## 3 Results and Discussion
### Characterization and Properties of Hybrid Foams ss-CRMFoams@PCMs
#### 3.2.1. Leaching Tests and Thermal Properties
According to previous studies, the n-octadecane crystals consist of two crystalline phases \(\alpha\)- and \(\beta\), which exhibit very close melting temperatures overlapping each other [67]. The similar asymmetric appearance of DSC peaks of RT18 HC, could be explained based on its structure, which seems according to the Rubithem data sheet [68], to be composed of more than one hydrocarbon (the main phase should be the hexadecane, C\({}_{16}\)H\({}_{34}\)). The areas of exothermic (melting) and endothermic (solidification) transition peaks of DSC curves were used for the calculation of enthalpies of n-octadecane and RT18 HC, which were found to be 261.2 J/g (\(\Delta\)H\({}_{\text{m}}\)), \(-\)254.2 J/g (\(\Delta\)H\({}_{\text{s}}\)) and 305.0 J/g (\(\Delta\)H\({}_{\text{m}}\)), \(-\)298.0 J/g (\(\Delta\)H\({}_{\text{s}}\)), respectively. Moreover, Figure 10 shows the melting and freezing temperatures (T\({}_{\text{m}}\), T\({}_{\text{s}}\)) as well as the corresponding enthalpies (\(\Delta\)H\({}_{\text{m}}\), \(\Delta\)H\({}_{\text{s}}\)) of the two PCMs stabilized into CRMFoam-2.5. As shown in that figure, the melting temperature (T\({}_{\text{m}}\)) of octadecane (OD) increases (+3.7 \({}^{\circ}\)C, curve of ss-CRMFoam-2.5@OD), while the solidification temperature (T\({}_{\text{s}}\)) of RT18 HC decreases (\(-\)3.5 \({}^{\circ}\)C, curve of ss-CRMFoam-2.5@RTH18). The DSC thermograph of CRMFoam-2.5, which is also illustrated in Figure 10, did not show exothermic or endothermic peaks. Furthermore, the theoretical melting enthalpies of ss-CRMFoam-2.5@OD and ss-CRMFoam-2.5@RTH18 hybrids were calculated using the following equation [69]:  
\[\Delta_{m}^{Thoretical}=\Delta_{m}^{PCM}\ (1-\varphi\%) \tag{6}\]  
where \(\Delta_{m}^{Thoretical}\) and \(\Delta_{m}^{PCM}\) are the theoretical melting enthalpy of ss-CRMFoam-2.5@PCM hybrids and the measured melting enthalpy of PCM, respectively, and \(\varphi\)% is the weight fraction of CRMFoam-2.5 sample. Using the above equation, the theoretical melting enthalpies of ss-CRMFoam-2.5@OD and ss-CRMFoam-2.5@RTH18 hybrids were found to be 126.1 J/g and 183.5 J/g, respectively. The \(\Delta_{m}^{Thoretical}\) value of octadecane (126.1 J/g), seems consistent with the measured value (126.9 J/g) using DSC. In contrast, the \(\Delta_{m}^{Thoretical}\) value of RT18 HC (183.5 J/g) was found to differ significantly from the experimental value (115.5 J/g). A possible explanation for this disagreement could be attributed to the nonhomogenous encapsulation of RT18 HC, which in conjunction with the small weight of the sample (30 mg), significantly affected the accuracy of the DSC measurement. In addition, the encapsulation efficiency of n-octadecane and RT18 HC in the ss-CRMFoam-2.5 was calculated based on enthalpies of pure octadecane and RT18 HC after leaching tests, utilizing the following equation:  
\[\text{PCM content in ss-CRMFoam-2.5 (wt\%)}=(\Delta\text{H}_{\text{m}}/\Delta\text{H}_{\text{PCM}})\times 100 \tag{7}\]  
where \(\Delta\text{H}_{\text{m}}\) is the enthalpy of melting for the PCM encapsulated into ss-CRMFoam-2.5 (J/g) and \(\Delta\text{H}_{\text{PCM}}\) is the enthalpy of melting for pure octadecane or RT18 HC (J/g). Thus, the latent heat storages of ss-CRMFoam-2.5@OD and ss-CRMFoam-2.5@RTH18 were calculated using Equation (6) and found to be 48.8% and 37.8% for octadecane and RT18 HC, respectively. Figure 9: DSC curves of pure n-octadecane and RT18 HC paraffin.