Effect of Phase Transition on the Thermal Transport in Isoreticular DUT Materials

Soft porous crystals (SPCs) or flexible metal-organic frameworks have great potential applications in gas storage and separation, in which SPCs can undergo phase transition due to external stimuli. Thus, understanding the effect of phase transition on the thermal transport in SPCs becomes extremely crucial, because the latent heat generated in aforementioned applications is needed to be effectively removed. In this paper, taking the isorecticular DUT series as an example, the thermal transport property of SPCs during the phase transition from the large pore (lp) phase to the narrow pore (np) phase is comprehensively investigated by molecular dynamics simulations together with the Green-Kubo method. According to our calculations, all DUT structures exhibit an ultralow thermal conductivity smaller than 0.2 Wm^-1K^-1. In addition, we find that the effect of phase transition on the thermal transport property of different DUT materials considered here strongly depends on their porosity. As for DUT-48, its lp phase has a thermal conductivity larger than that of its np phase. However, in other DUT materials, i.e, DUT-47, DUT-49, DUT-50, and DUT-151 the thermal transport property of their lp phase is found to be weaker than that of their np phase. This complicated effect of phase transition on the thermal transport in SPCs can be explained by a porosity-dominated competition mechanism between the increased volumetric heat capacity and the aggravated phonon scattering during the phase transition process.