Examine individual changes

'{{Nanomat}} {{Nanotech}} '''Nanomaterials''' is a field that takes a [[materials science]]-based approach to [[nanotechnology]]. It studies materials with morphological features on the [[nanoscale]], and especially those that have special properties stemming from their nanoscale dimensions. Nanoscale is usually defined as smaller than a one tenth of a micrometer in at least one dimension,<ref>{{cite journal| url=http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=BJIOBN00000200000400MR17000001&idtype=cvips&gifs=Yes| author = Cristina Buzea, Ivan Pacheco, and Kevin Robbie|title =Nanomaterials and Nanoparticles: Sources and Toxicity| journal= Biointerphases| volume= 2|year = 2007| pages= MR17–MR71| doi=10.1116/1.2815690| pmid=20419892| issue=4}}</ref> though this term is sometimes also used for materials smaller than one micrometer. ==Background== An important aspect of nanotechnology is the vastly increased [[ratio]] of surface area to volume present in many nanoscale materials, which makes possible new [[quantum mechanical]] effects. One example is the “[[quantum]] size effect” where the electronic properties of solids are altered with great reductions in particle size. This effect does not come into play by going from macro to micro dimensions. However, it becomes pronounced when the nanometer size range is reached. A certain number of [[physical properties]] also alter with the change from macroscopic systems. Novel mechanical properties of nanomaterials is a subject of [[nanomechanics]] research. Catalytic activities also reveal new behaviour in the interaction with [[biomaterial]]s. Nanotechnology can be thought of as extensions of traditional disciplines towards the explicit consideration of these properties. Additionally, traditional disciplines can be re-interpreted as specific applications of nanotechnology. This dynamic reciprocation of ideas and concepts contributes to the modern understanding of the field. Broadly speaking, nanotechnology is the synthesis and application of ideas from science and engineering towards the understanding and production of novel materials and devices. These products generally make copious use of physical properties associated with small scales. As mentioned above, materials reduced to the nanoscale can suddenly show very different properties compared to what they exhibit on a macroscale, enabling unique applications. For instance, opaque substances become transparent (copper); inert materials attain catalytic properties (platinum); stable materials turn combustible (aluminum); solids turn into liquids at room temperature (gold); insulators become conductors (silicon). Materials such as [[gold]], which is chemically inert at normal scales, can serve as a potent chemical [[catalyst]] at nanoscales. Much of the fascination with nanotechnology stems from these unique quantum and surface phenomena that matter exhibits at the nanoscale. trolololololololololololololoolololololol ==Uniformity== The chemical processing and synthesis of high performance technological components for the private, industrial and military sectors requires the use of high purity [[ceramics]], [[polymers]], [[glass-ceramic]]s and material [[composites]]. In condensed bodies formed from fine powders, the irregular sizes and shapes of [[nanoparticles]] in a typical powder often lead to non-uniform packing morphologies that result in packing density variations in the powder compact. Uncontrolled [[agglomeration]] of powders due to [[Force|attractive]] [[van der Waals forces]] can also give rise to in microstructural inhomogeneities. Differential stresses that develop as a result of non-uniform drying shrinkage are directly related to the rate at which the [[solvent]] can be removed, and thus highly dependent upon the distribution of [[porosity]]. Such stresses have been associated with a plastic-to-brittle transition in consolidated bodies, and can yield to [[crack propagation]] in the unfired body if not relieved.<ref>{{cite book|editor=Onoda, G.Y., Jr. and Hench, L.L. Eds|title=Ceramic Processing Before Firing|publisher=Wiley & Sons|place=New York|year=1979|isbn=0471654108|author=Edited by George Y. Onoda, Jr., and Larry L. Hench}}</ref><ref>{{cite journal|author=Aksay, I.A., Lange, F.F., Davis, B.I.|journal=J. Am. Ceram. Soc.|volume= 66|page= C-190|year=1983|doi=10.1111/j.1151-2916.1983.tb10550.x|title=Uniformity of Al₂O₃-ZrO₂ Composites by Colloidal Filtration}}</ref> <ref>{{cite journal|author=Franks, G.V. and Lange, F.F.|journal=J. Am. Ceram. Soc.|volume=79|page=3161|year=1996|doi=10.1111/j.1151-2916.1996.tb08091.x|title=Plastic-to-Brittle Transition of Saturated, Alumina Powder Compacts}}</ref> In addition, any fluctuations in packing density in the compact as it is prepared for the kiln are often amplified during the [[sintering]] process, yielding inhomogeneous densification. Some pores and other structural [[Crystallographic defect|defect]]s associated with density variations have been shown to play a detrimental role in the sintering process by growing and thus limiting end-point densities. Differential stresses arising from inhomogeneous densification have also been shown to result in the propagation of internal cracks, thus becoming the strength-controlling flaws. <ref>{{cite journal|author=Evans, A.G. and Davidge, R.W.|journal=Phil. Mag.|volume=20|issue=164|page=373|year=1969|doi=10.1080/14786436908228708|title=The strength and fracture of fully dense polycrystalline magnesium oxide|bibcode=1969PMag...20..373E}}</ref> <ref>{{cite journal|journal=J Mat. Sci.|volume=5|page=314|year=1970}}</ref> <ref>{{cite journal|author=Lange, F.F. and Metcalf, M.|journal=J. Am. Ceram. Soc.|volume=66|page=398|year=1983|doi=10.1111/j.1151-2916.1983.tb10069.x|title=Processing-Related Fracture Origins: II, Agglomerate Motion and Cracklike Internal Surfaces Caused by Differential Sintering}}</ref> It would therefore appear desirable to process a material in such a way that it is physically uniform with regard to the distribution of components and porosity, rather than using particle size distributions which will maximize the green density. The containment of a uniformly dispersed assembly of strongly interacting particles in suspension requires total control over particle-particle interactions. It should be noted here that a number of dispersants such as ammonium citrate (aqueous) and imidazoline or [[oleyl alcohol]] (nonaqueous) are promising solutions as possible additives for enhanced dispersion and deagglomeration. [[Monodisperse]] nanoparticles and colloids provide this potential.<ref>{{cite journal|author=Evans, A.G.|journal=J. Am. Ceram. Soc.|volume=65|page=497|year=1987|doi=10.1111/j.1151-2916.1982.tb10340.x|title=Considerations of Inhomogeneity Effects in Sintering}}</ref> Monodisperse powders of colloidal [[silica]], for example, may therefore be stabilized sufficiently to ensure a high degree of order in the [[colloidal crystal]] or [[polycrystalline]] colloidal solid which results from aggregation. The degree of order appears to be limited by the time and space allowed for longer-range correlations to be established. Such defective polycrystalline colloidal structures would appear to be the basic elements of sub-micrometer colloidal materials science, and, therefore, provide the first step in developing a more rigorous understanding of the mechanisms involved in microstructural evolution in high performance materials and components. <ref>{{cite journal|author=Whitesides, G.M., et al.|title=Molecular Self-Assembly and Nanochemistry: A Chemical Strategy for the Synthesis of Nanostructures|journal=Science|volume=254|page=1312|year=1991|doi=10.1126/science.1962191|pmid=1962191|bibcode=1991Sci...254.1312W}}</ref><ref>{{cite journal|author=Dubbs D. M, Aksay I.A.|title=Self-Assembled Ceramics|journal=Ann. Rev. Phys. Chem.|volume=51|page=601|year=2000|doi=10.1146/annurev.physchem.51.1.601|pmid=11031294|bibcode=2000ARPC...51..601D}}</ref> ==Classification== Materials referred to as "nanomaterials" generally fall into two categories: fullerenes, and inorganic nanoparticles. See also [[List of nanotechnology topics#Nanomaterials|Nanomaterials in List of nanotechnology topics]] ===Fullerenes=== [[File:Buckminsterfullerene animated.gif|thumb|right|Rotating view of Buckminsterfullerene C₆₀]] {{main|Fullerene}} The fullerenes are a class of [[allotropes of carbon]] which conceptually are [[graphene]] sheets rolled into tubes or spheres. These include the [[carbon nanotube]]s (or [[silicon nanotubes]]) which are of interest both because of their mechanical strength and also because of their electrical properties. For the past decade, the chemical and physical properties of fullerenes have been a hot topic in the field of research and development, and are likely to continue to be for a long time. In April 2003, fullerenes were under study for [[Nanomedicine|potential medicinal use]]: binding specific [[antibiotic]]s to the structure of resistant [[bacterium|bacteria]] and even target certain types of [[cancer]] cells such as [[melanoma]]. The October 2005 issue of Chemistry and Biology contains an article describing the use of fullerenes as light-activated [[antimicrobial]] agents. In the field of [[nanotechnology]], heat resistance and [[superconductivity]] are among the properties attracting intense research. A common method used to produce fullerenes is to send a large current between two nearby graphite electrodes in an inert atmosphere. The resulting [[carbon]] [[Plasma (physics)|plasma]] arc between the electrodes cools into sooty residue from which many fullerenes can be isolated. There are many calculations that have been done using ab-initio Quantum Methods applied to fullerenes. By [[Density functional theory|DFT]] and TDDFT methods one can obtain [[Infrared|IR]], [[Raman spectroscopy|Raman]] and [[Ultraviolet|UV]] spectra. Results of such calculations can be compared with experimental results. ===Nanoparticles=== {{main|Nanoparticle}} Nanoparticles or [[nanocrystal]]s made of metals, semiconductors, or oxides are of particular interest for their mechanical, electrical, magnetic, optical, chemical and other properties. Nanoparticles have been used as [[quantum dot]]s and as chemical [[catalyst]]s. Nanoparticles are of great scientific interest as they are effectively a bridge between bulk materials and [[atom]]ic or [[molecular]] structures. A bulk material should have constant physical properties regardless of its size, but at the nano-scale this is often not the case. Size-dependent properties are observed such as [[quantum confinement]] in [[semiconductor]] particles, [[surface plasmon resonance]] in some metal particles and [[superparamagnetism]] in [[magnetic]] materials. Nanoparticles exhibit a number of special properties relative to bulk material. For example, the bending of bulk [[copper]] (wire, ribbon, etc.) occurs with movement of copper atoms/clusters at about the 50&nbsp;nm scale. Copper nanoparticles smaller than 50&nbsp;nm are considered super hard materials that do not exhibit the same [[malleability]] and [[ductility]] as bulk copper. The change in properties is not always desirable. Ferroelectric materials smaller than 10&nbsp;nm can switch their magnetisation direction using room temperature thermal energy, thus making them useless for memory storage. [[suspension (chemistry)|Suspension]]s of nanoparticles are possible because the interaction of the particle surface with the [[solvent]] is strong enough to overcome differences in [[density]], which usually result in a material either sinking or floating in a liquid. Nanoparticles often have unexpected visual properties because they are small enough to confine their electrons and produce quantum effects. For example [[gold]] nanoparticles appear deep red to black in solution. The often very high surface area to volume ratio of nanoparticles provides a tremendous driving force for [[diffusion]], especially at elevated temperatures. [[Sintering]] is possible at lower temperatures and over shorter durations than for larger particles. This theoretically does not affect the density of the final product, though flow difficulties and the tendency of nanoparticles to agglomerate do complicate matters. The surface effects of nanoparticles also reduces the incipient [[melting point|melting temperature]]. ===Sol-gel=== {{main|Sol-gel}} The sol-gel process is a wet-chemical technique commonly used to synthesise a wide variety of nanomaterials. ==Characterization== The first observations and size measurements of nano-particles were made during the first decade of the 20th century. They are mostly associated with the name of Zsigmondy who made detailed studies of gold sols and other nanomaterials with sizes down to 10&nbsp;nm and less. He published a book in 1914.<ref>Zsigmondy, R. "Colloids and the Ultramicroscope", J.Wiley and Sons, NY, (1914)</ref> He used an [[ultramicroscope]] that employs a ''dark field'' method for seeing particles with sizes much less than [[light]] [[wavelength]]. There are traditional techniques developed during 20th century in [[Interface and Colloid Science]] for characterizing nanomaterials. These are widely used for ''first generation'' passive nanomaterials specified in the next section. These methods include several different techniques for characterizing [[particle size distribution]]. This characterization is imperative because many materials that are expected to be nano-sized are actually aggregated in solutions. Some of methods are based on [[light scattering]]. Other apply [[ultrasound]], such as [[ultrasound attenuation spectroscopy]] for testing concentrated nano-dispersions and microemulsions.<ref>{{cite book|author=Dukhin, A.S. and Goetz, P.J.|title=Ultrasound for characterizing colloids|publisher=Elsevier|year=2002}}</ref> There is also a group of traditional techniques for characterizing [[surface charge]] or [[zeta potential]] of nano-particles in solutions. This information is required for proper system stabilzation, preventing its aggregation or [[flocculation]]. These methods include [[microelectrophoresis]], [[electrophoretic light scattering]] and [[Acoustical engineering|electroacoustics]]. The last one, for instance [[colloid vibration current]] method is suitable for characterizing concentrated systems. ==Safety== {{see also|Regulation of nanotechnology}} Nanomaterials behave differently than other similarly-sized particles. It is therefore necessary to develop specialized approaches to testing and monitoring their effects on human health and on the environment. The OECD Chemicals Committee has established the Working Party on Manufactured Nanomaterials to address this issue and to study the practices of OECD member countries in regards to nanomaterial safety.<ref>{{cite news|title=Safety of Manufactured Nanomaterials: About, OECD Environment Directorate|publisher = OECD.org|date= 18 July 2007|url =http://www.oecd.org/about/0,3347,en_2649_37015404_1_1_1_1_1,00.html}}</ref> While nanomaterials and nanotechnologies are expected to yield numerous health and health care advances, such as more targeted methods of delivering drugs, new cancer therapies, and methods of early detection of diseases, they also may have unwanted effects.<ref name=oecd>{{cite news|title=|publisher = Small Sizes that Matter: Opportunities and Risks of Nanotechnologies, Joint report of the Allianz Center for Technology and the OECD International Futures Programme|author = C. Lauterwasser|publisher = OECD.org|date = 18 July 2007|url = http://www.oecd.org/dataoecd/37/19/37770473.pdf}}</ref> Increased rate of absorption is the main concern associated with manufactured nanoparticles. When materials are made into nanoparticles, their surface area to volume ratio increases. The greater specific surface area (surface area per unit weight) may lead to increased rate of absorption through the skin, lungs, or digestive tract and may cause unwanted effects to the lungs as well as other organs. However, the particles must be absorbed in sufficient quantities in order to pose health risks.<ref name=oecd/> As the use of nanomaterials increases worldwide, concerns for worker and user safety are mounting. To address such concerns, the [[Sweden|Swedish]] [[Karolinska Institute]] conducted a study in which various nanoparticles were introduced to human lung [[epithelial cell]]s. The results, released in 2008, showed that [[iron oxide]] nanoparticles caused little [[DNA]] damage and were non-toxic. [[Zinc oxide]] nanoparticles were slightly worse. [[Titanium dioxide]] caused only DNA damage. Carbon nanotubes caused DNA damage at low levels. [[Copper oxide]]{{dn|date=August 2011}} was found to be the worst offender, and was the only nanomaterial identified by the researchers as a clear health risk.<ref>[[Chemical & Engineering News]] Vol. 86 No. 35, 1 Sept. 2008, "Study Sizes up Nanomaterial Toxicity", p. 44</ref> ==See also== *[[Gradient Multi-Layer nanofilm|GML nanofilm]] *[[List of emerging technologies]] *[[Nanostructures]] *[[Nanotechnology]] *[[Nanocomposite]] *[[Printed electronics]] ==References== {{reflist|2}} ==Further reading== *''Sol-Gel Science: The Physics and Chemistry of Sol-Gel Processing'' by C. Jeffrey Brinker and George W. Scherer, Academic Press (1990) ==External links== * [http://www.nanopartikel.info/cms/lang/en/Wissensbasis Acquisition, evaluation and public orientated presentation of societal relevant data and findings for nanomaterials (DaNa)] *[http://www.oecd.org/department/0,3355,en_2649_37015404_1_1_1_1_1,00.html Safety of Manufactured Nanomaterials: OECD Environment Directorate] *[http://copublications.greenfacts.org/en/nanotechnologies/index.htm Assessing health risks of nanomaterials] summary by [[GreenFacts]] of the European Commission SCENIHR assessment *[http://www.liposome.org International Liposome Society] *[http://nanotextiles.human.cornell.edu/ Textiles Nanotechnology Laboratory] at [[Cornell University]] *[http://www.iop.org/EJ/article/0957-4484/14/3/201/t303R1.pdf?request-id=NENUvFK63BGH-Bna2wi7Kg IOP.org Article] *[http://books.google.com/books?id=_pbtbJwkj5YC&pg=PA5&lpg=PA5&dq=catalyst+hartog+1972&source=web&ots=fTTD2SA5Dh&sig=3phv63YeG9raeAZdvlm_4JH07-Y#PPR7,M1 Nano Structured Material] *[http://nanohub.org/resources/1914 Online course MSE 376-Nanomaterials by Mark C. Hersam (2006)] *[http://nanohub.org/resources/376 Nanomaterials: Quantum Dots, Nanowires and Nanotubes] online presentation by Dr Sands {{Emerging technologies}} {{Use dmy dates|date=June 2011}} [[Category:Nanomaterials|*]] [[Category:Emerging technologies]] [[ar:مواد نانوية]] [[bg:Наноматериал]] [[es:Nanomateriales]] [[fa:نانومواد]] [[fr:Nanomatériau]] [[it:Nanomateriali]] [[he:ננו-חומרים]] [[pl:Nanomateriały]] [[pt:Nanomateriais]] [[ro:Nanomaterial]] [[ru:Наноматериал]] [[vi:Vật liệu nano]]'