Nanotechnology

"Next big thing is small"
The word ‘nano’ meaning ‘dwarf’ in Greek language refers to dimensions on the order of magnitude of 10-9. Nanotechnology, focusing on special peoperties of materials emerging from nanometer size, for e.g. In biological systems, occurs at the nanoscale structures where all the fundamental properties and functions are systematically defined “Purposeful engineering materials at nano scale- Nanotechnology”
Nanotechnology as it impacts fields of electronics and information, biology, chemistry and medicine, energy, the environment, transportation, and especially that of materials, is briefly considered.
Nanoparticles:
Three dimensions in the nm range – the three dimensions are of similar size i.e. particles approximate to being spherical. Examples include polymer particles generated by emulsion polymerisation, by polymerisation of micelles, vesicles etc.
Two dimensions are of similar size and are in the nm range whereas the third is longer.
Examples include oblate/acicular particles, nanotubes (carbon, protein) or whiskers (boron nitride, cellulose). One dimension in the nm range with the other two dimensions being longer. Examples are sheets of material which are a few nm thick but may be 100 to 1000nm long. Materials having such structures are layered silicates (phyllosilicates) Particles having three dimensions in the nm range.
Routes and Means:

Micelles:

• Micelles have been used as micro reactors.
• Generation of small metallic particles e.g. gold, silver, platinum. Generation of nm particles of semiconducting sulfides etc. These particles possess very useful luminescent properties–Quantum dots. These dots should find application in security devices and as biological markers.
• Polymersiation of micelles to generate nanospheres (useful for controlled release of drugs or “marker” materials).

Particles generated by sol-gel chemistry:

• Titanium dioxide particles stabilised by means of a protective colloid have been prepared and shown to possess special luminescent and catalytic properties.
• Silica particles have been produced. These have been generated possessing reactive groups on the surface which allows them to be polymerised into a coating (e.g. (meth)acrylate groups – Hanse Chemie GmbH). The particles have very little effect upon the clarity or the viscosity of formulations. The cured coatings possess improved scratch and abrasion resistance, toughness and hardness. Polymerisable monomers such as acrylates, containing derivatised silica particles are available from Clariant France. Others functionalised silica particles have been generated which allow controlled polymer growth via a free radical mediated process.
• Silica and titanium dioxide particles for near infra-red reflective coatings. Coatings having refractive indices from 1.47 to 1.93 have been generated.
  Gold citrate sols for generation of nm dots of gold (via electron beam radiation) for nm circuitry.

Hyperbranched Polymers:

Hyperbranched polymers may be considered as imperfect dendrimers since they do not possess a unique molecular weight but nevertheless have a polydispersity close to unity. Some of these materials are now commercially available. Perstorp Speciality Chemicals have an aliphatic polyester which can be rendered polymerisable.
Uses:
Generation of surface coatings
Production of nanoporous organosilicates (low dielectric constant materials – nano and microcircuitry).

Emulsion polymerization:

• Controlled chemical reaction .
• Generation of dyes and pigments by means of a microreactor (Clariant GmbH). Such particles are suitable for use as ink jet colourants. Hybrid polymers based on polyhedral oligomeric silsesquioxanes POSS. The silsesquioxane unit, which has an outer diameter of 1.5 nm has been incorporated into polymers to impart greater thermal and mechanical stability to the polymer.

Titanium dioxide:
Titanium dioxide for sun screens (ICI) - ~50nm.
Titanium dioxide for fibre treatment (BASF) - ~ 500nm
Three scenarios
A nano sized matrix containing smaller crystallites
True nanoparticles of titanium dioxide can be generated by sol-gel chemistry. These particles show photocatalytic properties and analysis shows that the oxide is of the anatase modification. A micron sized matrix containing nano sized crystallites.
Precipitation of titanium dioxide from its alkoxides appears to give an amorphous powder which in fact contains nano and sub-nano sized crystallites of anatase. When this material is heated crystallization occurs and the crystallites grow in size. The particles produced may have dimensions of several microns but the anatase crystallites may still have nanometer dimensions.
True nanosized particles as used in sunscreens (ICI)
Some current uses and developments:
Oxonica – nanosized phosphors for electronic displays, catalysts, cosmetics and quantum dots.
QinetiQ – use of plasma processing technology for production of nanoparticles by the tonne.
Enact Pharma – nano sized structures for tissue growth
Nanoco – manufacture of quantum dots (samples available on request!). Materials could be of great value for security devices including printing of currency.
Carbon nanotubes – electronics (transistors, field emitters), electrically conducting paints.
Nanotubes:
These structures are found in nature e.g. cellulose and self-assembling proteins. Designer protein nanotubes have the potential to kill bacteria which are resistant to antibiotics e.g. Staphylococcus aureus. Undoubtedly, as far as composites are concerned, carbon nanotubes offer the greatest potential. They are formed from sheets of graphite which are rolled up into tubes having a diameter of a few nanometers. Depending on the way the sheets are rolled up, the nanotubes may either be semiconducting or conducting. The semiconducting material has been used to make nm sized Field-effect transistors. Conducting carbon nanotubes can render paints conducting when incorporated at the 2% level. This is of great potential benefit for electropolymer design. Nanotubes being commercially produced have ~10nm diameter and are composed of layers of graphite. Carbon nanotubes are 200 times stronger than steel and now that they can be produced in lengths up to 20cm they should be of great value as reinforcing materials for automobile components where their lightness will benefit fuel economy. Another advatage is that the nanotubes can be used at such a low loading that they do not interfere with the mechanical properties of the composite.

One dimension in the nm range –layered silicates

The layered silicates are being used as nano composites. They offer the following:

• Efficient reinforcement with minimal loss of ductility and impact strength.
• Thermal endurance.
• Flame resistance.
• Improved barrier properties.
• Improved abrasion resistance.
• Improved chemical resistance.
• Reduced shrinkage and residual stress.
• Altered electrical, electronic and optical properties.
• Their use to improve scratch, mar and abrasion resistance.
• Use of their barrier properties to make more ecofriendly packaging with the possibility of reducing our dependence upon laminates.
• To utilise their effectiveness in reducing the flammability of coatings thereby aiding compliance with new EC regulations.
• Improving the strength and durability of coatings.

Structure :
The layered silicates commonly used in nanocomposites are the 2:1 phyllosilicates. Their crystal lattice consists of two-dimensional layers where a central octahedral sheet of alumina or magnesia is fused to two external silicate layers. The layers organise themselves to form stacks with a regular van der Walls gap between them called an interlayer or gallery. Isomorphic substitution within the layers e.g. Al3+ by Mg2+ generates negative charges that are counterbalanced by alkali or alkaline earth cations. The forces holding the stacks together are relatively weak and hence intercalation of small moleucules between the layers is easy. The phyllosilicates can be rendered organophilic by exchanging the sodium ions for alkylammonium ions. Layered silicates may be incorporated into polymers in three different ways: Intercalation of polymers Intercalation leads to a single extended polymer chain being threaded through the gallery.
Direct intercalation by mixing the silicate and the polymer e.g. poly (ethylene oxide). Most polymers are incompatible with the silicate making this method unsuitable.
Exchange of the sodium ions in the gallery by means of alkylammonium salts followed by mixing with the polymer e.g. poly(styrene), polyamides, polyesters, polycarbonates, polyphosphazenes and polysiloxanes. Intercalation has been achieved by mixing the modified silicate with polymers in the melt e.g. poly(styrene), poly(propylene) modified with maleic anhydride, ethylene-vinyl acetate copolymers, poly(styrene-b-butadiene) copolymer.
Intercalation of polymer precursors e.g. 12- aminolauric acid - caprolactam, e-caprolactone, or a reactive component e.g. diglycidyl ether of bisphenol A followed by reaction with multifunctional amines, (vinlybenzyl)trimethylammonium chloride.
Template synthesis: Intercalation of polymerization initiators such as Ziegler-Natta catalyst for polyolefin production, photoinitiators and initiators for controlled free radical polymerization e.g.
The Impact of Nanotechnology in Drug Discovery:
Pharmaceutical and biotechnology companies are under immense pressures to produce a steadystream of innovative, well-differentiated drugs at reduced costs. Currently it takes an estimated 7-10 years to develop and market a drug at a cost that exceeds $800 million. In simple terms, drugdiscovery requires the identification of a disease, knowledge of the disease mechanism and identification of a target (point of intervention).The human genome project is expected to identify approximately 100,000 targets that will require evaluation against many compound libraries to compare gene sequences and structure. This represents a very time-consuming process and a major bottleneck in the drug discovery process as millions of compounds can be screened for each target. Novel discovery and validation technologies can expand the hit rate for promising compounds in the pipeline, and expedite their progress through to market. The introduction of microarrays and lab-on-a-chip technologies has already revolutionized the drug discovery process. Where once it took the effort of a single chemist to view anything from one to 12 gene variations at a time, microarrays can view thousands in the same time frame. Now, nanotechnology promises to exponentially increase even the volume of microarrays by working at a level far smaller than conventional microarrays and according to one source the pharmaceutical market will represent
approximately $180 billion of the forecasted $1 trillion nanotech industry. Nanotechnology can enhance the drug discovery process, through miniaturization, automation, speed and reliability of assays. Although at an embryonic stage of development, nano-enabled drugs are already bringing clinical benefits to thousands of patients. This report provides an overview and a detailed analysis of the major drivers, restraints and challenges for current and emerging applications of nanotechnology in drug discovery. Areas covered include nano-enabled drug discovery technologies/tools, nano-enabled drugs and an assessment of key market engineering parameters. The technologies/tools covered include, nanoarrays, nanomasspectrometry, nanolithography arrays, biological chips, congruent force
intermolecular test and solubility and reformulation methods. This report provides global market coverage and discusses funding, regulatory and ethical issues in the major industrial countries, with worldwide market forecasts over a 5-year forecast period. This report will be of vital interest to strategic planners, marketing managers and product development managers at all pharmaceutical, diagnostic, life science and biotechnology companies that may be interested in nanotechnology. Currently the estimated market for nanoparticles is valued at ~£27,000m a year of which ~23% is concerned with nanocomposites.
Improvement in mechanical properties through the use of nanocomposites:
Examples include:
Nylon nanocomposites where addition of 4 wt. % alumino-silicate creates a substantial increase in strength and modulus and this is not accompanied by a decrease in impact resistance.
Silicate-epoxy nanocomposites. 4 wt. % incorporation led to a 60% increase in storage modulus in the glassy region and in the rubbery region a 450% increase was observed. Other epoxy nanocomposites having a sub-ambient Tg exhibited a 10 fold improvement in modulus.
Nylon-6 nanocomposites show a drastic increase in Young’s modulus at low filler content. Improvements in mechanical properties are dependent upon the nature of the interactions between the matrix and the filler (intercalative versus exfoliated structures, ionic interactions as determined by the structure of the alkylammonium salt, the polarity of the polymer). Thermal stability and flame retardant properties. Thermal stability.

Examples include:

• PMMA at 10 wt.% loading resisted degradation under conditions where PMMA itself is completely degraded.
• Polydimethylsiloxane (a 1400 C higher decomposition temperature achieved.
• Polyimide (magnitude depend upon whether clay is intercalated or exfoliated).
• Poly (styrene) (effectiveness dependent upon type of alkylammonium compound used).

Flame retardent properties:

• Two main classes of “flame-safe” coatings.
• Flame retardent coatings (delay ignition and flame spread).
• Intumescent coatings (delay ignition and flame spread and also protect the substrate by forming an insulation layer during combustion. The multilayered silicate appears to act as an excellent insulator and mass transport barrier thereby slowing down the escape of volatile products generated on pyrolysis. The heat release ratio is much lower for nanocomposites compared with the unmodified polymers.

Examples of flame retardency:

• Delaminated nylon-6 and nylon-12 nanocomposites.
  Poly(styrene).
• Ethylene-vinyl acetate copolymer
  Poly(caprolactone) .
• An intumescent nanocomposite based on Nylon-6 and ammonium polyphosphate has been produced.

Nano nutrition for plants :
Nano nutrients are highly efficient interms of plant uptake mobility and utilisation. Nano particles of ZnO, FeO, CuO, MnO, MgO and CaO with different sizes were synthesised and their formulations were designed, for enhanced plant growth and yields.