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

<p></p><p>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.</p><p></p>

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

<p></p><p>Soft porous crystals (SPCs) can undergo large-amplitude phase transitions under external stimulus such as mechanical pressure, gas adsorption, and temperature while retaining their structural integrity. During the gas adsorption process, the generated latent heat is needed to be effectively removed. Thus, understanding the effect of phase transition on the thermal transport in SPCs becomes extremely important for their applications in storage and separation applications. </p> <p>In this paper, taking isorecticular DUT series as an example, the evolution of the thermal transport in SPCs during the phase transition from the large pore (lp) phase to the narrow pore (np) phase is comprehensively investigated by molecular dynamics (MD) simulations together with the Green-Kubo method. After the phase transition, an abnormal thermal transport property is found in the np phase of DUT materials. We find that although the transformed np phase of DUT-48 has a density much larger than its parent phase, the thermal conductivity of its np phase is smaller than its lp phase. This result is in contrast to the previous finding that SPCs with larger density possess a larger thermal conductivity. However, as 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 is in accordance with the previous finding. This complicated effect of phase transition on thermal transport in SPCs can be explained by the porosity-dominated competition mechanism between the increased volumetric heat capacity and the aggravated phonon scattering during the phase transition process. Overall, the finding extracted from the present study can greatly expand current knowledge about the thermal conductivity of metal-organic frameworks that is previously found to grow usually with increasing porosity.</p><br><p></p>

The intrinsic thermal transport property of biphenylene network and the influence of hydrogenation: A first-principles study

Utilizing first-principles calculations combined with phonon Boltzmann transport theory up to the fourth-order anharmonicity, we systematically investigate the thermal transport properties of biphenylene network [BPN, recently synthesized experimentally by Fan...