Abnormal Effect of Phase Transition on Thermal Transport in Soft Porous Crystals

Soft porous crystals (SPCs) have attracted a lot of attention recently due to their great potential for a wide range of gas storage and separation applications. They can undergo large-amplitude phase transitions under external stimulus such as mechanical pressure, gas adsorption, and temperature while retaining their structural integrity. However, the thermal conductivity of SPCs is usually very low, owing to the porous structure and weak coordination bond, which would heavily influence their work performance. Hence, understanding the thermal transport in SPCs especially considering their dynamic features becomes extremely crucial. In this paper, taking the isorecticular DUT series as an example, the effect of phase transition from the large pore (lp) phase to narrow pore phase (np) on thermal transport in SPCs is comprehensively investigated by molecular dynamics (MDs) simulation together with the Green-Kubo method. According to our calculations, all DUT structures exhibit an ultralow thermal conductivity (). Specifically, we demonstrate here that the np phase of DUT-48 crystal after phase transition has a larger density but owns a smaller thermal conductivity. This abnormal effect of phase transition is in contrast to the previous finding that the SPCs with larger density possess a larger thermal conductivity. For other DUT crystals including DUT-47, DUT-49, DUT-50, and DUT-151, the np phase is found to have a higher thermal conductivity than their lp phase counterpart, which are as expected. This complicated effect of phase transition on 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. This finding is expected to fill the gap in understanding the complicated effect of phase transition on the thermal transport in SPCs.