Crystallization of C18 in mesoporous silica: Effect of surface functionalization and nanoconfinement

Abstract

Fully releasing the thermal storage capacity of Phase change materials (PCMs) requires the integration of surface functionalization and nanoconfinement effect and therefore ingenious design of the pore size and surface property of supports. Herein, this work thoroughly explores the influence of synergistic coupling between nanoconfinement effect and interfacial hydrogen bonding strength from the carriers and the core materials on the crystallization behavior of C18 PCMs molecules. Rejoicingly, the fusion enthalpy of octadecanol/NH2-LP-SBA-15-CH3 composite can be as high as 186.08 J/g, which is much higher than those of other composite PCMs. The interfacial interaction plays a dominant role in the crystallization of C18 PCMs in large nanopores (e.g., 6.79 ~ 12.55 nm), hence the more suitable hydrogen bond strength between the supports and C18 may be advantageous to trigger the nucleation of more molecular chains. However, the decisive factor for the crystallization of C18 PCMs will be converted to nanoconfinement effect in small nanopores (e.g., 2.53 ~ 3.78 nm). Density functional theory (DFT) calculations are employed to propose atomic-level surface interactions. The obtained shape-stable composite PCMs exhibit excellent chemical compatibility, ultrahigh thermal stability, elevated thermal conductivity and outstanding cyclability, which are important prerequisites for the fascinating energy storage system.