Nanoconfinement effects of N-doped hierarchical carbon on thermal behaviors of organic phase change materials

Nanoconfinement behaviors of organic phase change materials (PCMs) in the nanoscale porous supports greatly influence the efficiency of thermal energy transformation and utilization when they undergo phase transition. To comprehensively elucidate the effects of nanoconfinement induced by the host-guest interactions on the thermal behaviors of organic PCMs, in-situ N-doped nanoscale hierarchical host carbon is successfully prepared via pyrolysis of polyaniline hydrogel. Distinctly different phase change behaviors were found for small molecular organic guest PCMs with various organic functional terminals and carbon chain lengths in the confined nanoscale N-doped hierarchical pores. The host-guest interactions at the interfaces in the composite PCMs determine the nanoconfinement behaviors of PCMs via influencing the free mobility of PCM molecules, which mainly depend on the hydrogen bond intensity between PCMs and N-doped hierarchical carbon, and space restriction effect of the hierarchical pore on the PCMs. However, these two dominant factors are interchangeable when the carbon chain length of carboxylic acid molecules is different. Moreover, the nanoconfinements of PCMs are gradually enhanced from octadecane, octadecylamine, octadecanol to stearic acid. The atomic-level mechanism is proposed via density-functional theoretical (DFT) calculations. This study provides insights into the nanoconfinement mechanism of small molecular organic PCMs inside the confined nanoscale N-doped hierarchical carbon.