We are all familiar with elastic bands and other soft, rubbery materials, but familiarity should not diminish our surprise at their properties. What other solids can be stretched many times their original length without breaking, then returned perfectly to their original shape?
The theoretical physicist Mark Warner, who has died aged 69 of cancer, not only explained the behaviour of existing soft materials but also predicted the existence and properties of entirely new classes of them – not just once but several times. He imagined the consequences of combining the long, chainlike molecules that make up “elastomers”, such as rubber, with the smaller, rodlike molecules that are found in all liquid-crystal displays, for example on smartphones.
By intuitive reasoning and theoretical calculation he realised that when flexible chains and rods are linked (rather like a multi-pendant necklace) they form materials with entirely new emergent properties, that defy simple classification into one of the traditional states of matter. Though solid overall, these “liquid crystal elastomers” show extreme softness in specific, liquid-like directions.
His subsequent calculations predicted that by incorporating certain dye molecules, they could be made to completely change shape in response to weak stimuli, including visible light. This has opened a new technology for creating optically actuated switches and artificial muscles.
Exploiting mathematics that Einstein had used to describe the curvature of spacetime owing to gravity, Mark calculated that pliable sheets of these new materials could be designed with an imprinted molecular patterning that would cause them to form complex shapes, otherwise impossible to manufacture. Spontaneous folding into these shapes could be triggered by small changes in lighting or temperature – “The material is the machine” became his mantra.
He also showed how inclusion of molecules with chirality, or “handedness”, enables the design of mechanically tuneable rubber lasers, and of membranes that could separate otherwise identical molecules of opposite handedness. This problem of chiral selectivity goes back to the work of Louis Pasteur and remains crucial in the pharmaceuticals industry.
Each of the astute and imaginative theoretical foresights that Mark arrived at in Cambridge were later confirmed experimentally, through collaborations elsewhere in the UK and Germany, especially with Heino Finkelmann of the University of Freiburg; these opened up new scientific and technological avenues. Mark’s book, Liquid Crystal Elastomers, co-authored with his longstanding collaborator and colleague Eugene Terentjev, became the standard research text in the field.
This work was recognised by Mark’s election to the Royal Society in 2012, and the award of the Humboldt prize in 2000 and the Europhysics prize in 2003 (both with Finkelmann). Alongside his work on elastomers, Mark made important contributions to many other areas of science, including neutron scattering and the mechanics of foams.
Much of his groundbreaking research was shared with early-career scientists; Mark’s supervision of his many graduate students and postdoctoral researchers was an unflagging model of generous and selfless mentoring.
He was equally determined about physics education, and a founding director of the Senior Physics Challenge, a national project that provides intensive theory and laboratory classes at Cambridge to gifted school students.
That experience led Mark to a much larger vision. Believing that UK school pupils lacked opportunities to study physics at a sufficiently quantitative level, preventing many of them from accessing the best that higher education could offer, Mark sought a personal interview with Michael Gove, then education secretary, to explain the problem. A resulting grant from the Department for Education launched Isaac Physics, a nationwide resource of graded physics problems and methods, supported by online tutorials, automatic marking and residential events.
More than 200,000 pupils and their teachers in more than 3,000 schools have participated in the scheme, started by Mark and Lisa Jardine-Wright in 2013, and for which in 2019 they were awarded the Institute of Physics’ Lawrence Bragg medal.
Born in Wellington, New Zealand, the son of Gunther and Patricia (nee Raven), a secondary and primary schoolteacher, respectively, Mark studied at Auckland grammar school. From there he went to Corpus Christi College, Cambridge, where he gained his first degree in 1974.
After a PhD at Imperial College London (1976), under the supervision of Sir Sam Edwards, he worked as an IBM research fellow in San Jose, California, and then at the Rutherford Appleton Laboratory near Oxford. In 1986 he returned to Cambridge, initially as a lecturer, and in 2001 was appointed professor. At Corpus Christi he was senior tutor (1992-97) and a life fellow.
In 1977 he married Adele Matthaus. While they were on a holiday in a remote part of Greece in the early 1980s his characteristic determination to overcome difficulties came into play when he contracted Guillain-Barré syndrome. He had to drive over rough terrain with his hand strapped to the gear lever so he could operate it, despite encroaching paralysis, before Adele could complete the rest of the route. Mark’s eventual recovery was ascribed by his doctors to his fitness, and a strenuous rehabilitative swimming schedule.
He is survived by Adele, their children, Max and Jessica, and a grandson.