Meanwhile the encapsulation efficiency Een of

As shown by Fig. 5 and Table 1, the encapsulation of n-alkanes significantly influences their phase-change behaviors. For the odd n-alkanes/silica composites, their phase change behaviors in the cool and heating processes are similar to the pure ones. It should be noted that the two crystallization peaks show an obvious shift toward a lower temperature while the melting peak temperatures increase slightly. This phenomenon is attributed to the confinement effect of silica wall on the crystallization of encapsulated n-alkanes. As the n-alkanes were encapsulated within a micrometric space, the motion of their Sildenafil was restricted in confined geometry. This leads to an increase in crystallization activity energy, thus resulting in a decrease in crystallization temperature [34]. In the case of the even n-alkanes/silica composites, the phase change behavior in the heating process is similar to that of the pure ones, which is related to the phase transition between the triclinic phase and the melt. However, the phase change behaviors of cooling process are quite different, in which double exothermic peaks appear. It is reasonable to believe that the confined crystallization environment may induce a metastable rotator phase for the encapsulated even n-alkanes [35]. However, the metastable rotator phase lacks the long-range order in the rotational freedom degree of molecules and, therefore, promptly completes the rotator-to-crystal transition. As a result, a single melting peak and the bimodal crystallization peaks could be observed in Fig. 5. Furthermore, it should be notable that there is a small peak observed below the main crystallization peak temperature by 20 °C in the crystallization process of n-eicosane/silica composite. This is assigned to the solid–solid phase transition resulting from the heterogeneous nucleation of the inner silica wall [36].