Evaluation of paraffin infiltrated in various porous silica matrices as shape-stabilized phase change materials for thermal energy storage

Abstract

Phase change behaviors of organic phase change materials (PCMs) confined in porous silica matrices, which are determined by the pore characteristics as well as interfacial interactions between PCM molecules and supporting solid, are crucial to PCMs for thermal energy storage performance. In this paper, a series of shape-stabilized phase change materials (ss-PCMs) were engineered with three silica matrices as support and paraffin as PCMs through solution impregnation. These porous silica matrices serve as an ideal skeleton for shape stabilization of melted paraffin PCMs and yield desirable thermal properties of paraffin confined in silica pores. The textural and chemical properties, crystallization, interfacial interactions, and thermal properties and stability are investigated using various techniques including nitrogen adsorption-desorption isotherms, Fourier transformation infrared (FT-IR) spectroscopy, small- and wide-angle X-ray diffraction (XRD), and scanning electron microscopy, as well as differential scanning calorimetry (DSC) analysis. The effect of the pore structure on crystallization of PCMs was studied and a novel phase change was unveiled. The phenomena of melting point depression and confinement effects are in line with theoretical thermodynamics, and the physical state of paraffin at the interfacial region in mesopore channel is analyzed considering pore geometric factors, revealing a non-melting interface layer in MCM-41. This evaluation of various silica matrices may provide important and general implications for the fundamental understanding of porous silica ss-PCMs performance with cost-effective and readily available raw materials.