Obituary: Professor John Sherwood, pioneer in fields of organic crystal growth and solid-state chemistry

Crystals are periodic structures of 3D ordered molecules, though they can be imperfect due to missing or misplaced molecules or the same when dimensionally extended.

Such defects are highly important as they affect the material’s properties and, hence, performance.

Understanding, characterising and defining the crystal growth of these materials and, in particular, the pivotal inter-relationship between their growth conditions, defect types and resulting properties owes so very much to the seminal work, spanning six decades, of Professor John N Sherwood of the University of Strathclyde, who died, aged 87, last month.

John was born in Redruth, Cornwall, the son of William Henry Cyril, a teacher, and Lily Rose, who worked for a local family. When he was 12 the family moved to Bradford. He attended Aireborough Grammar School then studied chemistry at Bede College, University of Durham. There, he met his future life partner, Margaret Enid Shaw from Huddersfield, who was studying at Neville’s Cross College.

It was at Durham, through his PhD studies under the supervision of Dr Sam Thomson, that John became interested in the crystal growth of organic materials. By growing large single crystals of anthracene he was able to quantify, for the first time, the key roles played by point and line defects in facilitating the material’s molecular mobility.

John and Margaret married in 1958 and, following post-doctoral work at the University of Hull, he was appointed lecturer in chemistry at the Royal College of Science and Technology in Glasgow, later the University of Strathclyde.

At Strathclyde, he established the first research centre into the crystal growth and perfection of organic single crystals with the aim of producing ultra-pure, highly perfect and large single crystals. The crystal quality achieved by the centre has yet to be matched even today.

He studied in fine detail the mechanical behaviour of organic materials ranging from the “normal” characteristics of brittleness, through “waxiness” with increased plasticity, to the extreme case of “plastic crystals”, which can even deform under their own weight.

Innovative collaborative work with Danish researchers revealed that molecules in the former two categories diffused slowly by point defect motion. In contrast, diffusion in the plastic crystals occurred much faster, being facilitated by far more complex defect structures.

In the late 1970s, John was awarded his DSc, promoted to a Professorship and elected as a Fellow of both the Royal Society of Edinburgh and the Royal Society of Chemistry.

His group attracted a steady stream of researchers from India and built up a very strong alumni there. He made many visits to India giving lecture tours, attending conferences and provided advice to their crystal growth community. John and Margaret often travelled to India together and greatly enjoyed the country’s stunning architectural history and vibrant culture.

John built up a research team at the new Daresbury synchrotron radiation source and, together with other university groups, built up new facilities for characterising crystals.

His group exploited the synchrotron’s unique capabilities to examine in-situ the migration of defects during the deformation of explosives. This groundbreaking work provided a critical insight into the potential behaviour defects in these materials at the higher stresses involved in shock initiation and, through this, their operational stability.

Through his membership and, later, chairmanship of the research council’s Synchrotron Radiation Facility Committee, John was a great champion for the UK’s synchrotron radiation scientists. As a member of the council’s Science Board he played a major role in making a case for the establishment of the European Synchrotron Research Facility at Grenoble and, ultimately, today’s Diamond light source at Harwell.

Industry uses crystal growth to both isolate and purify materials and to prepare large crystals for electronic device applications. Careful control of the crystal growth process is vital to ensure the quality and efficacy of crystalline ingredients.

John’s group worked extensively with industry on many projects: improving product purity for polymer fibres (DuPont, ICI); controlling wax crystallisation in fuels in cold weather (Exxon); and solving problems in the crystallization of pharmaceutical particulates (Astra-Zeneca, GSK, Pfizer and Roche).

Strategic research, inspired by industrial need, led to more fundamental work, notably in secondary nucleation where he addressed the issue of why some crystals grew whilst others did not. This is a significant problem in industrial processes as it results in a wide dispersion of particle sizes. Through a multi-technique approach his group quantified the role of the different types of defects in both reducing and promoting crystal growth.

He also developed new approaches for the preparation of organic crystals for fibre-optic communications systems demonstrating strong correlation between their optical performance with both polymorphic form and crystal perfection. Many new compounds were prepared with both excellent optical properties and high potential for device performance.

John published more than 250 research papers and his work has made a massive contribution to our understanding of the nature and properties of the imperfections in organic crystals providing, in turn, a route map as to how their desired perfection can be achieved.

He also contributed widely to the scientific community through research council work, industrial consultancy and his leadership activity within the crystal growth community. He was a founder member of the British Association for Crystal Growth and, as its Chair, led its re-vitalisation in the mid-1990s, enhancing its inclusivity and scientific diversity, and promoting emerging talent through his instigation of the Young Scientist Award.

John Sherwood was an excellent mentor to both students and colleagues. He readily and unconditionally provided critical appraisals of their scholarly work, encouraging them to collaborate and gain wider international experience. Such support, helped them to develop their own career pathways into leading positions within both academia and industry.

Over the twenty year period up to 1998, he held a succession of senior academic offices. He was elected to many of them, including the most senior post open to staff, Vice-Principal. He won the confidence of his fellow academics and the respect of all those he worked with by his courtesy and personal warmth to all, regardless of their position, and by the sure and certain knowledge that he stood for the core values of the academic community, even in challenging times.

He retired into emeritus status in 2002 but continued to write and publish his work for many more years, only stopping quite recently when ill health took its toll.

John Sherwood was, without doubt, a giant within the organic crystal growth and solid-state chemistry fields (and his presence will be greatly missed by the community to which he made such a significant contribution.

John’s wife Margaret predeceased him earlier in 2020 and he grieved deeply at her loss. He is survived by his daughters Rosemary and Jennifer, his four grandchildren, one great grandchild and his younger brother David.

KEVIN ROBERTS

Brotherton Professor of Chemical Engineering at the University of Leeds