A molecular dynamics study of the effects of crystalline structure transition on the thermal conductivity of pentaerythritol as a solid-solid phase change material

A typical polyol that experiences solid-solid phase transitions, pentaerythritol (PE) has been proposed as a promising phase change material candidate for latent heat storage pertinent to the temperature range for industrial waste heat recovery. Upon increasing the temperature to over the solid-solid phase transition point (similar to 459 K), body-centered tetragonal crystalline structure of PE (alpha phase) is transformed into orientationally disordered face-centered cubic crystalline structure (gamma phase). The thermal conductivity of PE at both alpha and gamma phases is of great practical interest. In this work, the in situ X-ray diffraction and Fourier transformer infrared spectroscopy were used to characterize the crystalline structure transition of PE, in combination with the differential scanning calorimetry results. Molecular dynamics simulations were performed to elucidate the relationship between the thermal conductivity variation of PE and its crystalline structures at the atomic level. It was found that after the alpha-to-gamma phase transition, the rearrangement and rotation of the O-H center dot center dot center dot O bonds lead to indeterminate positions of the O and H atoms in the y phase. The destruction and weakening of the hydrogen bonds can be the major change in the crystalline structures, leading to the reduction of the thermal conductivity of PE by a half after the alpha-to-gamma phase transition. (C) 2019 Elsevier Ltd. All rights reserved.