Professor Alan James Leadbetter passed away peacefully on 11 March 2019 in Exeter, aged 84, leaving his wife Brenda, two adult children, Andrew and Jane and two grandchildren.
1. Alan pointing out the hexatic structure of the cables on the Golden Gate Bridge in San Francisco during the ILCC Berkeley (1986).
Alan was born on 28 March 1934 in Southport. He graduated from Liverpool University with a BSc in Chemistry in 1954 and completed a PhD under the supervision of John E. Spice in 1957. He then spent two years at the National Research Council, Ottawa, Canada, as a post-doctoral fellow with Jim Morrison. They worked on low temperature heat capacity as a means of investigating structural disorder and phase changes in solids. In 1959 he moved to the University of Bristol as a Research Assistant. He was soon offered a lectureship in the Department of Physical Chemistry. In those days, the decision to offer a job was made simply by the Head of Department, Prof Douglas H Everett, MBE. He had enjoyed discussions with Alan and the promotion to lecturer was offered without formalities. Prof Everett always claimed that Alan had never been ‘knowingly’ interviewed and history confirms that he made a good decision. Alan continued to work on the thermodynamics and structural properties of disordered materials such as simple liquids and glasses. In particular, he set up an X-ray diffractometer and was able to demonstrate the structural origins of properties of crystals and glasses.
Alan’s interest in the role of disorder in materials brought him into contact with Cyril Hilsum and Peter Raynes at the Royal Signals and Radar Establishment at Malvern and with George Gray at the University of Hull. This initiated a new and substantial strand of his research, focussed on the fascinating mesophases formed by elongated molecules, ie liquid crystals. The new cyanobiphenyl compounds from Hull were generating excitement as some (eg 5CB) showed room temperature nematic phases which could be used for information display and, importantly, were UV stable because a troublesome double bond was absent. An X-ray investigation by the Leadbetter group found the ‘overlapping cores’ structure which explained the unexpectedly high clearing temperature of the cyanobiphenyls, despite the absence of the double bond; a useful insight for chemists aiming to understand the material properties.
In 1975, Alan took the chair of Physical Chemistry at Exeter University. Here, he led many X-ray diffraction studies of liquid crystal phases. The Hull group were producing materials that exhibited a nematic phase but with more ordered phases at lower temperatures. Using X-ray diffraction, the Leadbetter group identified these layered structures. Some were smectics and others were really crystals and the different variants were labelled from A to K. An elegant scheme was established for the formation of different phases by variation of translational order, molecular tilt and the orientational order about the long axes. At the time, there was some mild divergence between different groups about what letter was assigned to which structure. It was the comprehensive studies of Gray and Leadbetter that finally got everyone singing from the same hymn sheet.
Structural investigations of nematics and their precursor smectic phases continued to give insight as to how small changes in molecular structure influenced the packing of the molecules and their phase behaviour. Many interesting stories came out. In nematics, the strength of the smectic-like local ordering was measured by X-ray diffraction and was found to correlate well with the ratio of elastic constants (k33/k11) that is important in display cell performance. In the crystal smectic B phase, comprising layers with a hexagonal 2D structure, stacking transitions analogous to the well-known transitions of close packed spheres were found. Coexisting smectic layers with incommensurate repeat distances were found in Sm A systems. Crystal smectic B phases with in-layer modulations were studied. His methodology to extract the orientational order parameter from the equatorial arcs of a nematic diffraction pattern is now widely adopted. He also unravelled the mystery of the smectic D, which turned out not to be layered at all.
In the early 1970s neutron scattering techniques to measure the structure and dynamics of materials were emerging. Alan was an early adopter, using the spectrometers at reactors at Harwell and Aldermaston. He applied Incoherent Quasi Elastic Neutron Scattering methods to study the dynamics of rotator phases in molecular crystals. Intensity and energy resolution were limitations on these reactors but in 1974 the research reactor at the Institut Laue Langevin, Grenoble, France was made available to UK scientists and provided the high energy resolution necessary to study the slow diffusive motions in liquid crystals. Partnership with the chemistry group at Hull was also essential for the supply of specifically deuterated molecules. Alan’s group characterised the anisotropic translation diffusion and the complex internal and external molecular rotation in several nematic and smectic systems. At the same time, studies of small molecules (eg tertiary butyl cyanide) were studied in detail to explore the role of internal rotations in the onset of rotator phases. He also developed neutron diffraction method to utilise the differently deuterated versions of the same molecule to obtain a more detailed picture of the packing in cyanobiphenyl smectics.
Alan was closely involved in the inception of the Liquid Crystals journal. An initial suggestion by Geoffrey Luckhurst to Taylor and Francis led to detailed discussions between Alan, Geoffrey and Michael Dawes from the publisher. They invited Ed Samulkski to be co-editor with Geoffrey and an impressive editorial board was assembled for the new journal. The rest is history, with the first issue in February 1986 and then regular, high-standard, interdisciplinary issues which still continue .
In 1982, Alan joined the Rutherford Appleton Laboratory as Associate Director, Head of Science Department and Head of Neutron Division. Here, he oversaw the completion of the ISIS pulsed neutron source with the first neutrons being extracted in December 1984. This was a very difficult time for science funding, and the possibility that a pulsed source could rival a steady state reactor was unproven. It was a case of steering through troubled waters but by 1988 ISIS was a world class facility with an excellent and expanding science program, based on innovative neutron (and muon) instruments that complemented those at reactors. For instance, specular neutron reflection for the study of surface structure worked rather well at a pulsed source and the CRISP instrument established neutron reflectivity as a vital tool for Surface Chemistry.
In 1988 Alan was appointed as Director of Daresbury Laboratory where he helped to establish the Synchrotron Radiation Source as a leading international research facility. Its successor, Diamond, has continued in this direction. He officially retired from Daresbury in 1994 and, in the same year, was awarded the honour of Commander of the British Empire (CBE). Also, in that year, he moved on to become Director of Science at the Institut Laue Langevin from which he really did retire in August 1999.
Following his successful career as an academic, he was equally successful at the challenges of managing scientific facilities. He would make meetings work. Thousands of researchers now benefit from the facilities that Alan headed. He was an effective leader who enthusiastically promoted science. Even in the top jobs, he remained approachable and was often seen talking to facility users, at the experimental stations as much as in formal meetings. He was strongly of the opinion that science should be fun, and he did much to make it so. His warm personality and sense of humour will be remembered.