Abstract
Miniaturization is a key aspect of materials science. Owing to the increase in quality experimental and computational tools available to researchers, it has become clear that the crystal size and morphology of porous framework materials, including metal-organic frameworks and covalent organic frameworks, play a vital role in defining the physicochemical behaviour of these materials. However, given the multiscale and multidisciplinary challenges associated with establishing how crystal size and morphology affect the structure and behaviour of a material–from local to global structural modifications and from static to dynamic effects–a comprehensive mechanistic understanding of size and morphology effects is missing. Herein, we provide our perspective on the current state-of-the-art of this topic, drawn from various complementary disciplines. From a fundamental point of view, we discuss how controlling the crystal size and morphology can alter the mechanical and adsorption properties of porous framework materials and how this can impact phase stability. Special attention is also given to the quest to develop new computational tools capable of modelling these multiscale effects. From a more applied point of view, given the recent progress in this research field, we highlight the importance of crystal size and morphology control in drug delivery. Moreover, we provide an outlook on how to advance each discussed field by size and morphology control, which would open new design opportunities for functional porous framework materials.
Highlights
Reports of novel crystalline materials, including metal-organic frameworks (MOFs) and covalent organic frameworks (COFs), are ubiquitous in the literature
This opens a wealth of new possibilities to material engineering and design, and opens questions to how the crystal size and morphology affect important properties?
In DUT-49 adsorption-induced structural contraction is found to be absent for samples with mean crystal sizes below ca. 1 μm. In both cases this behaviour is primarily associated with the stiffening of the material and enhanced activation barriers for structural transitions in the solid state
Summary
Reports of novel crystalline materials, including metal-organic frameworks (MOFs) and covalent organic frameworks (COFs), are ubiquitous in the literature. In both cases this behaviour is primarily associated with the stiffening of the material and enhanced activation barriers for structural transitions in the solid state (discussed in Mechanical Properties and Altering the Phase Stability in Soft Porous Crystals Through Crystal Size Engineering). A recent study demonstrates that ZIF-8 becomes more flexible with decreasing crystal size by probing micro and nanocrystals with nanoindentation (Tiba et al, 2019) The fact that this trend is opposite to the evolution of adsorption-induced stress shows how important a global analysis of these effects with respect to mechanical properties of the host and adsorption properties of the fluid as a function of crystal size are. This will change in the near future, because the information about the carrier design gained from such studies is essential to boost the field of nanomedicine and to facilitate the transition of nanodrugs from bench to bedside
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