Smart Materials & Devices

Dr. Pramod Kumar SinghDepartment of Physics

School of Basic Sciences & ResearchSharda University, Greater Noida

Email: pramodkumar.singh@sharda.ac.in

Syllabus7.01 SMDXXX.A Unit A Materials- Basic Concepts

7.02 SMDXXX.A1 Unit A Topic 1 Classification of Materials, Bonding in solids

7.03 SMDXXX.A2 Unit A Topic 2 Crystal structure, Bravais lattice, Miller Indices

7.04 SMDXXX.A3 Unit A Topic 3 Imperfections of crystals

7.05 SMDXXX.B Unit B Dielectrics, Superconductors and Magnetic Materials

7.06 SMDXXX.B1 Unit B Topic 1 Dielectic materials and their properties

7.07 SMDXXX.B2 Unit B Topic 2 Superconductors and their applications

7.08 SMDXXX.B3 Unit B Topic 3 Magnetic materials and their properties

Syllabus7.09 SMDXXX.C Unit C Composite & Nanocomposite materials

7.10 SMDXXX.C1 Unit C Topic 1 Introduction of composite and Nanocomposite materials

7.11 SMDXXX.C2 Unit C Topic 2 Metal-Ceramic nanocomposite

7.12 SMDXXX.C3 Unit C Topic 3 Polymer based nanocomposites

7.13 SMDXXX.D Unit D Characterization Techniques

7.14 SMDXXX.D1 Unit D Topic 1 X-ray diffraction

7.15 SMDXXX.D2 Unit D Topic 2 UV-Visible spectroscopy

7.16 SMDXXX.D3 Unit D Topic 3 Infrared spectroscopy

7.17 SMDXXX.E Unit E Devices

7.18 SMDXXX.E1 Unit E Topic 1 Devices for energy conversion

7.19 SMDXXX.E2 Unit E Topic 2 Storage Devices

7.20 NSTXXX.E3 Unit E Topic 3Sensors and Microelectronic devices

References

9 References

9.1 Text book

1. Material Science and Engineering An Introduction by: William D. Callister

2. Nanocomposite Science and Technology, P. M. Ajayan, L. S. Schadler, P. V. Braun

9.2 Other references

3. Chemistry of nanomaterials: Synthesis, properties and applications by CNR Rao (Taylor & Francis 2008)

4.Structure and Properties of Engg. Materials by: V R S Murthy, A K Jena

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

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.

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.

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

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 ceramics do 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)

Composites

Classification of Artificial Composites

Composites

Particulate Fiber

Structural

ContinuousDiscontinuous

Laminates SandwichPanels

LargeParticle

DispersionStrengthened

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 dependParameters on which properties depend

Concentration

SizeShape

Distribution Orientation

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

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)

NANOCOMPOSITES

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).

• 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

Why Nanocomposites? Multi-functionality

Strain

Stre

ss

polymer

nanocompositeTraditional

TEM of the 16.7wt% nano alumina filled gelatin film

Visible

Ultraviolet

Scratch Resistant, Transparent, Filtering Coatings

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

Modulus ~1000 GPa (SWCNT)~1200 GPa (MWCNT)

Tensile Strength ~ 100 GPa

ThermalConductivity

2000 W/m/K

Density 1300 –1400 kg/cm3

Length up to microns

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.

Nanocomposite VS Composite

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.

– 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

Nanocomposite as a Multiscale System

0.5

1

1.5

0 1 2 3 4 5

unbondedbonded

diff

usi

on

/bu

lk d

iffu

sio

n

distance from the particle

Rg

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).

Synthesis of Nanocomposites

• Chemical Synthesis: 1. Gas Phase Synthesis2. Chemical Vapor Condensation3. Combustion Flame Synthesis4. Liquid Phase Synthesis

• Others –• Mechanical Deformation• Thermal recrystallization

Gas Phase Synthesis(Synthesis of ultra pure metal powders and compounds of metal oxides(ceramics) )

• 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.

Nanocomposites

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.

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.

As this capability is developed, it will be important to characterize the interactions of the nano particles with environmental effects including moisture, temperature and stress to assess potentional degradation of the nano composite’s properties through its life. Thus, the nano composite must have multiple new and unique properties for a specific application, but those properties must not degrade significantly through the life of the material.  Developing these capabilities will require significant research into interactions of the nano materials in the polymer matrix and how these are changed with temperature, moisture and mechanical stress. In general, two idealized polymer layered nano composite structures are possible; intercalated and exfoliated. The greatest property enhancements are generally observed for exfoliated nano composites. These consist of individual nano meter filler layers suspended in a polymer matrix. In contrast, intercalated hybrids consist of well ordered multilayer’s with alternating polymer / nano mater filter layers with a repeat distance of a new nano meters. In reality many systems fall short of the idealized exfoliated morphology.

Engineering Properties of Materials

• Normal stress is the state leading to expansion or contraction. The formula for computing normal stress is:

Where, is the stress, P is the applied force; and A is the cross-sectional area. The units of stress are Newtons per square meter (N/m2 or Pascal, Pa). Tension is positive and compression is negative.

• Normal strain is related to the deformation of a body under stress. The normal strain, , is defined as the change in length of a line, L, over it’s original length, L.

A

P

L

L

PP

L L

A

The mechanical, electrical, thermal, optical, electrochemical, catalytic properties of the nanocomposite will differ markedly from that of the component materials.

• For uniaxial loading (e.g., tension in one direction only): = E

1

E

Stress

Strain,

u

y

Rupture

Young's modulus of elasticity (E) is a measure of the stiffness of the material. It is defined as the slope of the linear portion of the normal stress-strain curve of a tensile test conducted on a sample of the material.

Yield strength, y, and ultimate strength, u, are points shown on the stress-strain curve below.

• Shear stress, , is the state leading to distortion of the material (i.e., the 90o angle changes). The corresponding change in angle, in Radians, is called shear strain, . The slope of the linear portion of the -is called shear modulus of elasticity, G.

54

1

G

Stress

Strain,

• Poisson’s ratio, , is another property defined by the negative of the ratio of transverse strain, 2, over the longitudinal strain, 1, due to stress in the longitudical direction, 1.

55

2

1

1

Original shape

11

2

1

212

• Anisotropic materials have different properties in different directions. In the most general case, they are defined by 21 independent constants. Special cases include:– Orthotropic: wood and some composites– Transversely isotropic: some continuous fiber reinforced composites

56

Fibers

A group of Chinese researchers prepared dye synthesized solar using micro / nano composite TiO2 porous films. Bloo solar is developing and manufacturing revolutionary nano structured ultra thin film solar PV products that will provide affordable clean renewable energy for everyone. In addition to a large potential impact on solar energy production, nano composites also have an impact on nuclear energy. Nano composites also can save energy when incorporated into paints; TAG technology has developed a nano particle that when added to paint only allows heat flow in one direction. 

Other industries are also influenced by nano composites, including computers, electronic magnetic, industrial components, water remediation and medical devices. Nano composite permanent magnet materials are a new type of permanent magnet material consisting of magnetically hard and soft grains, both in nano meter size.

Those materials have a high potential to be developed into high performance permanent magnets with very high energy product. The new magnets will have lower cost, high magnetic performance, and better corrosion resistance as a result of the significantly reduced rare earth content.

The new magnets will also have improved fracture toughness as a result of fine nano grain structure and the existence of a relatively soft α-Fe.

Nano composites of cyanate esters were prepared by dispersing organically modified layered silicates (OLS) into the resin. Inclusion of only 2.5% by weight of OLS led to a marked improvement in physical and thermal properties.

The mechanical response of nano scale materials and structure has important implications diverse areas of science spanning topics that include understanding of biological recognition, development of light weight structural materials, to exploration of new concepts for switches and chemical sensors.

Engineering Applications: Composite materials have been used in aerospace, automobile, and marine applications (see Figs. 1-3). Recently, composite materials have been increasingly considered in civil engineering structures. The latter applications include seismic retrofit of bridge columns (Fig. 4), replacements of deteriorated bridge decks (Fig. 5), and new bridge structures (Fig. 6).

Figure 1 Figure 2 Figure 3

Figure 4 Figure 5 Figure 6

The nanocrystalline grains should have random orientation (i.e. high angle grain boundaries) to minimize incoherent strain and facilitate many nanocrystalline grains to slide in amorphous matrix to release strain and obtain high toughness.

The amorphous phase must possess high structural flexibility in order to accommodate coherent strains without forming dangling bonds, voids, or other defects.

The presence of amorphous phase on the boundaries helps to deflect and terminate nanocracks in addition addition to the enhancement of grain boundary sliding, thusimproving coating toughness.

To design a nanocomposite coating with both high hardness and high toughness, one must take all the above into consideration. Probably the best way is to use ternary, quaternary or even more complex systems, with high strength amorphous phase as matrix (such as a-SiNx, a-BN, a-C, etc.) and hard transition metal-nitride nanocrystals (such as TiN, W2N, BN, etc.) as nanocrystalline phase to increase grain boundary complexity and strength.

These nanocrystalline phases should be refractory and immiscible with each other, and could result in compositional modulation, segregation and high thermal stability of the nanostructure.

Synthesis methods

Different techniques are now available for preparation of nanocomposite coatings.

The most promising methods are magnetron sputtering and chemical vapor deposition(CVD), although other methods, such as laser ablation , thermal evaporation , ion beamDeposition and ion implantation, are also used by various researchers.

High deposition rate and uniform deposition for complicated geometries are the advantages of CVD method compared to sputtering.

However, the main concern for CVD method is that the precursor gases TiCl4, SiCl4 or SiH4 may pose problems in production because of their corrosive nature and dangerof fire hazard.

Moreover, the incorporation of chloride in protective films deposited from plasma CVD may induce interface corrosion problems during exposure to elevated temperatures under working condition.

For most application, a low deposition temperature is required to prevent substrate distortion and loss of mechanical properties.

This is difficult to realize in CVD processes.

Evaluation of mechanical properties

Good mechanical properties of a coating require high hardness, high toughness, low friction, high adhesion strength on substrate, good load support capability and chemical and thermal stability, etc.

Of all these, hardness is probably of number one importance for an industrialcoatings especially in tribological applications.

At present, nanoindentation is regarded as a good method in hardness determination of thin films and coatings.

In nanoindentation test, a diamond indenter is forced into the coating surface.

The load and depth of penetration (the indentation profile) is recorded, from which thehardness and elastic properties are calculated.