# A Review on the Deformation Behavior of Silver Nanowire Networks under Many Bending Cycles
## 5 Deformation Behavior of Silver Nanowire Network with Protective Coating  
Silver nanowires are vulnerable to oxidation and high temperatures [24]. To overcome these limitations, various studies have attempted to coat materials with good thermal, electrical, and chemical properties on silver nanowire networks to protect them [44; 45]. Among candidates for coating materials, reduced graphene oxide (RGO) coating is emerging as a method to improve the chemical stability of silver nanowires [46]. RGO can be prepared easily by exfoliating graphite and, similar to the graphene, it is used as a passivation layer to prevent the oxidation of metals [45; 47]. In addition, good electrical conductivity makes RGO a promising material [48]. Despite the good chemical and electrical properties of coating materials, the mechanical stability of a silver nanowire can be affected as it combines with other materials to form hybrids. Thus, investigation of the mechanical reliability of protective-material-silver-nanowire hybrids should be conducted; in the following, the mechanical stability of the RGO-coated silver nanowire network under repeated deformation testing, using a cyclic bending tester, is discussed. Figure 13: (**a–c**) TEM images of silver nanowires with sub-grain boundaries due to buckling, and (**d**) high-magnification image taken at the magenta square in (**c**). Reproduced with permission from ref. [43]. Copyright 2016, Elsevier. Figure 14 is the result of cyclic bending tests of the RGO-coated silver nanowire network. After repeated bending for over 800,000 cycles at 1.5% strain, the change in the resistance of the silver nanowire network with and without RGO showed a small difference. As shown in the SEM images of the RGO-coated silver nanowire network after cyclic bending (Figure 15), the microstructure of the samples with and without RGO coating showed similar results that failures occurred at thermally fused junctions. This refers to how the deformation mechanisms of the silver nanowire networks with and without RGO coatings were similar. In addition, the presence of RGO without forming strong bonds between silver nanowires had a negligible effect on the change in the deformation mechanism of the silver nanowire network. This resulted from the additional, electrically conductive pathway provided by the dispersion of RGO on the silver nanowire. Therefore, the decrease in the resistance was harder to observe for the RGO-coated silver nanowire network due to the larger, electrically conductive pathway. The cyclic bending test of the oxidized silver nanowire network demonstrated that the RGO-coated silver nanowire network had a smaller increase in the fractional resistance, as shown in Figure 16a. Exposing the RGO-coated silver nanowire and bare silver nanowire network to air at 70 \({}^{\circ}\)C for 132 h oxidized both the silver nanowire networks. However, the SEM image of the bare silver nanowire network in Figure 17 shows the prominent formation of oxides on the surface of the network as it was further exposed to ambient air at an elevated temperature. Such formation of oxides increased the sheet resistance of the silver nanowire networks; thus, the bare silver nanowire networks showed a much higher increase in resistance during the exposure to air at 70 \({}^{\circ}\)C than silver nanowire networks with RGO coating as shown in Figure 16b. Such enhancement of chemical stability by the RGO coating was also confirmed in the work by [PERSON] et al., where, compared with that of the bare silver nanowires, the increase in the resistance of the silver nanowire electrodes with RGO coating was much lower when exposed to air at 120 \({}^{\circ}\)C (Figure 16c) and at 85 \({}^{\circ}\)C with 85% relative humidity (Figure 16d) [50]. Figure 14: Cyclic bending test results of annealed silver nanowire networks with and without RGO coating. Reproduced with permission from ref. [49] with permission from The Royal Society of Chemistry.