The FlexMat group's research focuses on understanding and exploiting unusual properties of flexible framework materials. Central to this work is the ability to reveal the atomic structure—how atoms are arranged in 3D space—using crystallography. Knowing the atomic structure allows us to design better materials, and push materials with unique properties towards application.
In our work we make significant use of large-scale national and international neutron and synchrotron X-ray facilities. You can learn more about our research below, explore publications, and read research highlights in the the blog.
From 2015–17 Andrew was a postdoctoral scientist at the ESRF, Europe's brightest X-ray source, based at the high pressure diffraction beamline ID27. Before this he completed both undergraduate and postgraduate studies at the University of Oxford, the latter under the supervision of Prof. Andrew L. Goodwin. In 2016 he received the ESRF Young Scientist Award and PANalytical PCG Thesis Prize from the British Crystallography Association.
Alongside research, Andrew is an advocate for openness and diversity in science.
Flexibility is something that we encounter in everyday life. Elastic bands are flexible: when stretched the material from which they are made deforms easily. By contrast, some materials are extremely inflexible. What determines if a material is flexible is how the building blocks making up the material are arranged and held together. The group's research aims to make, understand and apply structural flexibility in a class of materials known as coordination polymers.
A key goal of our research is to find and characterise flexible materials with very unusual structures or mechanical properties. One such unusual property is negative linear compressibility (NLC). This occurs when, under uniform pressure, a material actually expands along one or more directions during the process of densification, like a folding wine-rack. As rare as it is counterintuitive, such "negative compressibility" behaviour might have application in the design of ultra-sensitive pressure sensors, “smart” responsive devices, artificial muscles and actuators.
This, and other, unusual behaviours arise because of structural topology—how building blocks are arranged. So, for example, the model auxetic structure in this demonstration video has a specific topology that means it expands as it is stretched. As materials chemists our aim is to design these counterintuitive properties on the atomic scale. We do this using coordination polymers—scaffold-like hybrid materials synthesised by self-assembly of cationic metal nodes with anionic molecular linkers in one, two or three-dimensions.
As crystallographers, we use in-situ diffraction techniques to reveal structural features that give rise to these unusual properties. Our research makes use of variable-pressure and variable-temperature single crystal and powder X-ray or neutron diffraction. Large scale national and international research facilities—such as those that produce brilliant synchrotron light or pulsed beams of neutrons—offer unique access to experiments that reveal unprecedented atomic detail using diffraction, but also a range of other techniques including EXAFS, SANS and spectroscopic measurements that can help aid our understanding of a material's properties.
Effect of Extra-Framework Cations on Negative Linear Compressibility and High Pressure Phase Transitions: A Study of KCd[Ag(CN)2]3
A. B. Cairns*, J. Catafesta, P. Hermet, J. Rouquette, C. Levelut, D. Maurin, A. van der Lee, V. Dmitriev, J.-L. Bantignies, A. L. Goodwin, and J. Haines
Journal of Physical Chemistry C 124, 6896–6906 (2020)