Nanomaterials synthesis and technology 1

Nanomaterials introduction

1. PST1208: Spl 16 Nanomaterials and their Applications A.B.Samui

2. Nanomaterials There’s plenty of room at the bottom By RICHARD P. FEYNMAN (1953) Feynman : In principle, we can make nanoscale machines that "arrange the atoms the way we want", and do chemical synthesis by mechanical manipulation. Drawbacks: We did not have instrument to see smaller things How small can we read? Can we see? Can we write???  

3. Why nanomaterials ? “Imagine dissociating a human body into its most fundamental building blocks. What we get : Hydrogen, oxygen, and nitrogen; carbon and calcium; small fractions of iron, magnesium, and zinc; and tiny levels of many other elements What will be total cost??? Less than cost of a good pair of shoes. Are we humans worth so little? In this context, What if we could follow nature & build whatever we want: Atom by atom and/or molecule by molecule?” Obviously not, mainly because it is the arrangement of these elements and the way they are assembled that allow human beings to eat, talk, think, and many more

4. 1990s: Feynman’s prediction was rediscovered and publicised as a seminal event in the field, to boost history of Nanotechnology STM developed in 1981 & earned its inventors, Gerd Binnig & Heinrich Rohrer (IBM, Zürich), the Nobel Prize in Physics in 1986. Scanning Tunneling Microscopy For an STM, good resolution is considered to be 0.1 nm lateral resolution and 0.01 nm depth resolution Si-atom on SiC surface

5. Nanoscience is the study of phenomena and manipulation of materials in atomic, molecular and macromolecular scales, where properties differ significantly from those at a larger scale. Nanotechnologies are the design, characterisation, production and application of structures, devices and systems by controlling shape and size at nanometre scale.

6. Nanoparticles Nanotechnology is considered engineering at the atomic scale. Nanoparticles are particles with lengths in at least one dimension between 1 and 100 nanometers (1.0 nm = 10 -9 m). At these length scales, materials begin to exhibit distinct properties that affect biological, chemical, and physical behaviour. Divide 1 metre to 100 crore parts. Each part 1 nm. A mesoporous material has pores with diameters between 2 and 50 nm , according to IUPAC nomenclature. For comparison, IUPAC defines microporous material has pores smaller than 2 nm in diameter and macroporous material has pores larger than 50 nm in diameter.

7. Nanomaterials /Nanostructured materials : Condensed material comprises structural elements between a few atoms and a few tens of thousands of atoms Types of nanocrystalline materials by size of their structural elements: clusters; nanotubes, fibres and rods; films & coats; polycrystals 0D 1D 2D 3D

8. Nanomaterials Two principal factors cause the properties of nanomaterials to differ significantly from Bulk materials: • Increased relative surface area • Quantum effects These factors can change or enhance properties such as reactivity, strength and electrical characteristics Surface Effects • As a particle decreases in size, a greater proportion of atoms are found at the surface compared to those inside Example: a particle of• Size-30 nm- > 5% of its atoms on its surface• Size-10 nm->20% of its atoms on its surface• Size-3 nm-> 50% of its atoms on its surface • Nanoparticles are more reactive than large particles (Catalyst)

9. Quantum confinement effect is observed when the size of the particle is too small to be comparable to the wavelength of the electron We break the words like quantum & confinement **Confinement means to confine the motion of randomly moving electron to restrict its motion in specific energy levels (discreteness) ** Quantum means smallest possible discrete unit of any physical property, such as energy or matter

10. In the bulk matter, the bands are actually formed by the merger of bunch of adjacent energy levels of a LARGE number of atoms and molecules. As the particle size reaches the nano scale, where every particle is made up only a VERY SMALL number of atoms or molecules, the number of overlapping of orbitals or energy level decreases. This will cause an INCREASE IN ENERGY GAP BETWEEN THE VALENCE BAND AND THE CONDUCTION BAND. This explains the higher energy gap in NP than the corresponding bulk matter. The band gap is the region forbidden for the electrons. THE LARGER THIS FORBIDDEN REGION, THE GREATER WILL BE RESTRICTION ON THE MOVEMENT OF ELECTRONS. Hence the NP exhibit the lower electrical conductivity than the bulk from which they are prepared . So there is a shift of absorption spectrum toward lower wave length or blue region. b) Schematic representation of the size effect on the gap between the valence band (VB) and the conduction band (CB) and the absorption (up arrow) and fluorescence (down arrow). Smaller particles have a wider band gap.

11. Medieval Stained Glass One of the most documented examples of nanotechnology known in history is medieval stained glass artisans. They were the first nanotechnologists, as they, although unaware, trapped gold nanoparticles in the 'glass matrix' in order to generate the ruby red colour in the windows. They also trapped silver nanoparticles which gave it a deep yellow colour . As in today's finding it is the size of the metal (whether it be gold or silver) nanoparticles that define the variations in colour Deruta ceramicists ‘ Deruta ceramicists’ are another example of the practise of the early forms of nanotechnology. The people in Umbria, Italy during the Renaissance Period (1450-1600AD), used nanotechnology to produce iridescent or metallic glazes . They achieved these effects by using particles of copper and silver metal (between 5 and 100 billionth of a metre) particles in their glazes, this caused light to bounce off their surface at different wavelengths, thus giving it the ‘iridescent’ look . The Italians weren't the only people experimenting with nanotechnology in ceramics. More than a thousand years ago, the Chinese were known to use gold nanoparticles as an 'inorganic dye' to create a red colour in their ceramic porcelains.

12. Polymer Nanocomposite Nanocomposites are composites in which at least one of the phases shows dimensions in the nanometre range These are high performance materials that exhibit unusual property combinations and unique design possibilities Fullerene: dia. 1.1 nm SWCNT: dia 1nm MWCNT : interlayer distance: 3.4  Graphene Interlayer spacing: 0.335 nm Clay

13. Symmetric shape (1 nm dia.) Large surface area—catalyst Stable at high temp. (750 C) Stable at high pressure Hollow-Caging particles

14. Carbon nanotubes Rolled up sheet of sp 2 bonded carbon atoms

15. Graphene

16. Magnetic nanoparticles Nanoparticles made from magnetic materials are, rather unsurprisingly, referred to as “magnetic nanoparticles”. This particles can be moved by applying magnetic fields, which allows them to be controlled inside body. Magnetic nanoparticles suspended in solution are called “ ferrofluids ” and have many applications in medicine, acoustics, and electronics

17. Gold Nanoparticles Gold nanoparticles   Emerging as promising agents for cancer therapy and are being investigated as drug carriers, photothermal agents, contrast agents and many more Liquid is usually either an intense red colour (for particles less than 100 nm) or blue/purple (for larger particles). Absorption of various wave length

18. Silver nanoparticles Silver particles of between 1 nm and 100 nm. Unique optical, electrical, and thermal properties and are being incorporated into products that range from photovoltaic to biological and chemical sensors .

19. DNA DNA, or deoxyribonucleic acid, is the hereditary material in humans and almost all other organisms. Nearly every cell in a person’s body has the same DNA. DNA stores biological information

20. Nanostructured Materials in Nature This type of material consists of having both nano and micro structures organized in such a fashion that the property gained will be mostly better than both Waxy coating makes it hydrophobic Nano/micro structure does not allow the water drop to touch the surface and spread

21. Nanostructured silicon/lithium alloy for lithium ion battery Nanostructured alloying reduces the mechanical damage of anode occurring due to intercalation/de-intercalation of lithium ion extending it to more than 50 cycles showing high capacity Nanostructured polyaniline electrode based supercapacitor shows high voltage window higher capacitance extended cycle life

22. Lithium ion battery Silicon nanoparticles can be surrounded by graphene cages. The idea is that when the silicon expands and cracks form in the nanoparticles the silicon remains in the graphene cage without degrading the anode. Silicon nanowires can be grown on a stainless steel substrate and demonstrated that batteries using these anodes could have up to 10 times the power density of conventional lithium ion batteries. ---- Using silicon nanowires, instead of bulk silicon fixes a problem of the silicon cracking , that has been seen on electrodes using bulk silicon. While the silicon nanowires swell as lithium ions are absorbed during discharge of the battery and contract as the lithium ions leave during recharge of the battery the nanowires do not crack, unlike anodes that used bulk silicon.

23. Aligned carbon nanotubes can be deposited on a substrate for use as the anode, and possibly the cathode, in a lithium ion battery. The carbon nanotubes have organic molecules attached that help the nanotubes align on the substrate, as well as provide many oxygen atoms that provide points for lithium ions to attach to.---This could increase the powe r density of lithium ion batteries significantly, perhaps by as much as 10 times. Lithium sulfur batteries (the cathode contains the sulfur ) have the capability of storing several times the energy of lithium-ion batteries. ----Cathodes are made up of carbon nanofibers encapsulating the sulphur. ( 16 electron reduction of a S 8 molecule at the cathode, S 8 +16e− +16Li+ →8Li 2 S) Cathodes also made up of mesoporous carbon nanoparticles, with the sulfur inside the nanopores .

24. Known origins that cause physical properties to change: (i) large fraction of surface atoms, (ii) large surface energy, (iii) spatial confinement, and (iv) reduced imperfections Physical Properties of Nanomaterials

25. Physical Properties of Nanomaterials Reduced Melting Point -- May have significantly lower M. P. or phase transition temp. and appreciably reduced lattice constants, due to a huge fraction of surface atoms in the total amount of atoms. – Surface atoms bind with less cohesive force due to less no. of neighbors Ultra Hard – Mech. Props. may reach the theoretical strength, which are one or two orders of magnitude higher than that of single crystals in the bulk form. The enhancement in mechanical strength is simply due to the reduced probability of defects . Optical properties can be significantly different from bulk crystals. --- Semiconductor Blue Shift in absorption and emission due to an increased band gap. Quantum Size Effects , --- Metallic Nanoparticles Color Changes in spectra due to Surface Plasmons Resonances Lorentz Oscillator Model

26. Electrical conductivity ( Dual characteristics ) ---decreases with a reduced dimension due to increased surface scattering. When the critical dimension is smaller than the mean free path, motion of electron will undergo elastic and inelastic scattering. ---I ncreases due to better ordering 5. Magnetic properties Ferromagnetism disappears and transfers to superparamagnetism in the nanometer scale due to huge surface energy . 6. Self-purification is an intrinsic thermodynamic property of nanostructures and nanomaterials due to enhanced diffusion of impurities/defects/dislocations to the nearby surface. 7. Increased perfection enhances chemical stability Most are tunable with size!

27. Types of Nanomaterials Most nanomaterials can be organized into four types: •        Carbon Based Materials •        Metal Based Materials •         Dendrimers •        Composites

28. Dendrimer Dendrimer = a family of nanosized , 3D polymer, a class of macromolecules having highly branched architecture Tree Neuron Dendrimer

29. Surface groups Dendrimer Schematic 2D presentation 3D presentation

30. Dendrimer Surface functional groups has many role to play : Provides plenty of reactive functionalities for particular application The functionalities may be more than one type In some composition it can function as plasticizer Can act as drug or other chemical carrier

31. Contd ….. One important characteristics of dendrimer : Being highly branched the viscosity of solution does not rise like linear polymer making it an excellent candidate for high loading paint binder

32. G0 Core Monomer GX = generation Generation Growth

33. G1 GX = generation Core Monomer Generation Growth

34. G2 GX = generation Core Monomer Generation Growth

35. G3 GX = generation Core Monomer Generation Growth

36. Fullerene Highly hydrophobic molecule --Limited solubility in many organic solvents --Completely insoluble in water Non-covalent or covalent complexes enhance water solubility (1:1) C 60 is stable to : Weak acid/base Mild oxidizing agents Some mild reducing agents Cycloaddition chemistry Diels-Alder 1,3-Dipolar cycloadditions etc. Essential for biological applications Can be made water soluble by modifying it with various agents via covalent linkage

37. Carbon nanotube Various folding modes of graphene to CNT Carbon nanotube is composed of perfect arrangement of C=C & C-C bonds SWCNT Dia 1 nm; MWCNT: Interlayer distance: 0.34 nm Mechanical Extremely high Young’s modulus Material Young’s modulus (GPa) Steel 190-210 SWCNT 1,000+ Diamond 1,050-1,200

38.   Application of CNT Similar adsorption capacities as activated carbons for removal of contaminants A CNT nano-structured sponge containing S & Fe is effective at soaking up water contaminants such as oil, fertilizers, pesticides and pharmaceuticals . Their magnetic properties make them easier to retrieve after clean-up job is done. In military equipment for defusing unexploded mines as CNT is very stable to laser Radar frequency (MW range) can be absorbed by CNTs In solar panels--strong UV/Vis-NIR absorption Hydrogen storage , Actuator and MEMS/NEMs applications

39. Biological applications: Bio-sensing Larger inner volumes – can be filled with chemical or biological species. Open mouths of nanotubes make the inner surface accessible. Distinct inner and outer surface can be modified separately CNT as AFM probe tips: Small dia. – max. resolution Polymer CNT nanocomposite for sensing, Battery, Supercapacitor & structural application

40. Graphene properties Monolayer graphite (0.345 nm): C=C & C-C bonds Electrical conductivity is excellent It has enhanced energy capacity and charge rate in rechargeable batteries ; superior supercapacitor ; graphene electrodes for promising solar cells  that are inexpensive, lightweight and flexible Multifunctional graphene mats are promising substrates for catalytic systems Functionalized graphene holds exceptional promise for biological and chemical sensors

41. Ideal for next-generation electronics , having mechanical flexibility, high electrical conductivity, and chemical stability Graphene sheets can create a superhydrophobic coating material that shows stable superhydrophobicity under both static as well as dynamic (droplet impact) conditions Most  effective for EMI shielding-- Thin and strong structure with low surface energy make it a good candidate A relatively new method of purifying brackish water is  capacitive deionization  (CDI) technology . The advantages of CDI are that it has no secondary pollution, is cost-effective and energy efficient

42. CDI Anions are removed from the water and are stored in the positively polarized electrode. Likewise, cations are stored in the cathode, which is the negatively polarized electrode. Adsorption and desorption cycles The operation of a conventional CDI system cycles through two phases: an adsorption phase where water is desalinated and a desorption phase where the electrodes are regenerated. During the adsorption phase, a potential difference over two electrodes is applied and ions are adsorbed from the water. In the case of CDI with porous carbon electrodes, the ions are transported through the interparticle pores of the porous carbon electrode to the intraparticle pores, where the ions are electrosorbed in the so-called electrical double layers (EDLs). After the electrodes are saturated with ions, the adsorbed ions are released for regeneration of the electrodes. ----The potential difference between electrodes is reversed or reduced to zero. In this way, ions leave the electrode pores and can be flushed out of the CDI cell resulting in an effluent stream with a high salt concentration, the so-called brine stream or concentrate. Part of the energy input required during the adsorption phase can be recovered during this desorption step.

43. Graphene in superhydrophobic coating Robustness is one of the principle limitations to widespread application of many superhydrophobic coatings. Graphene is robust enough to sustain rigour of abrasion and other damages. Graphene based coatings with PDMS are robust enough to retain the superhydrophobic properties after abrasion. Sandpaper abrasion does not reduce the superhydrophobicity Bouncing effect distinguishes it from hydrophobic coatings

44. Gold Nanoparticles properties Colloidial gold nanoparticles have been utilized for centuries by artists due to the vibrant colors produced by their interaction with visible light . --For small (~30nm) monodisperse gold nanoparticles the SPR causes an absorption of light in the blue-green portion of the spectrum (~450 nm) while red light (~700 nm) is reflected Gold nanoparticles are designed for use as conductors from printable inks to electronic chips When light is applied to a tumor containing gold nanoparticles , the particles rapidly heat up, killing tumor cells in a treatment also known as hyperthermia therapy .

45. As sensor: A colorimetric sensor based on gold nanoparticles can identify if foods are suitable for consumption Gold nanoparticles are used to detect biomarkers in the diagnosis of heart diseases, cancers, and infectious agents The surface of a gold nanoparticle can be used for selective oxidation or in certain cases the surface can reduce a reaction (nitrogen oxides) Biosensor can function in visible light when immobilized on gold nanoparticle

46. Silver nanoparticle properties As sensors -When 60 nm silver nanoparticles illuminated with white light --Bright blue point source scatterer under a dark field microscope Toxic effects on cells and microbes due to a low level of silver ion release from the nanoparticle surface – DNA contain S & P which can interact with Ag nanoparticle-DNA get destroyed Silver nanowires can be used to provide conductive coatings for transparent conductors and flexible electronics Metallic nanoparticles attached to silver nanowires function as antennas for sensing and imaging applications Single layers of silver nanowires used to construct arrays for molecule specific sensing in conjunction with Raman Spectroscopy

47. Nano-TiO 2 properties A thin layer of Nano-TiO 2 is subjected to a light of energy higher than its band gap (3.2eV) Electron in TiO 2 get excited & jumps from valance band to conduction band generating electron & hole pair This electron-hole pair reacts with atmospheric oxygen & water molecule & forms highly oxidative species as shown in the reaction

48. Nano Velcro • Imagine manufacturing assembly without solder or adhesive • A joint stronger than many traditional assembly methods…. and materials • Manufactured at room temperature; Estimated ideal pull strength = 3 GPa ; High wear resistance Nano elements in tires ---c ould enable tires to last the lifetime of the car Electronic Devices • Displays • OFETS • Nano pockets • Memory • Super Capacitors, etc . Multifunctional Composites • Self-cleaning • Color changing plastics • Self-healing • Structural materials, • ‘Aware’ materials, etc . Composites : stronger, tougher, stiffer, lighter materials ( adhesives, structural, electronic, optical functionality ), nanobiotech for sensing, actuating, power functions Nano antennas : Nano scale fractal antennas for multiple spectra and broadband Nanodisplays : Large, lower cost and brighter displays based on embedded carbon nanotubes Nano power: High capacity power sources (storage, conversion, advanced fuel cells, photonic energy), parasitic energy harvesting, nanobiotech related functionality.

49. Nanotechnology in health and medicine Drug Delivery Cancer treatment Perkinson’s and Alzeimer’s deseases Opthalmology , Denstistry Nanotechnology in textiles

50. Nanostructured materials and coatings offer the potential for significant improvements in engineering properties based on improvements in physical and mechanical properties resulting from reducing microstructural features by factors of 100 to 1000 times compared to current engineering materials. The potential benefits include higher hardness and strength in metals and cermets resulting from reduced grain size and slip distance, respectively. In ceramics, higher hardness and toughness may be accomplished with reduced defect size and enhanced grain boundary stress relaxation, even at ambient temperature. Diffusivity is greatly increased, associated with a larger volume of grain boundaries. Thermal conductivity may be reduced because of enhanced phonon scattering from grain boundaries and other nanoscale features. ( Phonon is collective excitation in a periodic, elastic arrangement of atoms/molecules in condensed matter ) Thermal barrier coatings (TBCs ) are used extensively in gas turbine applications to insulate superalloy turbine blades and vanes from the hot gas stream. There is a need for thermal barrier coatings with improved durability and performance. In thermal sprayed TBCs, failure of the coating occurs by spallation in the ceramic "splat" boundaries near the ceramic-to-metal interface. --- It should be possible to strengthen the boundaries by refining the structure to the nanoscale . In addition, it may be possible to develop TBCs with improved performance, by reducing thermal conductivity resulting from enhanced phonon scattering at grain boundaries . The coatings industry Coatings are needed to prevent wear, erosion, and corrosion, and to provide thermal insulation. For both commercial and military applications there is a need for coatings with improved durability and performance. Nanostructured coatings show promise based on initial laboratory trials. Durability improvements of 3 to 5 times can be projected for a number of coating applications.

51. Nanocrystalline metal One of the benefits of nanostructuring is the ability to impart strength levels in pure metals that approach and even exceed the levels of alloys. Nanostructured metals which have nano -scale microstructure are classified into ultrafine grained metals and nanocrystalline metals. Bulk nanostructured metals are characterized by a high density of grain boundaries .  Since the grain boundaries interact with crystal defects such as dislocations, bulk nanostructured metals have potential to show properties significantly different from those in conventionally grained metals.