Surface functionalization engineering driven crystallization behavior of polyethylene glycol confined in mesoporous silica for shape-stabilized phase change materials

Abstract

Crystallization behaviors of organic phase change materials (PCMs) confined in porous supports, which are determined by the interactions between PCM molecules and channel surface of the supports, are a prerequisite for the storage and release of latent heat in PCMs. In this work, surface functionalization was engineered to regulate the interactions between a PCM of polyethylene glycol (PEG) and internal/external surfaces of a support of SBA-15 and the crystallization/stabilization behavior of PEG, and yield desirable thermal properties of the PEG confined in SBA-15 channels. To investigate the effect of the internal/external surfaces of SBA-15 on the crystallization/stabilization behavior of PEG, SBA-15 supports were modified with various functional terminals, such as NH2-SBA-15-NH2 and NH2-SBA-15-CH3. The fusion enthalpy was increased from 0J/g of PEG/HO-SBA-15-OH composite to 88.2J/g of PEG/NH2-SBA-15-CH3 composite. The amino groups modified on the internal surface of SBA-15 reduced the hydrogen bond interactions between PCM molecules and the channel surface of the supports, and also altered the adsorption conformation of the PEG chains from train structure to loop structure, which is conducive to the stretching and crystallization of the PEG chains. Further, the methyl groups grafted on the external surface of SBA-15 restrained the spillover of PEG molecules from the channels due to the opposite polarities of PEG molecules and methyl groups. Crystallization behavior of the PEG molecules in channels of SBA-15 driven by surface functionalization engineering yields a controllable phase change enthalpy of PEG/SBA-15 composite and provides a general approach for the controlling of the thermal properties of PCMs.