Nanoparticles Nanoparticles A particle is defined as a

Nanoparticles

Nanoparticles �A particle is defined as a small object that behaves as a whole unit with respect to its transport and properties.

Nanoparticles �According to diameter ü Ultrafine particles (nanoparticles), 1 -100 nm ü Fine particles , 100 nm- 2. 5 µm ü Coarse particles, 2. 5 -10 µm

Nanoparticles �Suspensions of nanoparticles are possible since the interaction of the particle surface with the solvent is strong enough to overcome density differences, which otherwise usually result in a material either sinking or floating in a liquid.

Nanoparticles �According to morphology Ø Scientists have taken to naming their particles after the real-world shapes that they might represent.

Nanoparticles �Nanospheres

Nanoparticles �Nanorods

Nanoparticles �Nanoboxes

Nanoparticles �Nanoneedles

Nanoparticles �And more have appeared in the literature

Nanoparticles �These morphologies sometimes arise Ø Spontaneously Ø Templating

Carbon �It All Starts with Carbon

Carbon �If the ability of each atom to attract all those negatively charged electrons (called electronegativity) are reasonably close (that is, if the difference in electronegativity is no more than 2), then they can form covalent bonds. �Because the electronegativity of carbon atoms is 2. 5 (roughly in the midrange), they can form strong, stable, covalent bonds with many other types of atoms with higher or lower values.

Graphite �What you fine at the tip of your pencil.

Graphite �Graphite, is essentially sheets of carbon atoms bonded together into one huge molecule.

Graphite �Because the only bonding between sheets is the van der Waals’ force, the sheets slide easily over each �other. Drag the graphite across paper, and it leaves a trail of itself on the page.

Graphite �Hydrogen atoms hanging on only at the edges.

Graphite

Fullerene

Fullerene �A fullerene is any molecule composed entirely of carbon, in the form of a hollow sphere, ellipsoid or tube. �Fullerenes are similar in structure to graphite, which is composed of stacked graphene sheets of linked hexagonal rings; but they may also contain pentagonal (or sometimes heptagonal) rings.

Fullerene �Spherical fullerenes are: Buckyball Ø Smallest member is C 20 (unsaturated version of dodecahedrane C 20 H 20 ) and the most common is Buckminsterfullerene (C 60). C 70, C 80

Buckminsterfullerene �The first fullerene molecule to be discovered buckminsterfullerene (C 60). �The name was homage to Buckminster Fuller

Buckminsterfullerene �The suffix "-ene" indicates that each C atom is covalently bonded to three others (instead of the maximum of four), a situation that classically would correspond to the existence of bonds involving two pairs of electrons ("double bonds").

Buckyball clusters �While many of the atoms in buckyballs are connected together in hexagons (just as in graphite sheets), some of the atoms are connected together in pentagons.

Buckminsterfullerene �The pentagons allow the sheet of carbon atoms to curve into the shape of a sphere. Every buckyball surface contains 12 pentagons and 20 hexagons. �

Buckminsterfullerene �No two pentagons share an edge (which can be destabilizing, as in pentalene C 8 H 6 ).

Creating buckyballs �Vaporizing carbon with a laser and allowing the carbon atoms to condense. Produce a very small number of buckyballs.

Creating buckyballs �Vaporized carbon by placing two carbon electrodes close together and generating an electric arc between them in a reaction chamber filled with a low pressure of helium or neon. �generated much larger quantities of buckyballs

Creating buckyballs �Combustion synthesis �Mixes a hydrocarbon with oxygen and burns the hydrocarbon at a low pressure.

Using buckyballs in the real world �As antioxidants �C Sixty, Inc.

As antioxidants �A free radical is a molecule or atom that has an unp �aired electron which makes it very reactive. �An antioxidant is a molecule that can supply an electron and neutralize a free radical. �When a buckyball meets a free radical, the unpaired electron in the free radical pairs up with one of the buckyball’s delocalized electrons, forming a covalent bond between the free radical and a carbon atom in the buckyball.

As antioxidants �Buckyballs are not naturally soluble in water, and therefore not soluble in the bloodstream. �C Sixty has added a water-soluble molecule to buckyballs. Functionalization �Buckyballbased antioxidants are several times more effective than antioxidants available today. �Each buckyball-based antioxidant can counteract several free radicals because each buckyball has many carbon atoms for the free radicals to bond to.

As antioxidants �Antioxidant molecules currently in use can only counteract one free-radical molecule apiece

Drug delivery

Drug delivery

Additional buckyball-based antioxidant type drugs �Anti-aging or anti-wrinkle creams �Buckyball-based drug to fight arteriosclerosis. �C Sixty is working on both burn creams and an HIV drug. �Sony is developing more efficient fuel cell membranes. �Siemens has developed a buckyball-based light detector.

Boron buckyball (B 80) �A type of buckyball which uses boron atoms, instead of the usual carbon, was predicted and described in 2007 by Rice University scientists. �Build a "buckyball" using silicon atoms , it would collapse. �Boron is nearby (one atomic unit from carbon)

Boron buckyball (B 80) �Initial work with 60 boron atoms failed to create a hollow ball that would hold its form. �So another boron atom was placed into the centre of each hexagon for added stability.

Boron buckyball (B 80) �With each atom forming 5 or 6 bonds, is predicted to be more stable than the C 60 buckyball.

Boron buckyball (B 80) �B 80 is actually more like the original geodesic dome

Nanoonions �Spherical particles based on multiple carbon layers surrounding a buckyball core; proposed for lubricants.

Buckybowl �C 20 H 10. The molecule consists of a cyclopentane ring fused with 5 benzene rings, so another name for it is Circulene.

Nanotubes

Nanotubes �In 1991 Sumio Iijima placed a sample of carbon soot containing buckyballs in an electron microscope to produce some photographs of buckyballs — which he in fact did — but some odd, needleshaped structures caught his attention.

Nanotubes �Cylinders of carbon atoms that were formed at the same time that the buckyballs were formed. �These cylinders are each a lattice of carbon atoms — with each atom covalently bonded to three other carbon atoms.

Nanotubes �like a sheet of graphite rolled into a cylinder

Nanotubes �Some of these cylinders are closed at the ends and some are open.

Nanotubes �lattice can be orientated differently

Nanotubes Ø Armchair nanotubes, there is a line of hexagons parallel to the axis of the nanotube.

Nanotubes Ø Zigzag nanotubes, there’s a line of carbon bonds down the center.

Nanotubes Ø Chiral nanotubes, exhibit a twist or spiral (called chirality) around the nanotube.

Nanotubes �Single-walled carbon nanotubes (SWNT) or multi- walled carbon nanotubes (MWNT).

Producing nanotubes �By adding just a few percentage of nickel nanoparticles to the vaporized carbon (using either the arc-discharge or laser-vaporization) as many nanotubes as buckyballs or even more can be made. �Carbon atoms start sweating onto the surface of the particle and bond together, growing a nanotube. �When you anchor one end of the growing nanotube to the metal nanoparticle, it can’t close into the sphere shape of a buckyball.

Producing nanotubes �There are three methods that various companies have developed to produce carbon nanotubes in bulk quantities and at a lower cost.

Producing nanotubes �high-pressure carbon monoxide deposition, or Hi. PCO Ø Involves a heated chamber through which carbon monoxide gas and small clusters of iron atoms flow. When carbon monoxide molecules land on the iron clusters, the iron acts as a catalyst and helps a carbon monoxide molecule break up into a carbon atom and an oxygen atom. The carbon atom bonds with other carbon atoms to start the nanotube lattice; the oxygen atom joins with another carbon monoxide molecule to form carbon dioxide gas, which then floats off into the air.

Producing nanotubes �Chemical-vapor deposition, or CVD Ø A hydrocarbon — say, methane gas flows into a heated chamber containing a substrate coated with a catalyst, such as iron particles. The temperature in the chamber is high enough to break the bonds between the carbon atoms and the hydrogen atoms in the methane molecules resulting in carbon atoms with no hydrogen atoms attached. Those carbon atoms attach to the catalyst particles, where they bond to other carbon atoms forming a nanotube.

Producing nanotubes �A new method uses a plasma process to produce nanotubes. Methane gas, used as the source of carbon, is passed through a plasma torch. Nobody’s revealed the details of this process yet, such as what, if any, catalyst is used? !

The properties of nanotubes �They’re really, really strong. �The tensile strength of carbon nanotubes is approximately 100 times greater than that of steel of the same diameter. �Young’s modulus for carbon nanotubes, a measurement of how much force it takes to bend a material, is about 5 times higher than for steel.

The properties of nanotubes �There are two things that account for this strength: Ø carbon-to-carbon covalent bonds Ø nanotube is one large molecule, same as diamond.

The properties of nanotubes �Nanotubes are strong but are also elastic. �This means it takes a lot of force to bend a nanotube, but the little guy will spring right back to its original shape when you release it.

The properties of nanotubes �Carbon nanotubes are also lightweight, with a density about one quarter that of steel.

The properties of nanotubes �High thermal conductivity, more than 10 times that of silver. �Metals depend upon the movement of electrons to conduct heat. �Carbon nanotubes conduct heat by the vibration of the covalent bonds holding the carbon atoms together. �A diamond, which is also a lattice of carbon atoms covalently bonded, uses the same method to conduct heat, so it’s also an excellent thermal conductor.

The properties of nanotubes �A little bit sticky, Ø The electron clouds on the surface of each nanotube provide a mild attractive force between the nanotubes. This attraction is called van der Waals’ force.

The properties of nanotubes �Conducts electricity �Nano-sensors

Nano-sensors �Functionalization

Nano-sensors �Functionalization

Nanobuds

Megatubes �Megatubes are larger in diameter than nanotubes and prepared with walls of different thickness; potentially used for the transport of a variety of molecules of different sizes.