Controlling Thermal Expansion: a Metal Organic Frameworks Route

TL;DR

This study introduces a novel method using metal organic frameworks (MOFs) and molecular dynamics simulations to control and switch the thermal expansion of materials across negative, zero, and positive regimes by adsorbate molecules.

Contribution

It presents the first conceptual design and atomistic analysis of MOF-based systems for tunable thermal expansion through host-guest interactions.

Findings

Adsorbate molecules can colligatively control MOF thermal expansion.

Changing adsorbates induces positive, zero, or negative expansion.

Detailed mechanisms involve ligand and junction distortions.

Abstract

Controlling thermal expansion is an important, not yet resolved, and challenging problem in materials research. A conceptual design is introduced here for the first time, for the use of MOFs as platforms for controlling thermal expansion devices that can operate in the negative, zero and positive expansion regimes. A detailed computer simulation study, based on molecular dynamics, is presented to support the targeted application. MOF-5 has been selected as model material along with three molecules of similar size and known differences in terms of the nature of host--guest interactions. It has been shown that adsorbate molecules can control, in a colligative way, the thermal expansion of the solid, so that changing the adsorbate molecules induces the solid to have positive, zero or negative thermal expansion. We analyze in-depth the distortion mechanisms, beyond the ligand metal junction to cover the ligand distortions, and the energetic and entropic effect on the thermo-structural behavior. We provide an unprecedented atomistic insight on the effect of adsorbates on the thermal expansion of MOFs, as a basic tool towards controlling the thermal expansion.