Obit - Moti Lal

Professor Moti Lal, Ph.D., C.Chem., FRSC (1937 - 2010)

Moti Lal, who passed away in March 2010, was one of the Unilever's most respected scientists. He pioneered the application of computer simulation methods in physical chemistry, and was remarkable for his skill in formulating and solving fundamental science questions relevant to Unilever's R&D problems.

Moti was born in the Punjab, in India, in 1937. He took an MSc in Chemistry at the University of Punjab, and a PhD in Physical Chemistry at what is now the University of Strathclyde. He then spent two years at St Catherine's College, Oxford, as Sir William Ramsay Memorial Research Fellow, where he worked with Dr E.B. (latterly Sir Brian) Smith. In 1967, Moti joined Unilever Research, eventually working in a wide range of areas including polymers, surfactants, colloids, emulsions, adsorption, transport processes, and rheology. Early in his career Moti was seconded briefly to work with one of the leading pioneers of polymer science, Walter H. Stockmayer, at Dartmouth College, Hanover, USA.

Moti was often well ahead of his time and consequently perhaps did not receive as much recognition in the external world as some of his contemporaries. A striking example is a 1969 paper entitled "Monte-Carlo computer simulation of chain molecules" in which Moti introduced the 'pivot method' [1]. When this was published, the leading figures in the then-nascent field of computer simulation (such as Berni Alder and Tom Wainwright) were still wrestling with the properties of hard sphere fluids, but Moti was already boldly thinking about how to simulate polymers. The pivot method paper was certainly 20 years ahead of its time (see figure): in the period 1970-1989 it received just 18 citations, but in the period 1990-2009 it received 236 citations!

Citations of the pivot method paper [1], by year.

In 1981, working with long-time colleague Alec Clark, Moti discovered by means of computer simulations that colloidal forces induced by non-adsorbing polymers could be partly repulsive in a good solvent [2], rather than purely attractive as in conventional theory of polymer-induced depletion flocculation. At the time this was so counter to the accepted wisdom that it caused a big stir. Sir Sam Edwards and the future Nobel laureate Pierre-Gilles de Gennes were brought in to adjudicate, finding in Alec and Moti's favour. This work was again significantly ahead of its time; it would be 15 years before depletion stabilisation was realised by the scientific community to be a generic effect -- in the mid 1990s the phenomenon was rediscovered at least twice: firstly in the context of perturbation theory by Walz and Sharma [3], and secondly in the context of rod-polymer depletion by Mao, Cates and Lekkerkerker [4].

In the last decade or so of his Unilever career, Moti's interests moved more towards colloidal hydrodynamics with particular reference to particulate soil removal. On these problems, he worked closely with Bob Jones of Queen Mary College, London. After retiring from Unilever, Moti took up a research chair at Liverpool University, where his interests turned once again to a new area, that of nanoparticle technology. He was physically active up until illness overtook him in the middle of 2009, and mentally active right until the end.

He was unique, in many ways.

Moti at an award ceremony in 1997. L-R: Prem Paul, Moti Lal, Noel Ruddock, 
Dominic Tildesley, Rob Groot, Ged Clarkson, Patrick Warren, Alec Clark

[1] M. Lal, Monte-Carlo computer simulation of chain molecules, Mol. Phys. 17, 57-64 (1969).
[2] A. T. Clark and M. Lal, Statistical thermodynamics and configurational structure of chains confined between surfaces, J. Chem. Soc. Faraday Trans. II 77, 981-996 (1981).
[3] J. Y. Walz and A. Sharma, Effect of long range interactions on the depletion force between colloidal particles, J. Coll. Int. Sci. 168, 485-496 (1994).
[4] Y. Mao, M. E. Cates and H. N. W. Lekkerkerker, Depletion stabilization by semidilute rods, Phys. Rev. Lett. 75, 4548-4551 (1995).