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ENGINEERING CHEMISTRY (22CH101)

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Table of Contents

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Table of Contents

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COURSE OBJECTIVES

Objectives:

The goal of this course is to achieve conceptual understanding of the applications of chemistry in engineering and technology. The syllabus is designed to:

• To understand the water quality criteria and interpret its applications in water purification.

• To gain insights on the basic concepts of electrochemistry and implement its applications in Chemical Sensors.

• To acquire knowledge on the fundamental principle of energy storage devices and relate it to Electric Vehicles.

• To identify the different types of smart materials and explore its applications in Engineering and Technology.

• To assimilate the preparation, properties and applications of nanomaterials in various fields.

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22CH101-ENGINEERING CHEMISTRY

L T P C

3 0 2 4

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COURSE OUTCOMES

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Course Outcome mapping with POs / PSOs

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LECTURE PLAN

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ACTIVITY BASED LEARNING

• Activity based learning helps students express and embrace their curiosity.

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• Once the students become curious, they tend to explore and learn by themselves.

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• To evoke curiosity in students the following activities are given

Semantic Mapping

Mind Mapping

Example:

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Think-Pair-Share

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UNIT - IV

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SMART MATERIALS

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4.1 Smart Materials:

Smart materials are the materials that can significantly alter one or more of their inherent properties in response to its environment. The several external factors to which the smart materials are sensitive to stress, temperature, moisture ,pH, electric field, magnetic field. It can respond in various ways, by altering colour or transparency, becoming conductive, permeable to water or by changing shape.

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Smart Materials

Significant Features of Smart Materials:

• Materials which can think on their own & have
• Mental alertness
• quick perception
• speedy activity
• Effectiveness
• spirited liveliness
• Intelligence
• Smart materials can respond to a change & are
• able to receive information(sensing the problem)
• able to analyze & decide(processing the information)
• able to act on the decision(actuating the process)

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TYPES OF SMART MATERIALS:

Different types of Smart Materials are

• Shape Memory Alloys
• Piezoelectric Materials
• Magnetostrictive Materials
• Magneto-Rheological Fluids

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Applications of Smart Materials

• Smart switches & actuators
• Safety device, fuse, alarms
• Artificial limbs, blood vessels & muscles Adhesive tapes/bands (time bound adhesive property

/painless removal/healing property)

• Food packaging industry-wrappers
• Smart spoons ( Temperature sensitive polymers)
• Smart nose & tongue ( recognition characteristics)
• Smart clothes ( Adaptive to temperature changes)
• Aircraft which will incorporate "smart materials” that will allow the wings of a craft to change shape for optimal flying conditions.

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4.2 Introduction

The word ‘polymer’ was introduced by the Swedish chemist Jone Jakob Berzelius. In Greek, the two words ‘poly’ means many and ‘meros’ means parts or units. Christian Friedrich Schonbein, in the year 1847, produced cellulose nitrate out of cellulose-nitric acid reaction. Leo Hendrik Baekeland, during 1907, produced the first synthetic plastic Bakelite (phenol-formaldehyde resin).

Polymers are essential and used in our daily life. It finds many applications like various industries and medical fields because they possess good mechanical strength, thermal stability, chemical resistance, resistant to corrosion, easy to fabricate and safe to use. Polyurethanes are emerging as next-generation artificial heart valves because of their durability. Blended polymers are used as light-emitting devices because of their flexibility and lightweight. Biopol (Polyhydroxybutyrate) has a wide range of uses such as packaging, shampoo bottles, disposable razors, disposable cups, surgical stitches, surgical pins, disposable knives, etc., because of its biodegradability. The discovery of the electrical conductivity of polyacetylene has paved the way for electronic industries. (Hideki Shirakawa, Alan Heeger, and Alan MacDiarmid received the Nobel Prize in Chemistry in 2000 for their research on conductive polymers).

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4.3 Terminologies:

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4.3.1 Monomer:

The term ‘monomer’ combines the prefix mono-, which means ‘one’, and the suffix-mer, which means ‘part’. A monomer is a small molecule that reacts with a similar molecule to form a larger molecule.

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E.g. Vinylchloride, tetrafluoroethylene, etc.

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4.3.2 Polymers:- Polymers are macromolecules (large molecule) formed by the repeated linking of large number o f small molecules called polymers

E.g. Polyethylene, Polyvinylchloride etc.

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4.3.3 Polymerisation:

• Polymerisation is a process by which two or more identical or different types of monomers combine with or without eliminating small molecules such as water, methanol, etc to form a macromolecular substance.

E.g. 1. Polyvinylchloride formed by the combination of vinyl chloride monomers.

2. Bakelite formed by the different types of repeating units of phenol and formaldehyde monomers.

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Example 1: Polyethylene is a polymer formed by the repeated linked of large number of ethylene molecules.

Example 2: PVC is a polymer formed by the repeated linking of large number of Vinyl Chloride molecules

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4.4 Classification of polymers:

Polymers are classified in different ways, as given below:

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Polymers are classified into four main categories. They are as follows:

 (1) Based on the source. (Origin)

(2) Based on the structure.

(3) Based on the Intermolecular Forces

(4) Based on the mode of synthesis

1. Based on the source (Origin)

On the basis of source or origin, the polymers are sub-classified into two types. They are:

1. Natural Polymers : The polymers which are isolated from natural materials such as plants and animals are called natural polymers.

(Eg) (i) Starch, (ii) Cellulose, (iii) Proteins, (iv) Nucleic acid, (v) Natural rubber.

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(b) Semi-synthetic Polymers: A Semi-synthetic polymers is also a natural polymers, which undergoes some chemical modification, to improve its properties is called Semi-

synthetic polymers.

(Eg) (i) Cellulose Acetate, (ii) Cellulose nitrate.

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(c) Synthetic Polymers: The polymers which are prepared artificially in the laboratories are referred to as synthetic polymers (or) man- made polymers.

(Eg) (i) Polyethylene, (ii) Teflon, (iii) Nylon, (iv) PVC, (v) Polyester, (vi) Polystyrene.

(2) Based on the structure:

Based on the structure, the polymers are classified as follows:

(a) Linear polymers: In Linear polymers, the monomeric units are linked together to form a long straight chain. (Eg) Polyethylene, polyester

(b) Branched chain polymers: Monomers join together to form a long straight chain with some branched chains of different lengths. (Eg) Glycogen

(c) Cross-linked polymers: In this type of polymers,  monomers are linked together to form a three-dimensional network. (Eg) Bakelite, Formaldehyde resin

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Polymers based on the structures

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(3) Based on the Intermolecular Forces:

Based on the Intermolecular forces, the polymers are classified as follows:

(a) Elastomers : Elastomers are rubber-like solid polymers, that are elastic in nature.

(Eg) Rubber (Natural / Synthetic)

(b) Fibers : Strong, thread like in nature, high tensile strength , less elasticity and can

easily be woven in to fabrics. (Eg) Silk, Nylon

(c) Thermoplastic polymers : Thermoplastic long-chain polymers in which inter-

molecules force holds the polymer chains together.

These polymers are softened on heating and hardened

on cooling.(Eg) PVC, Polyethylene

(d) Thermosetting polymers : These polymers greatly improve the material’s

mechanical properties. It provides enhanced chemical

and heat resistance. (Eg) Bakalite

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(4) Based on the mode of synthesis

Based on the Intermolecular forces, the polymers are classified as follows:

1. Addition Polymers: These type of polymers are formed by the repeated addition of

monomer molecules. (Eg) Polyethylene, PVC.

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1. Condensation Polymers: These polymers are formed by the combination of

monomers, with the elimination of small molecules like

water, alcohol etc.  (Eg) Nylon-6,6 , polyesters.

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4.5 Smart Polymeric materials

Smart polymers, also called stimuli-responsive polymers or intelligent materials, are 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.

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Factors sensitive to smart polymers

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4.5.1 Examples of Smart polymeric materials:

• Synthetic spider web: This material is not only five times stronger than steel, but also has great elasticity. Its potential uses include: bulletproof clothing, artificial skin for burns or waterproof adhesives.

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Synthetic spider web

• Shrilk: Its main component is chitin, a carbohydrate found in krill shells. Its decomposition time is only two weeks and it also works as a stimulant for plant growth

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Shrilk

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Graphene: Its potential uses are almost unlimited: batteries with more

autonomy, Cheaper, photovoltaic solar cells, faster computers, flexible electronic devices, more resistant buildings, bionic limbs, etc.

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Graphene

4.5.2 Types of Smart Polymeric Materials:

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• Piezoelectric materials

• Shape memory materials

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• Chromo active materials

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• Electro active materials

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• Biodegradable materials

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4.5.3 Applications of Smart polymers:

Smart polymers appear in highly specialized applications and everyday products alike. They are used for sensors and actuators such as artificial muscles, the production of hydrogels, biodegradable and to a great extent in biomedical engineering.

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Applications of Smart polymers

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4.6 Piezoelectric Polymers:

Piezoelectric polymers are polymers that can generate electric charges on the surface under pressure/strain thus convert mechanical energy into electrical energy.

 Criteria for polymers to exhibit piezoelectricity:

The presence of permanent molecular dipoles

The ability to orient or align the molecular dipoles

The ability to sustain the dipole alignment once it is achieved

The ability of the material to undergo large strains when it mechanically stressed

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Applications of piezoelectric polymers:

•  Piezoelectric motors
• Sensors in medical sectors
• Microphones
• Piezoelectric igniters

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Applications of piezoelectric polymers

4.6.1 Polyvinylidene fluoride (PVDF):

• PVDF is a semi-crystalline, specialty plastic material belonging to the fluoropolymer family. It is a highly non-reactive thermoplastic fluoropolymer, produced by the polymerisation of vinylidene fluoride.

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Synthesis:

• PVDF is synthesised by the polymerisation of Vinylidene fluoride in the presence of suitable catalysts.

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Polyvinylidene fluoride

Properties:

• Some of the most characteristic features of PVDF are
• It has a excellent abrasion resistance
• It has a Piezoelectric, pyroelectric properties, Good thermal stability and high crystallinity
• It is resistance to ultraviolet light (UV) , high energy radiation, most chemicals and solvents
• It has high dielectric strength
• It has Low water absorption; absorbs less than 5% water at room temperature

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Applications:

•  The unique property of piezoelectricity, makes it a good material for transducers in devices such as headphones, microphones, and sonic detectors.
• As piezoelectric films with commercial adhesives.
• Pyroelectric sensor and laser beam profile sensor and also in filtration and separation equipment, etc.
• PVDF membrane can be used as separators in lithium-ion batteries
• It is used as a Filaments for additive manufacturing 
• It is used in Wire and cable isolators
• It is used in the Water treatment membranes, Biomedical, artificial membranes

Food and pharmaceutical processing.

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4.7 Electro Active polymers

• Electro active polymers or EAP’s are polymers that exhibit a change in size or shape, when stimulated by an electric charge. It has a very simple structure comprises of films (elastomers) sandwiched by two compliant electrodes made of a flexible and elastic materials, and can operate as an electric control generator and actuator. Electro active polymers are lighter, cheaper and can be made in many different forms. Electro-active polymer can operate in room condition for a long time. Exhibits high mechanical energy density

4.7.2 Polyaniline (PANI):

Polyaniline (PANI) is one of the most studied conducting polymer or electro activpolymers due to

its high electrical conductivity. It belongs to a semi-flexible rod polymer family (kind of organic

polymer which may be converted to conducting polymers by appropriate oxidations or doping)

and produced as bulk powder, cast films or fibers. Polyaniline (PANI) is high temperature

resistance, good environmental stability, and excellent electrical conductivity

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Synthesis

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Aniline Polyaniline

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• Polymerized from the inexpensive aniline, poly-aniline can be found in one of the three idealized oxidation states.
• Leucoemeraldine - white/clear and colourless
• Emeraldine – green/blue colour
• Pernigraniline – blue/violet colour

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Polyaniline

Properties:

• The change in the colour of polyaniline associated with different oxidation states can be used in devices such as sensors and electro chromic devices.
• These are environmentally stable and inert.
• These are optically active.
• Its electrical conductivity lies between the metals Cu and Ag.
• Good catalytic character with photoactivity.
• Lightweight and flexible material.

Applications:

• In sensors, transistors, microchips.
• Used in intelligent packaging (based on colour change, the spoilage of food items can be known).

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4.8 Biodegradable polymers:

Every Polymer is biodegradable. They degrade in mass, strength and molecular weight with time. Most of the polymers have a period of 100-1000 years to degrade fully. The specialty of biodegradable polymers are, they degrade quickly compared to non-biodegradable polymers and their byproducts are eco-friendly (biocompatible) such as CO₂, water, methane and inorganic compounds or biomass that is easily scavenged by microorganisms.

Biodegradable plastic states that "A plastic designed to undergo a significant change in its chemical structure under specific environmental conditions. Biodegradable polymers are the degradable plastics in which degradation results from the action of naturally occurring microorganisms such as bacteria, fungi and algae.

Applications of biodegradable polymers:

• Biodegradable polymer for ocular, tissue engineering, vascular, orthopedic, skin adhesive & surgical glues and gene therapy.
• Bio degradable drug system for therapeutic agents such as anti tumor, antipsychotic agent, anti-inflammatory agent.
• Polymeric materials are used in and on soil to improve aeration, promote plant growth and health.
• Many biomaterials, especially heart valve replacements and blood vessels, are made of polymers like Dacron, Teflon and polyurethane.

4.8.1 Classification of Biodegradable polymers:

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4.8.2 Poly-lactic acid (PLA)

• Poly –lactic acid (PLA) is one of the most promising biopolymer produced from non toxic renewable and naturally occurring organic acid-lactic acid.
• It is thermoplastic with good mechanical property profile, high biocompatibility and biodegradability properties.
• Latic acid monomers can be produced from100% renewable resources, like corn and sugarbeets.
• Therefore, PLA can be produced and used in an environmentally friendly cycle.

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Poly-lactic acid

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Synthesis:

Poly Lactic acid prepared by different polymerization process from lactic acid including poly-condensation, ring opening polymerization and by direct methods like azeotopic dehydration and enzymatic polymerization.

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Ring opening

polymerization

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Application of Poly (lactic acid)

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• As poly (lactic acid) is biodegradable, it is used in many biomedical implants in the form of plates, pins, rods and screws
• It is also used in other biomedical applications like sutures (commonly called stitches), dialysis medium, drug delivery devices, etc.
• Its biodegradability made it suitable for disposable items such as food packaging, compost bags, tableware, cups, etc.
• It is used in the preparation of fibers which are used to make disposable garments, hygiene production etc.

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Properties of Poly (lactic acid)

• It is a linear and thermoplastic polymer.
• It has around 37% crystalline in nature
• Its glass transition temperature is in the range of 50-80^o C.
• Melting point-In the temperature range of 70-180 ^o C
• It can be processed into fibers.
• Soluble in chlorinated solvents, dioxane, benzene and THF.
• Based on its chiral nature, available in l and d forms.
• It is a biodegradable polymer.

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Application of Poly (lactic acid)

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Composites:

A materials system composed of two or more physically distinct phases whose combination produces aggregate properties that are different from those of its constituents.

Generally, one material forms a continuous matrix while the other provides the reinforcement.

Examples: Concrete reinforced with steel

Epoxy reinforced with graphite fibers.

Plastic molding compounds containing fillers, Rubber mixed with carbon black. Composite materials have a profound place in engineering and high-tech applications. They have an essential place in the engineering material world. In general, composite materials consist two of phases or components inside them.

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COMPOSITES

4.9 INTRODUCTION

Each class of basic engineering materials like metals, high polymers and ceramics has its own outstanding and distinct characteristics as well as limitations. However very stringent requirements of supersonic aircraft, gas turbines and high temperature reactors have forced to develop a new class of materials called “composites”.

The composite materials are generally made by placing the dissimilar materials together to work as a single mechanical unit. The properties of new materials so produced are different in kind and scale from those of any constituents. Thus, it has become possible to incorporate or alter properties. More than that, it introduces a combination of properties like high strength and stiffness at elevated temperatures.

Metals for instance, lose their strength at elevated temperatures. High polymeric materials in general can withstand still lower temperatures. Ceramics, due to their brittleness are unsatisfactory structural materials. This led to the exploration of combinations of metals and polymers with ceramics, resulting in composites having required properties that seem to be the future hope.

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One of these phases is ‘matrix’ that givesthe general shape and bulk of composite material. Matrix materials in composites can be metals, ceramics or polymers. The other component in composite materials is called the ‘secondary phase’ or ‘reinforcement phase’ added to the matrix to give reinforcement. With this reinforcement, composite materials have their superior properties.

Concrete is a composite building material made from a mixture of sand, gravel, crushed rock, or other aggregates (coarse and fine) held together in a stone like mass with a binder such as cement and water. Hardened concrete has a high compressive strength and a very low tensile strength. Steel bars added to concrete which can resist high stretching forces to form reinforced concrete.

Thus, using composites, it is possible to have such a combination of properties like high strength and stiffness, corrosion resistance and ability to withstand extremely high- temperature conditions.

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Characteristics of composite:

• The importance of composite materials over metals and polymers are given below.
• Higher specific strength.
• Lower specific gravity.
• Higher specific stiffness.
• (Specific modulus is a materials property consisting of the elastic modulus per mass density of a material. It is also known as the stiffness to weight ratio or specific stiffness. High specific modulus materials find wide application in aerospace applications where minimum structural weight is required.)
• Lower electrical conductivity.
• Better corrosion and oxidation resistance.
• Good impact and thermal shock resistance.
• Can be fabricated easily.
• Better creep and fatigue strength.

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Constituents of Composites:

Two essential constituents of composites are:

Matrix phase

Dispersed phase.

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Matrix phase:

A continuous body constituent which encloses the composite and gives a bulk form is called matrix phase.

The matrix acts as a medium which protects and binds the dispersed phase.

The matrix phase may be metals, ceramics or polymer. Composites using these matrixes are known as metal matrix composites (MMC), ceramic matrix composites (CMC) and polymer matrix composites (PMC) respectively. Polymer matrix materials used in composites are epoxy, polyamide (nylons), phenols, silicons and polysulphones.

Dispersed phase:

The substance which is dispersed in the matrix phase is called the dispersed phase. It constitutes the internal structure of the composite.

Reinforcing phase used in composites

Glass fibres, Carbon fibres, Aramid fibres, Particulates, Flakes, Whiskers etc., are the reinforcing phase used in composites

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Types of composites:

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Composites classified based on the matrix and reinforcing type of material.

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Composites can be classified into three main groups according to the matrix material, viz., polymer matrix composites (PMCs), metal matrix composites (MMCs) and ceramic matrix composites (CMCs). Polymer materials have found extensive use as matrix materials in aerospace applications. Only in the late seventies, metals and ceramics were explored as matrix materials. MMCs offer higher ductility than CMCs and better environmental stability than PMCs. In addition, MMCs offer considerable improvement in transverse strength, shear strength, electrical and thermal conductivities and resistance to erosion and abrasion.

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4.10 Fibre-reinforced plastic (FRP)

• Fibre-reinforced plastic (FRP) also called fibre-reinforced polymer, is a composite material made of a polymer matrix reinforced with fibres.
• The fibres are usually glass (in fibreglass), carbon (in carbon-fibre-reinforced polymer), aramid, or basalt. Rarely, other fibres such as paper, wood, or asbestos have been used.
• The polymer is usually an epoxy, vinyl ester, or polyester thermosetting plastic, though phenol formaldehyde resins are still in use.

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Fibre-reinforced plastic

FRP composites exhibit high specific strength and specific stiffness. Due to these advantageous characteristics, FRP composites have been included in new construction and rehabilitation of structures through its use as reinforcement in concrete, bridge decks, modular structures, formwork, and external reinforcement for strengthening and seismic upgrade.

Additionally, FRP reinforcements offer a number of advantages such as corrosion resistance, non-magnetic properties, high tensile strength, lightweight and ease of handling.

FRPs are commonly used in the aerospace, automotive, marine, and construction industries. They are commonly found in ballistic armour and cylinders for self-contained breathing apparatuses.

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4.11 Kevlar

• Kevlar is a Du Pont trade name for poly p-phenyleneterephthalamide (PPD-T).
• It is an aramid, i.e. an aromatic polyamide polymer fiber with a very rigid molecular structure.
• Kevlar has unique combination of high strength, high modulus, toughness and thermal stability.
• It is used for high-performance composite applications where light weight, high strength and stiffness, damage resistance, and resistance to fatigue, creep, and stress rupture are important. It was developed for demanding industrial and advanced-technology applications

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Kevlar has higher tensile modulus and strength than steel and possess high breaking tenacity. It also has very high kinetic energy absorption. Kevlar 29 is used in industrial applications such as cables, asbestos replacement, brake linings, and body armor. Kevlar 49 is considered to have the greatest tensile strength of all the aramids, and is used in applications such as plastic reinforcement for boat hulls, airplanes, and bikes.

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Polymeric Kevlar

Aramid/kevlar Fibre-Reinforced Polymer Composites

The aramid fibers are most often used in composites having polymer matrices like epoxies and polyesters. Since the fibres are relatively flexible and somewhat ductile, they may be processed by textile operations. Aramid fiber (Kevlar) was the first organic fiber used as reinforcement in advanced composites with better mechanical properties than steel and glass fibers. Aramid fibers are inherently heat- and flame-resistant, which maintain these properties at high temperatures. The choice of resin system for use with aramid fibers is an important one. Epoxy resins give better translation of fiber properties than do polyesters, producing better shear strength and flexural properties but lower impact resistance. Vinyl ester resins give both good shear strength and impact resistance.

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Preperation of epoxy-kevlar composite laminates

This method made use of 300 g of Kevlar fiber mat as reinforcement phase

The matrix phase consist of pure bifunctional epoxy resin and hardener usually LY556 and HY951mixed in the ratio 10:1 and completely homogenized.

The reinforcements and matrix material were added in 1.5:1 weight ratios while fabricating different composite laminate configurations, the composite laminates were produced by combining seven layers in different configurations and the hand layup technique was chosen to make the composite laminates.

The production of each hybrid composite was initiated by placing a 30 cm × 30 cm frame over a flat surface followed by placing a waxed thin mylar sheet over the frame.

The first layer of reinforcement fiber was placed on the mylar sheet. The epoxy resin mixed with the hardener was laid over the exposed surface of the reinforcement fiber and distributed evenly using a metal flat spatula. The second layer was placed over the resin, followed by a rolling process. Care was taken to ensure that the fibers were oriented with the fibers of the previous layers. The rollers were applied with even an pressure to ensure that the resin was pressed and distributed within the fibers. The process was repeated until all of the seven layers of the reinforcement fibers were placed one over the other. Another mylar sheet was placed over the top layer of the composite. A uniform pressure was applied with the help of concentrated weights placed over the top surface, and the wet laminate was made to cure at atmospheric temperature for an about 24 h.

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Hybrid composite of Epoxy resin-Kevlar fibre laminates

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Properties:

Composites reinforced with para-aramid fibers (Kevlar) have

(i) low density

(ii) high strength and specific modulus

(iii) good tensile fatigue properties

(iv) low compressive strength and inter laminar shear strength

It is generally difficult to obtain both good diametric tolerance and shredding-free surfaces for the composites reinforced with aramid/kevlar fibers. To prevent it, this type of composite structure is preloaded by tensile stress and cut by shear force.

Applications:

(i) The use of these composites can reduce the weight by 30% comparing with glass fibre composite materials.

(ii) To reduce weight and improve economic efficiency, generally, aramid composites have been widely used in commercial aircraft and helicopters.

(iii) They also have found application in production of a composite toe cap.

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  Aramid/kevlar composite toe cap

(iv) Typical applications of these composites are in ballistic products (bulletproof vests and armor), sporting goods, tires, ropes, missile cases, pressure vessels, and as a replacement for asbestos in automotive brake and clutch linings, and gaskets.

(v) Common commercial uses include body armor, flame-resistant clothing, heat protective gear, ropes and cables, rubber reinforcement, fiberoptics and thermoplastic pipes.

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Polymeric Kevlar

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Did you know?

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Similar to Kevlar FRP, there are Carbon-reinforced polymer composites are currently being utilized extensively in sports and recreational equipment (fishing rods, golf clubs), filament-wound rocket motor cases, automobile parts pressure vessels, and aircraft structural components—both military and commercial, fixed wing and helicopters (e.g., as wing, body, stabilizer, and

rudder components)

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4.12 SHAPE MEMORY ALLOYS (SMA)

A group of metallic alloys which shows the ability to return to their original shape or size when they are subjected to heating or cooling are called shape memory alloys.

Generally, shape memory alloys are intermetallic compounds having super lattice structures and metallic - ionic - covalent characteristics. Thus, they have the properties of both metals and ceramics.

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They are simple, compact highly safe and light in weight. bio - compatible. It possess super elasticity, wear resistance and corrosion-resistance properties.

Examples of shape memory alloys

Ni – Ti alloy (Nitinol), Cu – Al – Ni alloy, Cu – Al – Ni alloy, Cu – Zn – Al alloy, Au – Cd alloy

Ni – Mn – Ga and Fe based alloys

Types of Shape memory alloys:

There are two types of shape memory alloys

1. One - way shape memory alloy
2. Two - way shape memory alloy

A material which exhibits shape memory effect only upon heating is known as one-way shape memory alloy.

A material which shows shape memory effect during both heating and cooling is called two-way shape memory alloy.

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Phases of shape memory alloys

Martensite and austenite are two solid phases in SMA

1. Martensite is relatively soft. It is easily deformable phase which exists at low temperature (monoclinic)
2. Austenite is a phase that occurs at high temperature having a crystal structure and high degree of symmetry (cubic)

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Difference between Austenite and Martensite

4.13 Shape memory effect:

The change in shape of a material at low temperature by loading and regaining of original shape by heating it, is known as shape memory effect. The shape memory effect occurs in alloys due to the change in their crystalline structure with the change in temperature and stress.

∙ While loading, twinned martensite becomes deformed martensite at low temperature.

∙ On heating, deformed martensite becomes austenite (shape recovery) and upon cooling it gets transformed to twinned martensite (Fig. 2).

Fig. 2. Material crystalline arrangement during shape memory effect

Explanation:

Shape Memory effect describes the effect of restoring the original shape of a plastically deformed sample by heating it. This phenomenon results from a crystalline phase change known as thermoelastic martensitic transformation. At temperatures below the transformation temperature, shape memory alloys are martensitic. In this condition, their microstructure is characterized by self-accommodating twins. The martensitic is soft and can be deformed quite by de-twinning. Heating above the transformation temperature recovers the original shape and converts the material to its high strength, austenitic, condition. The transformation from austenite to martensite and the reverse transformation from martensite to austenite do not take place at the same temperature.

Mechanism:

One Way Shape Memory Effect (OWSME):

Consider a single crystal in parent phase (T ≤ Mf)(a). The single crystal is cooled to a temperature below Mf (b). Then, martensite are formed in a self-accomodation manner(c). Thus, if an external stress is applied, and if the stress is high enough, it will become a single variant of martensite under stress. Such a high mobility of the Twin Boundary, in which a single variant of martensite change into the twin orientation by shear. When the specimen is heated to a temperature above Af, reverse transformation occurs. The reverse transformation induced by heating recovers the inelastic strain; since martensite variants have been reoriented by stress, the reversion to austenite produces a large transformation strain having the same amplitude but the opposite direction with the inelastic strain and the SMA returns to its original shape of the austenitic phase (d). This phenomenon is called One–Way Shape Memory Effect. (OWSME).

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Macroscopically Mechanism of One Way Shape Memory Effect: (a) Marten- site, (b) Loaded and Deformed in martensite phase T≤ Mf, (c) Heated above T G As (austenite),(d) Cooling to martensite T≤ Mf.

Two Way Shape Memory Effect (TWSME):

The two-way shape-memory effect is the effect that the material remembers two different shapes: one at low temperatures, and one at the high temperature. A material that shows a shape-memory effect during both heating and cooling is said to have two-way shape memory. This can also be obtained without the application of an external force (intrinsic two-way effect). The reason the material behaves so differently in these situations lies in training. Training implies that a shape memory can "learn" to behave in a certain way. Under normal circumstances, a shape-memory alloy "remembers" its low-temperature shape, but upon heating to recover the high-temperature shape, immediately "forgets" the low-temperature shape. However, it can be "trained" to "remember" to leave some reminders of the deformed low-temperature condition in the high-temperature phases. 

Macroscopically Mechanism of Two Way Shape Memory Effect: (a) Martensite state, (b) Several deformation with an irreversible amount, (c) Heated, (d) Cooled.

4.14 FUNCTIONAL PROPERTIES OF SHAPE MEMORY ALLOYS:

1. SMAs exhibit changes in electrical resistance, volume and length during the transformation with temperature.

2. The mechanism involved in SMA is reversible (austenite changes to martensite and vice versa.)

3. Stress and temperature have a great influence on martensite transformation.

4. Pseudo elasticity:

Pseudo - elasticity occurs in shape memory alloys when it is completely in austenite phase (temperature is greater than Af austenite finish temperature). Unlike the shape memory effect, Pseudo-elasticity occurs due to stress induced phase transformation without change in temperature. The load on the shape memory alloy changes austenite phase into martensite (Fig. 3.7) As soon as the loading decreases the martensite begins to transform to austenite and results in shape recovery. This phenomenon of deformation of a SMA on application of large stress and regaining of original shape on removal of the load is known as pseudo elasticity. This pseudo elasticity is also known as super elasticity.

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Load diagram of pseudo elastic effect

Where,

Ms : Temperature at which austenite starts to transform to martensite upon cooling

Mf : Temperature at which transformation of austenite to martensite is complete upon cooling

As : Temperature at which martensite begins to transform to austenite upon heating

Af : Temperature at which transformation of martensite to austenite is complete upon heating

5. Hysteresis:

The temperature range for the martensite to austenite transformation which takes place upon heating is somewhat higher than that for the reverse transformation upon cooling. The difference between transition temperature upon heating and cooling is called hysteresis. The hysteresis curve for SMAs is shown in fig. . The difference of temperature is found to be 20 - 30 °C.

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4.15 Nickel Titanium Alloy (Nitinol)

Nickel titanium, also known as Nitinol, is a metal alloy of nickel and titanium, where the two elements are present in roughly equal atomic percentages. This metal alloy is denoted by the symbols of its constituent metals. The formula for this alloy is NiTi. In 1962, William J. Buehler and Frederick Wang first discovered the unique properties of this metal at the Naval Ordnance Laboratory. This alloy exhibits the super-elasticity or pseudo-elasticity and the shape memory properties. It means this unique metal can remember its original shape and shows great elasticity under stress.

Nitinol Production

Extremely tight compositional control is required for making this alloy. Due to this reason it is very difficult to prepare this alloy. The extraordinary reactivity of titanium is another obstacle in its preparation. Two primary melting methods are presently used for this purpose:

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• Vacuum Arc Remelting: In this method, an electrical arc is struck between a water cooled copper strike-plate and the raw materials. Water cooled copper mold is used for melting the constituents in high vacuum to prevent carbon introduction.
• Vacuum Induction Melting: The raw materials are heated in a carbon crucible using alternating magnetic fields. This is also accomplished in high vacuum; however, carbon is introduced in this process.

Physical Properties

Appearance: It is a bright silvery metal.

Density: The density of this alloy is 6.45 gm/ cm3

Melting Point: Its melting point is around 1310 °C.

Resistivity: It has a resistivity of 82 ohm-cm in higher temperatures and 76 ohm-cm in lower temperatures.

Thermal Conductivity: The thermal conductivity of this metal is 0.1 W/ cm-°C.

Heat Capacity: Its heat capacity is 0.077 cal/ gm-°C.

Latent Heat: This material has a latent heat of 5.78 cal/ gm.

Applications:

1. Nitinol Wires

Nitinol is used for making shape-memory actuator wire used for numerous industrial purposes. This wire is used for guidewires, stylets and orthodontic files. This wire is ideal for applications requiring high loading and unloading plateau-stresses as well as for eyeglass frames and cell phone antennas. However, the main uses of this wire are in stents and stone retrieval baskets.

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2. Nitinol Stent

This alloy is used for manufacturing endovascular stents which are highly useful in treating various heart diseases. It is used to improve blood flow by inserting a collapsed Nickel titanium stent into a vein and heating it. These stents are also used as a substitute for sutures.

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3. Nitinol Stone Retrival Basket

Nickel titanium wire baskets are well-suited for many medical applications as it is springier and less collapsible than many other metals. This basket instrument is highly useful for the gallbladder.

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4. Other Uses

• It is also used as an insert for golf clubs for its shape changing abilities.
• It is a popular choice for making extremely resilient glass-frames.
• Nitinol is used for making self-bending spoons used in magic shows.
• It is used in aerospace industries.

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4.16 APPLICATIONS OF SHAPE MEMORY ALLOYS

Shape memory alloys have a wide range of applications.

1. Microvalve (Actuators):

One of the most common applications of SMAs is microvalves. Actuator is a microsensor which triggers the operation of a device. The electrical signal initiates an action. When an electrical current of 50 to 150 mA flows in Ni - Ti actuator, it contracts and lifts the poppet from the orifice and opens the valve.

2. Toys and novelties:

Shape memory alloys are used to make toys and ornamental goods. A butterfly using SMA moves its wings in response to pulses of electricity.

3. Medical field :

1. Blood clot filters are SMAs, properly shaped and inserted into veins to stop the passing blood clots. When the SMA is in contact with the clot at a lower temperature, it expands and stops the clot and blood passes through the veins.
2. Orthodontic applications Ni-Ti wire holds the teeth tight with a constant stress irrespective of the strain produced by the teeth movement. It resists permanent deformation even if it is bent.
3. SMAs (Ni-Ti) are used to make eye glass frames and medical tools. Sun-glasses made from superelastic Ni-Ti frames provide good comfort and durability.
4. Broken bones can be mended with shape memory alloys. The alloy plate has a memory transfer temperature that is close to body temperature, and is attached to both ends of the broken bone. From body heat, the plate wants to contract and retain its original shape, therefore exerting a compression force on the broken bone at the place of fracture.

4. Antenna wires:

The flexibility of superelastic Ni - Ti wire makes it ideal for use as retractable antennas.

5. Cryofit hydraulic couplings:

SMAs materials are used as couplings for metal pipes.

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7. Springs, shock absorbers and valves:

Due to the excellent elastic property of the SMAs, springs can be made which is used in Engine micro valves , Medical stents, Firesafety valves and Aerospace latching mechanisms.

8. Stepping motors:

Digital SMA stepping motors are used for robotic control.

9. Titanium-aluminium shape memory alloys:

They offer excellent strength with less weight and dominate in the aircraft industry. They are high temperature SMAs, for possible use in aircraft engines and other high temperature environments.

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4.17 Chromogenic materials

The word "Chromo-" originates from the Greek language means that something is coloured. All chromogenic materials change their colour depending on external stimuli. Materials that change colour are scientifically termed chromogenics and they are described as “chameleonic” because they change their colour reversibly as a response to changes in environmental condition (such as change of temperature, brightness, etc.) or by induced stimuli. The phenomena in which color is produced when light interacts with materials, often called chromic materials. The technical principle, by which these materials change colour, can be explained by an alteration in the equilibrium of electrons caused by the stimulus, like cleavage of the chemical bonds or changes occurring inside the molecule, among electrons, with a consequent modification of optical properties, such as reflectance, absorption, emission, or transmission . When the stimulus ceases, the material returns to its original electronic state, regaining the original optical properties, thus the initial colour or transparency. This process, named chromism, implies ‘pi’ and ‘d’ electron positions so that the phenomenon is induced by various external stimuli bearing the ability of altering electronic density of the compound or a substance

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Many natural compounds exhibit chromism and now a number of artificial compounds of specific chromic properties have been synthesized. Color-changing materials have recently received considerable attention and the use of these materials has been widely considered in various fields.

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4.18 Types of chromogenic materials

There are various types of chromogenic materials and they are split into categories depending on what type of external stimuli triggers the change in colour. Based on the origin of the stimulus, the color-changing process in smart materials is mostly classified into photochromic, thermochromic, electrochromic, Mechanochromic, Solvatochromic, Biochromic and chemochromic materials.

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Chromogenic Materials

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Photochromic materials

Photochromic materials change colour when the intensity of incoming light changes. These materials work on the principle of absorption of light as in the case of optical lenses for solar protection or smart windows for adaptive solar control.

Photochromic materials can be used for the design of optical switches, optical data storage devices, energy-conserving coatings, eye-protection glasses, and privacy shields. Photochromic materials and systems have several important uses depending on the rates of the optical transformations.

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Photochromic glass

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A photochromic glass is produced by embelding a layer of silver halides (usually silver chloride) in glass or transparent plastic. Photochromic glass darkens when is exposed to sunlight. When the light fades, it become transparent again. It is suitable for making optical lenses, windshields and windows.

Thermochromic materials

Thermochromic materials respond to a variation in environmental temperature by changing their colour. Their capacity of acquiring different states of colours at different temperatures and through temperature variations countless times makes them particularly interesting. For example, titanium dioxide, zinc sulfide and zinc oxide are white at room temperature but when heated change to yellow.

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These materials have many useful and creative applications like thermometers, clothing, paint, drink containers, toys, battery indicators, plastic products etc.,

Eg. Thermochromic T-shirt. A hairdryer was used to change the blue to turquoise

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Did you know?

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Forehead strip thermometers change color with temperature to reveal whether someone's suffering from a fever. They're inexpensive, safe, easy-to-use, and hygienic.

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A well-known product that makes use of this phenomenon is a ceramic mug, which changes colour when a hot drink is poured inside. The transformation is reversible; thus the colour of the mug goes back to its original one when it cools down to room temperature.

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Electrochromic materials

Electrochromic materials are characterised by an optical change upon the application of an electric field. Electrochromism is probably the most versatile of all chromogenic technologies because it is the easiest to control and because it can easily be used in combination with different stimuli such as stress or temperature. Electrochromic materials are able to vary their coloration and transparency to solar radiation, in a reversible manner, when they are subjected to a small electric field (1–5 V). The electrochromic materials available today command a big market for dynamic antiglare mirrors that detect glare and automatically compensates for it, especially for night time driving safety.

Eg. Electrochromic window in a Boeing 787-8 Dreamliner aircraft

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Did you know?

Electrochromic windows, also known as smart windows, are a technology for energy efficiency in buildings by controlling the amount of sunlight passing through. They can also produce less glare than fritted glass. Their efficiency depends on their placement, size, and weather, which affect the amount of sunlight exposure. These windows usually contain layers for tinting in response to increases in incoming sunlight and to protect from UV radiation.

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Energy-Efficient Electrochromic windows

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An interesting example of these electrochromic smart windows in application is Chrysler Pacifica car; the driver is able to dim the rear view mirror according to his need and preference. Electrochromic materials are very useful and have many applications including systems to reduce glare, thermal control and as lenses in cameras and sun glasses.

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Mechanochromic materials

Mechanochromic materials show a change in colour when a mechanical stimulus, i.e. stress, is applied. These materials are currently studied intensely because of their potential use in stress detection, particularly for in situ failure monitoring due to fracture, corrosion, fatigue, or creep. This is an important group of materials with a huge range of applications such as data storage, information encryption, sensors, memory chips, security inks, and light devices due to its simple operation, obvious and rapid response.

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You tube video - https://youtu.be/tY1zpwYOX74

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Mechanochromic materials have been potentially applied to biological and healthcare systems. This kind of material has received extensive attention in the field of solid-state optics because of its potentially extensive applications in several advanced technologies, such as fluorescence switches, mechanosensors, optoelectronics and data storage. 

Piezochromic materials:

Piezochromism (from the Greek piezô "to squeeze, to press" and chromos "the color") describes the tendency of certain materials to change color with the application of pressure. This effect is closely related to the electronic band gap change, which can be found in plastics, semiconductors and hydrocarbons.

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Piezochromic material changes its color by applying a pressure

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In the aeronautical, space and Defense fields, the use of piezochromic coatings is studied to control the health of composite structures. The use of piezochrome materials is also of great interest for the visual detection of potential shocks or deformations of some industrial parts.

Chemochromic materials

Chemochromic materials respond to chemical changes in the environment by changing colour. Chemochromic Materials are materials which react with different chemicals and exhibit a change in color, transmission, or reflection properties.

Chemochromic materials are available in a number of forms, and are used in a number of applications. Chemochromic materials are primarily used in the manufacture of dyes. Chemochromic materials are also used in the material present in litmus paper which detects the acidity and alkalinity of chemicals.

Chemochromic materials are also used to show the ripeness of the fruit as the chemical reacts with the gases released by the fruit when it ripens. The major application of chemochromic materials is its use in gas leak detection in rocket engines and industrial sites.

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(a) (b)

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Chemochromic materials are used in (a) Fruit Ripening Gas Sensors

(b) For conducting pregnancy tests

Halochromic materials

Halochromic materials can be considered a subgroup of chemochromic materials that change colour as a response to pH changes in the environment. Halochromic materials are commonly used materials that change their color as a result of changing acidity. �Halochromic substances are suited for use in environments where pH changes occur frequently, or places where changes in pH are extreme. Halochromic substances detect alterations in the acidity of substances, like detection of corrosion in metals.

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Halochromic Polymer Nanosensors for detection of pH in coatings

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pH-sensitive (halochromic) smart packaging films based on natural food colorants for the monitoring of food quality and safety

Solvatochromic materials

Solvatochromic materials display the phenomenon called solvatochromism, typical of some chemical substances that are sensitive to a given solvent. The solvatochromic effect is the way the spectrum of a substance (the solute) varies when the substance is dissolved in a variety of solvents. These materials are used to predict the colors of solutions.

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Solvatochromic Pyrene Analogues in apolar and polar solvents

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In the field of chemical research, solvatochromism is used in environmental sensors, in probes with the capacity of determining the presence and the percentage of a solvent, and in molecular electronics for the construction of molecular switches.

Biochromic materials

Biochromic materials were developed to detect and report the presence of pathogens with a colour shift. Potential applications of biochromic materials include colorimetric detection of pathogens against food poisoning or bioterrorism. Researchers developed a green and sustainable smart biochromic and therapeutic bandage using red cabbage extract encapsulated into alginate nanoparticles.

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Note: CNF : Cellulose nanofibers; TCFH: Tricyanofuran hydrazone

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Latest Applications of chromogenic materials

1. Chromogenics have unique properties for applications such as glazing, large area displays, and electronic paper.
2. Chromogenic polymers are a type of smart packaging system that alert consumers of potential safety or quality problems in packaged products optically.
3. Chromogenic materials and devices promise smart management of solar energy under the influence of external stimulus.
4. As a passive and green solar energy system, chromogenics may find a variety of applications such as energy-efficient windows for buildings and automobiles, smart displays, optoelectronic and medical industry as well as environmental technology as emitting and sensing devices.
5. Electrochromic materials show similar working mechanism to supercapacitors which can be used as energy storage materials and devices as well.

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Practice Quiz Unit-IV

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Assignment

Unit IV

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Part-A Question and Answer

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Part-B Questions

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Supportive online certification courses

• https://onlinecourses.nptel.ac.in/noc20_ch41/preview
• Polymers: concepts, properties, uses and sustainability
• Swayam 12-week course.

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• https://youtu.be/okfCOfn7qWQ-
• Introduction to composite materials nptel course

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• Online course : https://onlinecourses.nptel.ac.in/noc22_mm40/preview
• Advanced Materials and Processes – Shape memory alloy

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Real time Applications in day to day life and to Industry

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Various Fields Applications

1.Automotive industry

Polymer and allied materials are rapidly capturing the share of metal usage in automotive.

http://www.ijirset.com/upload/march/36_Advances%20in. pdf

2. Textile industry

Textiles are materials composed of natural or synthetic fibers. This includes animal-based materials such as wool and silk, plant-based materials such as cotton, flux and hemp, and synthetic materials such as polyester, acrylics and nylon.

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Real time Applications in day to day life and to

Industry

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Real Time Applications of Shape memory alloys

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In the 1990s, the term shape memory technology (SMT) was introduced into the SMM community. SMA application design has changed in many ways since then and has found commercial application in a broad range of industries including automotive, aerospace, robotics and biomedical. Currently, SMA actuators have been successfully applied in low frequency vibration and actuation applications. Therefore, much systematic and intensive research work is still needed to enhance the performance of SMAs, especially to increase their bandwidth, fatigue life and stability.

Recently, many researchers have taken an experimental approach to enhance the attributes of SMAs, by improving the material compositions (quantifying the SMA phase transition Temperature) to achieve a wider operating temperature range, and better material stability, as well as to improve the material response and stroke with better mechanical design (or approach), controller systems and fabrication processes. Research into alternative SMMs, forms or shapes, such as MSMA, HTSMA, SMP, shape memory ceramic, SMM thin film or a combination of them (i.e. hybrid or composite SMMs), are also intensively being conducted, and the number of commercial applications is growing each year.

Some of the important applications are listed below.

1. Aerospace application

• Plane wings with SMA wires can change shape by inducing voltages in them. This can replace hydraulic and electromechanical actuators.
• Boeing, General Electric Aircraft Engines, Goodrich Corporation, NASA, and All Nippon Airways developed the Variable Geometry Chevron using shape memory alloy that reduces aircraft's engine noise.

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SMA used in aerospace applications

Real Time Applications of Shape memory alloys

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2. Biomedical

Shape memory alloys are applied in medicine, for example, as fixation devices for osteotomies in orthopaedic surgery, in dental braces to exert constant thooth moving forces on the teeth and in stent grafts where it gives the ability to adapt to the shape of certain blood vessels when exposed to body temperature.

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Applications of SMAs in biomedical field

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3. Robotics

There have also been limited studies on using these materials in robotics (such as Roboter frau Lara), as they make it possible to create very light robots. Weak points of the technology are energy inefficiency, slow response times, and large hysteresis.

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Applications of SMAs in robotics

Content beyond the syllabus

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Fabrication technique of Polymers

• Fabrication techniques of polymers include:
• Thermoforming
• Extrusion of polymers
• Injection molding of polymers
• Blow molding
• Compression molding of polymers
• Transfer molding of polymers
• Selective laser sintering

Injection Molding is a process in which molten polymer is forced under high pressure into a mold cavity through an opening (sprue). Polymer material in form of pellets is fed into an Injection Molding machine through a hopper. The material is then conveyed forward by a feeding screw and forced into a split mold, filling its cavity through a feeding system with sprue gate and runners. Screw of injection molding machine is called reciprocating screw since it not only rotates but also moves forward and backward according to the steps of the molding cycle.

• It acts as a ram in the filling step when the molten polymer is injected into the mold and then it retracts backward in the molding step. Heating elements, placed over the barrel, soften and melt the polymer.
• The mold is equipped with a cooling system providing controlled cooling and solidification of the material. The polymer is held in the mold until solidification and then the mold opens and the part is removed from the mold by ejector pins.
• Injection Molding is used mainly for Thermoplastics. In this case cross-linking occurs during heating and melting of the material in the heated barrel.

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Content beyond the syllabus

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2. Polymerblends:

A polymer blend, or polymer mixture, is a member of a class of materials analogous to metal alloys, in which at least two polymer are blended together to create a new material with different physical properties.Polymer blends can be broadly divided into threecategories:

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• Immiscible polymer blends (heterogeneous polymer blends): This is by far the most populous group. If the blend is made of two polymers, two glass transition temperatures will be observed.
• Compatible polymer blends: Immiscible polymer blend that exhibits macroscopically uniform physical properties. The macroscopically uniform properties are usually caused by sufficiently strong interactions between the component polymers.
• Miscible polymer blends (homogeneous polymer blend): Polymer blend that is a single-phase structure. In this case, one glass transition temperature will be observed.

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Content beyond the syllabus

Advantages/ Reasons for blending:

• To extend engineering resin performance by diluting it with low cost (commodity/ tonnage) polymer.

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• To develop materials with a full set of desired properties.
• To utilize the scrap generated at various steps. [sometimes blending is also done to develop a recyclable material, e.g. using starch as second component]
• To get a high performance blend from synergistically interacting polymers.

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• To achieve customer specifications in a product.

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• Lower capital expense involved with scale-up & commercialization.

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Limitations of blending:

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• Recycling is complex in some cases.
• No specific test methods and standards are available. (used that of plastic/rubber)

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Content beyond the syllabus

Hybrid Composites

A relatively new fiber-reinforced composite is the hybrid, which is obtained by using two or more different kinds of fibers in a single matrix; hybrids have a better all around combination of properties than composites containing only a single fiber type. A variety of fiber combinations and matrix materials are used, but in the most common system, both carbon and glass fibers are incorporated into a polymeric resin.

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Do it yourself

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Make polymer from Milk Procedure: What You Need:

• A tall, clear glass
• Non-fat or skim milk
• White vinegar
• Coffee filters or paper towels

What You Do:

• In a glass, put seven tablespoons of non-fat or skim milk— whole milk contains more fat, which can change the experiment results.
• Add a tablespoon of white vinegar to the milk; you should see solids begin to form that are suspended in the liquid. The solids will have a grainy appearance. Allow them to settle toward the bottom of the glass, then drain the liquid off, using a coffee filter or paper towel.

• Now, pat the solids with a paper towel to absorb any excess liquid. You can use the resulting slimy substance as glue— coat two pieces of paper with it, stick them together, and let it dry.
• When you added the vinegar to the milk, it caused the milk’s protein, the polymer casein, to separate from the liquid part of the milk and clump together to form solids. Casein is used in adhesives, paints, and even plastics.

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Did you know it’s possible to turn milk into plastic? All you need to do is warm it up with a little bit of vinegar. This would make a good exploration when looking at chemical changes.

It’s called Casein Plastic, and in the early 1900’s it was a common way to make plastic for household use or jewellery. Casein is the name of the protein in milk.

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Make Casein Plastic from Milk Procedure: What You Need:

• One cup (or 250ml) of milk
• 4 teaspoons of white vinegar
• A bowl
• A sieve or strainer
• Paper towels
• A saucepan or access to a microwave
• Plastic cookie cutter shapes.

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What You Do:

• First you will need to warm up the milk. You can either do this in a saucepan on a hob, or put it in the microwave for 90 seconds. You want it warm but not boiling.
• Then stir in 4 tablespoons of white vinegar. Keep stirring for about a minute.

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• Once the milk has gone all lumpy, pour it into a sieve (do this over a sink or over another bowl) to drain away the excess liquid.

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• The plastic will stay in the sieve. Press it down with a spoon to squeeze out all the liquid.

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• Transfer the plastic to a paper towel and squeeze out any more liquid.
• You can then shape the plastic using your hands or use cookie cutters to cut out shapes.
• The plastic will stay in the sieve. Press it down with a spoon to squeeze out all the liquid.
• Transfer the plastic to a paper towel and squeeze out any more liquid.
• You can then shape the plastic using your hands or use cookie cutters to cut out shapes.
• Leave the plastic to dry for a few days until it’s hard and ready to use��

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PIC MICRO-CONTROLLER PROJECT

MUSCLE WIRE

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The diagram above shows a battery and switch connected to muscle wire. A small weight stretches the muscle wire approximately 3 to 5 percent of its length. However, when a current is applied to the wire, it shortens lifting the weight. This cycle of turning on and off the current has the effect of lifting and then lowering the weight. A clever use of muscle wire and a PIC micro-controller circuit is seen below. A robotic hand has ‘stretched muscle wires’ attached to the base of each finger. When current is applied to the muscle wire it contracts to its ‘natural’ length, pulling on the ordinary wire ,making the fingers look as if they are moving �A PIC micro-controller can be programmed so that outputs are switched ON or OFF. When switched ON the muscle wire contracts (shrinks) to its original length. In the example, five of the outputs have been programmed to switch on and off, making the fingers of the hand move.

Prescribed Text Books & Reference Books

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• https://books.google.co.in/books?id=mvCzE_AflUIC&printsec=frontco ver&source=gbs_ge_summary_r&cad=0#v=onepage&q&f=false

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Polymer Science

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• By Vasant R. Gowariker, N. V. Viswanathan, Jayadev Sreedhar
• https://www.pdfdrive.com/engineering-chemistry-fundamentals-and- applications-2nd-edition-d191456798.html

Engineering Chemistry: Fundamentals and Applications, 2nd Edition by Shikha Agarwal

Engineering Chemistry- 17 th edition by PC.Jain and Monika jain

https://www.academia.edu/37796622/Engineering_Chemistry_by_Jain_and_Jain

Shape Memory Alloy Engineering: For Aerospace, Structural and Biomedical Applications

https://g.co/kgs/BL7y5a

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Mini project suggestions

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Thank Youyou

Disclaimer:

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