## 3 Shape-Memory Polymer Nanocomposites (SMPNCs)
### Carbon-Based Nanocomposites
#### 3.2.4 Graphene Oxide Nanocomposites
Upon exposure to 808 nm NIR light (1.5 W/cm\({}^{2}\)), the TCPI-0.3/rGO-3% nanocomposites displayed a rapid temperature rise to approximately 300 \({}^{\circ}\)C within 10 s, while TCPI-0.3/rGO-1% reached 238 \({}^{\circ}\)C in 9 s, surpassing its glass transition temperature (T\({}_{\text{g}}\)) of 221 \({}^{\circ}\)C. The rate of heating and the steady-state temperature exhibited a linear relationship with the rGO content, demonstrating that TCPI-0.3/rGO-1% could rapidly recover its original shape from a deformed \(\pi\)-shape within 7 s, with shape fixation (R\({}_{\text{f}}\)) and recovery (R\({}_{\text{r}}\)) rates exceeding 99% and 98%, respectively, due to the effective activation of macromolecular chains by localized NIR irradiation (Figure 24b). [PERSON] et al. utilized a simultaneous polymerization method to integrate functionalized reduced graphene oxide (f-rGO) into smart polyurethane and polystyrene, forming multi-stimuli responsive nanocomposites with interpenetrating polymer networks (IPN) [232]. Incorporating 1 wt.% f-rGO into IPN nanocomposites significantly enhanced their mechanical properties and thermal stability, and enabled efficient heat transfer, achieving 100% shape recovery within 33-44 s under microwave irradiation, surpassing the efficiency of sunlight exposure. In another study, they developed a functionalized-hydroxy iron oxide-anchored rGO nanohybrid to improve the thermal behavior of the nanocomposites, which exhibited faster shape recovery (20-40 s) with thermal heating than similar materials under sunlight exposure [237]. Additionally, these nanocomposites demonstrated exceptional chemical resistance, self-cleaning capabilities through surface hydrophobicity, and thermally actuated artificial muscle-like behavior [232; 237]. [PERSON] et al. focused on electroactive SMPNCs composed of polyurethane/graphene nanosheets, where the polyurethane was synthesized from polycaprolactone, hexamethyl-lene diisocyanate, and 1,4-butanediol through solution processing [238]. The incorporation of graphene into polyurethane significantly improved electrical conductivity, reaching a percolation threshold at 1.5 wt.%, where applying 75 V for 60 s facilitated shape recovery, although not complete at 1-1.5 wt.% graphene content (Figure 24c). Nanocomposites with 2-3 wt.% graphene nanofiller exhibited complete shape recovery within 60 s and showed enhanced shape fixity (83.4%) and recovery (100%) compared to neat polyurethane, underscoring the role of matrix-nanofiller compatibility in augmenting shape-memory performance. In another work, [PERSON] et al. reported an epoxy-based SMPC utilizing reduced graphene oxide paper (rGOP) that achieved approximately 100% recoverability in just 5 s under 6 V, offering a more energy-efficient composite for applications purpose [239]. [PERSON] et al. utilized commercially available PVA/PEG to develop nanocomposites through solution casting, incorporating varying amounts of graphene, where the composite with 0.2 wt.% graphene achieved nearly 100% shape-memory recovery within 8 s [240]. However, increasing graphene content (0.5 and 1.0 wt.%) reduced the recovery ratio (R\({}_{\text{r}}\)) to approximately 45% due to the enhanced brittleness hindering shape deformation [241; 242]. Additionally, the inclusion of GO in PVA composites, facilitated by water as an athermal stimulus, significantly improved shape-memory properties by cross-linking within the PVA matrix, thereby improving response under various actuations [243]. Figure 24: (**a**) (i) Schematic depiction of chemically bonded DGEBA-f-GO/EDA/DGEBA photothermal cross-links and (ii) surface temperature changes with varying nanofiller content in the HBPU/EP composite during NIR irradiation. Reproduced with permission from ref. [230]. Copyright 2020 Elsevier. (**b**) Graphical illustration of (iii) mechanical properties, (iii) temperature change as a function of GO content (wt.%) in TCPI/rGO composites, and (iv) the process of shape recovery of the TCPI-0.3/rGO-1% composite with a fixed \(\pi\)-shape under NIR irradiation.