Pergamon Radiat. Phys. Chem. Vol. 51, No. 1, pp. 3 5, 1998

© 1998 Published by Elsevier Science Ltd. All rights reserved Printed in Great Britain

PII: S0969-806X(97)00250-8 0969-806x/98 $19.00 + 0.00

PROFESSOR ARTHUR CHARLESBY PERSONAL REMINISCENCES

(RECOLLECTIONS OF MY FRIEND AND SCIENTIFIC COLLEAGUE)

ANDREW KELLER H. H. Wills Physics Laboratory, University of Bristol, Tyndall Avenue, Bristol, BS8 ITL, U.K.

The first time I met Arthur Charlesby was at the IUPAC Polymer Conference in Strasbourg, in 1952. Myself was then a young employee of ICI, Dyestuffs Divisions Manchester and was sent to the Conference to report on people and events. Those were frugal days of austerity in Britain, but France, and particularly Strasbourg was overflowing with food and wine. Myself was lavishly provided with travel funds for entertaining scientific colleagues and so it came about that Arthur Charlesby, after we had met and found much common ground, became a beneficiary of ICI's generosity. It was there in Strasbourg that I first heard from Arthur about the effect of ionizing radiation on polyethylene. Arthur carried with him a series of polyethylene rods having received increasing irradiation doses (precisely what kind of radiation I do not remember). Even by inspection one could see that those which had received the highest doses did not look like polyethylene any longer: they were stiff and glass-like even if discoloured, But even those which had received lower doses and remained recognizably polyethylenes were drastically affected in one important respect. Arthur demonstrated this by placing a flame from a lighter beneath it (he always had a lighter with him as an adjunct to his inseparable pipe) when in contrast to the unirradiated polyethylene the irradiated object kept its shape, i.e. it did not seem to melt. These demonstrations, instantly performed by Arthur at every possible occasion, caused quite a sensation.

To appreciate the significance of the above findings I need to recall that when I entered ICI and was told about the wonders of the then new product Polythene I was also reminded of its single major drawback, namely that it softened at the temperature of boiling water posing serious limitations to its use as a structural material. Overcoming this limitation would be the discovery of the century, so we were told, and here a young man from Imperial College has just achieved it. I duly reported it back, with glowing praise, to my company. The rest we all know. British industry was slow to react and the discovery found utilization elsewhere. But anyhow, the Ziegler

discoveries, which soon followed, achieved the same goal, (namely raising the softening point of polyethylene beyond the boiling point of water) by the more practical and economical chemical means and had the upper hand ultimately, (as often happens in the polymer field the chemical solution of a practical problem wins over the physical). Even so, as we all know, irradiated polyethylene, discovered by Arthur Charlesby (simultaneously with Malcolm Dole in the U.S.A.) secured for itself a significant speciality niche in industrial use and daily appli- cations. This is not to speak of its scientific significance as providing a starting point for the whole vast subject area of interaction of ionizing radiation with macromolecular matter, characterized by the fact that here a single event along the chain becomes vastly magnified in its consequences for physical properties, the science which owes its inception to Arthur Charlesby.

Soon afterwards I left industry and myself became an impecunious contract researcher in Academia. In my own career single crystals and much else followed as a result of which I was invited to visit Tube Investment in Cambridge where, amongst other people, Arthur Charlesby (who had moved there in the meantime) was my host. This was the first occasion that my ICI backed hospitality in Strasbourg some years earlier proved a good investment: Arthur generously reciprocated it, and not for the first time: it was to be repeated decades later in Shrivenham. On the scientific front, there in Cambridge, I heard for the first time of the scientific advances in the understanding of the effect of irradiation on polymers, polyethylene in particular, the Charlesby-Pinner equation and all the rest. I remembered all this later when myself had to face up to the effect ionizing radiation on polymers. This was, in the first instance the inevitable radiation damage in the electron microscope affecting all that was seen, whether recognized or not, the latter being the usual at that time. Myself recognized it and took interest in the subject accordingly. So it happened that I became associated with polymer radiation science proper in the course of a summer visit to the Bell Laboratories

4 Andrew Keller

leading afterwards to my continuing, and by now active contacts with Arthur Charlesby.

Before enlarging on the above, first 1 wish to invoke two early works by Arthur Charlesby predating his involvements in the irradiation of polymers. They both concern electron diffraction, are of great scientific merit and also interacted with my own interests. The first was, to my knowledge, the first utilization of a molecular transform (even if the authors did not call it as such) in the interpretation of diffraction patterns. The particular work of Charlesby et al. (1939) was on anthracene which possessed a characteristically structured transform. I myself learnt to appreciate the power of the transform method through the paper which 1 kept using as illustration in some of my subsequent teachings. The second work, closer to my own researches, utilized electron diffraction in the study of thin polyethylene films. Amongst others these studies at that remarkably early date in polymers studies Charlesby et al. (1954) showed that the polymer chains were at a large angle (closely normal) to the film surface. This seemed highly anomalous at the time but fell into place after chain folding had been recognized by myself exactly ten years later. I gave due reference to this work in my key paper on chain folding as predating and greatly reinforcing my own.

Returning to the subject of irradiation, the effect I found at the Bell Laboratories (together with my colleague Dr Salovey there) seemed to challenge some existing notions, including Arthur Charlesby's and called for continuing investigation. On both counts l contacted Arthur, by that time at Shrivenham, on my return to Bristol. Contrary to my apprehension 1 met with genuine appreciation and helpfulness from the word go leading to a close personal and working association of over two decades (from the early 60s until the mid 80s). Arthur placed the Shrivenham radiation source at our disposal for the irradiation of our prepared specimens and afterwards evaluated in Bristol with specific objectives in mind, involving often non-standard irradiation conditions (e.g. placing special instrumentation such as heating stages etc into the source) causing delays in his own researches and extra work for his own staff. Generations of research workers from my laboratory (e.g. Kawai, Patel, Grubb, Stejny, Ungar, names which became familiar in the subject later) benefited from these arrangements. Arthur himself took active interest in these works which ranged from giving advice to active participation in the design of the experiments and evaluation of the results. Two of our publications bear his name as coauthor: Kawai et al.

(1964, 1965. The first is a summarizing paper of a six part series to follow, hence of key importance, while the second is the first member of the actual series itself. After that he stepped out from actual authorship but retained a keen interest in the works which followed, continuing to provide facilities and advice.

The above described interest and forthcoming assistance is the more remarkable because, as already indicated, our Bristol based works were, implicitly, in some respects at least, in contradiction with the views by which his own work is best known and mostly quoted. Specifically, we have shown (and this was my own motivation for entering the field) that the cross-linking efficiency of the irradiation in polyethylene, for a given dose, as assessed through the conventional insolubility ("gel content") test could be strongly affected by the morphology of the sample which was being irradiated. This had the far reaching implication that the cross-link production of the irradiation cannot be definitively determined through the "gel content" as was generally being done in those days which meant, in other words, that there is no unique, g(cross-link) value, at least not by the method used to assess it. This is a core issue, as far as it qualifies (to say the least) the validity of the Charlesby-Pinner equation and raises question marks to all claims for having established material and energy balance as regards absorption of dose and creation of irradiation products.

To explain the current situation, there is still no direct method by which the number of cross-links in polyethylene created by irradiation can be assessed. What is generally being done is to measure some physical consequence of cross-linking (and the "gel content" is one of them) and derive from these the absolute number of cross-links. The latter requires assumptions and this is what the Bell Lab. and the following Bristol works have challenged. More specifically, the physical methods, such as the "gel content" are assessing only a fraction of the cross-links, that which is effective in forming networks, a fraction, which,as we ourselves have shown, varies according to the morphology (e.g. in regularly chain folded structures a larger fraction of the cross-links is intra-molecular, hence ineffective in network formation). Incidentally, a method for determining the number of cross-links absolutely is in sight through NMR methods, presently in the hands of workers in Japan, but indicated first by ourselves thanks to support provided by Arthur Charlesby.

Faced with this situation Arthur was generous and open minded which, given the circumstances, was truly admirable. In fact he said once that the applicability of the Charlesby-Pinner equation must be purely fortuitous. He took a most benign attitude to my own enthusiasm and the apparent pleasure 1 found in seemingly demolishing the wisdom of the older generation which, as ! am now recognizing, goes with the exuberance of youth. As I see it now, from a more consolidated perspective coming with maturity, both of us were right, or rather neither of us was wrong. Namely, the usually available polyethylenes, as quickly cooled from the melt, do not differ too much in morphology, hence the traditional Charlesby approach, assigning to them an

Obituary 5

invariant G (cross-link) applies. To show up the morphology related differences in radiation induced cross-linking effects, our own claim samples prepared under rather extreme conditions need to be compared. This, while not diminishing the scientific importance of our own findings, safeguards the applicability of the Charlesby-Pinner approach at least in everyday practice on standard commercial products. Arthur was wise enough to see through all this and also generous enough to give our own approach its scope, in fact helping it along. This is the hallmark of a great man both in scientific and human terms.

Last, but not least, I wish to recall Arthur Charlesby's services to the British Polymer Commu- nity, specifically to the younger generation as it was in the mid-60s. Myself and colleagues in a similar position forging ahead with new ideas and great enthusiasm were feeling somewhat frustrated by not having a forum in which to present our works, rather having to wait for the favour of an invitation from our elders which we then regarded as the "establish- ment". I suggested the formation of an independent society of our own, a suggestion taken up enthusiastically by like-minded souls of our age group. The obstacles, at first, seemed unsurmount- able and, in the eyes of many of our peers, the enterprise was doomed to failure. The scene brightened up somewhat through a financial gift by IC1 coupled with secretarial assistance via Ian Ward (now Professor at Leeds) who was then with ICI and became one of the founding members of our society. Still, we could not get going, even with those resources, without a meeting place. This was provided by Arthur Charlesby at Shrivenham with all its superb facilities and at an affordable minimal cost. So what were to become the famous "Shrivenham Conferences" were launched. These conferences, held first annually, then biannually provided that much needed platform for the young upcoming generation at that time of world wide expansion of scientific research and soon formed the backbone of British Polymer Physics, first as the meeting point of the British Polymer Physics Group as an independent organization and sub- sequently as the Polymer Physics Group of the Institute of Physics after becoming part of that Institute with affiliation also with the Royal Society of Chemistry. The Shrivenham Conferences were rather unique. This was due not only to the consistently high quality of the scientific contri- butions but chiefly to the freshness and directness of

these contributions. It was ensured that they came directly from the source producing the new work without undue formality and protocol. In this and all other respects, professors and research students were on equal footing. The meetings soon attracted international representations, without this, however, affecting its essentially national and "classless" character. They became envied and admired as such and served as models for similar efforts abroad. Arthur Charlesby was absolutely central to it all, not only through the facilities provided but, once a meeting was running, through his own personal input in the Conference itself, helping to create an atmosphere which was characteristically Shriven- ham's own.

By the mid 80's the conferences moved from Shrivenham, our own Bristol irradiation program petered out, (lack of funding) and Arthur Charlesby was retired. My own regular working contacts with Arthur ceased, yet we kept meeting on and off at conferences.

By the time we were reaching the 90s we were losing contact. I myself retired, and although still active in research we were treading different paths. I had been hearing of Arthur's continuing activities in different countries, notably Poland, Japan and, if I recall correctly, India, on my travels abroad but we did not meet any more. So it was a sad reminder when the next news of him was the invitation to this Memorial Symposium. While nothing can relieve the sadness of this occasion it gave me some sombre pleasure to recollect these memories of a remarkable man, who not only with his incisively outstanding science but also with his truly individualistic personality, both jovial and sarcastic, yet always deeply humane, never conforming, in fact iconoclas- tic, so much in contrast with the conformity descending on the present scientific scene, has left an indelible mark on the memory of all who knew him. This is a feeble attempt to pay him homage and to pass something at least of what he stood for onto future generations.

REFERENCES

Charlesby, A., Finch, (3. I. and Wilmann, H. (1939). Proceedings of the Physics Society (London) 51, 479.

Charlesby, A. (1954). Proceedings of the Physics Society (London) 59, 496.

Kawai, T., Keller, A., Charlesby, A. and Ormerod, M. (1964). Phil Magazine 10, 779.

Kawai, T., Keller, A., Charlesby, A. and Ormerod, M. (1965). Phil Magazine 12, 657.