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 *Designed materials that have one or more properties that can be significantly changed in a controlled fashion by external stimuli, such as stress, temperature, moisture, pH, electric or magnetic fields.

Composites Multiphase material that exhibits a significant proportion of the properties of both constituents such that a better combination of properties is realized.

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.

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 .

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.

Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Engineering Applications:Composite materials have been used in aerospace, automobile, and marine applications. (Mechanical Engee.) 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). Electrical Engineering : Designing of panels for Energy devices

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

Parameters on which properties depend Concentration Orientation Distribution Size Shape

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

Composite: Example • 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 composites.

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)

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).

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.

Nanocomposite Nano composites are found in nature also. It is found in abalone (small or very large-sized edible sea snail) and bones.

Nanocomposite: Advantages • Greater tensile /flexural strength • Reduced weight for the same performance • Flame retardant properties • Improved mechanical strength • Higher electrical conductivity/chemical resistance

Chemical Synthesis: Gas Phase Synthesis Chemical Vapor Condensation Combustion Flame Synthesis Liquid Phase Synthesis 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 Gas Phase Synthesis(Synthesis of ultra pure metal powders/metal oxides(ceramics) )

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, 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/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

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.

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.

Smart Materials & Devices