Society News

People in the News: Antoine Skoulios

Skoulios joined the CNRS (National Scientific Research Centre) in 1955, supervised by V. Luzzati at the Centre for Macromolecular Science in Strasbourg. He gained his PhD in 1959 with his thesis ‘Structure of liquid crystalline phases obtained with pure sodium soaps and with binary mixtures of sodium soaps and hydrocarbons’. He was the leader of the X-ray group in this Centre from 1963 to 1987 when he moved into the new Institute for Physics and Chemistry of Materials, also in Strasbourg. His main contributions are based on the concept of the amphiphatic character that he used extensively to describe the mesomorphic structures of thermotropic and lyotropic liquid crystals: soaps, polysoaps, calamitic and discotic liquid crystals. This concept was generalized to the case of block copolymers to describe their different lamellar, columnar and cubic phases (Mol. Cryst. Liq. Cryst., 165, 317 (1988)).

At the beginning of his career, he studied lyotropic liquid crystals, describing the main structures of lyotropic phases of soaps through concepts of intramolecular segregation. He determined the local disorder of aliphatic chains and the long range order within lyoptropic mesophases (Nature, 180, 600 (1957); Coll. Interf. Sci., 1, 79 (1967)). He also considered the thermotropic phases of amphiphiles, finding that their mesomorphic behaviour was due to stepwise melting of the molecules’ aliphatic chains and polar groups. The structures of many soaps were described in detail: lamellae, ribbons, cylinders or disks were found to be the fundamental structural objects (Ann. de Physique, 3, 421 (1978)). Similary, the mesomorphic behaviour of calamitic liquid crystals was attributed to the amphipathic character of their molecules; long rigid polarizable moities and aliphatic chains prefer to segregate into different microdomains. The mesomorphic state exists due to the melting of the aliphatic chains which ensures the fluidity of the mesophases, while the nature of the mesophases is determined by the degree of order of the polarizable parts (J. de Physique, 37, 797 (1976)).

During the 60s, A. Skoulios was involved in pioneering work associated with the first lyotropic and thermotropic mesophases in block copolymers, finding the main structures to be based on lamellae (smectic), cylinders (columnar) or spheres (cubic) (in Brown, G. H. (ed.) (1975) Advances in Liquid Crystals, volume 1, New York: Academic Press, p. 169). By comparing the structure of semi-crystalline polymers with that of virtual block copolymers containing crystalline and amorphous sequences, Dr A. Skoulios showed it was possible to determine the folding ratio of the polymer chains within the crystalline lamellae. He also found that the ratio varies discontinuously with the crystallisation temperature or the aging temperature. Being coiled in the melt state, the chains cannot adopt the ideal stretched conformation when the very fast process of crystallisation occurs. Therefore, they crystallize only at a local scale and freeze into a folded conformation (Koll. Zeit., 234, 1059 (1969)).

The structure of the first side-chain polymers was investigated by Dr Skoulios when he considered polysoaps formed by polyelectrolytes carrying aliphatic side-chains. These systems exhibit lyotropic mesophases similar to those of low molecular weight soaps. He then studied mesomorphic polymers containing mesogenic side-groups, and in particular substituted polymethacrylates. By taking into account the syndiotactic nature of the backbone and steric constraints, the mesogenic side groups were found to be organized in double rows and all on the same side of the backbone in the smectic phases. The rather stretched macromolecules adopt the shape of very long ribbons with a width close to the side-group length and a thickness corresponding to that of a double row of mesogens (J. de Physique, 49, 1455 (1988)). For the lyotropic nematic mesophases observed with aromatic polyamides, he showed via an analysis of the kinetic variation of optical textures as a function of the polymer molecular weight, its chemical nature and its concentration in solution, that the threads in the textures correspond to a pure divergent local distortion, in agreement with the rather important rigidity factor of the polymer chains (J. de Physique, 38, 307 (1977)).

A. Skoulios also participated in numerous structural studies of columnar mesophases including transition metal soaps, phthalocyanine derivatives, polycatenar compounds and polydialkylsilanes. The structures found have the same symmetry as those he had described many years previously with alkaline and alkaline-earth soaps. However, it was possible now to describe in much more detail the internal structure of the columnar core: pseudo-polymeric chains of metal atoms in the case of transition metal soaps, stacking of the phthalocyanine rings normal or tilted with respect to the columnar axis, stacking of clusters of a few molecules with polycatenar compounds, gauche conformation of the silicone backbone with polydialkylsilanes (Europhys. Lett., 3, 67 (1987); Liq. Cryst., 9, 369 (1991)). More recently, A. Skoulios was very much interested in the study of liquid crystals showing hydrogen bonds and dipolar interactions. For example, in the case of N-substituted alkylammonium bromides, a tetragonal organization of the polar heads is found within the polar sublayers when the substituents are inactive (methyl, alkyl). The tetragonal order is destroyed when the ionic heads carry only one active group, but it is reinforced when they carry two active groups, leading to the building of supramolecular assemblies (‘grid’ type) through hydrogen bonds (Liq. Cryst., 13, 201 (1993); Liq. Cryst., 22, 51 (1997)). These last years, he has also been involved in the field of metallomesogen liquid crystals, for example of copper complexes, obtained with 2,2’-bipyridine derivatives. In this case the mesophases are no longer obtained through the classical rod-like or disk-like shaped molecules, but through supramolecular assemblies of ‘helicate’ type, organized in columnar mesophases (Angew. Chem. Int. Ed., 37, 1255 (1998)).

This brief overview of major achievements shows how productive and remarkable the research of A. Skoulios in liquid crystals and polymers bas been during 45 years. A. Skoulios is the author of more than 250 publications, has supervised more than 40 PhD theses during his career and has also been invited to many international conferences. Finally I would like to express my gratitude to you, Antoine, for my personal training but also for the illuminating discussions in our laboratory.

Daniel Guillon

Volume 10, Issue 2

+ All Science & Technology News

+ All Society News