## 2 Results and Discussion
\begin{table}
\begin{tabular}{l c c c c c c c c} \hline \hline  & **Ts** & **Tm** & \(\Delta\)**Hs** & \(\Delta\)**Hm** & \begin{tabular}{c} **OD** \\ **\(\Delta\)Hs(\%)** \\ \end{tabular} & \
\begin{tabular}{c} **OD** \\ **\(\Delta\)Hm(\%)** \\ \end{tabular} &
\begin{tabular}{c} **g OD/g** \\ **Carbon** \\ \end{tabular} & **OD \%w.t.** \\ \hline OD & 21.5 & 28.8 & \(-\)251.9 & 249.6 & 100 & 100 & \(-\) & 100 \\ AC/OD & 23.2 & 29.9 & \(-\)98.83 & 118.4 & 39.23 & 47.44 & 2.738 & 73 \\ AC/CNTs/OD & 22.2 & 30.1 & \(-\)146.0 & 155.2 & 57.96 & 62.18 & 2.743 & 73 \\ CCF/OD & 21.3 & 32 & \(-\)139.8 & 135.5 & 55.49 & 54.29 & 1.966 & 66 \\ CCF/CNTs/OD & 22.0 & 32.3 & \(-\)146.0 & 142.8 & 57.96 & 57.21 & 1.345 & 58 \\ EG/OD & 23.3 & 27.9 & \(-\)152.0 & 155 & 60.34 & 62.10 & 1.914 & 65 \\ EG/CNTs/OD & 24.8 & 28.3 & \(-\)163.6 & 163.3 & 64.95 & 65.42 & 1.990 & 67 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Melting and solidification temperatures and enthalpies. The DSC curve for pure octadecane exhibits an exothermic peak at 28.8 \({}^{\circ}\)C and an endothermic peak at 21.5 \({}^{\circ}\)C corresponding to its melting and solidification processes, respectively. The latent heat for melting (\(\Delta\)Hm) and solidification (\(\Delta\)Hs) is 249.6 and \(-\)251.9 J/g, respectively, which is inconsistent with the literature values for pure octadecane [32]. On the other hand, the DSC curves for the AC/OD and the AC/CNTs/OD composites (Figure 5a) show slightly shifted and broader endothermic and exothermic peaks compared to pure OD. The inclusion of carbon nanoparticles creates a heat conduction channel within the paraffin, potentially altering the mode of energy transfer in the paraffin [22]. The solicitation peaks slightly shifted to higher temperatures, compared to the pure OD. According to previous studies, this phenomenon is related to the presence of porous carbon, which facilitates the heterogeneous nucleation of the PCM, resulting in a reduced extent of suppercoling in the composite PCMs and this is a crucial thermal property for the practical application of PCMs [24; 33]. Additionally, the pore characteristics and surface tension can significantly influence the phase transition temperature of the synthesized composite PCMs [33]. Moreover, in the composite's DSC curves, a reduction in \(\Delta\)Hs and \(\Delta\)Hm values is observed, reaching 39 and 47% of the corresponding values of pure OD (Table 1), which are lower than the expected theoretical values according to their PCM content (green lines in Figure 6). This also could happen due to the pore structure of AC carbon which limits the regular movement of the PCM chain [24]. Similar features are also shown in the DSC curves of the EG and the CCF composites (Figure 5b,c) and among the three carbon matrices without CNTs, the composite containing AC exhibited the lowest \(\Delta\)H values and the greatest reduction from the theoretical \(\Delta\)H values. The values for CCF show a smaller reduction, while the values for EG are very close to the theoretical ones. In addition, the DSC curves of the EG exhibit a similar shape to those of the pure PCM (they do not broaden as observed in the other two materials). These findings could be explained according to carbon matrice's pore structure. The microporous structure significantly hinders the movement of PCM chains, the mesoporous structure to a lesser extent, and the macroporous structure even less. In the case of AC, which has mainly a microporous structure [26], OD molecules are probably impregnated into the micropores, while in the case of CCF and EG, which have larger meso and macropores, the OD molecules are arranged in the larger pores and the movement of the PCM chains is less obstructed. The DSC curves of the carbon/CNTs/OD composites also show similar features. However, according to Table 1 and the comparative graphs for \(\Delta\)Hm% and \(\Delta\)Hs% (Figure 6a and b,  
Figure 6: Comparative graphs for: (**a**) \(\Delta\)Hm% and (**b**) \(\Delta\)Hs% of the composites derived from DSC curves.