Materials Research Activities

1990-2000

1970-1990: Composites and mixed-disciplinarity

1990-2000: Complexity and the nanoscale

The emergence and evolution of MSE may be more adequately described in terms of responses to challenges than in terms of "organic growth". In the beginning, the generic notion of materials science has been forged in response to the Soviet challenge of Sputnik. Then in the 1980s, the Japanese challenge prompted a re-orientation towards processing and industrial competition.

Over the last decade, materials scientists and engineers invented (or discovered) their most serious challenger: nature itself. While striving to design high-performance, multi-functional composites, materials scientists realized that such materials existed already in nature. Optimal combination of properties and adaptive structures are exemplified in living organisms. Through the eye of materials engineers, wood is a composite material made out of long, orientated fibers immersed in a light ligneous matrix. Sea-urchin or abalone shells are wonderful bio-mineral structures made out of a common raw material: calcium carbonate. They present a complex morphology and assume a variety of functions [51] . Similarly, spider silk is a fiber extremely thin and robust that offers an unchallenged high strength-to-weight ratio. How could such efficient structures be designed? Suddenly the metaphysical entity  "Nature" surfaced among the technical and esoteric terminology of specialized journals in MSE. Nature is called upon to provide materials scientists or engineers with novel concepts for crystal engineering and materials designing.

"We can be encouraged by the knowledge that a set of solutions have been worked out in the biological domain", wrote Stephen Mann. "The challenge then is to elucidate these biological strategies, test them in vitro, and to apply them with suitable modification, to relevant fields of academic and technological inquiry." [52]

Turning from the military and industrial competition with rival nations to the rivalry with nature, the style, conditions and practices of research changed deeply. The political momentum of the 1950s to create MSE declined and is still declining. Despite the continuous pressure for miniaturization, despite an extensive mobilization around environmental issues and the cycle of materials, it is more and more difficult to present MSE as an answer to "man's needs". There are many sophisticated materials on the shelves, without applications. In a way, the supply exceeds industrial demand.

This situation was reflected in the dramatic reduction by 50% of the research staff in most industrial companies by the end of the 1980s: DuPont, Exxon, Bell laboratories only maintained programs focused on improving their company products. Many industrial researchers joined the university laboratories. Academic materials centers found new recruits. The academic community was thus reinforced but it had to rely on its own resources, on its own dynamics.

From Micro through Bio to Nano

Academic scientists successfully invented their own program. Looking back into the past, they found a prophet of the coming age of nanotechnology. A lecture delivered by Richard Feynman in 1959 and published in 1960 became their bible. "There's plenty of room at the bottom", Feynman declared, in order to invite physicists to enter the field of nanometer scale and to construct objects atom by atom. Feynman made various and often playful suggestions of technological applications such as writing the Encyclopedia Britannica on a pinhead using beams of electrons. His predictions were already inspired by a biological model: "This fact - that enormous amounts of information can be carried in an exceedingly small space - is, of course, well known to the biologists (…)The biological example of writing information on a small scale has inspired me to think of something that should be possible. Biology is not simply writing information; it is doing something about it. A biological system can be exceedingly small. Many of the cells are very tiny but they are very active; they manufacture various substances; they walk around; they wiggle; and they do all kinds of marvelous things - all on a very small scale." [53]

Feynman's suggestions were made reality thanks to advances in scanning tunnelling microscopy (STM) and the Atomic Force Microscope (AFM). Such instruments allow not only the visualization but also the manipulation of individual atoms. [54] Writing with atoms, the dream inspired by Feynman's metaphors, was achieved in 1990 when Peter Zippenfeld published the atomic logo of IBM in xenon atoms. The IBM release entitled "IBM Scientists Position Individual Atoms - First to Build Structures One Atom at A Time" epitomizes the combination of advertising and cognitive interests. [55] IBMs image was soon joined by the Japanese company JEOL's Japanese characters for "nanoworld". This was clearly intended to convince both the public and the scientific community that controlling and manipulating the small world was possible. Atoms and molecules can be placed at selected positions so that it is possible to build structures to a particular design atom by atom.

Thus MSE shifted from the microscale to the nanoscale (1nm=10-9m). A new approach developed with nanotechnology. Until then, materials had been carved out like a statue out of a block of marble: for instance electronic chips are made by slicing a cylinder of single-crystal silicon into thin wafers, and later divided into tiny pieces. This "top-down" approach is now replaced by a "bottom-up" approach where a nanostructure is built by bonding atoms or groups of atoms. The key issue becomes the assembly of building blocks. Instead of the chemical interactions used in traditional chemical synthesis, materials scientists are looking for processes of spontaneous association of molecules similar to those employed by nature in the design of living organisms. Molecular self-assembly is thus one major reason of the interest of materials scientists in biomaterials. Nature makes the mortar and the bricks at the same time in biominerals and self-assembles them through the use of templates with a close control of the process at each level. The biological macromolecules are involved in controlling nucleation, growing, shaping the crystal and adapting its mechanical properties to the functions of the bio-mineral. [56]

A second motif of the materials scientists' interest in bio-structures is that they reveal a complex hierarchy of structures. Each different size scale, from the Angström to the micron and millimeter scale, presents different structural features. The remarkable properties of bulk materials, such as bone or tendon are the result of this complex arrangement at different levels, with each level controlling the next one. [57] Here is a form of complexity far beyond the complex composite structures that materials scientists had been able to design.

A third feature of biomaterials that scientists are trying to achieve in their own man-made materials is their adaptability to the environment. Designing responsive, self-healing structures has been one the major objectives of materials research in the 1990s. For this purpose, programs on smart or intelligent materials were launched. Basically, intelligent materials are structures whose properties can vary according to changes in the environment or in operating conditions. For example, materials whose chemical composition varies according to its surroundings are used in medicine as prostheses. Materials whose structure varies according to the degree of damage due to corrosion or radiation are thus able to repair themselves. The whole problem is to have inbuilt intelligence. This means at least having sensors (for strain, temperature, or light) and actuators embedded in the structure in order for the structure to adapt to external stimuli. In Japan attempts were made to promote smart materials as a new discipline built up around a hard core of axioms and concepts. [58]

Nanotechnology, biomimetism, and smart materials - all three trends are manifestly inter-related and converge towards similar targets. They could or should prompt the unification of the field of materials science. However, and quite surprisingly, until now they are not really acting as converging forces nor are they creating any unified set of concepts and practices.

One major reason is that not all materials scientists are involved in these recent technologies. There is still a future in exploring microstructures and designing bulk materials. Whatever their importance in the recent science policy measures [59] , nanotechnologies will never cover the entire field of materials science. Moreover, the new perspectives opened up by the nanoscale, act as diverging rather than converging forces. On the one hand, they extend the frontiers of MSE to such territories as bioengineering or artificial intelligence. Multidisciplinary cooperation is intensified. For instance, the programs of smart materials emerged from close collaboration among electronic engineers, computer scientists, and materials engineers. The efforts to understand biominerals and to mimic the natural processes of self-assembly require an interaction with structural and molecular biologists. [60] Computer science and biology have entered the field of materials science. As a result, if one were to map out the territory of MSE today one would get nothing like a center and a periphery or a mainstream split into various little branches. Rather, MSE appears as a booming field without clear borderlines and with dozens of streams flowing in various directions.

A Variety of Approaches

In addition to its undefined territory, MSE is characterized by a variety of approaches. Without attempting a general survey of the field, not even at a typology, I will show the diversity of approaches at three different levels:

  1. a survey of textbooks suggests that there are different approaches to teaching
  2. a survey of research articles or review articles will provide a sample of diverse practices used for designing materials
  3. finally I will try to characterize the underlying views of nature.

1. From a brief survey of a few dozen general textbooks of materials science published over the past decades one gets the impression that the discipline is not stabilized (See the list in Appendix).

Certainly most textbooks emphasize the contrast between the old, traditional, empirical knowledge about materials and scientifically based knowledge. After centuries of routine, the birth of a new scientifc age took place whose origin varies from the mid-19th to the mid-20th century. This common positivistic historical scheme undoubtedly helps cement a disciplinary community.

However, the core knowledge of the discipline of MSE, that all students around the world are supposed to know, is very small. Most textbooks begin with general notions about the structure of matter and move to the presentation of the traditional groups of materials: metallic, non-metallic, polymers, ceramics. The portion of theroretical and basic knowledge about the structure of matter varies from one introductory chapter to 12 chapters over a total of 15. Indeed, such variations depend on the audience targeted because materials are involved in many diverse science and engineering curricula. Texts aimed at engineers present the theroretical notions about structure as tools for selecting materials for design while in other texts the purpose is simply to help the reader understand how and why materials behave as they do. There is a large spectrum of formulas between the two extremes of science-centered texts and engineering-centered texts, as noticed by Robert Cahn. [61]

However, the overall organization does not convey the image of unified discipline. Rather it suggests an aggregation of fragments of knowledge taken from various disciplines around a core of atomic physics. In other words they suggest that materials science is an applied science of quantum and statistical mechanics and solid-state physics. In fact, there is no inner logic presiding over the organization of the discipline 40 years after its emergence. Rather, the organization of most textbooks simply reflects the successive layers of its historical development textbooks. One could not find a materials science textbook without a chapter on metallurgy, whereas ceramics and polymers remain on the periphery. The introductory chapters providing the fundamental notions mainly deal with metallic structures, dislocation, crystal lattices, etc. The core knowledge still consists in crystals and solid-state physics. Although the textbooks published in the 1980s emphasize processes in addition to structures and properties, they still derive their basic principles from crystalline structures and simply extend their scope to include polymers and ceramics. [62] Composites are introduced in more recent textbooks but only towards the end, after chapters devoted to semi-conductors, polymers, ceramics, and structural materials. They do not induce a new general approach to materials. The theoretical foundations, borrowed from physics, do not determine a definite way of ordering the particular chapters dealing either with classes of materials or with types of properties such as mechanical, magnetic, and optical. There is no general law to govern the multitude of particular cases and few efforts are made to frame a generic discipline. Among these attempts to rethink the whole in a more general way, Allen's and Thomas's The Structure of Materials can be singled out. The authors explicitly set out the four basic concepts structure, properties, performance and process in order to describe materials in "a catholic way". [63] Rather than deriving their basic concepts from solid-state physics, they start from general notions about symmetry and bonding that allow them to deal with various states of matter.

Since the discipline of MSE does not look remarkably stabilized, it is ironic that the textbooks enjoy a remarkable longevity. Some of them were circulated for 20 and sometimes 30 years, showing no significant evolution of the genre over four decades. This stability is quite surprising given the rapid advances and the deep reorientations described above. It is also remarkable that the most recent developments did not bring about new concepts susceptible of reorganizing a didactic exposition of the field. In particular, the notion of complexity, a candidate unifying concept, remains extremely loose and no consensus on a standard definition has come into being. A number of materials scientists refer to the hierarchy of structures instantiated in biomaterials [64] , while others rely on a physicist's notion of complexity referring to dynamic processes creating order out of disorder without dissipation of energy. [65]

2. The research strategies of materials scientists and engineers are no more unified than their textbooks. Even within the restricted domain of nanomaterials - let alone the design of bulk materials for industrial uses - there is no uniformity. Some materials scientists use and advocate rational design with the aid of computer simulation. Computational materials science developed in several universities in the 1990s, and Elsevier now publishes a journal of Computational Materials Science. [66]   Its prestige was reinforced with the award of a chemistry Nobel Prize to Walter Kohn and John A. Pople for their work in quantum chemistry. Beyond the objective of calculating the properties and stability of different structures, the ambition of computational materials science is to "model the real world by computer in a reasonable amount of time" as Uzi Landman, director of the Georgia Tech Center puts it. [67] The supreme achievement is to build up a material ab initio, using computer calculations and starting with the most fundamental information about the atoms and from the basic rules of physics. Despite the strong theoretical inclinations of computational materials scientists, their effort is oriented towards industrial applications. For instance, Gerbrand Ceder (from MIT Materials Science Laboratory) has used computers to design new aluminium oxide electrodes for batteries. Because it was one of the first materials that had been predicted on a computer before it was synthesized, this achievement revived the hubris of the ancient alchemist. It has been reported in semi-popular journal in 1999 under the title "The virtual alchemist". [68]

This a priori method, dispensing with the cumbersome manipulation of real substances in the laboratory, contrasts with the combinatorial approach. First introduced in pharmaceutical industry for the design of new drugs, the combinatorial method consists in synthesizing a large array of compounds up front before screening them. [69] Peter Schultz of the University of California, Berkeley, transposed it to materials science in a quest for high-temperature superconducting materials. This kind of Darwinian strategy - given an equivalent of biodiversity artificially created by combinatorial techniques, the materials designer selecting the fittest structures - has been licensed and commercialized. [70] Combinatorial techniques are mainly developed to speed the process of looking for new materials in various strategic applications.

Both the computational and the combinatorial methods are extremely systematic in comparison with the strategies developed by materials scientists to explore new ways of designing novel materials. A number of them are trying to use genetic information in order to design new structures. There are many attempts to synthesise novel proteins not observed in nature but engineered for specific purposes. Stephen Mann and his team at the University of Bath are using proteins as processing plants. After studying the structure and properties of native proteins and finding that they form small cages, Mann realized that he could "use the protein as a reaction vessel for controlling the particle size of other materials". [71] He and his group use proteins to cage several compounds by altering the chemical affinities of the protein. Other kinds of biological resources can be exploited for designing new materials too: DNA can be used as a rigid template to direct the spatial disposition of nanoclusters; genetically engineered bacteria are used to produce biodegradable polymers, and so on. Bionanotechnology programs are developed both in Japan and in the USA with the idea that proteins could in the future replace the components of today computers. Efforts are made to make biotransistors, biosensors, and biomolecular switches.

Whereas a number of materials scientists pursue biotechnological strategies, others rely on chemical stategies for the synthesis of nanostructures. "How can one make structures of the size and complexity of biological structures, but without using biological catalysts or the information coded in genes?" [72] Such is the program developed by chemists and physico-chemists like George Whitesides, among others. Gathering all possible resources, from covalent bonds to weaker forces like ionic bonds and van der Waals interactions, and playing with the action of thermodynamics, chemists let various building blocks self-assemble into various structures of two and three dimensions. [73] In response to the challenge of biomaterials they work at the mesoscale and deploy an artillary of techniques like etching, stamping, coating. They thus generate a variety of active or passive structures, a jungle of shapes - knots, bagels, shells - out of very ordinary materials like mesoporous silica using sol-gel techniques or surfactants [74] . Whether chemical or genetic, those semi-empirical approaches have nothing in common with the former more systematic strategies. They use trial and error, through a kind of astute tinkering or "bricolage", rather than deductive method.

3. Underlying these different practices for designing manomaterials are very different views of nature and of the relations between art and nature. The scientists who use rational and systematic strategies are led by a deterministic view of nature as a rational system governed by a few simple and general laws entirely transparent to the human mind. In particular, both the ab initio and the bottom-up strategies imply that individual materials are just a specific configuration of atoms deducible from the universal laws of matter. For these scientists, the route from atoms up is smooth, without obstacles.

In the writings of the pioneers, one can find visionary views that magnify and emphasize the main features of the emerging technological culture. Several promoters of smart materials technologies seriously planned to design materials endowed with some of the functions of human mind: from sensors and actuators, they would move to consciousness. [75] Eric Drexler, devoted a number of popular writings announcing that "nanotechnology would bring changes as profound as the industrial revolution". [76] Drexler depicted atoms and molecules as nanomachines. They are "universal assemblers", to be used by engineers as machine tools to create performance-enhanced molecular machines. Improving on nature is the main objective and there is no limit to the power of those handling the "universal assemblers". Like Marcellin Berthelot one century ago, Drexler develops an ambitious program for reproducing the bio-structures and outdoing nature. [77] This program is based on a simplistic view of the complexity of material structures. Drexler does not doubt the feasibility of his program because the existing "molecular machines" serve a range of basic functions nor that they can be combined to design more and more complex machines. One remarkable feature is that although the systematic strategies for designing complex structures are generally based on quantum physics, they rely on a view of nature close to that developed by classical mechanics. The material designer is like a clockmaker, who by adjusting small units can make a complex machine allowing mankind to dominate time. In this perspective, the ideal is the mastery of nature and there is little doubt this ideal can be achieved through fundamental science. Knowledge is power.

In stark contrast to this mechanistic view of nature underlying the systematic approaches to materials design, the more empirical approaches are based on a more teleological view of nature. Nature is presented as a subtle and unrivaled engineer, a wizard who has invented elegant solutions to most of the problems that confront materials designers. [78] Nature is the mentor that guides, encourages and teaches lessons because "Nature can produce complex structures even in simple situations and can obey simple laws even in complex situations." [79] The complexity of nature is no longer viewed as a combinatorial association of the ultimate, homogeneous and universal units composing matter. Rather it exemplifies the composites principle, a strategy of mixing heterogeneous ingredients in order to obtain the optimal combination of properties. [80] The lessons of nature concern not only the design of materials but also their repair, and their destruction thanks to recycling processes. Nature is the master of time. In this view, we cannot improve on, not even rival nature since she spent billions of years for designing and perfecting high-performance structures capable of sustaining life. Steven Boxer, a chemist from Stanford who uses proteins as transistors in electronic circuits, thus expresses his strategy: "We've decided that since we can't beat them (biomolecular systems), we should join them." [81] Materials designers have no choice but to start from the building blocks provided by nature - whether they be proteins, bacteria, micelles or colloids - in order to achieve their goal. In this perspective the relation between nature and artifice is one of partnership, not of domination. This attitude, however, does not limit the Promethean ambitions of materials scientists. Some of them develop grand technocratic views, based on this cooperation with nature.

Conclusion


[51] Lowenstam, H.A., S. Weiner, On Biomineralization (Oxford & New York: Oxford University Press, 1989). The microstructure of abalone shell directly inspired a material designed by I. Aksai's group at the Princeton Material Institute.

[52] Mann, Stephen "Crystallochemical sStrategies" in Stephen Mann, John Werbb, Robert JP Williams (eds), Biomineralization, Chemical and Biological Perspectives, (Weinheim, VCH, 1989),  pp. 35-62, quote on p. 35.

[53] Feynman R. "There is plenty of room at the bottom", the lecture delivered on Descember 1959 a the Annual Meeting of the American Physical Society was reprinted several times in Engineering and Science, the Caltech Alumni Magazine, February 1960 see Science, vol 254, 29 november 1991, p1300-1301.

[54] See Stroscio, Joseph A and Eigler,  "Atomic and molecular manipulation with the Scanning Tunnelling Microscope", Science, 254, 29 November 1991, p. 1319-26.

[55] Various atomic pictures have been achieved by the IBM laboratories thanks to the STM: a surface layer of gold atoms in 1988 a benzene molecule in 1989 and a « molecular man » in 1990. See Jed Z. Buchwald, "How the ether spawned the Microworld", in Lorraine Daston (ed.) Biographies of Scientific Objects, (Chicago and London, The University of Chicago Press, 2000), pp. 203-225.

[56] Weiner, S., Addadi lia, "Design strategies in mineralized biological materials", Journal of Material Chemistry, 7 (5) (1997) 689-702.

[57] Baer, Eric; Hiltner, Anne; Morgan R., "Biological and Synthetic Hierarchical Composites", Physics Today, october 1992, 60-67; Mational Advisory Board, Hierarchical Structures in Biology as a Guide for New Materials Technology, (Washington DC, National Academy Press, 1994)

[58] Tagaki, T., "A concept of intelligent materials", in Iqbal Ahman & Andrew Crowson (eds.), US/Japan Workshop on Smart/Intelligent Materials and Systems (Lancaster, PA: Proceedings series, 1990), p. 1-10. A. Mc Donach, P.T. Gardiner, R.S.McEwen, B. Culshow (eds), Smart Structures and Materials, Second European Conference (Society of Photo-optical Instrumentation Engineers (SPIE), Proceedings series, volume 2361, 1994).

[59] On January 21, 2000, President Clinton announced the National Nanotechnology Initiative (NNI) with a federal budget of hundreds of millions of dollars for the year 2001.

[60] Such collaborations are the basis of the most recent centers of materials science such as Princeton Materials Institute or Santa Barbara Materials Research Laboratory.

[61] Robert W. Cahn, "Materials Engineering for Nobody", in Artifice and Artefacts - 100 Essays in Materials Science (Bristol, Philadelphia: Institute of Physics Publishing, 1992), pp. 333-335.

[62] See for instance William F. Smith, Principles of Materials Science and Engineering (New York, McGraw Hill, 1986); James A Jacobs, Thomas F. Kilduff, Engineering Materials Technology (Structure-Processing-properties and Selection), (Upper Saddle River, N.J., Prenctice Hall, 1st edition 1985, 2nd 1994, 3rd ed, 1997).

[63] S.A. Allen, E.L. Thomas, Structure of Materials (New York, 1999) p. vi.

[64] Goldenfeld, Nigel, Kadanoff Leo, "Simple Lessons from Complexity", Science, 284, (April 2, 1999), p. 87-89 

[65] G. Whitesides, "Complexity in Chemistry", Science, 284 (April 2, 1999), p. 88-92

[66]   A multidisciplinary and multi-institutional Center for Theoretical and Computational Materials Science (CTCMS) was created in 1994 by Pr Sharon Glatzer. Its mission is to develop software and tools for modeling structures and to sponsor workshops. A Center for Computational Materials Research exists at GeorgiaTech (Atlanta), at George Mason University.

[67] See the GeorgiaTech Center for Computational Materials Science website.

[68] Technology Review July-August 1999, pp. 56-61

[69] This approach was first developed by Affymax Research Institute a biotechnology company created by Alejandro Zaffaroni and later purchased by Glaxo.  See Gary Stix, "Cracking the combination: A new screening tool may supercharge materials science", Scientific American Explorations, 3 June 1996.

[70] Combinatorial techniques were put on the market by the company Symyx (created in 1995), whose name derived from a Greek word meaning « co-mingle substances to form something new ».

[71] S. Mann, "Exploiting the Nanotechnology of Life", Science, 254, 29 November 1991, p. 1308-09.

[72] G.M. Whitesides, John P. Mathias, Christopher T. Seto, "Molecular Self-Assembly and Nanochemistry: A Chemical Strategy for the Synthesis of Nanostructures", Science, 254, 29 November 1991, pp. 1312-1318.

[73] Bowden N., Terfort A., Carbeck J., and Whitesides G. Science 276 (1997) 233) ; Breen, T. , Tien J., Oliver S., Hadzic T. , and Whitesides G., Science, 284 (1999) 948.

[74] Asefa Tewodros, MacLachlan Mark J., Coombs Neil & Ozin, Geoffrey A., "Periodic mesoporous organosilicas with orgnic groups inside the channelwalls", Nature 402 (1999), number 6764, 867-871.

[75] Tagaki T., "A concept of intelligent materials", in Iqbal Ahmam, Andrew Crowson (eds) U.S./Japan Workshop on Smart/Intelligent Materials and Systems, Lancaster Pennsylvania, 1990, p.1-10.

[76] K. Eric Drexler, Engines of creation, (New York, Anchor ress/Doubleday, 1986); see also "The coming era of nanotechnology" in Tom Forester (ed) Materials Revolution: Superconductors new materials and the Japanese Challenge, op.cit.

[77] On Marcellin Berthelot's ambitious program see Jean Jacques, Berthelot - Autopsie d'un mythe (Paris, Belin, 1987), and B. Bensaude-Vincent, I. Stengers, A History of Chemistry (Cambridge, MA: Harvard University Press, 1996).

[78] See for instance Julian F.V. Vincent, in Materials Today, 1998, p. 3-6

[79] Nigel Goldenfeld, Leo Kadanoff "Simple Lessons from Complexity", Science, 284, 2 April 1999, p. 87-89.

[80] See for instance, Paul Calvert, « Biomimetic Ceramics and Composites » MRS Bulletin, October 1992, p. 37-40

[81] Steven Boxer quoted in "Exploiting the Nanotechnology of Life", Science, 254, 29 November 1991, p. 1308-09.