9.1 Aerospace and Automotive Industries

The dominant goal is to reduce vehicle weight without compromising the chemical and other attributes. For spacecraft, launch is one of the highest cost factors and is directly related to mass, but aircraft and even road vehicles benefit from reduced weight—less fuel is required to accelerate them. Hence there is much activity in seeking to replace the heavy metals used in components by lightweight polymers strengthened by nanoparticulate or nanofibrous additives (see Section 5.1.5). Other more specific aims include formulating lightweight electrically conducting materials for use in fuel lines to avoid the build up of static electricity, ultrahard (abrasion-resistant) paint, low-friction finishes, and so forth. A significant difference between aerospace and automotive is that the lead time for the introduction of an innovation is typically ten times longer in the former then in the latter (in which it is about three years), due to the more stringent needs for testing. Since sports equipment has many similar requirements, but is not usually safety-critical, it offers an interesting path for materials development and innovation to manufacturers in these sectors.

There is much interest in using nano-enhanced coatings to boost vehicle performance in various ways. Motor-cars and airplanes are customarily painted for decoration and corrosion resistance, but nanoparticles can confer other attributes such as hardness (useful for scratch resistance), colors that change with temperature or other environmental parameters, and textured coatings to diminish aerodynamic drag. Coatings nanostructured to make them omniphobic (cf. the hemoresistant surfaces being developed for medicine, see Section 6.3) are thought to be able to resolve the impasse in antifouling coatings for ships and boats due to the banning of most traditional antifouling materials because of their toxicity to other forms of marine life apart from the species unwantedly adhering to hulls. A more sophisticated application is self-healing coatings [1].

Sometimes the added nano-objects have an auxiliary function, such as metallic carbon nanotubes added to paint to make it sufficiently electrically conducting for use in electrostatic spray painting.

9.2 Agriculture

The main effect of nanotechnology is to introduce more precision into agriculture. Nano-enabled, powerful microprocessors enable computation to be all-pervasive. The farmer can integrate satellite and field data to optimize plowing, fertilization and planting schedules, and can even use a geographical information system to drive robots in his fields. Nanofertilizers can be custom-formulated for the particular conditions found in each of his fields, and the constituents of the fertilizers may themselves be nano-enabled, such as the nanochelates that are turning out to be especially useful for the delivery of essential metal ions. In the future, butchers may routinely employ tomography on carcasses to determine the optimal dissection. The tomography itself requires heavy computations; nanotechnology-enabled processing power may become powerful enough to enable the optimal dissection to be automatically executed by robots as well. Cold storage systems—and indeed the logistics of the entire global distribution system—are nowadays efficiently controlled by microprocessors.

There is considerable interest in sensors for detecting various kinds of contaminants in food, such as toxins, pathogenic microbes, or alien genes. Many of these sensors are based on the lab-on-a-chip concept and belong to the micro domain (cf. Chapter 6).

A nanosensor to gauge fruit ripeness, possibly even prior to plucking, may be useful but it is difficult to make a strong commercial case for its development, based on cost:benefit.

Nanostructuring fertilizers and pesticides (including fungicides and herbicides) may improve delivery and, hence, efficacy; it remains to be seen whether such approaches are truly cost-effective.

Looking back over the past millennia of human civilization, improvements in technology have enormously increased agricultural output, but this has also led to a concomitant increase in world population, hence global nutritional difficulties remain. Geographical mismatch of supply and demand is frequently mentioned as a contributor to malnutrition—somewhat ironically, in an age of unprecedentedly large global trade volumes. A serious current problem is that it is becoming increasingly clear that productivity increases imply product quality decreases. This goes well beyond mere unpalatability [2]. The output of the agro-industrial complex, unfortunately including residues of pesticides and the presence of hormone-active substances, may solve the basic malnutrition problem, but may introduce new problems of ill-health that seem to be deeply unsustainable, although the manufacturers of pharmaceuticals may see it as a source of new opportunities.

9.3 Architecture and Construction

The main application for nanotechnology in this sector is currently in materials, especially concrete enhanced using nanoparticles. Even though superior properties can be demonstrated, however, market penetration of nano innovations can be expected to be slow, because of the traditional low-tech attitudes prevailing in much of the industry. Nano-enhanced concrete is expected to be stronger (lessening the need for reinforcement) and more durable. Ultimately, the availability of dramatically new nano-engineered materials (e.g., ultrastrong and ultralight diamondoid panels) may usher in a totally new era of architecture.

The continuing penchant of architects for designing large buildings predominantly covered in glass has provided a welcome accelerator, however, because glass offers many possibilities for nanotechnological enhancement. In particular, nanostructured superhydrophobic surfaces imitating those of the leaves of plants such as the lotus enable raindrops to scavenge dirt and keep the surfaces clean. Nanoparticles of wide band-gap semiconductors such as titanium dioxide can be incorporated into the surface of the glass, where they absorb ultraviolet light, generating highly oxidizing or reducing or both species able to decompose pollutants adsorbed from the atmosphere. Ultrathin film coatings, even of metals, can be applied to the surface of glass, in order to control light and heat transmittance and reflectance. Sophisticated glasses with electrically switchable transmittance are now available. “Anti-graffiti” paint, from which other paint sprayed on can be easily removed, has also gained a certain popularity (although a social, rather than a technological, solution might be more effective at stopping the graffiti from appearing in the first place).

Multifunctional coatings, made by incorporating nano-objects in a matrix, achieve their multifunctionality (for example, fire resistance, thermal resistance, water resistance, color) through the incorporation of different kinds of particles. Typically they can be applied to exterior surfaces at any time after construction and offer a more versatile and cost-effective solution to refurbishment challenges than cladding.

Interiors can benefit from similar attributes, along with antimicrobial and anti-odor capability using the photocatalytic approaches described in Section 6.9.

9.4 Catalysis

About a quarter of the world market for catalysts is accounted for by oil refining, and over half is nowadays counted for by automotive exhaust catalysts. Concerns about air pollution in China are now increasing the proportion of smokestack catalysts used to decompose NO_x and SO_x.

It has long been recognized that the specific activity of heterogeneous catalysts increases with increasing state of division. This is of course an old market that has long been a very significant part of the chemical industry. The world market amounts to almost $$30\times {10}^9$, a very large proportion of which could be supplied by nanotechnology. However, even though many catalysts use nanosize metal clusters (for example), they cannot be called examples of atomically precise engineering. Indeed, the whole field is remarkable for the high degree of empirical knowledge prevailing. In the future, nanotechnology offers the chance to assemble catalysts atom-by-atom. There is a general feeling in industry that there is still considerable potential for increasing the activity of catalysts (that is, through both more effective acceleration of the desired reaction and more effective suppression of undesired side reactions).

9.5 Environment and Air Quality

“Environment” is a concept even more amorphous than energy in a commercial context. Here, we mainly consider the remediation of contaminated soils and groundwater by the addition of nanoparticles [3]. Regarding the latter, if a source of ultraviolet light is available (sunlight is adequate), titanium dioxide is a useful material; absorption of light creates electron–hole pairs acting as strong reducing–oxidizing agents for a large variety of organic compounds adsorbed on the nanoparticle surface. By this means many recalcitrant potential pollutants can be destroyed [4]. Until now attention has been mainly concentrated on the actual science of the photoassisted chemical decomposition rather than devising a complete process in which the nanoparticles, having done their work, would be collected and possibly regenerated for further use. A very convenient way to accomplish this is to first produce superparamagnetic nanoparticles (e.g., from magnetite) and then the coat them with the photocatalytic material to make a “core–shell” particle that can be conveniently displaced using an external magnetic field.

Soil remediation is also mainly concerned with eliminating pollution. In particular, iron-containing nanoparticles are being promulgated as superior alternatives to existing remediation procedures for soil contaminated with chlorinated hydrocarbons using more or less comminuted scrap iron—their decomposition is catalyzed by magnetite (Fe₃O₄). Hence the addition of nanoparticulate iron oxide to soil is a possible remediation method. Unfortunately there is minimal documented experience to guide the would-be practitioner. These environmental applications would have to operate on a large-scale in order to be effective. The effects of releasing large numbers of nanoparticles into the biosphere are not known. Iron is generally presumed to be a rather benign element, but nanoparticles may be able to penetrate within the microbial organisms ubiquitous in cells with unknown effects on their vitality and on interspecies interactions. In other words, this proposed technology raises a number of questions—to start with there does not seem to be any conclusive evidence that it is actually efficacious, and furthermore there is the still open question of the effect of dispersing a significant concentration of nanoparticles (and it has to be significant, otherwise there would be no significant remediation) on the ecosystem, especially microbial life in the soil.

One often hears it stated that nanotechnology will enable the environment to be returned to a pristine state, without an accompanying explanation of the process by which this rather vague assertion might be realized. It seems that there are going to be two principal impacts of nanotechnology on the environment. The first is immediate and direct (the use of nanoparticles for cleaning up pollution, as has just been discussed), the second long-term and indirect. The latter effects follow from the obvious corollary of atomically precise technologies—they essentially eliminate waste during fabrication. This applies not only to the actual fabrication of artifacts for human use, but also to the extraction of chemical elements from the geosphere (should those elements still be necessary). If the manufacture of almost everything becomes localized, the transport of goods (a major contributor to energy consumption and environmental degradation) should dwindle to practically nothing; the localized fabrication implied by the widespread deployment of productive nanosystems and personal nanofactories should eliminate almost all of the currently vast land, sea, and air traffic involved in wholesale and retail distribution; this elimination (and a commensurate downscaling of transport infrastructure) will doubtless bring about by far the greatest benefit to the environment of any aspect of nanotechnology. Furthermore, atom-by-atom assembly of artifacts implies that discarded ones can be disassembled according to a similar principle, hence the problem of waste (and concomitant environmental pollution) associated with discarded obsolete objects vanishes.

In the intervening period, the general effect of nanotechnology in promoting energy efficiency (see Chapter 7) will of course be beneficial to the environment—less transport of fossil fuels, less pollution from combustion, and so forth.

Concerns have, however, been expressed that some of the nanoparticles being promoted for use in a variety of products, especially those with some kind of antibiotic activity, among which silver nanoparticles are the most widespread, are harmful if released into the environment. The environment contains innumerable bacteria and other microbes, and nanoparticles designed for their antibacterial activity are evidently going to continue that activity wherever they are. Release is almost inevitable. Many textiles are already sold conjugated with silver nanoparticles; some of them will be released when the textiles are laundered. Once nanoparticles, not just silver ones, and other objects become routinely produced industrially, it is inevitable that they will find their way into watercourses in soils. Food chains will ensure that they are disseminated throughout the ecosystem. Being ultrasmall, nanoparticles are highly mobile and it will be extraordinarily difficult to contain them even during the manufacture of finished products incorporating them. Furthermore, there can be little control over their fate once the artifact containing them is discarded.

This is why there are already widespread calls for stricter regulation of the deployment of nanotechnology, particularly nano-objects in consumer products. These calls are driven by a growing awareness of the potential dangers of nano-objects penetrating into the human body, and by the realization that understanding of this process is still rather imperfect, and prediction of the likely effects of a new kind of nano-object is still rather unreliable. Furthermore, there have been a sufficient number of cases, albeit individually on a relatively small-scale, of apparently unscrupulous entrepreneurs promoting nano-object-containing products that have turned out to be quite harmful.

These calls, while seemingly reasonable, raise a number of difficulties. One is purely practical: once nano-objects are incorporated into a product they are extraordinarily difficult to trace. Traceability is only feasible up to the point of manufacture, and even then only if the manufacturer has sourced materials through a regulated or self-regulated commercial channel such as a commodity exchange. Establishing the provenance of nanoparticles that might turn up in a waste dump, for example, poses a very difficult forensic challenge.

Furthermore, regulation will become essentially meaningless if productive nanosystems become established: every individual would be producing his or her own artifacts according to his or her own designs and it is hard to see how this could be regulated.

Hence, we conclude that although on the whole nanotechnology must have a favorable impact on the environment, there are also some problematical aspects, which might partly be alleviated by regulation (cf. Chapter 15).

9.6 Lubricants

Low-friction coatings are classically made from layered materials such as graphite (C), molybdenum disulfide (MoS₂) or tungsten disulfide (WS₂). As well as the transition metal dichalcogenides, bismuth selenide (Bi₂S₃) and telluride and boron nitride (BN) are also important, and some transition metal oxides (e.g., MoO₃ [5]). Physical vapor deposition (e.g., sputtering) is suitable for applying the coatings. Coating thicknesses are typically several micrometers, and are not therefore in the nanoscale. The layered sulfides can yield a friction coefficient of less than 0.05 (0.005 appears to be possible), depending on environmental conditions (including humidity). This compares with steel on steel, which has a friction coefficient of about 0.8, falling to about 0.1 when lubricated with motor oil. Wear is also an issue, which is why thicknesses of less than a few hundred nanometers are not recommended. Some of these materials do not perform well over a wide range of temperature, especially in air, in which oxidation of the non-oxide materials might become problematical at higher temperatures.

Composite films can be used to combine properties. For example, cosputtering gold and molybdenum sulfide creates a low-friction electrically conducting coating useful for sliding electrical contacts.¹ More sophisticated composites are designed to adapt their structure and surface composition in order to maintain their tribological properties under varying conditions. For example, silver and molybdenum nanoparticles in an yttrium-stabilized zirconium oxide matrix, produced by cosputtering, provide a silver-rich surface for low friction at temperatures up to 500 ^∘C, above which diffusion causes the surface to become enriched in MoO₃; the diffusion can be controlled by incorporating a porous TiN layer within the structure [6]. The long-term behavior of these materials under storage is unknown; at low temperatures (i.e., after fabrication) the structure is metastable.

A successful low-friction coating might make the use of a liquid lubricant superfluous (which are anyway likely to be problematical in electrical applications).

As an alternative to precoating surfaces, the materials can be added to the lubricant in the form of nano-objects (e.g., nanoplatelets, which can be made from a wide variety of tribologically advantageous materials [7]) to lubricating fluids. The observed effects, which may include wear reduction, depend on the deposition of the nano-objects on the moving surfaces.

It is typical of the intermediate situation in which we currently find ourselves that nanotechnology can sometimes be used to enhance “subnano” technologies (i.e., finished with a precision lower than that of nanotechnology), the need for which will ultimately disappear. For example. If machining can routinely achieve a surface roughness of 1 nm combined with ultrahardness, lubricants may not be necessary, but as long as surfaces are still rougher or softer, nano-engineered lubricants (e.g., Au/MoS₂ solid lubricant films) offer better performance than conventional lubricants. Other examples of such intermediate or bridging technologies are to be found in the field of thermal management (Section 8.3).

A very hard carbon film called “near-frictionless carbon” (NFC), better than diamond-like carbon, has been developed by the Argonne National Laboratory which combines low friction (achieving a friction coefficient of about 0.04 in air and as little as 0.001 in dry argon) with great hardness. Hence, wear rates are extremely low ($<{10}^{-10}$ mm³ N⁻¹ m⁻¹, compared with ${10}^{-7}$ mm³ N⁻¹ m⁻¹ for unlubricated steel and ${10}^{-7}$ mm³ N⁻¹ m⁻¹ for conventionally lubricated steel).

9.7 Minerals and Metal Extraction

The current technologies based on pyrometallurgy used to extract metal from ores use vastly more energy than is theoretically required [8]. For example, currently a sulfide ore might be roasted to create the oxide, which is then reduced using carbon monoxide at high temperature. Not only is much energy required to maintain the high temperature of the process, but free energy is also wasted in the sense that the reaction of metal sulfides with oxygen is energetically downhill. There is also an enormous production of waste material (e.g., sulfur oxides), the dispersal of which is damaging to the environment.

Nanotechnology can be brought to bear on this problem in many different ways. Biomimicry seems a very attractive route to explore, especially since living organisms are extremely good at extracting very dilute raw materials from their environment, operating at room temperature and, seemingly, close to the thermodynamic limit (i.e., in a highly energetically efficient manner). The kidney is perhaps the most remarkable example of these features [9]; diatoms have the remarkable ability to concentrate silicon from the sea for use in their rigid cell walls. Nano-engineered “artificial kidneys” could be used not only to extract desirable elements from very dilute sources, such as seawater, but also to extract from elements or extractable compounds from natural water polluted with them. Catalysts will in this field too doubtless play a very important rôle, especially if nanotechnologists succeed in creating durable artificial enzymes able to catalyse the necessary reactions at room temperature.

In order to directly harness this general ability of living organisms to extract metals, higher forms of life are less suitable than prokaryotic microbes (bacteria and archaea), because prokaryotes have far more diverse metabolisms than eukaryotes. In prokaryotes it seems that for every naturally occurring metal there is a gene for handling it! Lithotrophic prokaryotes are perhaps of the greatest interest, especially those converting sulfides to soluble sulfates (and using this reaction as their energy source). They are indeed presently used in a few dozen plants around the world to leach cobalt, copper, gold, nickel, and zinc from their ores. Organisms expressing metal reductases may have even greater potential for extraction. Another approach is to use complex biomolecules (proteins) to specifically bind the metals to be extracted. Microbes proliferate exponentially and hence essentially unlimited quantities can be rapidly and usually economically obtained. The same applies to the products of microbial metabolism, such as metal-binding proteins. Furthermore, one is no longer restricted to what nature has evolved, but specific functionality can be engineered into a molecule or, indeed, into the entire microörganism.

9.8 Paper

This commodity is made in vast quantities (globally, about 100 million tonnes per annum) in most countries in the world. The primary constituent is cellulose fiber, but as much as half of the annual production of paper contains small particles (typically 10–20% of the total mass). The use of such fillers in papermaking has a long history [10]. The purpose is partly economic, the fillers being generally cheaper than the cellulose, and partly to better control attributes such as porosity, reflectance, ink absorption (printability), permeability, stiffness, and gloss. The particles may be present as a surface coating or incorporated within the bulk of the sheet. A new application for nanoparticles is to tag sheets of paper with distinguishable nanoparticles (for example, made up from different metals) for security and identification purposes. Such particles would, of course, only need to be present in minute quantities. Individual cellulose fibers are being coated with nanoscale polyelectrolyte films in order to enhance strength and other attributes of paper such as electrical conductivity [11]. The coating is a self-assembly process whereby the fiber is merely dipped in a solution of the polyelectrolyte. Ease of manufacture makes the treatment quite cost-effective (e.g., by doubling the tensile strength, single-ply sacks can be used instead of double-ply, but the cost per unit area of the paper is less than double that of the untreated material).

9.9 Security and Military

Military history is peppered with examples of lightly armed armies besting heavily armed opponents, by virtue of the superior mobility and speed of response conferred by the light weaponry. Every English schoolchild knows that the battle of Agincourt in 1415 was won by the English because of the decisive superiority of their light longbows, an innovative, superior technology in comparison with the powerful but heavy crossbow favored by the French. Even the much earlier (ca 1000 BC) story of the lightly armed, hence agile, David beating the lumbering Goliath illustrates this general principle at the level of the individual warrior; the innovation of the battlecruiser, championed by Admiral Fisher at the beginning of the 20th century, versus the heavier, slower battleship may be considered as yet another example. Seen in this light, nanotechnology is simply the latest means whereby military ordnance can be reduced in size and weight while keeping the same performance or even enhancing it.

Although military organizations such as the Department of Defense in the USA are spending a great deal on nanotechnology, most of the applications are generic, covering almost every aspect, ranging from essentially civilian applications such as ultralight clothing and footwear for an individual warrior to the sophisticated information-processing electronics that are embedded in almost everything. In other words, most military applications of nanotechnology currently under investigation are adaptations of civilian products (and many can be sourced from the civilian market) [12].

The traditional approach to making energetic materials is to mix separate oxidizer and fuel substances. The more finely substances are divided, faster the material will burn; that is, the greater its power density. If $d(t)$ is the nanoparticle diameter, writing $d(t=0)$ as $d_0$ we have

$d{(t)}^2=d_0^2-kt$

where k is the combustion rate coefficient, typically of the order of 1 mm² s⁻¹. Other beneficial effects of more finely dividing the two substances include diminution of the ignition delay time. Hence, there is a clear benefit in nanification. The ultimate degree of miniaturization might be considered to be a monomolecular energetic materials, in which each individual molecule has an oxidizing and fuel moiety. Although the power density is then higher than the mixture, the energy density (total energy released) is typically 10–12 kJ/cm³, only about half that of a mixture, although this limitation might be overcome by polymeric monomacromolecular energetic materials.

Furthermore, the smaller the fuel particles, the less severe the erosion of the walls of the system in which the fuel is flowing. This is an example of a situation in which there is an unmitigated advantage in nanification. Moreover, there is no absolute requirement for (expensive) atomic precision in the nanoparticle fabrication; some polydispersity can usually be tolerated.

Instead of using intimate mixtures of particles (powders), another approach is to create porous sol–gel materials, the gel of which is made from fuel and the pores of which are filled with oxidizer (or vice versa). These kinds of materials have been especially developed by the Lawrence Livermore National Laboratory in the USA.

The ultimate aim of nanotechnology is to perfectly order the components of the structure. In the case of energetic materials comprising separate fuel and oxidizer particles, this can be achieved by perfectly ordering the particles (“nanoblocks”).

The long-term stability of nano-energetic materials needs more research. How will their properties evolve during up to 20 years' storage? The enhanced reactivity of finely divided material suggests that degradation will be more rapid than for coarsely divided material.

Whereas a propellant should deflagrate, the explosive material in a warhead should detonate. The key question is how nanification affects the deflagration–detonation transition. This still needs to be researched. At present, there is still no definitive theory of energy release mechanisms applicable to real, three-dimensional materials (e.g., the deflagration–detonation transition has been largely studied using model one- and two-dimensional systems; the idea of the highly localized hotspot has been highly fruitful but is perhaps still used merely for want of anything better).

It is known that the sensitivity of explosive crystals such as RDX can be diminished by improving the crystal quality, diminishing crystal or molecular defects, eliminating voids (pores), eliminating chemical impurities, and eliminating multiple phases [13]. The sensitivity depends in a complex fashion on the particle size distribution, the optimization of which is still largely a matter of empirical testing. All of these features point to the great value of nanotechnology in achieving a generation of insensitive energetic materials.

The main effect of nanification is to increase the combustion rate (provided the particles are properly dispersed), cf. equation (9.1). There is, however, another effect due to the enormous increase in surface:volume ratio. The surface molecules have a significantly different coördination environment and, hence, reactivity compared with their bulk congeners. This not only affects the way the fuel reacts with the oxidizer, but may also lead to the surface of either component or both becoming slightly passivated. Provided this can be controlled, it is of interest for conferring insensitivity on munitions. At present, the main strategy for achieving relative insensitivity is indeed to cover the energetic material particles with a relatively inert ultrathin coating.

Homeland security is heavily focused on the detection of explosives. This calls for chemical sensors of trace volatile components, using the same kind of technology as is used for medical diagnostics applications (see Chapter 6), except that the focus tends to be on detection in the gas phase. Nanotechnology also enters into the video surveillance systems rapidly becoming ubiquitous in the civilian world, notably through the great processing power required for automated pattern recognition.

If ultralight nanocarbon electrical cabling with adequate power transmission capability becomes available (Section 7.3.3), it will doubtless become incorporated into missiles, in which the mass of copper cabling is presently significant.

9.10 Textiles

A natural textile fiber such as cotton has intricate nanostructure; the comfortable (to feel and to wear) properties of many traditional textiles result from a favorable combination of chemistry and morphology. Understanding these factors allow the properties of natural textiles to be equaled or even surpassed by synthetic materials. Furthermore, nano-additives can enhance textile fibers with properties unattainable in the natural world, such as ultrastrength, ultradurability, flame resistance, self-cleaning capability, modifiable color, antiseptic action, and so forth. Textiles releasing useful chemicals, either passively or actively, are also conceivable (of which the antiseptic textile, in which silver nanoparticles are incorporated, is a simple example; such functionally enhanced textiles are typically used in specialty applications, such as serving as a living cell scaffold assisting tissue regeneration, and as wound dressings; it should not be forgotten that these nanoparticles are fairly fugitive and may end up polluting the environment).

The addition of nano-objects to textiles essentially creates a particular kind of nanocomposite. It is also possible to nanostructure the textile fiber surface and to weave the textile from a nanoporous material. The nanomodification can be carried out either during preparation of the fibers, or during a subsequent stage, working with the finished fibers or even with the finished woven fabric. In general, nano-objects embedded within the fiber rather than on the surface using covalent chemical bonds will provide the most durable composition. Table 9.1 gives an indication of the relationship between nano-object type and novel property conferred onto the textile.

A general-purpose technology for fabricating nanofibers is electrospinning: a high electric field is applied to a liquid droplet (e.g., of a polymer solution), electrostatic repulsion opposes the surface tension to stretch the droplet until, above a certain threshold, a Taylor cone is formed [14], from which a stream of liquid emerges (if the molecular cohesion of the liquid is insufficient to prevent the stream breaking up, the phenomenon of electrospraying occurs); elongation and thinning of the fiber as the stream dries in-flight results in uniform nanofibres [15]. Inorganic nanofibers have been made by an ingenious extension of the process in which an organometallic precursor is mixed together with the polymer and the fibers are subsequently pyrolysed [16]. Inorganic nanofibers can also be produced by electrospinning molten ceramics at high temperatures.

9.11 Transport

Transport encompasses a heterogeneous set of applications, some of which have already been covered. Table 9.2 summarizes where they fit in.

The attraction of nanocomposites for the structure of vehicles is a low weight/strength ratio, making the vehicles more energy-efficient. Given the already sophisticated level of tire development, it seems doubtful that nanotechnology can be used to achieve any major improvement in rubber tires (e.g., by finding non-carbon substitutes for carbon black as a reinforcing filler).

Some of the most useful sensors for automotive vehicles, such as accelerometers, perform optimally in the microscale and their performance will degrade if further miniaturized. Motor-cars are already well sensorized. The introduction of autonomous road vehicles will make further demands on high-performance sensors. Anticollision sensors will make an important contribution to public safety. Whether the vehicles will be autonomous enough to allow the “driver” to sit in the back seat and become wholly absorbed in some other activity, as most people can nowadays in a railway train or an airplane, is questionable—at the very least the windows will probably have to be made translucent rather than transparent.

Given that about one third of global consumption of fossil fuels is used for transport in one form or another, planning software that can lessen the need for personal travel and the shipment of goods will potentially make a far greater contribution to the global economy and planetary sustainability than any improvements in materials and devices.