Atomistic insights into the effects of hydrogen bonds on the melting process and heat conduction of erythritol as a promising latent heat storage material

Molecular dynamics (MD) simulations were performed to give insights into the effects of hydrogen bonds (HBs) on the melting process and heat conduction of erythritol as a promising latent heat storage material. First, among four force fields (GAFF, GROMOS, OPLS and CHARMM), the applicability of GROMOS force field was verified by comparing the predicted density and heat capacity of erythritol at various temperatures of interest with the measured values. The microscopic melting process of erythritol was simulated using the interface/NPT method, leading to a predicted melting point of ~394 K that agrees well with the measured value (~392 K). It was demonstrated that the variation of HBs energy associated with changes of molecular structure is the primary contribution to the latent heat. Upon melting, the strong inter-molecular HBs in solid erythritol break off and form weaker intra- and inter-molecular HBs in the liquid phase. In addition, non-equilibrium MD simulations were performed to study the microscopic heat conduction in erythritol molecules and to examine the dependence of the van der Waals (vdW) and Coulomb heat currents on the interatomic distance. It was revealed that the heat transfer capability of HB interactions is better than those of the Coulomb or vdW interactions. In the solid phase, the amount of heat transfer through HBs becomes greater with increasing the number of HBs. The results shed light on a promising approach to improving the latent heat storage capacity and thermal conductivity of erythritol (and other sugar alcohols) by manipulating the number and strength of HBs.