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Lecture 15 Composites And Nanochemistry Nanomaterial reinforcement in composites Nanofibers in use Nano-reinforced composites • Processing them into various matrices follow earlier composite developments 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 Benefits of nanotech for composites • Nanotechnology provides new opportunities for radical changes in 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. Multifunctionality in materials • This always implies “structure +” since in most cases the major function 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 Multifunctional materials: sensing • Building in additional functionalities into load-bearing structures is 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 Examples of multifunctional materials • Possible, in principle, to design any number of composites with multiple levels of 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 protection generate power during sunlight for charging the batteries of various devices in the soldier-gear NRC Report, 2003 Composite materials • 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 A self-healing material ‘Self-healing plastic’ by Prof. Scott White (U. of Illinois) Nature (Feb. 15, 2001) • Plastic components break because of mechanical or thermal fatigue. Small cracks and large cracks: catastrophic failure. ‘Self-healing’ is a way of repairing these cracks without human intervention. • Self-healing plastics have small capsules that release a healing agent 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 contact with a catalyst embedded in the plastic. The chemical reaction forms a polymer to repair the broken edges of the plastic. New bond is complete in an hour at room temperature. Fine Particle Technology • 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 Particles 2 • 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. Reactions of shaped carbons Detection Reactions The electron microscope Electron Microscopy and tube wall measurements Raman vibrational modes in SWNTs 16000 Intensity 14000 12000 ID/IG 10000 ratio 8000 6000 4000 2000 0 G D -2000 0 200 1200 1400 Wavenumbers/ cm -1 1600 1800 2000 Chemistry A. Hirsch, Angew. Chem. Int. Ed., 41 (2002) 1853. The main approaches for the modification of these quasi one-dimensional structures can be grouped into three categories: (a) the covalent attachment of chemical groups through reactions onto the ð-conjugated skeleton of CNT; (b) the noncovalent adsorption or wrapping of various functional molecules; and (c) the endohedral filling of their inner empty cavity. SWCNT chemistry Chem Rev, 106 (2006) 1105 Functionalisation of CNTs: Prato reagent CNT-Polymer mixtures Nanotubes – different scale lengths The Space Elevator Application of f-CNTs in Medicine/Pharmacy C. Klumpp et al. / Biochimica et Biophysica Acta 1758 (2006) 404– 412 Confocal microscopy images of 3T6 cells incubated with fluorescent CNT f-CNT penetrated into the cells Antifungal activity of AmB conjugated to carbon nanotubes (CNT 2). Candida parapsilosis (black bar); Candida Albicans (dashed bar); Cryptococcus neoformans (grey bar).