On the Potential Auxeticity of Covalent Organic Frameworks

Muscat G. A.1, Grima, J.N.1,2, Farrugia P. S.1, Cardona M. A.1, Gatt R.1
1 Metamaterials Unit, Faculty of Science, University of Malta, Msida, MSD 2080, Malta
2 Department of Chemistry, Faculty of Science, University of Malta, Msida, MSD 2080, Malta
grace.muscat.16@um.edu.mt

Introduction

Covalent Organic Frameworks (COFs) are a class of engineered porous, molecular crystals composed of organic building blocks linked together through covalent bonds.1 These compounds are characterised by a large surface area, tuneable pore size and structure, low density and structure customisation.2 Due to such properties, COFs have versatile applications such as adsorbents, for the removal of organic pollutants,3 & metal ions from aqueous solutions4 and the capturing of gas molecules.5 Current mechanical investigations on the potential of observing auxeticity in COFs have been confined to 2D COFs, where Poisson's ratio of approaching -1.5 have been demonstrated.6 Conversely, no prior literature on the mechanical properties of 3D COFs has been published. In view of this, a cohort of 3D COFs were studied, and COF 320 was identified as a potentially auxetic 3D COF using molecular simulations in Materials Studio 6.1.7 A method to study the effect of guest molecules was developed to mimic the effect of air on caged systems, thereby better predicting the potential auxetic properties of experimental structures. This study offers insight into the potential auxeticity of existing 3D COFs, paving the way for the design of other inherently auxetic 3D COFs.

Methodology

1. Literature Search

•Identification of existing 3D COFs

2. Sorption Simulations