Periodic Reporting for period 1 - ToughMOF (Tailoring Metal-Organic Framework Glasses with Higher Fracture Toughness)
Reporting period: 2021-08-01 to 2023-07-31
This Marie Skłodowska Curie Action (MSCA) has investigated the interplay of composition, structure, and mechanical properties of zeolitic imidazolate framework (ZIF) glasses, ultimately paving the way for the development of more fracture-resistant materials without compromising the ability to fabricate bulk samples.
Among metal-organic frameworks (MOFs), ZIFs stand out as a crucial subset due to their exceptional glass-forming ability. This has enabled the vitrification of various ZIF crystals into glasses, with some of them maintaining the porosity of their parent crystals. Consequently, the emergence of ZIF glasses has attracted significant attention, primarily due to their distinct physical and chemical characteristics compared to traditional glass families. Despite the recent progress in understanding the structure-property correlations in ZIF glasses, there are still many unanswered questions regarding their mechanical properties, greatly hindering their potential engineering and functional applications.
In detail, the project aimed at exploring the structure vs. mechanical property relationship of ZIF glasses. To this end, the objectives of this MSCA have been achieved through the following key factors:
(a) Enable prediction and control of the ZIF glass structure: We aimed at producing ZIF glasses with different structures. The glass structures were controlled by compositional design combined with the change in the synthesis conditions. First, we investigated the modification effect of water on the glass forming behaviour of MOFs by combining experiments and ab initio simulations. Second, we investigated the structure change of ZIF-4 (the first ZIF to be melt-quenched to a glassy state) upon ion irradiation. We observed irradiation-induced disordering of ZIF-4 crystal and glass, which resulted in to the formation of a “forbidden state,” i.e. a state that is inaccessible through simple thermal treatment such as heating and cooling. Third, we investigated the structure of ZIF-4 upon hot compression which could potentially be a method to improve the mechanical properties.
(b) Understand the fracture behavior and mechanical properties of ZIF glasses with different structures: We systematically investigated the fracture behavior and properties of ZIF glasses with different structures. To this end, fracture simulations were carried out on two series of ZIF glasses: (i) ZIF-4 subjected to different degrees of irradiation, and (ii) ZIF-62 with different compositions, i.e. Zn(Im)2-x(BIm)x, where x = 0, 0.1 0.25 0.35 0.5 0.65 0.8. 1.0. The outcome of this object enables the establishment of the correlation of structure and mechanical properties in ZIF glasses.
(c) Reveal the origin of the low fracture toughness of ZIF glasses and identify suitable routes for improvement: The structure vs. mechanical property relationship of ZIF glasses was then explored by identifying the structure fingerprint responsible for the fracture patterns. To identify the atomistic origin of the fracture behavior of ZIF glasses, a new deep learning-based force field (DLFF) has been developed in this project. Furthermore, the influence of the structural parameters on the mechanical properties was clarified to facilitate the design of ZIF glasses with tailored fracture patterns.
The overall findings will help to enable the rational design of MOF glass materials with the ability to sustain higher stress and plastically deform without fracture. The effect of glass composition and post-processing routes on the atomic structure and microstructure has been identified, including irradiation treatment and control of the thermal and pressure history. The influence of the structural parameters on the mechanical properties has been clarified to facilitate the design of ZIF glasses with tailored fracture patterns.
Among metal-organic frameworks (MOFs), ZIFs stand out as a crucial subset due to their exceptional glass-forming ability. This has enabled the vitrification of various ZIF crystals into glasses, with some of them maintaining the porosity of their parent crystals. Consequently, the emergence of ZIF glasses has attracted significant attention, primarily due to their distinct physical and chemical characteristics compared to traditional glass families. Despite the recent progress in understanding the structure-property correlations in ZIF glasses, there are still many unanswered questions regarding their mechanical properties, greatly hindering their potential engineering and functional applications.
In detail, the project aimed at exploring the structure vs. mechanical property relationship of ZIF glasses. To this end, the objectives of this MSCA have been achieved through the following key factors:
(a) Enable prediction and control of the ZIF glass structure: We aimed at producing ZIF glasses with different structures. The glass structures were controlled by compositional design combined with the change in the synthesis conditions. First, we investigated the modification effect of water on the glass forming behaviour of MOFs by combining experiments and ab initio simulations. Second, we investigated the structure change of ZIF-4 (the first ZIF to be melt-quenched to a glassy state) upon ion irradiation. We observed irradiation-induced disordering of ZIF-4 crystal and glass, which resulted in to the formation of a “forbidden state,” i.e. a state that is inaccessible through simple thermal treatment such as heating and cooling. Third, we investigated the structure of ZIF-4 upon hot compression which could potentially be a method to improve the mechanical properties.
(b) Understand the fracture behavior and mechanical properties of ZIF glasses with different structures: We systematically investigated the fracture behavior and properties of ZIF glasses with different structures. To this end, fracture simulations were carried out on two series of ZIF glasses: (i) ZIF-4 subjected to different degrees of irradiation, and (ii) ZIF-62 with different compositions, i.e. Zn(Im)2-x(BIm)x, where x = 0, 0.1 0.25 0.35 0.5 0.65 0.8. 1.0. The outcome of this object enables the establishment of the correlation of structure and mechanical properties in ZIF glasses.
(c) Reveal the origin of the low fracture toughness of ZIF glasses and identify suitable routes for improvement: The structure vs. mechanical property relationship of ZIF glasses was then explored by identifying the structure fingerprint responsible for the fracture patterns. To identify the atomistic origin of the fracture behavior of ZIF glasses, a new deep learning-based force field (DLFF) has been developed in this project. Furthermore, the influence of the structural parameters on the mechanical properties was clarified to facilitate the design of ZIF glasses with tailored fracture patterns.
The overall findings will help to enable the rational design of MOF glass materials with the ability to sustain higher stress and plastically deform without fracture. The effect of glass composition and post-processing routes on the atomic structure and microstructure has been identified, including irradiation treatment and control of the thermal and pressure history. The influence of the structural parameters on the mechanical properties has been clarified to facilitate the design of ZIF glasses with tailored fracture patterns.
The work conducted throughout this fellowship was organized into five work packages (WPs). Under WP1, the fellow participated in the career and project planning of the project, which included data management planning, safety training, and initial instrument training at the host laboratory. Under WP2, the fellow finished the preparation and structural characterization of MOF glasses. Based on the results, the fellow published one journal paper associated with the effect of water on MOF glass. The resulting structures from WP2 were used for the fracture simulations. Under WP3, the fellow has published one journal paper associated with the effect of irradiation on the fracture behavior of ZIF-4. Another journal paper about the mechanical properties of ZIF-62 glasses with different compositions is underway. In WP4, the fellow established the structure fingerprints of ZIF glasses, which are responsible for their fracture behaviors. Beyond this, the fellow developed a new deep learning-based force field (DLFF) that aims at reproducing the structure and mechanical properties of ZIF glasses with relatively high accuracy, but a much lower computational cost than ab initio simulations. Under WP4, the fellow finished one journal manuscript associated with the new DLFF for simulating ZIF-4 glass, which is now under review. Another paper about predicting the fracture propensity of ZIF-62 glasses is in preparation. WP5 intended to enhance the fellow's research competencies and foster the dissemination of his knowledge and expertise to others, thereby facilitating knowledge transfer. Upon the implementation of this project, the fellow has published a total of 12 peer-reviewed journal papers. These papers were disseminated within the academic community through various channels, including email, LinkedIn, and Twitter. The research results have also been disseminated at three prominent international conferences: (1) The International Year of Glass Symposium (Aalborg, 2022); (2) The International Congress on Glass (Berlin, 2022); and (3) 2023 Glass and Optical Materials Division Annual Meeting (New Orleans, 2023).
Within this project, we demonstrated that the atomic structure and microstructure of MOF glasses can be tuned by composition variation and/or post-processing, which ultimately can be used to regulate their macroscopic fracture behaviors. The developed models and machine learning force field from this project will significantly benefit the researchers both in the MOF and glass communities. The ToughMOF project thus opens a new avenue for designing this type of glasses using a bottom-up approach and provides fundamental knowledge to address the bottlenecks of MOF glasses.