Assessing negative thermal expansion in mesoporous metal–organic frameworks by molecular simulation

Abstract

Molecular simulations reveal that mesoporous metal–organic frameworks display large volumetric negative thermal expansion, which has a considerable effect on mechanical stability, outlining an alternative application for these ultra-porous materials.

Unravelling thermal stress due to thermal expansion mismatch in metal–organic frameworks for methane storage

“…A positive correlation between the magnitude of the thermal expansion coefficient and the pore size has already been demonstrated in other studies focusing on a particular topology 15,27 or on a limited set of frameworks. 17,18 Not surprisingly, we nd for our materials a similar result in Fig. 2 where the absolute value of the thermal expansion coefficient as a function of the void fraction is displayed.…”

“…Computational studies corroborate these ndings. 15,18,27,28 Thermal stress due to thermal expansion mismatch has received even less attention, 29 but it was mentioned in the context of MOF thin lm applications. 30,31 However, it could also be imagined to play a role when MOFs are used in conned environments such as volume-limited storage tank applications for natural gas and hydrogen storage.…”

Reversible switching between positive and negative thermal expansion in a metal–organic framework DUT-49

“…17,[22][23][24][25] NTE is a thermodynamic phenomenon and has been studied for a handful of MOF structures so far; however several aspects related to thermal transformation of MOFs are poorly understood. The largest NTE value of a V ¼ À87.6 MK À1 was theoretically predicted for MOF-399 by Evans et al 17 However, it is not accessible experimentally because of the low mechanical stability of the framework. Interestingly, only a few substances show both PTE and NTE in the entire temperature range.…”

Engineering micromechanics of soft porous crystals for negative gas adsorption

“…Interestingly, many of these crystalline frameworks demonstrate unusual mechanical properties 6 including negative Poisson's ratio 7 or negative linear compressibility 8 and are thus considered nanoscopic mechanical metamaterials. 6 Notably, the molecularscale architecture of these "meta-MOFs" routinely produces responses difficult to engineer on the macroscale, such as negative thermal expansion (NTE) [9][10][11] and other optical phenomena. 12,13 While most of these properties are based on elastic deformations of the crystal lattice, several MOFs are known to undergo large scale inelastic transitions under preservation of the framework connectivity.…”