Amorphous materials are disordered materials that lack long-range order. They often have greater applicability than crystalline materials, due to their improved processability and the possibility to be shaped into grain-boundary free bulk morphologies. In particular, amorphous microporous materials have potential for application as membranes for chemical separations, a technology that would require up to 90% less energy than distillation. Examples of these materials are porous organic polymers (POPs) and amorphous Metal‒Organic Frameworks (aMOFs). However, these materials are much more challenging to characterise compared to their crystalline counterparts, and their structure-property relationships are difficult to discover. In this scenario, molecular simulations can provide structural models that complete the missing information from experiments and help both rationalise the material’s behaviour through atomistic level understanding and derive design rules to direct future experimental efforts.
In my PhD, I used simulations to investigate the bulk structure of several POPs and aMOFs. In the case of POPs, I applied a well-established computational approach to understand the performance of two new families of linear spirocyclic polymers in comparison to PIM-1 (archetypal microporous polymer in literature) in separating crude oil. I then adapted the computational approach to the new family of aMOFs. Initially, to validate the workflow, I built bulk models of amorphous zeolitic imidazolate framework-4 (aZIF-4), a prototypical aMOF for which I could successfully reproduce experimentally observed properties. Then, I expanded the workflow to cover other MOF chemistries, such as aMIL-100(Fe), Fe-BTC and aUiO-66. I used the obtained models to understand, at a molecular level, the effect of defects and disorder on the final structure and porosity of Fe-BTC and I investigated the effect of different linkers on the final porosity of aUiO systems.
The approach used does not require any experimentally derived data for structure construction and refinement, allowing the structure prediction of hypothetical amorphous microporous materials that have not been synthesised yet in the lab. This approach opens the possibility to large scale screenings and derivation of design rules for porous polymers and aMOFs, with the future goal of finding promising candidates with properties tailored for specific applications.