|
|
Materials may be of two types: structural or functional. The former are essentially substances
designed to have specific structural purposes for construction. They may be constructed by exploiting
molecular self-assembly in a way which nature has mastered (supramolecular chemistry) or by thermal
methods using molecular precursors incorporating specific structure-forming templates. Functional
materials have an in-built special effect with physical responses to external forces, such as light
emission on the application of pressure, changing shape in response to an electric current or
emitting sound on exposure to changes in magnetic fields. These materials are often 'soft': liquid
crystal displays are an excellent example. They too can be made by molecular self-assembly processes.
Research on structural and functional materials is leading to many exciting things. These include ceramics as strong as and more wear-resistant than metal alloys, surface coatings which change colour with temperature as well as providing protection and the generation of a wide range of chemically-active particles - colloids - whose science and industrial applications are fascinating. The self-organisation of molecules into superstructures with channels and cavities suitable for ion and whole molecule transport, or with controlled shapes and symmetries, gives rise to a wide range of structured materials. Within this important group of substances are dispersions, glasses and synthetic minerals characterised by a micro structural order between molecular dimensions (1 nm) and macroscopic grains (1 mm). Their physical state may be deliberately altered by controlled changes in their environment; for example, changing from a viscous fluid to a free-flowing liquid when passed through a magnetic field. Such 'smart' materials may have applications in power transmission (automotive clutches), micro-switches and damping in medical prosthetic devices. Colloidal systems are stable dispersions of microscopic solid particles (ca. 1000 nm or 1 µm) in fluids. These are important in foods, paints, adhesives, cosmetic and medical preparations and in industrial processing. Environmental concerns mean that the production of colloidal dispersions is moving away from organic solvent-based dispersants towards predominantly water-based systems, so there is a need for a greater understanding of how colloidal particles may be stabilised in water and how aggregation can be prevented. This requires the development of a deeper understanding of adsorption phenomena of polymers on the surface of particles and the nature of inter-particle interactions. New applications can be expected for colloidal systems on the nanometre scale. This is achieved by progressively reducing the size of the particles to a point at which quantum effects change their physical properties. Their stabilisation in solids, polymers or glasses creates new materials for application in electronics (single electron tunnelling), photovoltaics (artificial photosynthesis), sensor technology (ultrafast response), information processing (opto-electronics) and, especially, catalysis.
|
|
|
Surfaces and surface technology have long interested chemists. Lacquers and varnishes protect against
the weather, abrasion, scratches, dirt, corrosion, radiation and ageing. They also embellish, as do
dyes and decorative structures. Techniques are now being developed to coat surfaces with layers of
only molecular dimensions, but with enormous physical effects. Such effects could include antistatic,
dirt-repellent, tacky, friction-creating or ultra-smooth characteristics.
New chemistry will have an enormous impact on lubrication, corrosion, surface wetting and compatibility of materials with bio-organisms. An extension of the application of the science of structured materials, the protection of surfaces against wear is a constant industrial demand. Clearly, the stable passivation of surfaces moving against each other is highly desirable for extending the life cycle of the material, and requires increasingly sophisticated chemistry, since the conditions of operation in some cases grow ever more extreme (high temperatures, pressures, corrosive atmospheres). Furthermore, the protection of paintings, statuary and buildings against pollution and corrosion is essential for the preservation of the continent's cultural heritage, and requires ever more sophisticated surface chemistry and analysis (see Mastering molecular matter). Today, chemists know much about surfaces and their engineering. This is due to the development of very sophisticated analytical tools, many of which had their origin in Europe. These techniques afford, for the first time, a real picture of the arrangement of, and the interactions between, atoms in the surfaces of crystals and materials. At the same time theoretical tools of quantum chemistry, developed over the past 15 years and to which European laboratories made very important contributions, are able to show interactions between atoms, molecules and clusters in a quantitative manner and, furthermore, single out the basic processes responsible for the interactions.
|
|
|
Early problems of chemistry were concerned with ionic and covalent interactions which form linkages
within molecules. Supramolecular chemistry is concerned with weak interactions between molecules
(hydrogen-bonding, van der Waals forces, etc) which lead to assemblies of molecules in specific
forms. Understanding the latter is now one of the main thrusts of modern chemistry and provides a
direct link to biology and materials science.
The self-organisation of molecules in supramolecular assemblies is based on molecular recognition phenomena and is relevant to replication processes occurring in living systems. The understanding of how replication occurs within the process of forming supramolecular assemblies will throw light on the origins of life itself, and will have a profound influence not only on life sciences, but also on many areas of chemistry, not least in the assembly of materials which have both structure and function (see Materials which make and do things). Parallel to the growth of activity in the area of supramolecular science is the drive towards nanotechnology. This parallel science often requires the construction of solid materials which have remarkable electronic, magnetic or optical properties.
|
|
|