Nanofluidic Energy Absorption of Metal-Organic Frameworks

Smart materials possessing efficient and controllable energy absorption characteristics are a critical step forward in the engineering of next-generation protection technologies against impact, vibration, and blast. For instance, such materials technology can provide soldiers and police with body armours or bomb suits that offer better protection than ever before. Similarly, it can prevent human body injuries in sports and vehicle crashes, or enhance comfort and reduce maintenance costs used as vibration-proof damping materials.

However, in order to design protection systems, engineers currently only have a very limited toolbox based on energy absorption mechanisms developed decades ago, such as plastic deformation of materials, buckling of structures, polymer damping, etc. These mechanisms are useful but have important intrinsic limitations in energy absorption density (i.e. capacity per unit mass), response rate, and most of them cannot be reused or controlled to cope with varying loading conditions. These hinder the delivery of the full potential of energy absorption for the benefit of society. The recent rise of nanoscience has allowed novel approaches to be developed and exciting new performances to be imagined for the first time.

The objective of the fellowship is to lay the foundations of a new era in energy absorption and protection systems by leveraging a multidisciplinary approach engaging the nanoscale material chemistry and physics. The underpinning novelty is to exploit a fundamentally new energy absorption phenomenon through the process of mechanically squeezing non-wetting liquid into extremely small spaces in a controllable way. These spaces will be made so small that the liquid, for example, water, must split into water molecules to be able to enter and flow inside, and therefore a substantial amount of mechanical energy can be absorbed during this process. A sponge-like porous material called Metal-Organic Frameworks (MOFs) will be used which provides these kinds of small pores. Their pore size is at the nanoscale, i.e. one-billionth of a metre, comparable to the size of water or other liquid molecules.

The idea is ground-breaking as it has the potential to lift the current major limitations of energy absorption systems, e.g. to achieve unprecedented efficiency, reusability, and controllability. One can design the nanoscale liquid intrusion and extrusion behaviours to achieve desired performances such as reusability, or even control their performance in real-time by applying external stimuli: rather than simply being a passive shield, it can provide protection that is customized for different situations and individual's body conditions.

The applicant has developed novel experimental techniques to apply and measure sudden shocks onto the system that replicate those experienced in practical impact, which also allows in-situ material characterisation and the application of physical stimuli. With experiments on material systems of different structures and properties, the fellowship aims to fully understand how liquid molecules transport under intensive pressure waves inside MOFs as a flexible and controllable nanoconfinement. It has the potential to revolutionize energy absorption materials and enhance our knowledge of MOF mechanics and nanofluidics. This will in turn benefit many sectors of engineering and society in the long term.