Nanomaterials and Nanocomposites

Synthesis, Properties, Characterization Techniques, and Applications

Rajendra Kumar Goyal

• Publisher: CRC Press
• Year: 2017
• ISBN:
  9781351649315
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Materials Science
• Index: Technology & Engineering

The main aims of this book are to summarize the fundamentals, synthesis methods, properties and applications of nanomaterials, so as to provide readers with a systematic knowledge on nanomaterials. In addition, the book covers most commonly used characterization tools pertaining to nanomaterials. Further, it deals with relevant aspects of nanocomposites which contains dispersion of nano-sized particulates, and carbon nanotubes (CNTs) in the matrices (polymer, metal and ceramic). It also discusses development of smart nano textiles (intelligent textiles), self-cleaning glass, sensors, actuators, ferro-fluids, and wear resistant nano coatings. Aimed at senior undergraduate and graduate students, the key features on this book include:

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• Top-down and bottom-up approaches for the synthesis of nanomaterials included

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• Illustrates sample preparation and basic principle of characterization tools for nanomaterials

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• Explains calculation of ratios of surface area to volume and surface atoms to bulk atoms

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• Reviews synthesis, properties and applications of carbon nanotubes and magnetic nanomaterials

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• Discusses size effect on thermal, mechanical, optical, magnetic and electrical properties

1

Introduction to Nanomaterials and Nanotechnology

1.1Introduction

The term nano is originated from the Greek word for dwarf or an abnormally short person. It is used as a prefix for any unit such as a second or a meter, and it means a billionth (10−9) of that unit. Therefore, a nanometer (nm) is a billionth of a meter. In a broad term, nanomaterials are the materials with sizes of the individual grain or particle in the range of 1–100 nm at least in one dimension. One nanometer is approximately the length equivalent to 10 hydrogen or 5 silicon atoms aligned in a line. A nanomaterial is often characterized by a dimension linked either to the dimension of the salient nanofeatures making up the material or to their organization. When some interesting property of a material emerges from the organization or pattern of random or well-ordered nanopatterns, the resultant material is referred to as nanostructure or nanostructured material. To get an idea about how much larger nanomaterials have compared to their bulk counterparts, think about a small particle with a diameter of a little >10 µm = 10−5 m, which itself is too small to be seen by naked eyes and compare it with a particle with a diameter of 1 nm = 10−9 m. The ratio of the diameters of these two objects is 104. In other words, nanoparticle with a size of 1 nm is smaller by 104 times than an object of 10 µm in size. In addition, this single micrometer-sized particle is equivalent to 1012 nanoparticles by mass. This simple comparison makes it clear that nanoparticles are really very small and also expose a large fraction of atoms on their surfaces, that is, >1% depending upon the size, whereas bulk has insignificant amount of surface atoms (i.e., <0.01%). Nanomaterials exhibit multifunctional properties which are distinctively different from that of bulk materials. For example, the crystals in the nanometer scale have a low-melting point, reduced lattice constants, different crystal structure, disappearance or shift of Curie temperatures (of ferroelectrics and magnetic materials), changed electrical conductivity of metals or oxides, increased oxidation and wear resistance, and higher sensitivity of sensors compared to their bulk counterparts. The semiconductors and metals become insulators and semiconductors, respectively, when the characteristic size of nanoparticles is few nanometers. Interestingly, gold, palladium, and platinum nanoparticles with size below ∼5 nm exhibit excellent catalytic properties at low temperatures. The decrease in gold particle size shows blueshift (i.e., a decrease in peak absorption wavelength). Similarly, when the size of semiconductors is reduced below their Bohr radius, a dramatic change in optical properties is found, for example, change in color. This property has been exploited to probe whether a certain DNA corresponds to a particular individual or not. Quantum dots are crystals consisting of a few hundred atoms, where the electrons are confined to widely separated energy levels. The shape and size of quantum dots determine their electronic, magnetic, and optical properties. Magnetic nanoparticles are now being used to detect the particular biological species that cause disease.

There are many methods to classify synthesis techniques of nanomaterials. Some of those methods are top-down and bottom-up approaches. Top-down includes mechanical alloying, nanolithography, electron-beam lithography, x-ray lithography techniques, soft lithography, and severe plastic deformation. The bottom-up approach includes synthesis of nanoparticles by physical vapor deposition, chemical vapor deposition, colloidal route, green chemistry route, and sol-gel method, where there is buildup of atoms or molecules layer by layer. In general, nanoparticles or nanoplatelets or nanotubes are energetically not favorable and therefore their properties have been exploited by embedding them in polymer or metal or ceramic matrices to make them thermodynamically stable nanocomposite.

In general, nanotechnology is the science and technology which involves design, fabrication, and applications of nanostructures and nanomaterials with typical size smaller than 100 nm. Nanotechnology is a broad interdisciplinary field, which requires expertise in physics, chemistry, materials science, biology, mechanical and electrical engineering, medicine, and their collective knowledge. It is the boundary between atoms/molecules and the macroworld. Nature provides numerous excellent examples of nanotechnology such as biomineralization (in abalone shell or human bones), lotus leaves, photosynthesis (in plants), strength and toughness of spider silk, adhesion mechanism in Gecko foots, peacock feather, and excellent antireflection property in moth eye, etc.

1.2Nanotechnology in Past

The twenty-first century has witnessed a tremendous upsurge in the field of Nanomaterials and Nanotechnology. However, this field is not new because its seeds have been sown in the past centuries. A well-known gold ruby glass, which consists of a glass matrix with dispersion of gold nanoparticles was first produced by the Assyrians in the seventh-century BC and reinvented by Kunkel in Leipzig in the seventeenth century [1]. The stained-glass windows and Lycurgus cup are the examples of Medieval era/Roman era which consist of a few tens parts per million (ppm) of gold and silver nanoparticles in the glass matrix and exhibit unique optical properties. Chinese are known to use gold nanoparticles as an inorganic dye to introduce red color into their ceramic porcelains for more than thousand years. In 1857, a stable colloidal gold has been prepared by Faraday which was destroyed during World War II. The colloidal gold was, and is still in use to diagnose several diseases and for treatment of arthritis. The beautiful Mayan blue paint of the ancient Mayan world has long been admired for its marvelous color qualities as well as its inherent resistance to deterioration and wear over long periods of time. The particular blue color has been attributed to the dispersion of the unique combination of oxide nanoparticles, indigo molecules, and clay particles.

Although some unique examples of nanomaterials or nanotechnology can be traced back for centuries, the current excitement of nanotechnology is toward shrinking of the devices such as personal computer, laptop, smart phone, embedded processors etc. In 1959, physics Nobel Laureate Richard Feynman gave a talk entitled “There’s Plenty of Room at the Bottom” at California Institute of Technology on the occasion of the annual meeting of the American Physical Society. Although, Feynman could not predict about nanotechnology, his lecture became a central point in the field of nanotechnology. The term nanotechnology was first used in 1974 by Norio Taniguchi to refer to the precise and accurate tolerances required for machining and finishing materials using top-down approach. The top-down approach describes the processes starting from large pieces of material to produce the intended structure by mechanical or chemical methods. The bottom-up approach processes are the chemical processes starting from atoms or molecules as the building blocks to produce nanoparticles, nanotubes, nanorods, thin films, or layered structures. The continued decrease in device dimensions has followed the well-known Moore’s law predicted in 1965 (Figure 1.1), which states that the dimension of a device halves approximately every 18 months and today’s transistors have well fallen in the nanometer range [2]. In fact, in 1965, Gordon Moore noticed that the number of components in integrated circuits had doubled every year between 1958 and 1965. Thereafter, the doubling period increased from 1 year to ca. 18–24 months. For example, there were 4500 transistors in the 8080 microprocessor (with memory size 64 KB) introduced in 1974. Compared to this, th...