurs in the conductance change when strain is applied to a polymer composite that is enriched with a conductive filler [39; 40]; this has been attributed to the viscoelastic nature of the polymer and the interaction between the conductive nanomaterial fillers and polymers. Our findings indicate that thermal treatment significantly affects the measured hysteresis (see Section 3.3), in accordance with the research results mentioned above [39; 40], showing that annealing alters the polymer microstructure, which changes from an amorphous state to a semi-crystalline state, affecting its viscoelastic behavior. Based on the above, we believe that this change in the polymer microstructure is the main cause of the observed decrease in \(\sigma_{\text{AR}}\) and the corresponding increase in GF. With regard to consecutive alternating bending, a nonmonotonic strain-sensing cycle was observed; that is, a different sensor response was recorded for the hogging and sagging modes of deformation. In more detail, as we can notice in Figure 12c, the minimum sensor resistance (\(\Delta\text{R}=-0.8\%\)) occurs during sagging (i.e., when it undergoes compression) at a displacement of 0.2 mm. Further displacement in the same direction results to an increase in the resistance. In addition, the sensor resistance reaches its maximum value (\(\Delta\text{R}=2.5\%\)) at hogging (i.e., when subjected to tension) at a maximum displacement of 1.2 mm. It has been previously reported [34] that the resulting entangled CNT structure (due to the van der Waals forces between individual CNTs) usually results in a nonmonotonic behavior during the strain cycle, arising from competition between the destruction and construction of the conductive network (percolation pathways); this is often observed for various types of CNT/polymer systems. Furthermore, [PERSON] et al. [41] also noted a double-peak (nonmonotonic) behavior during the strain cycle, which can be attributed to the restructuring of percolation pathways owing to competition between the formation of new pathways and the destruction of old ones; in general, the resistance decreases when the number of conductive nanofiller interconnections increases. According to the authors,the following mechanism applies: the interconnections between rod-like conductive fillers are maximized at a slight degree of alignment and not at a fully random state of orientation or at the maximum orientation state. In addition, increasing the applied strain leads to a corresponding increase in the alignment of the CNTs in the direction of stretching. Thus, it is reasonable to assume that the resistivity initially decreases at slight alignments until the number of interconnections reaches its maximum, beyond which further straining starts to disconnect the nanotubes, and consequently, the resistance increases. Based on the above, the minimum resistance value can appear near the mid-strain levels, in agreement with our findings (as shown in Figure 12c), and corresponds to the maximum number of CNT interconnections at an optimum strain, rather than the minimum or maximum applied strain. Additionally, with regard to the different maximum variation of resistance (\(\Delta\)R) for the hogging and sagging modes of deformation, it is important to consider that the 0.2 mm thick piezoresistive layer is situated on top of the 0.6 mm thick non-conductive substrate as presented in Figure 1. This configuration affects the location of the neutral axis during bending of the whole device. Specifically, the different thicknesses of the piezoresistive layer and non-conductive substrate create an asymmetric bending response, resulting in different strain distributions in the conductive layer during the two different modes of testing (hogging and sagging). Consequently, the mechanism involving CNT network restructuring described above is not solely responsible for the observed difference in the corresponding maximum variation of resistance. Future work can be categorized into two primary directions.