Molecular dynamics simulation of thermal properties and morphological stability of biochar-based composite phase change materials

Biochar-based composite phase change materials represent a novel class of composites with significant potential in phase-change energy storage technology, attributed to their excellent shape stability and enhanced thermal conductivity. To investigate the influence of biochar on the thermal properties of phase change materials and the underlying microscopic mechanisms, a molecular model of stearic acid /corn stalk biochar composite phase change materials was developed. Through molecular dynamics simulations, we analyzed the effects of temperature and biochar mass fraction on thermal conductivity, specific heat capacity, vibration density of states, internal energy composition, mean orientation shift, and self-diffusion coefficient of composite phase change materials. The results demonstrated that the incorporation of biochar significantly increased the specific heat capacity and thermal conductivity of stearic acid, with thermal conductivity positively correlated with the biochar mass fraction. Unlike graphene carbon nanomaterials, corn stalk biochar's phonon heat transfer is predominantly influenced by phonon vibrations in the 20–50 THz frequency range, exhibiting effective phonon coupling with SA, thereby enhancing heat transfer efficiency. The addition of corn stalk biochar increases the assembly bond energy and static energy of the composite system, reduces the diffusion coefficient and molecular distance, strengthening intermolecular connections and promoting shape stability during phase transitions. Specific functional groups within corn stalk biochar can form hydrogen bonds with stearic acid, further enhancing the thermal conductivity and overall stability of composite phase change materials.