# Shape Memory-Enhanced Electrical Self-Healing of Stretchable Electrodes
## 3 Results and Discussion
### Raman Spectra Investigations on the Microstructure Evolution  
The samples in different states of the stretched, cracked and healed were measured by Raman spectra which are shown Figure 3a-c. The dominant peaks, mainly distributing in the ranges, i.e., 1335-1390 cm\({}^{-1}\), 1551-1597 cm\({}^{-1}\) and 2417-2934 cm\({}^{-1}\), were assigned as the deformation or stretching of -CH\({}_{2}\) groups, aromatic hard segment as well as the -NH-C=O and -CH\({}_{3}\) groups in the polyurethane matrix. The peaks locating at 1597 cm\({}^{-1}\) shifted downwards to 1563 and 1559 cm\({}^{-1}\) in sequence as the crack-free sample was stretched by 10% and 20%, being indicative of the pre-storage of the strain energy in the composites. Furthermore, as for the samples without pre-stretching, the absorption intensities in the local cracked area dramatically reduced, which may result from the absence of the AgNPs in the scratch gap. The changes in Raman absorptions before and after the healing process were greatly magnified for the samples with the shape memory pre-stretching. For instance, the sample CSHP-15 had depressed adsorptions as scratched. By contrast, it significantly increased the intensities of the peaks distributing in the range 1182 and 1559 cm\({}^{-1}\) astransferred into the healed state from the cracked state. The spectra results indicated that the release of the strain energy magnified micro-structural variations in the shape memory-enhanced self-healing process. The internal stress and stored mechanical energy were found to be correlated to the shape/temperature memory behavior below and above the transition temperature [14]. It is well known that the \(T_{m}\)-type shape memory polymers, exhibited the so called stress-memory effect [15,16]. The extended samples after the thermo-mechanical programming to fix in the temporary states reversibly generated stress in the contraction directions as the macro-scale shape was constrained. Given that the shape memory-assisted self-healing involved closure of the crack surfaces driven by the shape memory recovery, the release of the strain energy improved the closure and the reconstruction of the conductive networks. Meanwhile,  
Figure 2: The plots of the current against time for the crack-free samples (**a**) and those exposed upon scratch (**b**) in the healing process; (**c**) The plot of healing efficiency against the pre-stretching percentages; (**d**–**f**) SEM images for the healed surface morphologies (triggered at 80 \({}^{\circ}\)C for 10 min) with different pre-stretching percentages.  
thermal stimulation allowed the healing reagent PCL to melt, which tended to move and enrich in the crack interfaces. The re-crystallization transition of the PCL in the crack area led to heal-ability of the electrode in micro-structures. The shape memory-enhanced self-healing of the stretchable electrodes is photographically demonstrated in Figure 3d. The sample was connected into a circuit with 1 V of voltage. Pre-stretching by 20% into the temporary shape made the LED lamp darken. Subsequently, exposure upon the crack led to complete loss of the conduction. Heating at 80 \({}^{\circ}\)C for several minutes triggered obvious shape recovery, along with the process of which the stretchable electrode was capable of healing the conductive pathways, enabling the lamp to enlighten again.