Anti-leakage mechanism of silica–paraffin material for building energy saving: Role of silica–paraffin interactions

Abstract

Phase-change materials (PCMs) are extensively used in passive renewable energy systems, yet the leakage of paraffin wax during phase transitions poses significant challenges to their practical application. Integrating silica porous structures with paraffin wax PCMs has shown potential to mitigate leakage, but the interactions between paraffin and silica, particularly their influence on paraffin diffusion at varying temperatures, remain critical. In this work, molecular dynamics simulations involving over 70 000 atoms are conducted to explore the effects of single and adjacent silica nanoparticles on paraffin wax behavior across different temperatures. A novel approach to centralize paraffin wax molecules is introduced to enhance dynamic analysis. The results highlight two primary roles of silica nanoparticles: 1) redistributing paraffin wax for tunable mobility and 2) anchoring long-chain paraffin molecules on silica surfaces, thereby restricting their movement. Also, the diffusion coefficient for each case is also calculated. Furthermore, paraffin near silica surfaces is categorized based on relative distance into a “dense paraffin shell” ($<$5 Å) and a “loose paraffin shell” (10–15 Å). The loose paraffin shell exhibits high sensitivity to temperature changes. These findings provide valuable insights for designing anti-leakage PCMs and offer a pathway to developing advanced energy-efficient building materials.