Download - Composites And Nanochemistry
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CompositesAnd
Nanochemistry
Lecture 15
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Nanomaterial reinforcement in composites
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Nanofibers in use
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• Processing them into various matrices follow earlier compositedevelopments such as
- Polymer compounding- Producing filled polymers- Assembly of laminate composites- Polymerizing rigid rod polymers
• Purpose- Replace existing materials where properties can be superior- Applications where traditionally composites were not a
candidate
Nano-reinforced composites
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• Nanotechnology provides new opportunities for radical changesin composite functionality
• Major benefit is to reach percolation threshold at low volumes(< 1%) when mixing nanoparticles in a host matrix
• Functionalities can be added when we control the orientation of the nanoscale reinforcement.
Benefits of nanotech for composites
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• This always implies “structure +” since in most cases the majorfunction of a structure is to carry load or provide shape. Additional functions can be:
• Actuation controlling position, shape or load
• Electrical either insulate or conduct
• Thermal either insulate or conduct
• Health monitor, control
• Stealth managing electromagnetic or visible signature
• Self-healing repair localized damage
• Sensing physical, chemical variables NRC Report, 2003
Multifunctionality in materials
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• Building in additional functionalities into load-bearing structuresis one key example:
- Sensing function* Strain* Pressure* Temperature* Chemical change* Contaminant presence
• Miniaturized sensors can be embedded in a distributed fashion to add “smartness” or multifunctionality. This approach is ‘pre-nano’ era.
• Nanotechnology, in contrast, is expected to help in assembling materials with such functional capabilities
Multifunctional materials: sensing
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• Possible, in principle, to design any number of composites with multiple levelsof functionality (3, 4, 5…) by using both multifunctional matrices and multifunctional reinforcement additives
- Add a capsule into the matrix that contains a nanomaterial sensitive to thermal, mechanical, electrical stress; when this breaks, would indicate the area of damage
- Another capsule can contain a healant
- Microcellular structural foam in the matrix may be radar-absorbing,conducting or light-emitting
- Photovoltaic military uniform also containing Kevlar for protectiongenerate power during sunlight for charging the batteries of
various devices in the soldier-gearNRC Report, 2003
Examples of multifunctional materials
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• Carbon nanotubes, nanofibers
• Polymer clay nanocomposites
• Polymer cross-linked aerogels
• Biomimetric hybrids
Expectations:- ‘Designer’ properties, programmable materials- High strength, low weight- Low failure rates- Reduced life cycle costs
Composite materials
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‘Self-healing plastic’ by Prof. Scott White (U. of Illinois) Nature (Feb. 15, 2001)
• Plastic components break because of mechanical or thermalfatigue. Small cracks and large cracks: catastrophic failure.‘Self-healing’ is a way of repairing these cracks without humanintervention.
• Self-healing plastics have small capsules that release a healingagent when a crack forms. The agent travels to the crack through capillaries similar to blood flow to a wound.
• Polymerization is initiated when the agent comes into contactwith a catalyst embedded in the plastic. The chemical reactionforms a polymer to repair the broken edges of the plastic. New bond is complete in an hour at room temperature.
A self-healing material
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• Frequently encountered powders:- Cement, fertilizer, face powder, table salt, sugar, detergents, coffee
creamer, baking soda…
• Some products in which powder incorporation is not obvious- Paint, tooth paste, lipstick, mascara, chewing gum, magnetic recording
media, slick magazine covers, floor coverings, automobile tires…
• For most applications, there is an optimum particle size- Taste of peanut butter is affected by particle size- Extremely fine amorphous silica is added to control the ketchup flow- Medical tablets dissolve in our system at a rate controlled by particle size- Pigment size controls the saturation and brilliance of paints- Effectiveness of odor removers is controlled by the surface area of
adsorbents.
From: Analytical methods in Fine Particle Technology, Webb and Orr
Fine Particle Technology
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• Adding certain inorganic clays to rubber dramatically improves the lifetime and wear-characteristics of tires.
Why ?
The nanoscale clay particles bind to the ends of the polymer molecules - which you can think of as molecular strings - and prevent them from unraveling.
Fine Particles 2
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Reactions of shaped carbons
Detection
Reactions
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Electron Microscopy and tube wall measurements
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Raman vibrational modes in SWNTs
0 200 1200 1400 1600 1800 2000-2000
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D G
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A. Hirsch, Angew. Chem. Int. Ed., 41 (2002) 1853.
Chemistry
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The main approaches for the modification of these quasione-dimensional structures can be grouped into three categories:(a) the covalent attachment of chemical groupsthrough reactions onto the ð-conjugated skeleton of CNT;(b) the noncovalent adsorption or wrapping of variousfunctional molecules; and (c) the endohedral filling of theirinner empty cavity.
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SWCNT chemistry
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Chem Rev, 106 (2006) 1105
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Functionalisation of CNTs: Prato reagent
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CNT-Polymer mixtures
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Nanotubes – different scale lengths
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The Space Elevator
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Application of f-CNTs in Medicine/Pharmacy
Antifungal activity of AmB conjugated to carbon nanotubes (CNT 2). Candida parapsilosis (black bar); Candida Albicans (dashed bar); Cryptococcus neoformans (grey bar).
Confocal microscopy images of 3T6 cells incubated with fluorescent CNT
f-CNT penetrated into the cells
C. Klumpp et al. / Biochimica et Biophysica Acta 1758 (2006) 404– 412