All technologies depend on the availability of materials, including energy supply, transportation, information, communication and healthcare. The design and manufacture of suitable materials are essential to a sustainable future. Materials are a subset of all matter, distinguished by their use in an existing or intended technology. Materials science is not taught as a separate subject in the Sixth Form, and it is barely mentioned in AS and A-level science subjects. Students may be aware of the importance of materials for a sustainable future, but unsure of what the study of materials involves at university. Teachers without experience of the subject may find it difficult to advise them.
Sixteen years ago Carmen Huber (2005) of the US National Science Foundation called for the introduction of materials science in school curricula: ‘Through the study of materials students gain a better understanding of fundamental concepts in physics, chemistry, biology and mathematics by connecting those concepts with real world applications.’ I agree, but I believe there is more to materials science. My views have been shaped by 45 years of research at the frontiers of the subject, teaching across the undergraduate curriculum at Oxford University, and establishing an internationally renowned Centre for Doctoral Training on Theory and Simulation of Materials at Imperial College London. Materials science provides a training in holistic scientific thinking across length and time scales, and across the disciplines of physics, chemistry, biology and mathematics. As the Nobel prize winner P W Anderson (1972) wrote, ‘The ability to reduce everything to simple fundamental laws does not imply the ability to start from those laws and reconstruct the Universe … The constructionist hypothesis breaks down when confronted with the twin difficulties of scale and complexity.’ Materials science trains students in how to approach the complexity of real scientific problems.
The link to technology explains why the study of materials involves scientists and engineers, and why it is often described as an enabling discipline. The engineering of materials exploits the relationships between the structure, properties and method of fabrication of a material, to design a material with optimum performance for a particular application. The science of materials is about understanding those relationships. Understanding and exploiting those relationships to design and create materials for particular applications is the essence of ‘Materials’ as a discipline.
In biology, chemistry and physics we can identify fundamental concepts – big ideas – such as the concept of fields in physics, the Periodic Table in chemistry and the cell as the unit of life in biology. Are there fundamental concepts unique to materials science? Or does materials science involve concepts from only mainstream sciences? To address these questions, I set out to identify ten fundamental concepts of materials science. After several years of research and reflection my conclusion is that it is a mixture of both.
I began with the observation that materials are rarely in thermodynamic equilibrium with their environments. Nevertheless, thermodynamics determines the state to which a material evolves if it is left alone in a constant environment. The concept of thermodynamic equilibrium immediately introduces the concept of change within materials towards the equilibrium state, and defects as the agents of change in crystalline materials (Sutton, 2020). The rate of change is determined by restless atomic motion in materials, both in facilitating the motion of defects in crystalline materials and in retarding them. These concepts apply only to non-living materials because life is an energy-consuming process that is never in thermodynamic equilibrium. Thermodynamic stability is an example of a fundamental concept not unique to materials science. Quantum behaviour and symmetry are also examples.
Materials scientists talk about the multi-scale and multi-physics nature of processes in materials. For example, failure of a material often results from the formation and growth of cracks, where atomic bonds at the crack tip are broken. The forces acting on those bonds originate from external loads on the material and from interactions with other defects and inhomogeneities within the material. The process is further complicated by the generation and movement of defects to and from the crack tip. To describe these interactions we have to use the theory of elasticity because they extend over length-scales much greater than that of atoms (Sutton, 2020). The theory of elasticity exemplifies the concept of emergence of new fundamental science at larger length scales from the collective behaviour of atoms at a smaller length scale. Emergence of new science at larger length scales is a fundamental concept in materials science. It is why there are different physical theories operating at different length scales for processes in materials. A physical theory at a larger scale must be consistent with the physics at smaller length scales, but it has a different mathematical structure and addresses questions inaccessible to theories operating at smaller scales. The concept of emergence embraces a more holistic view of materials than the reductionist approach focused on the atomic scale. The ability to model and manipulate the structure and properties of materials across the full range of length scales underpins the concept of materials design for applications in technology.
Size matters in materials because their properties are more obviously dominated by quantum physics at the nanoscale (the nanoscale is normally defined as 1 to 100 billionths of a metre). This has led to the rise of nanoscience and nanotechnology which have created the modern age of storage, processing and communication of information.
Until metamaterials were introduced around the turn of the 21st century there were no naturally occurring or man-made materials displaying certain properties, such as the negative refraction of light. Metamaterials removed this limitation because their properties are not determined by their chemistry but by their carefully designed structure. The concept of metamaterials has vastly extended the conceivable range of materials properties.
Treating biological matter as a material has led to the concept of active matter in which complexity and self-organisation emerge from the collective action of energy-consuming agents. The difference between living and non-living matter may appear obvious, but it is surprisingly difficult to define. For example, the jury is still out as to whether a virus is alive. The emergence of life from inanimate matter remains one of the great mysteries in science.
I have written a short book describing my selection of ten fundamental concepts of materials science (Sutton, 2021). I strived to make it intelligible to anyone with a pre-university education in physics, chemistry and biology. The use of mathematics is limited to elementary algebra and quoting the occasional useful formula. Only in the chapter on metamaterials is this self-imposed discipline relaxed slightly. I hope my book will convince students and teachers that materials science is an intellectually rich and challenging subject to study at university. Mark Miodownik (2013)has written a very successful popular science book about materials. The Royal Society provides resources for teachers on ‘animate materials’, one of the latest developments in materials science.
Anderson PW (1972) More Is Different: Broken symmetry and the nature of the hierarchical structure of science. Science 177 (4047): 393-396 DOI: 10.1126/science.177.4047.393
Huber C (2005) Materials science in secondary education. Nature Mater 4 105. DOI: 10.1038/nmat1314.
Miodownik M (2013) Stuff Matters. London: Penguin books.
Sutton AP (2020) Physics of Elasticity and Crystal Defects. Oxford: Oxford University Press.
Sutton AP (2021) Concepts of Materials Science. Oxford: Oxford University Press.