Smart Materials & Devices

Smart Materials & Devices Dr. Pramod Kumar Singh Department of Physics School of Basic Sciences & Research Sharda University, Greater Noida Email: pramodkumar.singh@sharda.ac.in

Syllabus

References

SMART MATERIALS SMART Materials are special solids which can be tailored to develop desired properties applied for fabrication of devices leading to societal benefits

Materials Engineering Materials, Materials Science and Materials Scientist play a very vital role in the development of a country Properties of materials are size dependent Materials scientist claim that 21st century is the century of materials and especially nanomaterials/smart materials

SMARTCOMPOSITES Properties of materials are size dependent

COMPOSITE/NANOCOMPOSITES

Fundamentals of Materials Science and Engineering, William D. Callister, Jr.

Atlantis Space Shuttle Orbiter, USA Fundamentals of Materials Science and Engineering, William D. Callister, Jr.

CLASSIFICATION OF MATERIALS • Solid materials have conveniently been grouped into • three classes • 1.Metals • 2.Ceramics • 3.Polymers • Combination of above materials give variety of other materials • Now most of the new materials come under the category of Smart Materials or Future Materials

THREE MAJOR ENGINEERING MATERIALS

*Modern technologies require materials with unusual combinations of properties that can not be met by the conventional metal alloys, ceramics and polymeric materials. This is usually true for materials that are needed for aerospace, underwater, and transportation applications.

For example aircraft engineers are increasingly searching for structural materials that have low densities, are strong, stiff and abrasion and impact resistant, and are not easily corroded. This is a formidable combination of characteristics. Frequently strong materials are relatively dense; also, increasing the strength or stiffness generally results in a decrease in impact resistance.

Atlantis Space Shuttle Orbiter, USA Fundamentals of Materials Science and Engineering, William D. Callister, Jr.

Composites Composite is considered to be any multiphase material that exhibits a significant proportion of the properties of both constituents such that a better combination of properties is realized. *Better property combinations are fashioned by the judicious combination of two or more distinct materials

Composites *In addition, the constituent phases must be chemically dissimilar and separated by a distinct interface. Thus most metallic alloys and many ceramicsdo not fit this definition because their multiple phases are formed as a consequence of natural phenomena.

Composites • Composites are a combination of two or more organic or inorganic components one of which serves as a matrix holding the materials together and then other of which serves as reinforcement in the form of fibers • Two inherently different materials that when combined together produce a material with properties that exceed the constituent materials. • Composites are lightweight and strong but they are complex to manufacture, expensive and hard to inspect for flaws

Composites Many composite materials are composed of just two phases; one is termed the matrix, which is continuous and surrounds the other phase, often called dispersed phase. The properties of composites are a function of the properties of the constituent phases, their relative amounts and the geometry of the dispersed phase.

Composites Composites often have only two phases • Matrix phase • continuous - surrounds other phase • Dispersed phase • discontinuous phase Matrix (light) Dispersed phase (dark)

Classification of Artificial Composites Composites Particulate Fiber Structural Large Dispersion Laminates Sandwich Particle Strengthened Panels Continuous Discontinuous Aligned Random

Properties of Composites Properties depend on: • constituent phases • relative amounts • geometry of dispersed phase • shape of particles • particle size • particle distribution • particle orientation

Parameters on which properties depend Concentration Orientation Distribution Size Shape

Composites Offer High Strength Light Weight Design Flexibility Consolidation of Parts Net Shape Manufacturing

Biocomposites • Biocomposites combine plant fibers with resins to create natural based composite materials. • High tensile plant fibers including, kenaf, industrial hemp, and flax, can be combined with traditional resins to create an alternative to traditionally steel or fiberglass applications. • Some advantages over traditional composites: • Reduced weight • Increased flexibility • Greater moldability • Less expensive • Sound insulation • Renewable resource • Self-healing properties

NANOCOMPOSITES A nanocomposite is as a multiphase solid material where one of the phases has one, two or three dimensions of less than 100 nanometers (nm), OR structures having nano-scale repeat distances between the different phases that make up the material.

NANOCOMPOSITES Constituents have at least one dimension in the nanometer scale. • Nanoparticles (Three nano-scale dimensions) • Nanofibers (Two nano-scale dimensions) • Nanoclays (One nano-scale dimensions)

Properties of Nanocomposites • Tiny particels with very high aspect ratio, and hence larger surface area. • Larger surface area enables better adhesion with the matrix/surface. • Improvement in the mechanical performance of the parent material. • Better transparency due to small size(>wavelength of light).

Why Nanocomposites?  Multi-functionality • Small filler size: • High surface to volume ratio • Small distance between fillers  bulk interfacial material • Mechanical Properties • Increased ductility with no decrease of strength, • Scratching resistance • Optical properties • Light transmission characteristics particle size dependent Traditional nanocomposite Stress polymer Strain

Visible Ultraviolet Scratch Resistant, Transparent, Filtering Coatings TEM of the 16.7wt% nano alumina filled gelatin film Transmittance rate of 16.7wt.% nanoalumina filled gelatin films coated on 0.1mm thick plastic substrate

Size limits for these effects have been proposed < 5 nm for catalytic activity < 20 nm for making a hard magnetic material soft < 50 nm for refractive index changes < 100 nm for achieving superparamagnetism, mechanical strengthening.

Nanoclays • Silicates layers separated by an interlayer or gallery. • Silicates layers are ~ 1 nm thick, 300 nm to microns laterally. • Polymers as interlayers. • Tailor structural, optical properties

Nanofibers - Nanotubes • Nanotubes in metal, metal oxide and ceramic matrix have also been fabricated. • Nanotubes in polymer matrices by mixing, then curing. • Most important filler category in nanocpomposites

Nanocomposite VS Composite In mechanical terms, nanocomposites differ from conventional composite materials *Exceptionally high surface to volume ratio of the reinforcing phase and/or its exceptionally high aspect ratio. The reinforcing material can be made up of particles (e.g. minerals), sheets (e.g. exfoliated clay stacks) or fibres (e.g. carbon nanotubes or electrospun fibres). The area of the interface between the matrix and reinforcement phase(s) is typically an order of magnitude greater than for conventional composite materials.

Nano composites are found in nature also. It is found in abalone (small or very large-sized edible sea snail) and bones. Advantage of using the nanocomposites:• Greater tensile /flexural strength• Reduced weight for the same performance• Flame retardant properties• Improved mechanical strength• Higher electrical conductivity• Higher chemical resistance

A simple example of a normal composite can be considered – we do have concrete for our houses. What exactly is this concrete? It’s a blend of cement, sand, and metal rod. These composition changes the total property of the material used. It becomes so hard that it can withstand tonnes of weight equally. It’s from this concept we device the idea about the nanocomposites.

1.5 R g unbonded 1 bonded diffusion/bulk diffusion 0.5 0 1 2 3 4 5 distance from the particle Nanocomposite as a Multiscale System • Macroscale composite structures • Clustering of nanoparticles - micron scale • Interface - affected zones - several to tens of nanometers - gradient of properties • Polymer chain immobilization at particle surface is controlled by electronic and atomic level structure

This large amount of reinforcement surface area means that a relatively small amount of nanoscale reinforcement can have an observable effect on the macroscale properties of the composite. For example, adding carbon nanotubes improves the electricaland thermal conductivity. Other kinds of nanoparticulates may result in enhanced optical properties, dielectric properties, heat resistance or mechanical properties such as stiffness, strengthand resistance to wear and damage. In general, the nano reinforcement is dispersed into the matrix during processing. The percentage by weight (called mass fraction) of the nanoparticulates introduced can remain very low (on the order of 0.5% to 5%) due to the low filler percolation threshold, especially for the most commonly used non-spherical, high aspect ratio fillers (e.g. nanometer-thin platelets, such as clays, or nanometer-diameter cylinders, such as carbon nanotubes).

Chemical Synthesis: Gas Phase Synthesis Chemical Vapor Condensation Combustion Flame Synthesis Liquid Phase Synthesis Others – Mechanical Deformation Thermal recrystallization Synthesis of Nanocomposites

The nano powder formed normally has the same composition as the starting material. The starting material, which may be a metallic or inorganic material is vaporized using some source of energy The metal atoms that boil off from the source quickly loose their energy. These clusters of atoms grow by adding atoms from the gas phase and by coalescence A cold finger is a cylindrical device cooled by liquid nitrogen. The nano particles collect on the cold finger The cluster size depends on the particle residence time and is also influenced by the gas pressure, the kind of inert gas, i.e. He, Ar or Kr and on the evaporation rate of the starting material. The size of the nano particle increases with increasing gas pressure, vapor pressure and mass of the inert gas used. Gas Phase Synthesis(Synthesis of ultra pure metal powders and compounds of metal oxides(ceramics) )

Chemical Vapor Condensation • the precursor vapor is passed through a hot walled reactor. The precursor decomposes and nano particles nucleate in the gas phase. The nano particles are carried by the gas stream and collected on a cold finger. The size of the nano particles is determined by the particle residence time, temperature of the chamber, precursor composition and pressure. Nanocomposites

Combustion Flame Synthesis • Energy to decompose the precursor may be supplied by burning a fuel-air mixture with the precursor. In order to reduce agglomeration of the particles in the flame, the flame is specially designed to be low pressure. • If you have observed the flame of a candle, you would have noticed that the flame consist of a blue center and a yellow to red periphery. This is because the temperature in the flame varies with position in the flame. Such a variation in the temperature profile of the flame would cause nanoparticles of different sizes to grow in the different regions of the flame. This is avoided by designing the flame to have a 'flat temperature profile' i.e. a constant temperature across its width.

Liquid Phase Synthesis • Two chemicals are chosen such that they react to produce the material we desire • An emulsion is made by mixing a small volume of water in a large volume of the organic phase. A surfactant is added. The size of the water droplets are directly related to the ratio of water to surfactant. The surfactant collects at the interface between the water and the organic phase. If more surfactant were to be added, smaller drops would be produced and therefore, as will become apparent, smaller nano-particles.

The progress in nano composites is varied and covers many industries. Nano Composites can be made with a variety of enhanced physical, thermal and other unique properties. They have properties that are superior to conventional micro scale composites synthesized using simple and inexpensive techniques. Materials are needed to meet a wide range of energy efficient applications with light weight, high mechanical strength, unique color, electrical properties and high reliability in extreme environments. Applications could be diverse as biological implant materials, electronic packages and automotive or aircraft components. Although some of the properties will be common between the applications, others will be quite different. An electronic package polymer composite must be electrically insulating, while an aircraft component may need to be electrically conductive to dissipate charge from lighting strikes.

The additions of small amounts of nano particles to polymers have been able to enable new properties for the composite material, but results are highly dependent on the surface treatment of the nano particles and processing used. It is important to determine whether nano materials could be integrated into nano composite to enable multiple desirable properties for a given application. While industry is seeking materials to meet challenges with unique properties, there are no “rule of mixtures” to identify how to mix multiple nano materials in a composite structure and all required properties nano materials often have unique properties that could enable composite materials with multiple unique properties simultaneously; however, it is often challenging to achieve these properties in large scale nano composite materials. Furthermore, it is important that nano materials have desirable properties that can’t be achieved through use of conventional chemicals and materials. To access the positional value of nano materials, it is important to determine which nano materials can be effectively integrated into nano composites and what new or improved properties this enables.

Then it will be important to determine the effectiveness of dispersion of the nano particles in the matrix and how this affects the structure of the polymer to enable optimization of the desired property. Once the basic models of this are developed, it will be resulting structure and properties of the nano composite. One nano composite may be required to improve the mechanical property, ad another may be required to change the electrical properties; however the addition of electrical material may also change the mechanical properties of the nano composite trough interactions with the polymer and nano particles. Thus, models of the interactions within the nano composite are needed to enable development of effective rules of mixtures. This may require a combination of numerical modeling, characterization and informatics to enable this nano composite with properties by design capability.

Smart Materials & Devices