The International Organisation for Standards (ISO) has described a “nano-tree” [2] for the categorisation of a wide ranges of nanomaterials, including nano-objects, nanostructures and nanocomposites of various dimensionality of different physical, chemical, magnetic and biological properties. The Institute of Nanotechnology (IoN) has published a glossary of nanotechnology terms [3].

References for the introduction

1. RC Evans, An Introduction to Crystal Chemistry - second edition, Cambridge University Press, Cambridge, 1966.  UOP Library
2. ISO/TR 11360:2010: Nanotechnologies - methodology for the classification and categorization of nanomaterials
3. Glossary of Terms (Institute of Nanotechnology)

Nanotechnology is an enormous subject.  For a comprehensive introduction see, for example, [1-3].  This page specifically addresses nanoscale composite materials and related structures.

• Carbon allotropes and nanotubes
• Curran^®: carrot fibres
• Exfoliated clays
• Fluid bicontinuous gels
• Nanocemology
• Micro Electro Mechanical Systems
• Nanotechnology probes

References

1. GA Ozin and A Arsenault - Nanochemistry: A Chemical Approach to Nanomaterials, Royal Society of Chemistry, Cambridge, 2005. ISBN 0-85404-664-x.
2. SC Tjong - Nanocrystalline Materials- Their Synthesis-Structure-Property Relationships and Applications, Elsevier, 2006. ISBN 0-08-044697-3.
3. WK Liu, EG Karpov and HS Park - Nano Mechanics and Materials, Wiley, 2006. ISBN-13: 978-0-470-01851-4.

Carbon allotropes and nanotubes

Elemental carbon can occur in an amorphous form or as either of two crystalline forms:

• diamond (cubic crystal structure with the neighbours of each atom symmetrically arranged at the corners of regular tetrahedron with a C-C bond length of 1.54Å), or
• graphite (parallel sheets of carbon atoms at the corners of contiguous regular hexagons with C-C bond length of 1.42Å within the sheet and 3.35Å between layers).

The carbon atom can also combine to form spheres and/or tubes at the nanoscale.  These structures include the Carbon 60 form known as buckminsterfullerene (named after the geodesic structures of Buckminster Fuller) discovered by Harry Kroto, Bob Curl and Rick Smalley in 1985 [1-3] which won them the Nobel Prize in Chemistry for 1996 [4].  James P Birk has presented a stereoscopic image of the C60 "bucky ball", while Jianyu Huang at Sandia National laboratories and Boris Yakobson at Rice University have used electron microscope video and computer simulations (YouTube Shrink Wrap buckyball video) show that buckyballs start life as distorted, unstable sheets of graphite which shed loosely connected threads and chains until all that remains is the perfectly spherical buckyball.

Iijima [5] discovered long, thin carbon nanotubes in 1991.  The topic was recently reviewed by Terrones [6].  The Iijima nanotubes were considered to be elongated fullerenes consisting of concentric graphene cylinders (multi-walled carbon nanotubes (MWNTs) with interlayer spacings slightly greater than that of graphite at 3.4Å.  Single-walled carbon nanotubes (SWNTs) have also been isolated.  The molecular configurations of SWNTs include "zigzag" (edges of the benzene rings running parallel to the tube axis), "armchair" (edges of the benzene rings running perpendicular to the tube axis) and "chiral" where the edges of the benzene ring follow a spiral path along the tube.

Terrones [6] suggests that optimal conditions for the arc discharge production of nanotubes involve passing a 80-100 amp DC current through high purity graphite electrodes (6-10 mm outer diameter at ~1-2 mm apart in a low pressure (500 torr) helium atmosphere.  A combination of carbon MWNTs and nested polyhedral graphite is deposited on the cathode at 1 mm/min while the anode is consumed.  Alternative production techniques [6] include:

• laser vapourisation of a graphite target sealed in an argon atmosphere inside a furnace at 1200°C.
• electrolysis of graphite electrodes immersed in molten lithium chloride under an argon atmosphere.
• chemical vapour deposition of hydrocarbons in the presence of metal catalysts.
• concentrating solar energy (flux equivalent to ~ 5 MW/m² producing a temperature of 2800K) onto a carbon-metal target in an inert atmosphere.

These production methods produce MWNTs and polyhedral particles from which they must be separated.  This might be achieved by oxidation at 700°C (<5% yield), filtering colloidal suspensions, ultrasonically assisted microfiltration or microwave heating together with acid treatments to remove residual metals.

Researchers at Cambridge University have produced live videos showing the nucleation and growth by chemical vapour deposition (CVD) of carbon nanofibres and nanotubes at minute particles of nickel catalyst.  The movies offer greater insight into the self-assembly of the microscopic structures.  The CVD process uses acetylene gas to deposit minute crystalline droplets referred to as "catalyst islands" (the nickel).  In nanofibre production, the catalyst was gradually squeezed upwards as carbon formed around it.  In single-walled nanotube production, the application of gas was reduced so that the carbon lifted off the catalyst to form a tubular structure.

The axial Youngs moduli and strengths of carbon nanotubes has been measured by a number of researchers:

Nanotube	Measured by	Young's modulus (GPa)	Strength (GPa)	Reference
MWNT	Thermal vibration inside TEM	1000-1800		7 (Treacy et al)
MWNT	Flexure of tubules in AFM	~1280		8 (Wong et al)
SWNT		320-1470 (mean = 1002)	13-52 (mean = 30)	9 (Yu et al)
MWNT	Tension/flexure in TEM	800	150	10 (Wang et al)

Tibbets et al [11] have reviewed the fabrication and properties of vapour-grown carbon nanofiber/polymer composites.  Gibson et al [12] have reviewed the vibration of carbon nanotubes and their composites.  The paper considers modelling and simulation of vibrating nanotubes, studies of nanomechanical resonators and oscillators, characterisation of nanotube mechanical properties, augmentation of the dynamic structural properties of composites, nanotube-based sensors and actuators, use of ultrasound to disperse the tubes in liquids (sonication), Raman scattering and interactions with high frequencies.

Poland et al [13] considered the similarities between the needle-like shape of carbon nanotubes and asbestos. They exposed the mesothelial lining of the body cavity of mice, as a surrogate for the mesothelial lining of the chest cavity, to long multiwalled carbon nanotubes. Asbestos-like, length-dependent, pathogenic behaviour included inflammation and the formation of lesions known as granulomas. On the basis of their results, they suggest there is a "need for further research and great caution before introducing such products into the market if long-term harm is to be avoided".

References for carbon allotropes and nanotubes

1. HW Kroto, JR Heath, SC O'Brien, RF Curl and RE Smalley, C60: Buckminsterfullerene, Nature, 1985, 318(6042), 162-163.
2. HW Kroto, Space, Stars, C60 and Soot, Science, 1988, 242(.), 1139-1145.
3. HW Kroto, C60: Buckminsterfullerene, the Celestial Sphere that Fell to Earth, Angewandte Chemie, 1992, 31(.), 111-129.
4. The Nobel Prize in Chemistry 1996, 9 October 1996
5. S Iijima, Helical microtubules of graphitic carbon, Nature, 1991, 354(.), 56.
6. M. Terrones, Carbon nanotubes: synthesis and properties, electronic devices and other emerging applications, International Materials Reviews, 2004, 49(6), 325-377.
7. MMJ Treacy, TW Ebbesen and JM Gibson, Exceptionally high Young's modulus observed for individual carbon nanotubes, Nature, 20 June 1996, 381(6584), 678-680.
8. EW Wong, PE Sheehan and CM Lieber, Nanobeam mechanics: elasticity, strength, and toughness of nanorods and nanotubes, Science, 1997,  277(5334), 1971-1975.
9. MF Yu, BS Files, S Arepalli and RS Ruoff, Tensile loading of ropes of single wall carbon nanotubes and their mechanical properties, Physics Review Letters, 2000, 84(24), 5552-5555.
10. ZL Wang, RP Gao, P Poncharal, WA de Heer, ZR Dai and ZW Pan, Mechanical and electrostatic properties of carbon nanotubes and nanowires, Materials Science and Engineering C: Biomimetic and Supramolecular Systems, 2001, C16(1-2), 3-10.
11. GG Tibbetts, ML Lake, KL Strong and BP Rice, A review of the fabrication and properties of vapor-grown carbon nanofiber/polymer composites, Composites Science and Technology, June 2007, 67(7-8), 1709-1718.
12. RF Gibson, EO Ayorinde and Y-F Wen - Vibrations of carbon nanotubes and their composites: a review, Composites Science and Technology, 2007, 67(1), 1-28.
13. CA Poland, R Duffin, I Kinloch, A Maynard, WAH Wallace, A Seaton, V Stone, S Brown, W MacNee and K Donaldson, Carbon nanotubes introduced into the abdominal cavity of mice show asbestos-like pathogenicity in a pilot study, Nature Nanotechnology, published online, 20 May 2008.

Other resources for carbon allotropes and nanotubes

• P Brown and K Stevens, Nanofibres and nanotechnology in textiles, Woodhead Publishing/CRC Press, cambridge/Boca raton, 2007.  ISBN: 1-84569-105-9.
• Peter JF Harris, Carbon Nanotubes and Related Structures: New Materials for the Twenty-First Century, Cambridge University Press, 1999. ISBN 0-521-55446-2 (hb) or ISBN 0-521-00533-7 (paper). Contents pages and Chapter 1
• Ado Jorio, Gene Dresselhaus and Mildred S Dresselhaus (editors), Carbon Nanotubes - Advanced Topics in the Synthesis, Structure, Properties and Applications Series: Topics in Applied Physics , Vol. 111 , 2008. ISBN-13: 978-3-540-72864-1.
• animated images from Shigeo Maruyama
• Thomas A Adams II, Physical properties of carbon nanotubes , 26 April 2000.
• Peter Harris, A carbon nanotube page, http://www.personal.rdg.ac.uk/~scsharip/tubes.htm
• David Tomanek, The Nanotube Site, 14 August 2006.
• Carbon nanotubes (Wikipedia).
• The nanotechnology era is here. The possibilities are endless. Ahwahnee Inc, 2003-2006.
• Nanotube Modeler: generation of nano-geometries (JCrystalSoft), 2005-2006.
    NanotubeModeler software download (4.2 MB, Version 1.3.3, 07/17/2006)

Curran^®: carrot fibres

David Hepworth and Eric Whale have founded a company, CelluComp (Burntisland, Fife, Scotland), to utilise nanofibres extracted from vegetables.  Their initial material choice is the carrot although turnips, swede (rutabagas) and parsnips are expected to also provide raw materials.  The fibres are claimed to have a modulus of 130 GPa, strengths up to 5 GPa and failure strains of over 5%.  The company's first product is the "Just Cast" fly-fishing rod.

References for vegetable fibres

• Donald Houston, Root Of Strength & Innovation, 09 February 2007.

• The future is orange for hi-tech material made from carrots, Guardian Unlimited, 09 February 2007.

Exfoliated clays

Many clays are layered inorganic compounds which can be delaminated (normally referred to as exfoliated in this context). These materials have potential as precursors for the development of various nanostructures.  The most common smectite clay used for nanocomposites is montmorillonite [1]. The montmorillonite nanoclay [2] has a plate structure with a thickness of one nanometre or less (a few atoms) and an aspect ratio of 1000:1 (hence a plate edge of ~ 1 μm) [with potential implications for health and safety].  Relatively low levels of clay loading are claimed to improve modulus, flexural strength, heat distortion temperature, barrier properties etc without compromising impact and clarity [2].

Maniar [2] identifies the first patent in this area as Carter et al (1950) [3] and the second as assigned to Unitka Limited in 1976 [4] with the market debut of a montmorillonite/polyamide-6 nanocomposite in 1989.

References for exfoliated clays

1. JN Hay and SJ Shaw, Clay-Based Nanocomposites (AZoM)
2. KK Maniar, Polymeric nanocomposites: a review, Polymer-Plastics Technology and Engineering, 2004, 43(2), 427-443 [103 references].
3. W Carter Lawrence, G Hendriks John and DS Bolley, Elastomer reinforced with a modified clay, United States Patent 2 531 396, 1950.
4. Unitka, Japanese Patent 109 998 , 1976 (no further detail in [2]).

Fluid bicontinuous gels

Colloidal particles (nanoparticles) can have equal affinity for two fluids and hence adsorb irreversibly to the fluid-fluid interface. Stratford et al have presented computer simulations of a pair of solvents containing such particles where the new interface formed on demixing sequesters the colloidal particles.  Interfacial tension forces the particles into close contact and the interface coarsens then is curtailed.  The jammed colloidal layer appears to enter a glassy state with a multiply connected, solid-like film in three dimensions. The resulting gel contains inter-penetrating domains of each fluid.

References for fluid bicontinuous gels

1. Philippe Poulin, New Gels for Mixing Immiscible Liquids, Science, 30 September 2005, 309(5744), 2174 - 2175 (Plymouth shelfmark 500SCI - not available in UoP electronic resources).
2. K Stratford, R Adhikari, I Pagonabarraga, J-C Desplat and ME Cates, Colloidal Jamming at Interfaces: A Route to Fluid-Bicontinuous Gels, Science, 30 September 2005, 309(5744), 2198 - 2201 (Plymouth shelfmark 500SCI - not available in UoP electronic resources) Supporting Online Material  Movie S1  Movie S2  Movie S3.

Nanocemology

Nanocemology [1] is the science of ultra-fine, micro- and nano-scale mechanisms occurring in, and affecting the performance of microscopic constituent materials and the pore structure of cement and concrete.  The Nanocem Marie Curie Research Training Network [2] aims to develop ultra-high-strength concrete of low permeability, high tensile strength whose density will be sufficient to secure high abrasion and chemical resistance.

References for nanocemology

1. D Ball, Nanocemology - the key to the future, Concrete, February 2007, 41(1), 29-30.
2. Nanocem Marie Curie Research Training Network

Nanotechnology probes

URLs for Atomic Force Microscope (AFM)

• Atomic force microscopy (Wikipedia)
• Atomic force microscopy: measuring intermolecular interaction forces - general concept and defining characteristics of AFM. from David Baselt, The tip-sample interaction in atomic force microscopy and its implications for biological applications, Ph.D. thesis, California Institute of Technology, 1993.
• Arunan Nadarajah, What is an Atomic Force Microscope?

URLs for Scanning tunnelling microscope (STM)

• Scanning tunneling microscope (Wikipedia)
• The Scanning Tunneling Microscope (NobelPrize.org)

URLs for Superconducting Quantum Interference Devices (SQUID)

• SQUID (Wikipedia)
• Superconducting Quantum Interference Device

URLs for nanotechnology

• AZojono - Journal of Nanotechnology Online
• Institute of Nanotechnology (IoN)
• Institute of Nanotechnology - Books

Further reading (most recent first)

1. Ignac Capek - Nanocomposite structures and dispersions, Elsevier, 2006. ISBN 0-444-52716-8.
2. EPS Tan and CT Lim - Mechanical characterization of nanofibers: a review, Composites Science and Technology, 2006, 66(9), 1102-1108. ISSN 0266-3538.
3. Kin-tak Lau, Chong Gu and David Hui - A critical review on nanotube and nanotube/nanoclay related polymer composite materials, Composites Part B: Engineering, 2006, 37(6), 425-436.
4. ET Thostenson, Chunyu Li and Tsu-Wei Chou - Nanocomposites in context, Composites Science and Technology, 2005, 65(3-4), 491-516.
5. R Murugan and S Ramakrishna - Development of nanocomposites for bone grafting, Composites Science and Technology, 2005, 65(15-16), 2385-2406.
6. Ludwik Leibler - Nanostructured plastics: Joys of self-assembling, Progress in Polymer Science, 2005, 30(8-9), 898-914.
7. Changchun Wang, Zhi-Xin Guo, Shoukuan Fu, Wei Wu and Daoben Zhu - Polymers containing fullerene or carbon nanotube structures, Progress in Polymer Science, 2004, 29(11), 1079-1141.
8. Zheng-Ming Huang, Y-Z Zhang, M Kotaki and S Ramakrishna - A review on polymer nanofibers by electrospinning and their applications in nanocomposites, Composites Science and Technology, 2003, 63(15), 2223-2253.
9. Suprakas Sinha Ray and Masami Okamoto - Polymer/layered silicate nanocomposites: a review from preparation to processing, Progress in Polymer Science, 2003, 28(11), 1539-1641.
10. Tianbo Liu, Christian Burger and Benjamin Chu - Nanofabrication in polymer matrices, Progress in Polymer Science, 2003, 28(1), 5-26.
11. Koji Ishizu, Keiichiro Tsubaki, Akihide Mori and Satoshi Uchida - Architecture of nanostructured polymers, Progress in Polymer Science, 2003, 28(1), 27-54.
12. ET Thostenson, Zhifeng Ren and Tsu-Wei Chou - Advances in the science and technology of carbon nanotubes and their composites: a review, Composites Science and Technology, 2001, 61(13), 1899-1912.