Carbon exists the nanoscale dimension as graphenes, carbon nanotubes, liquid crystals, nanoshells, and other soft matter. Fullerenes, which have atoms arranged in closed shells, include buckyballs (particles that have millions of atoms, with dozens of concentric shells like a set of Russian dolls that fit one into another from the smallest to the biggest one), carbon nanotubes, nanofibers, and carbon nanobuds.
In both the micro-scale and the macro-scale dimensions, pure carbon has the diamond-type bond and the graphite-type bond between carbon atoms (existing for example, in pencil lead). At the nanoscale, carbon develops a specific type of bonding: buckyball bonding, typical of the carbon nanotubes; covalent bonds between carbon atoms make buckyballs very strong, so they are used to strengthen composites (PennState modules, 2011).
In 1996 nanotech pioneers Richard E. Smalley, Harold Kroto, and Robert Curl won the Nobel Prize for Chemistry for their discovery of a new allotrope of carbon. In 1985 they discovered a molecule made of 60 carbon atoms, about 1 nm in diameter, which Smalley called a buckminsterfullerene or a buckyball because it resembled geodesic domes created in the 1960s by the architect Richard Buckminster Fuller. This discovery opened a new section of chemistry, with applications in astrochemistry, superconductivity, and chemistry/physics material science, for example for catalytic methane activation.
Fullerenes have atoms bonded in a form of an empty sphere, ellipsoid or a tube. Examples of fullerenes are buckminsterfullerenes (or buckyballs, spherical molecules where carbon atoms are connected in a pattern of hexagons and pentagons) and carbon nanotubes. The most common buckyball contains 60 carbon atoms and is called C60. Carbon nanotubes are cylindrical fullerenes, usually a few nanometers wide (tens of thousands times smaller than the diameter of human hair) but they may be micrometers up to centimeters long. Single walled carbon nanotubes are the rolled sheets of graphene. Multi walled nanotubes take form of the parchment or Russian doll model; their production is cheaper.
Smalley envisioned a power grid of nanotubes that would distribute electricity from solar farms. He believed nanoscale missiles would target cancer cells in human body. He spoke this on June 1999 but he died of non-Hodgkin lymphoma on October 2005. The IBM Research–Zurich scientists Gross, Mohn, Moll, Liljeroth, & Meyer (2009) provided images of single carbon molecules and their chemical structure with unprecedented atomic resolution by probing the short-range chemical forces with use of noncontact atomic force microscopy. They could imagine not only the physical shape of a single carbon nanotube but even the bonds to the hydrogen atoms could be seen (Palmer, 2009).
Fullerene C60 is a black solid that sublimes at 800 K and is soluble in common solvents such as benzene, toluene or chloroform. In 2007 Nasibulin et al. (2007) have synthesized NanoBuds – a hybrid material that combines fullerenes and single-walled carbon nanotubes into a structure where the fullerenes are covalently bonded to the outer sidewalls of carbon nanotubes. Nanobuds have combined mechanical and electrical properties of both these structures. Buckyball bonding is a specific type of bonding typical of the carbon nanotubes.
The soft condensed matter is in a state neither liquid nor crystalline. Liquid crystals, biological tissues: cells, and a cytoplasm, biological membranes, microfilaments and filamentous networks, e.g., a cytoskeleton present in all cells, molecular mono-layers, polymers and biopolymers (such as DNA or filaments in neuronal or muscle fibers), and also liquid crystals are called soft matter. We all can be called soft matter, as well. When we look at things in the nano scale we can credit a great amount of everyday things as soft matter including food, soap, ink, paint, cosmetics, putty, and gels. Research community has studied nanoparticles for several decades. Scientists and practitioners explore complex soft matter in order to understand general principles that drive behavior and properties of the nanoscale structures. They develop measuring tools, new chemical structures and new technologies, and examine processes going at the nanoscale.
Natural and engineered small particles range from one nanometer to tens of microns. In atmosphere, where there is from a few to a few thousand of small particles/cm3, they impact both warming and cooling of the climate. In Earth sub-surface, they impact soil and water quality. Small particles have an effect on catalysis and reaction engineering, material design, and synthesis. Isotopic signature (with krypton or xenon isotopes) of some nanodiamonds indicate they were formed outside the solar system, whether in supernova or in interstellar medium. The noble gas atoms such as neon can also be seen in a monolayer of carbon when it is trapped inside 60C cages that were formed at the same time as the nanodiamonds.
The developments in nanoscale and molecular-scale technologies let us study the nanoscale objects: liquid crystals, soft matter, nanoshells, and carbon nanotubes. We may learn about structures and actions going in the nanoscale and how can we use nanoparticles and nanotechnology. These technologies make a background for progress in energy conservation in micro and nano scale. Nanotechnology can impact cancer treatment, clinical neuroscience, tissue engineering, drug delivery, and diagnostics.
Size dependent properties of nanoparticles
Familiar materials develop odd properties when they’re nanosize because their atomic structure is determined differently at this level. Materials at the nanoscale level display quantum mechanics effects, distinct from those of materials controlled by laws of classical physics. At the nanoscale level only certain energy levels are allowed, and the levels allowed depend on the size of a particle; this creates difference in energy ΔE between a particle and its environment (ΔE becomes bigger when particles are smaller).
As the size of a particle decides on the value of ΔE, the same light wavelength would produce different colors of particles of silver and gold: silver spheres of a size about 40 nm look blue; gold spheres ~80 nm look light green; gold spheres ~120 nm look yellow; gold spheres ~50 nm look deep green; gold spheres ~100 nm look orange; and silver spheres ~100 nm look green deep red.
In the natural settings, nanostructures at the butterfly wings scatter and diffract light giving us the perception of different colors. When seen at different magnifications, butterfly wing scales look different: a wing that is dark blue when looked at without magnification becomes yellow at 220x magnification, purple at 5000x magnification, and green at 20000x magnification (PennState modules, 2009; Cook, 2005).
Metal nanoparticles become easily ionized and, when inserted into textiles, metal ions kill bacteria present there and thus make clothing odor-free and odor-resistant. When inside of a bacteria, silver ions prevent transport across the cell wall, metabolism, respiration, RNA replication, and thus reproduction of the bacteria. Soft materials have many other chemical and mechanical characteristics that are useful in technology, such as quantum size effects, responsiveness to small electrical fields and to chemical or thermal actions, and flexibility, so they are used in a fast growing number of applications (for example, in flat panel LCD TVs) (PennState modules, 2009; Cook, 2005).
Electrons can tunnel through a barrier formed by potential at semiconductor junctions. Leo Esaki and Ivar Giaver were awarded the 1973 Nobel Prize for the 1958 discovery of the tunneling phenomenon. Visible light has a wavelength λ between 400 and 750 nanometers. It is larger than the radii R of the nanostructures. Specific wave properties of the soft matter are caused by the size of nanostructures that is smaller than the wavelength λ of visible light, so light interacts with nanostructures (scatters and diffracts) differently.
Some properties of nano-scale objects are unique, such as a small size as compared to biological structures and macromolecules, and large surface to volume ratio resulting from the small size and the placing of particles on the surface of nano particles. Some properties of nanoparticles, for example, the melting temperature of gold, depend on the surface to volume ratio. The smaller is a nano particle the lower is its melting temperature because there is higher percentage of (not bound) atoms on the surface. If we succeed to cut familiar materials and reduce them to a nanoscale size they would develop odd properties. For example, aluminum foil, which would normally behave like aluminum, would explode when cut in strips 20 to 30 nanometers thick. Catalysis – the acceleration of chemical processes goes faster as the particles become smaller, the ratio of the surface area to the volume of the particles increases, and nanoparticle catalysts become more reactive.
The carbon nanotubes display several particular properties; they perform ballistic conduction – the flow of charged particles; they conduct phonons, which means quantum vibration; they absorb radiofrequency (which is promising in therapy); they also display surface plasmon (a quantum of plasma oscillation) resonance under an electrical field. There are also several forms involving other elements, such as perfluorocarbons, magnetic iron oxide nano particles, and also silver nanoparticles that are used to coat medical instruments. Buckyballs are good electron acceptors from other materials. They are used to improve efficiency of solar cells that transform sunlight into electricity.
Buckyballs can deliver drugs or radioactive particles to attack cancer cells. However, buckyballs may have different configurations: along with a plain buckyball, a tris configuration exists, which has three molecular branches coming off the main structural body in one hemisphere, and a hexa configuration that has six branches arranged in a symmetrical pattern. Toxicologists from the Los Alamos National Laboratory in New Mexico recommend the use of the non-toxic hexa configuration; the cells exposed to the tris buckyballs enter the suspended animation state where they don’t die, divide, or grow. The researches also work on turning the tris buckyballs into a weapon for halting the spread of cancer cells or delaying the onset of Parkinson’s or Alzheimer’s in nerve cells (Hsu, 2010). Chemotherapy kills cancer cells but it also kills a lot of healthy cells. Scientists from the Virginia Commonwealth University have devised a technique for placing radioactive molecules inside the buckyballs to deliver them to specific cancer cells. This method would provide a targeted chemotherapy that would avoid the painful and prolonged side effects caused by today’s full-body radiation treatments. Targeted radioactive buckyballs could possibly also serve for creating diagnostic techniques with super-accurate MRIs (Fox, 2009). Mroz et al. (2007) applied photodynamic therapy by producing functionalized fullerenes (biologically inert fullerenes changed into photosensitizers), which caused the death of the mouse cancer cells incubated for 24 h with fullerenes and illuminated with white light. Highly water-soluble fullerene C60 can deliver biologic and cancer drugs across biological barriers. With the use of a laser-scanning confocal microscopy and flow cytometry it can be seen how C60 nanoparticle (C60-serPF) is internalized in the nucleus (through the nucleus pore complex) within living cancer cells, and how the buckyballs escape engulfing by the endocytic vesicles (Raoof et al., 2012).
The mechanical tensile strength, high electrical and heat conductivity, and chemical inactivity of nanotubes make them useful in nanotechnology, electronics, optics, material and architectural science domains, and many other applications. They are applied for strengthening materials (e.g., carbon-fiber frames for bicycles), gluing, food processing, preservation with additives, and packaging, coating transparent conductive display films, building artificial muscles (Aliev, Oh, Kozlov, Kuznetsov, Fang, Fonseca, Ovalle, Lima, Haque, Gartstein, Zhang, Zakhidov, & Baughman, 2009), space elevators, a body armor (in the MIT’s Institute for Soldier Nanotechnologies: ISN, 2010), waterproof and tear-resistant textiles (Dalton, Collins, Muñoz, Razal, Von Ebron, Ferraris, Coleman, Kim, & Baughman, 2003), non-cracking concrete, and a lot of other implementations such as fold-away mobile phones, wallpaper-thin lighting panels, and the next generation of aircraft. Professional forensic investigation uses nano technology. Credit cards may possible soon contain as much processing power as current smart phones. Research teams focus on nanotechnology applications in countless areas of life. The precise delivery of drugs with the use of nanostructures (such as by the RNA strands 10 nano in diameter) may help avoid side effects. Nanotechnology applications serve in fighting cancer by attaching nanostructures and destroying cancer cells; in tissue engineering by building scaffolds for cell growth and differentiation; for clinical neuroscience, to enhance neuronal signaling and survival potential by supplementing the nervous system with nanoparticles or nanomaterials; in surgery by welding tissues: stem cell culture matrices by building scaffolds for stem growth and tissue differentiation for further transport; and for diagnostics, by utilizing contrast agents (Burgess, 2012). While nanoparticles had been considered extremely toxic, Chan (2007) concluded that the evidence, which has been gathered since the discovery of fullerenes, overwhelmingly points to C60 being non-toxic.
Nanofabrication – making nanoscale structures
Nanoparticles can be made “top down” by chopping a bulk material into nanosize bits or “bottom up” by growing molecules like crystals in controlled conditions. These approaches can be combined into a hybrid nanofabrication. Nanoscale structures may include nano particles such as macromolecules, beads, tubes, wires; planar structures built, for example by layers; and hybrid mixtures of particles and planar structures.
With a top-down approach, material is removed or added in layers using mechanical or chemical means, such as lithography. Thus, the top-down approach may involve several basic steps such as deposition (the additive process causing the film growth), material modification (designing chemical, physical, and electrical properties of the nano material), etching (the subtractive process – material removal), and lithography, externally imposed pattern transfer: writing where material should be added or removed. Usually, computer programming provides the content for transfer. In some cases there is inherent pattern, such as the self-assembling of an antigen and antibody due to shape, size, and chemical bonding. These processes allow forming the layers (films) into nano structures. Lithography of many kinds may include photolithography, electron beam lithography, ion beam lithography, dip pen lithography, embossing lithography, stamp lithography, molding lithography, and self-assembly lithography.
With the bottom-up approach, which can often be seen in nature, small components are building blocks for a structure. Nano structures are built from atoms, molecules, particles, their combinations, and layers. They grow molecule-by molecule and have often the ability to self-assemble spontaneously in response to a trigger (Cook, 2005). The bottom-up approach involves chemical or physical self-assembly, catalyzed nano-wire (nanotube, about 1.3 nm in diameter) growth, colloidal characterization with the use of optical means, scanning probes, and electron microscopy (NSF NACK Center, 2012). For example, with a bottom-up nanofabrication sequence a nanoparticles may be synthesized made functional, linked with antibodies, or attached to the antigen (PennState modules, 2009).
Both methods of the nanoscale structures production are used in the semi-conductor industry to fabricate integrated electronic circuitry. Microelectronics is changing into nanoelectronics. By making the nanoscale sized transistors engineers can put millions of transistors per square inch. The provide more processing per square inch, more memory, and faster communication, so computers become faster.
Knowledge about how can we use nanoparticles and nanotechnology inspires technology-oriented people to design biologically inspired models, materials, applications, tools, and devices. For example, graphene is considered the thinnest and the strongest material that can sustain great densities of current, has great thermal conductivity, stiffness, is impermeable to gases, and allows investigation of relativistic quantum phenomena in laboratory experiments (Geim, 2009). Freestanding monolayer graphene membranes, and also monolayers of graphene on silicon dioxide, are considered one of the strongest materials ever measured (Grantab, Shenoy, & Ruoff, 2010). Also, thermal conductivity of suspended graphene exceeds that of diamond and graphite, so this feature of graphene can be useful in nanoelectronics. Graphene can carry electric charges far faster than currently used materials. Graphene has been used as ‘electrodes’ for solar cells but it wasn’t used as semiconductor applications because it is a poor semiconductor and has been difficult to add metal contacts to shuttle electric charges into and out of it. In 2009, a solution has been found in the process of baking the wafers of crystalline silicon carbide (Palmer, 2012).
Nanoceramic filters allow water purification pushing water through nanotubes or the 10-9 m to 10-11 m membranes. Carbon nanotubes are distributed on small cement grain to achieve superior strength concrete for construction. A single silicon wafer, a macroporous silicon film has been produced as an anode material for lithium ion batteries (Thakur, Pernites, Nitta Isaacson, Sinsabaugh, Wong, & Biswal, 2012). Integrated scientific and educational program at the Institute for Complex Adaptive Matter (ICAM-I2CAM, 2012) includes exploratory workshops, symposia, fellowships, and research and educational networks. In a research on molecular and cellular biology Selvin (2012) and his group developed a method for recording the walking motion at a distance of 74 nm for the biggest motor (myosin V), and 16 nm for the smallest motor (kinesin), which is 30 times smaller than the diffraction limit of light. DeWitt, Chang, Combs, & Yildiz (2012) examined, with a 3 nm precision, a dynein motor that transports a multitude of cargos along the microtubule in the cell cytoplasm. Dynein takes part in many cellular processes including organelle transport and cell division. The dynein motor converts chemical energy of the ATP hydrolysis to mechanical work (ATP – adenosine triphospate transports energy within cells for metabolic processes). By recording single molecule fluorescence, Yildiz, Forkey, McKinney, Ha, Goldman, & Selvin (2003) could see steps sizes of each head of the myosin V that moves on a protein actin filament in a cell.
Carbon in New Materials
Carbon is often present in synthetic fibers, which may comprise small molecules or polymers, mostly synthesized ones. They include mineral fibers such as made of carbon, glass, basalt, or some metals, as well as polymers, which include acrylic, aramid, microfiber, nylon, polyester, polyethylene, spandex, and several other materials. Some fibers have been also artificially made from cellulose, for example acetate and triacetate, art silk, bamboo derived cellulose products, and rayon of several kinds. Synthetic fibers are usually formed through the melt-spinning process or by forcing synthetic materials through holes to make threads.