Nanoparticles and Nanofibers

Transcription

1 Nanoparticles and Nanofibers Why are nanoparticles important? The properties of nanoparticles can be controlled by engineering the size, shape, and composition of the particles. Engineers can incorporate them into other materials to create new nanocomposite materials with enhanced or entirely different properties from their parent materials. nanoparticle: a particle nm in diameter With the inclusion of appropriately selected nanoparticles: metals can be made stronger and harder ceramics can have enhanced toughness and formability insulating materials can be made to conduct heat or electricity protective coatings can become transparent 1

2 Nanocomposite manufacturer The small black lines in the image are tiny clay particles that add tremendous strength and resistance to high temperatures to this plastic bottle material. The clay particles are about 100 nm long and only about 5-10 nm thick! TEM Image: Imperm Layer of Three Layer PET/Imperm/PET Bottle a publicly-traded company Ceramics for use in a variety of demanding environments based on nanocrystalline aluminum oxide and ZTA (zirconia-toughened alumina). Transparent coatings for attenuating IR and UV radiation, abrasion resistance, static dissipation, and conductive films fabricated from antimony and indium/tin oxides. Catalysts for chemical and environmental applications, such as cerium oxide and iron oxide. Materials to improve topical healthcare products, including zinc oxide. 2

3 Immediate future nanomaterials applications: next few years polymer-based paints that defy scratching and corrosion iron-polymer batteries that generate twice as much power resilient metal-composite car-body panels that pop back into place woven nanotubes that are 100 times stronger yet lighter than steel Particle size also affects chemical properties Certain metal oxides such as calcium or magnesium oxide are relatively inert in their naturally occurring forms. However, in reactive nanoparticle form, their chemical reactivity is dramatically enhanced and they are capable of destroying many hazardous substances such as chlorinated hydrocarbons, polychlorinated biphenyls (PCBs), insecticides, acid gases, organophosphorous compounds, and even military chemical agents. 3

4 LITTLE DOTS ON THE PRAIRIE: KANSAS COMPANY CULTIVATES NANOCRYSTALS By Michael Becker, Small Times Correspondent Sept. 11, 2001 Few people would include Manhattan, Kan., on their list of hotbeds of technological innovation in the United States. The [Chemistry] department has been leveraging its experience to break into the emerging field of nanocrystals. This has resulted in the creation of Nanoscale Materials Inc. The company is now preparing two nanocrystal-based products a skin cream designed to protect against chemical and environmental hazards and a spray applied from a fire extinguishertype canister that provides similar protection. Both will be made commercially available in the first quarter of next year. Nanotech gets in your pants, and soon, your plane CNN, September 10, 2001 NEW YORK (AP) -- To help soldiers survive, the U.S. Army is developing a new generation of combat uniforms using tiny, doctored fibers that let air through while blocking toxins from chemical and biological weapons. The "chemical protective overgarment, expected to ship in as little as two years, is one of the early uses of nanotechnology: the science of manipulating single atoms and molecules to create new products. The importance of surface area For some applications, it is necessary for molecules to contact the particle surface. All the work is done by atoms at the surface. Examples: sorption: molecules stick to the surface (scavenging toxic molecules and metals) catalysis: causing reactions to occur (including degradation of toxic and hazardous chemicals) 4

5 Consider a model cubic particle, 2 µm on an edge. What is the total surface area? 2 µm each side: area = 2 µm 2 µm = 4 µm 2 (square microns) total area: 6 sides 4 µm 2 = 24 µm 2 Now divide the cube into smaller cubes, 1 µm on a side. 2 µm 1 µm How many smaller cubes are there? BLUE: 2 PINK: 4 GREEN: 8 YELLOW:

6 Now total surface area: each side: area = 1 µm 1 µm = 1 µm 2 (square microns) each cube: 6 sides 1 µm 2 = 6 µm 2 compared to 24 µm total area: 8 cubes 6 µm 2 = 48 µm 2 for 2 the original cube So the same amount of material, divided into pieces half the size has twice as much surface area! For applications that require large surface area, small particles are ideal. For a particle 3 µm on a side, only about 1 out of every 1000 atoms lies on the surface. For a particle 3 nm on a side, about half the atoms lie on the surface! Argonide Nanotechnology group launches the first of a new family of products. An alumina fiber with a diameter of only 2 nanometers, and a remarkably high surface area: Fiber reinforced plastics Aerospace structural material systems Medical and dental composites Nanofiltration NanoCeram fibers have unique sorption characteristics. Tests show that they are capable of scavenging trace metals, particularly gold, silver and other heavy metals from aqueous solution. For example, a 99.9% removal efficiency of lead from an aqueous solution containing 1 mg/l. In another test, a second cycle removed lead to below detectable limits. 6

7 How to make nanoparticles Templating a common biomimetic strategy (1) start with a self-organized molecular assembly (2) use the assembly as a template to create particles An everyday example of this would be using a stencil to paint neat letters on a sign. We will talk about some examples of this in nature in a later lecture Liposomes can be used as nano-containers to confine a reaction Load liposomes with cadmium ions and introduce hydrogen sulfide gas. The gas can pass through the membrane and react to form cadmium sulfide nanoparticles. These quantum dots are important because they are fluorescent and their color can be controlled by the particle size. H 2 S Cd 2+ Cd 2+ CdS H 2 S 7

8 Quantum Dot Com By David Rotman Technology Review January/February 2000 Quantum Dot is working on biological bar codes polymer beads packed with a known combination of thousands or even millions of [cadmium sulfide nanoparticle] quantum dots. Each of these beads would have a known color signature a spectral bar code. mouse cells labeled with two different sizes of quantum dots. cell nuclei are green and actin filaments are red. Reverse micelles and micelles can also be used this way 8

9 Nanoreactor example Swollen reverse micelles Gold chloride molecules are dissolved in the water droplets. Irradiation with UV light causes a reaction between gold chloride molecules to form gold metal gold nanoparticles 25 nm in diameter inside the reverse micelles 100 nm Without reverse micelles as templates, big chunks of gold would form. images courtesy of Dr. Jürgen Hartmann, Max Planck Instititute, Golm Polymer Nanoparticles Monomers are soluble in oil, so they are made inside swollen micelles (which have oil cores) instead of swollen reverse micelles. monomer molecules polymerization solid nanoparticle 9