Paulo J. Ferreira

Nanomaterials and Nanotechnologies: An Overview

This chapter presents an overview of nanomaterials and nanotechnologies. Nanotechnology is used as a prefix for any unit such as a second or a meter, and it means a billionth of that unit. Hence, a nanometer (nm) is a billionth of a meter, or 10 −9 meters. To get a perspective of the scale of a nanometer, observe the sequence of images. Despite the wide use of the word nanotechnology, the term has been misleading in many instances. This is because some of the technology deals with systems on the micrometer range and not on the nanometer range (1–100 nm). Furthermore, the research frequently involves basic and applied science of nanostructures and not basic or applied technology. Nanomaterials are also not undiscovered materials, but nanoscale forms of well-known materials such as gold, silver, platinum, iron, and others. Finally, it is important to keep in mind that some past technology such as, for example, nanoparticles of carbon used to reinforce tires as well as natures photosynthesis would currently be considered a form of nanotechnology.

Nanomaterials and Nanotechnologies in Health and the Environment

This chapter discusses the application of nanotechnology in health and environment. There is little doubt as to the importance of nanomaterials in evolving medical and pharmaceutical applications. Biosensing technologies can use nanomaterials and nanotechnologies to increase our understanding of both the fundamental understanding of cells and a host of disease-specific phenomena. Diagnostic techniques rely heavily on detection and sensing in relation to various disease markers. Nanoparticles have been explored for use in detecting specific viruses and precancerous cells as well as others. Nanoscale dendrimers are important here. Dendrimers are synthetic, three-dimensional branching molecules that can be of great complexity. Considerable excitement surrounds the potential of nanomaterials in the remediation of many environmental problems that affect our society. Many kinds of needs for environmental remediation technologies exist, but air and water purification stand out as particularly important. Improvements in these areas would help alleviate many of the pressing health problems facing large population segments throughout the world.

Nanomaterials: Synthesis and Characterization

In inert gas condensation , an inorganic material is vaporized inside a vacuum chamber into which an inert gas (typically argon or helium) is periodically admitted. The source of vapor can be an evaporation boat, a sputtering target, or a laser-ablation target. Once the atoms boil off, they quickly lose their energy by colliding with the inert gas. The vapor cools rapidly and supersaturates to form nanoparticles with sizes in the range 2–100 nm that collect on a finger cooled by liquid nitrogen. In inert-gas or free-jet expansion , evaporated atoms are carried by a high-pressure helium gas stream that is expanded from a nozzle into a low-pressure chamber at supersonic velocities. The adiabatic expansion of the gas leads to sudden cooling, causing the evaporated atoms to form clusters a few nanometers in diameter. As in the case of inert gas condensation, the agglomeration of nanoparticles is a problem, requiring careful control of evaporation rate and inert gas flow; it is these that determine the particle size and distribution.

Chapter 6 – Nanomaterials: Classes and Fundamentals

Publisher Summary nThe most typical way of classifying nanomaterials is to identify them according to their dimensions. Zero-dimensional nanomaterials are materials wherein all the dimensions are measured within the nanoscale (no dimensions, or 0-D, are larger than 100 nm). The most common representation of zero-dimensional nanomaterials is nanoparticles. On the other hand, 1-D nanomaterials differ from 0-D nanomaterials in that the former have one dimension that is outside the nanoscale. This difference in material dimensions leads to needle-like shaped nanomaterials. One-dimensional nanomaterials include nanotubes, nanorods, and nanowires. Two-dimensional nanomaterials are somewhat more difficult to classify. However, assuming for the time being the aforementioned definitions for 0-D and 1-D nanomaterials, 2-D nanomaterials are materials in which two of the dimensions are not confined to the nanoscale. As a result, 2-D nanomaterials exhibit plate-like shapes. Three-dimensional nanomaterials, also known as bulk nanomaterials, are relatively difficult to classify. However, in keeping with the dimensional parameters, it is true to say that bulk nanomaterials are materials that are not confined to the nanoscale in any dimension.

Design Environments and Systems

Buildings and products invariably have some type of supporting structural system that provides the necessary framework for maintaining overall integrity in the presence of forces induced by the environmental or use context. In all these systems, a variety of stresses and deformations are developed within component members. Engineers and designers working with materials in the design of force-carrying components or structures of one type or another know that there are a host of material properties and characteristics that must be carefully defined and quantified before the material can be effectively used in a design context. Even within the general class of metals, however, huge differences between a material such as steel and cast iron. Strengths may be comparable, but steel is a ductile material, whereas cast iron is a brittle one, and failure modes are extremely different. An understanding of these differences has long influenced the use and design of structures in both architectural and mechanical design spheres.

Material Classes, Structure, and Properties

This chapter highlights the various aspects of materials such as classes, structure and properties. Metallic materials consist principally of one or more metallic elements, although in some cases small additions of nonmetallic elements are present. Examples of metallic elements are copper, nickel, and aluminum, whereas examples of nonmetallic elements are carbon, silicon, and nitrogen. Ceramic materials are composed of at least two different elements. Among the ceramic materials, one can distinguish those that are predominantly ionic in nature (these consist of a mixture of metallic elements and nonmetallic elements) and those that are covalent in nature (which consist mainly of a mixture of nonmetallic elements). In the Bohr atomic model, there is a nucleus consisting of protons with a positive charge and a mass of 1.67 × 10 -27 kg and neutrons with no charge but with the same mass as the protons. Composite materials are formed of two or more materials with very distinctive properties, which act synergistically to create properties that cannot be achieved by each single material alone.

Nanomaterial Product Forms and Functions

The exploitation of optical properties and phenomena are naturally done with nanoproducts that are primarily surface oriented, such as nanofilms, or alternatively phrased, the purpose of many surface-oriented nanoproducts has to do with optical properties—self-cleaning, antimicrobial, and so forth. Primary strength properties are normally a less important consideration in nanocoatings than are other properties. The general need and desire to keep surfaces clean and free of dirt has been long. In medical facilities, the need to keep surfaces from contributing to the spread of bacteria is obvious—hence the need for surfaces that are easy to clean or that have antibacterial or antimicrobial properties. Other functional needs related to surfaces include abrasion and scratch resistance. A successful quest for self-healing or self-repairing surfaces that recall similar behaviors in the skins of humans and animals would provide an enormous benefit to all. Materials with special behaviors related to light and color also have widespread applicability.

The Design Context

Typical product development processes may be generally thought of as occurring in several broad steps: definition of design needs or requirements, concept development, concept and preliminary design, design development, preproduction prototyping and evaluation, and production design. The design process does not necessarily march so literally from one step to another without a backward look. Good design work often comes from processes characterized as being the result of convergent back and forth iterations. Well-received design proposals are typically those that both meet functional requirements and have the kinds of design appeal with respect to both visual and user interface qualities that have long been known to characterize successful product designs. The final stage of production design involves making initial runs of the product, normally done using the actual intended production process. Initial runs are quite carefully monitored for production quality. Some units may be again placed into a user context for further evaluation and testing. Normally, production levels are quite small at first while process bugs are worked out and the workforce is trained. In combination with a marketing and distribution plan timetable, the product then goes into higher-volume production and is subsequently officially launched.

The Broader Context

This chapter presents the broader context of nanotechnologies. The automotive industry is already one of the worlds largest users of nanomaterials, and expectations are that uses will increase. General Motors was an early adopter in 2002 with its use of thermoplastic olefin nanoclay composites in running board step-assists. Intensive research is in progress on many other fronts, including propulsion and energy systems that use nanotechnologies. The automotive industry is by no means homogeneous, and drivers vary according to product type and market. In some companies with high-value products, the potential of small performance increments can and does justify extensive design and material innovations. In other companies, cost concerns dominate, and new materials will be less likely to be introduced in a widespread way unless their costs are on a par with or below those of conventional materials for equivalent performance levels. The role of nanomaterials and nanotechnologies in this area can be rather simply thought of with respect to basic systems and components (including propulsion and energy systems, suspension systems, and others), frame and exterior body components, interiors, and control and communication systems. Surface appearances, including finishing and painting, are invariably important for visible components.

Material Property Charts and Their Uses

This chapter introduces the charts and selection methods of material properties. Property charts are of two types: bar charts and bubble charts. A bar chart is simply a plot of one property. The largest is more than 10 million times greater than the smallest, so it makes sense to plot them on logarithmic, not linear, scales. The length of each bar shows the range of the property for each of the materials. Metals and ceramics have high moduli. Those of polymers are smaller, by a factor of about 50, than those of metals. Those of elastomers are some 500 times smaller still. Selection involves seeking the best match between the attribute profiles of the materials—bearing in mind that these must be mutually compatible—and those required by the design. The first task is that of translation: converting the design requirements into a prescription for selecting a material. This proceeds by identifying the constraints that the material must meet and the objectives that the design must fulfill. These become the filters; materials that meet the constraints.