Functional and smart materials - WordPress.comSelf-healing materials . Classification content...

DEPARTMENT OF MATERIALS ENGINEERING

FUNCTIONAL MATERIALS

DR. EMMANUEL KWESI ARTHUR EMAIL: [email protected]

He, who wants to see something new, needs to invent it!

MSEP 514

mailto:[email protected]

Content

Piezoelectric materials

Shape memory alloys

Magnetic shape memory alloys

Thermochromic materials

Photochromic materials

Electrochromic materials

pH sensitive polymers

Halochromic materials

Classification Content • Materials:

• Type I (property change as a response of an external stimulus)

• Shape memory (alloys, ceramics, polymers, hydrogels)

• Magneto(electro)rheological

• Thermochromic

• Thermotropic (liquid crystals)

• Photomechanical

• Type II (energy conversion)

• Piezoelectric (pyroelectric, electro-optic)

• Electro(magneto)striction

• Thermoelectric

• Photoluminescent

• Photovoltaic

• Type III (phase change materials):

• Optical storage materials

• Magnetocaloric

• Others:

• Self-healing materials

Classification content (applications) • Applications (mechatronic):

• Mechanical, optical, electronic devices

• Actuators, positioning systems

• Sensors

• Applications (biomedical):

• dental wires, stents, micropumps, clamps and release systems

• suture wires, guides

• drug delivery systems

• Applications (energy):

• transformer

• sensors

• actuators

• Applications (generals):

• MEMS

• valves and controls

• antitheft systems, optical and dynamical protections

Reading List

• https://slideplayer.com/slide/4737196/

• https://www.slideshare.net/sc09b093/magneto-rhelogical-fluids

• http://www.ing.unitn.it/~luttero/materialifunzionali

• A. J. Moulson & J. M. Herbert, Electroceramics: Materials, Properties,

Applications, Chapman and Hall (1st ed.) / John Wiley & Sons Canada

(2003) (2nd ed.)

• Encyclopedia of Smart Materials

• M. Addington & D. Schodek, Smart Materials and

Technologies, Elsevier, 2005 (as lecture

http://www.ing.unitn.it/~luttero/materialifunzionali









What are Functional Materials

Functional materials are able to interact with their environment, be it responding to stimuli or acting upon that environment. Examples include piezoelectrics, thermoelectrics, pyroelectrics, ferroelectrics, electroluminescents, photocatalysts and ion conductors.

Functional materials are found in all classes of materials: ceramics, metals, polymers and organic molecules.

Functional materials are often used in

electromagnetic applications from KHz to THz and at optical frequencies where the plasmonic properties of metals assume particular importance.

Functional materials are also of critical

importance in materials for energy such as electro- and magnetocaloric materials, for energy storage and for solar harvesting functions.

Functional Materials

It is their special physico-chemical properties which make functional

materials so special. The research on their synthesis and their

characterization is crucial for future technologies.

Functional materials represent a fast growing set of advanced materials and

composites, some properties of which (shape, electrical conductivity,

mechanical properties, color etc.) are responsive to external stimuli

(thermal, electrical, mechanical, light etc.).

These can include, for example, ferroelectricity, thermoelectricity,

piezoelectricity, magnetism, energy storage functions, magneto and

electrostrictive materials for sensors and actuators, phase transforming

materials, shape memory alloys or modern functional coatings and films.

Engineering from past to present

One of the scopes of the engineers has always been the

realization of components to optimally respond to the requested

needs.The materials where just chosen to build the component in

a way it can resist to all the loads, conditions, temperatures,

vibrations etc.

So the process was focusing more on assembling all materials and

pieces to reach the goal, the device.

Now there is a different perspective: we can think about a

material able to directly perform some actions (active role) and

not only a passive role.

From functional to smart materials

The functional material is able to perform an action to

respond to a stimulus (temperature, electric field changes,

etc.). As for thermal expansion all materials should be

considered “functional” then.

A functional material is able to substitute an entire more

complex device composed by several parts (more simple and

compact).

The smart material is able to respond to different stimuli

and to adapt its response to the need.

In reality is more appropriate to talk about functional

materials and smart structures (composed by functional

materials).

The robot in the fiction: yesterday and today

Robbie the robot:

mechanic & electronic

Terminator II:

smart rheological materials

Smart building

• DUOX system to reduce seismic

vibrations and wind effect

• HMD system: Hybrid Mass

Damper

• With SMA it is possible to

realize a simpler system

Smart Materials

Content

Introduction to Smart Material

What is a Smart Material?

Examples of Smart Materials

Piezoelectric Materials

Shape Memory Materials

Magnetostriction Materials

Electrostriction Materials

Applications of Smart Material

What is a smart material?

Something is changing?

Traditional vs Smart Structure

Traditional structures

Designed for certain performance requirements eg. load, speed, life span

Unable to modify its specifications if there is a change of environment

Smart Structures

Can accommodate unpredictable environments

Can meet exact performance requirement Offer more efficient solutions for a wide range of applications

Smart Materials

Smart materials have one or more properties/features that can respond to external stimuli, such as stress, light, temperature, moisture, pH, electric or magnetic fields and return to there original state when the stimuli is removed. Passive smart materials, which can only sense the environmental condition or stimuli, Active smart materials, which sense and react to the condition or stimuli, Very smart materials, which can sense, react and adapt themselves accordingly, and Intelligent materials, which are those capable of responding or activated to perform a function in a manual or pre-programmed manner

Eg. low melting point wax in a fire sprinkler blocks the nozzle until it gets hot

Examples of Smart Materials

Piezoelectric materials

Shape memory alloys

Magnetic shape memory alloys

Magnetorheological

pH sensitive polymers

Halochromic materials


Electrochromic materials

Photochromic materials

Chromogenic systems

Smart Grease

Piezoelectric materials?

Piezoelectric materials are materials that produce a voltage when stress is applied and vice versa.

Since this effect also applies in the reverse manner, a voltage across the sample will produce stress within the sample.

Suitably designed structures made from these materials can therefore be made that bend, expand or contract when a voltage is applied.

Used in actuators and vibration reducers. Buzzers are piezoelectric.

Piezoceramic, PZT Piezoelectric film, PVDF


When subjected to an electric charge or a variation in voltage,

piezoelectric material will undergo some mechanical change, and

vice versa. These events are called the direct and converse

effects.

The Direct Effect The Reverse Effect


Piezoelectric materials have the ability to generate an electrical charge.

A mechanical stress is applied to the smart material.

This causes a small electrical charge to be generated.

In return, the shape of the solid changes by a small amount.

A car‟s cigarette lighter is a good example of how piezoelectric materials are used in a every day application.

Smart Materials as Sensors & Actuators

Direct Effect

Output – Electric Potential

Input Stress

Output Signal

Input Stimulus

Output Strain

Reverse Effect

Input: Electric/Magnetic/

Thermal

Piezoelectricity

23

The microscopic origin of the piezoelectric effect is the

displacement of ionic charges within a crystal structure.

In the absence of external strain, the charge distribution

is symmetric and the net electric dipole moment is zero.

However when an external stress is applied, the charges

are displaced and the charge distribution is no longer

symmetric and a net polarization is created.

This alters the net dipole length causing a dimensional

change.

Piezoelectricity

24

Piezoelectric and subgroup Utilizing symmetry elements, all crystals can be divided

into 32 different classes or point groups. These 32 point groups are subdivisions of 7 basic crystal

systems: triclinic, monoclinic, orthorhombic, tetragonal,

Of the 32 point groups, 21 classes do not possess a center of

symmetry (a necessary condition for piezoelectricity to exist) and 20 of these are piezoelectric.

One class, although lacking a center of symmetry, is not piezoelectric because of other combined symmetry elements.

rhombohedral (trigonal), hexagonal, and cubic.

25

Piezoelectric and subgroup

32 Symmetry Point Groups

21 PG: Noncentrosymmetric 11 PG: Centrosymmetric

20 PG: Piezoelectric (Polarized under stress)

10 PG: Pyroelectric (Spontaneously polarized)

Subgroup Ferroelectric (Spontaneously Polarized, Revesible Polarization)

26

Piezoelectricity

In some cases a crystal posses a unique polar axis even in the unstrained condition.

This can result in a change of the electric charge due to a uniform change of temperature.

This is called the pyroelectric effect. The direct piezoelectric effect is the basis for force,

pressure, vibration and acceleration sensors and The converse effect for actuator and displacement

devices.

27

Polarization of piezoelectric

Above a critical temperature, the Curie point, each perovskite crystal exhibits a simple cubic symmetry with no dipole moment.

At temperatures below the Curie point, however, each crystal has tetragonal or rhombohedral symmetry and a dipole moment.

Adjoining dipoles form regions of local alignment called domains.

The alignment gives a net dipole moment to the domain, and thus a net polarization.

The direction of polarization among neighboring domains is random, however, so the ceramic element has no overall polarization.

28

The domains in a ceramic element are aligned by exposing the

element to a strong, direct current electric field, usually at a

temperature slightly below the Curie point.

Through this polarizing (poling) treatment, domains most nearly

aligned with the electric field expand at the expense of

domains that are not aligned with the field, and the element

lengthens in the direction of the field.

When the electric field is removed most of the dipoles are

locked into a configuration of near alignment.

The element now has a permanent polarization, the remanent

polarization, and is permanently elongated.

Polarization of piezoelectric

29

Piezo Materials

Some examples of practical piezo materials are barium titanate, lithium niobate, polyvinyledene difluoride (PVDF), lead titanate, lead zirconate (PbZrO3), lead zirconate titanate (PZT), ammonium dihydrogen phosphate (NH4H2PO4), and quartz.

There are several different formulations of the PZT compound, each with different electromechanical properties.

31 31

Piezoelectric ceramics- applications The principle is adapted to piezoelectric motors, sound or ultrasound generating devices, microphones, and mechanical strain gauges.

32

Magnetostrictive Materials

• When subjected to a magnetic field, and vice versa (direct and

converse effects), this material will undergo an induced mechanical

strain. Consequently, it can be used as sensors and/or actuators.

(Example: Terfenol-D.)

Smart Actuators

Input Parameter Actuator Type/ Devices

Electric Field Piezoelectric/

Electrostrictive

Electrostatic (MEMS) Electro-

Rheological Fluid

Magnetic Field Magnetostrictive

Magneto-Rheological Fluid

Chemical Mechano-chemical

Heat Shape Memory Alloy

Shape Memory Polymer

Light Photostrictive

Smart Materials for Sensing & Actuation Output Current/

Charge Magne- tization

Strain Temperature Light

Input

Electric Field

Cond- uctivity Permitti- vity

Electro- magnetic Effect

Reverse Piezo- electricity

Ohmic Resistance

Electro- Optic effect

Magnetic Field

Eddy Current Effect

Perme- ability

Joule Effect Magneto-

Magneto caloric Effect

Magnet o-Optic effect

Stress Direct Piezo- Electric Effect

Villary Effect

Elastic Modulus

Thermo-Mechanical Effect

Photo- elastic Effect

Heat Pyro- electric Effect

Thermo- Magne- tization

Thermal Expansion Phase Transition

Specific Heat Thermo- Lumin- ecence

Light Photo- Voltaic Effect

Photo- Magne- tization

Photo- striction

Photo- Thermal effect

Refract- ive index

Properties of a few Smart Materials

Props. PZT PVDF T-D NiTiNOL

Free strain(ppm) 1000 700 2000 20000

E. Mod.

(GPa)

62 2.1 48 27– M

89 - A

Band .1Hz-GHz .1Hz-GHz .1Hz-MHz 0-10 Hz

Qualitative Comparison of Different Smart Technology

Content: Shape Memory Alloy

Martensitic transformation Superelastic effect Memory effect SMA applications

What are shape memory alloys?

Shape memory alloys and shape memory polymers are thermoresponsive materials where deformation can be induced and recovered through temperature changes.

SHAPE MEMORY ALLOYS

In 1930s, Arne Olander was first observed the shape memory effect while working with an alloy of gold and cadmium.

This Au-Cd alloy was plastically deformed when cold but returns to its original configuration when heated.

The shape memory properties of nickel-titanium alloys were discovered in the early 1960s.

Although pure nickel-titanium has very low ductility in the martensitic phase, the properties can be modified by the addition of a small amount of a third element. These groups of alloys are known as Nitinol™ (Nickel-

Titanium-Naval-Ordnance-Laboratories).

Shape memory alloys change shape at set temperatures.

They become deformed once heated above the transformation temperature, but

One of the most common alloys is a combination of nickel and titanium.

This shape memory alloy can be treated so that when it reaches a set temperature it contracts.

When it cools it then returns to its original shape.

Shape Memory Alloy

Shape memory alloy wire

Shape memory alloy wire is called smart wire as it remembers its shape.

When a small electrical current passes through the wire it becomes smart.

It remembers to change shape.

The wire becomes shorter.

This shortening can be used to control a robotic hand.

In the future, this may help scientists produce artificial motion that is more similar to the range of human movement.

Magnetic shape-memory alloys (MSMAs)

Magnetic shape-memory alloys (MSMAs), or ferromagnetic shape-

memory alloys (FSMAs), are ferromagnetic materials which exhibit

large strains under the influence of an applied magnetic field due to

martensitic phase transformation.

Shape Memory Alloys

Shape memory alloys and shape memory polymers are thermoresponsive materials where deformation can be induced and recovered through temperature changes.

An example is NiTinolTM (Nickel Titanium) Above its transformation temperature, Nitinol is superelastic, able to

withstand a large amount of deformation when a load is applied and return to its original shape when the load is removed.

Below its transformation temperature, it displays the shape memory effect. When it is deformed it will remain in that shape until heated above its transformation temperature, at which time it will return to its original shape.

SMA, Nitinol

How SMA Works?

SME occurs due to the change in the crystalline structure of materials.

Two phases are:

Martensite:

Low temperature phase

Relatively weak

Austenite:

High temperature phase

Relatively strong

Shape Memory Alloy

MARTENSITE

DEFORMING MARTENSITE

DEFORMED MARTENSITE

AUSTENSITE

MARTENSITE

NiTi Shape Memory Alloy

Transformation

Martensite to Austenite transformation occurs by heating.

Austenite to Martensite occurs by cooling.

Crystallography of NiTi SMA

Martensitic transformation

Displasive transformation involving only atom shifts and bond rotations (no diffusion = fast transformation)

Martensitic transformation and properties

Monitoring the properties, an hysteresis loop appears

Other alloys

Matrix constraint

The matrix constraint force the grain to maintain its original shape. To accommodate the large required strain it may undergo slip or twinning:

Shape memory

Starting from austenite, cooling, deforming the martensite (detwinning), heating and coming back to austenite.

The cell rotations force the grains to recuperate their original shapes.

Summary of shape memory

Shape memory alloys, types of

NiTi SMA properties

Others SMA

Comparison NiTi-Steel

SMA applications: one way memory

The simplest actuator: at low temperature the weight elongate the spring in the martensite state (Emart < Eaust).

At high temperature it come back to austenite recuperating the original shape.

Applications with SMA

Fasteners, bolt systems, pipe couplings Actuators Smart materials Biomedical systems MEMS Damping systems

Application of SMA

Nitinol is used in medicine for stents: A collapsed stent can be inserted into a vein and heated (returning to its original expanded shape) helping to improve blood flow.

Also, as a replacement for

sutures where nitinol wire can be weaved through two structures then allowed to transform into it's pre-formed shape which should hold the structures in place.

Other Examples include:-

Thermochromic Materials

Phosphorescent Materials

Photochromic Materials

Polymorph

http://en.wikipedia.org/wiki/File:PhotochromicLens.jpg

Polymorph (Polycaprolactone-PCL)

QTC (Quantum Tunnelling Composite)

Thermochromic Sheet

UV Beads (UV pigment) Aroma Pigments Phosphorescent Sheet

Smart & Modern Materials

Keywords: Polymorph, QTC, Thermochromic, Phosphorescent, UV, Aroma

https://www.youtube.com/watch?v=IhVuc6RNyaw




https://www.youtube.com/watch?v=3_9duPm-rzc



Polymorph

Quantum Tunneling Composites (or QTCs) are composite materials of metals and non- conducting elastomeric binder, used as pressure sensors.

As the name implies, they operate using quantum tunneling: without pressure, the conductive elements are too far apart to conduct electricity; when pressure is applied, they move closer and electrons can tunnel through the insulator.The effect is far more pronounced than would be expected from classical (non-quantum) effects alone, as classical electrical resistance is linear (proportional to distance), while quantum tunneling is exponential with decreasing distance, allowing the resistance to change by a factor of up to 1012 between pressured and unpressured states.

QTCs were discovered in 1996 and PeraTech Ltd was established to investigate them further.

http://www.mutr.co.uk/catalog/product_info.php?products_id=1144

Quantum Tunnelling Composite (QTC)

http://www.mutr.co.uk/catalog/product_info.php?products_id=1144

A QTC in its normal state is a perfect insulator

When compressed it becomes a perfect conductor

If only lightly compressed its conductivity is proportional to the pressure applied

How does it work?

In normal physics an electron cannot pass through an insulation barrier.

In Quantum physics theory a wave of electrons can pass through an insulator – this is what is happening!

Quantum Tunnelling Composite (QTC)

How QTC Works?

QTC

LED

Battery

Stuff is getting smarter

We might not realise it, but smart materials are starting to make a real impact on everyday life.

Kettles that change colour when they boil Garments that plug into MP3 players Batteries that „report‟ their condition

These are all examples of the application of new materials exhibiting „smart‟ behaviour.


Tiny capsules in thermochromic ink contain liquid crystals.

As the temperature changes these crystals move.

The reorientation of the crystals causes a change in colour at a specific temperature.

Thermochromic materials react to changes in temperature.

This sensitivity causes them to temporarily change colour when they are exposed to heat.

Examples include:- Kettles Thermometers Battery Testers Heat Sensitive Ceramics Heat Sensitive Paper Clothing

Colour Changing Kettles

Thermometers

Heat Sensitive fabric

Thermochromic Ceramics

Smart Materials - Thermochromic

Thermochromic liquid crystals can be incorporated into special ink and printed onto different surfaces such as plastic, paper, textiles and ceramics. They respond to heat by changing colour at specific temperatures.

Thermo = Heat, Chromic = Colour

http://en.wikipedia.org/wiki/File:Generra_Hypercolor.jpg


Colour-changing thermochromic pigments are now routinely made as inks for paper and fabrics – and incorporated into injection moulded plastics.

A new type of phosphorescent pigment, capable of emitting light for up to 10 hours, has opened up entirely new design opportunities for instrumentation, low-level lighting systems etc.

Warm Cool

Interesting gimmicks!

Useful for marketing materials

2D heat-sensitive temperature gauge


Has your egg been hot enough for long enough?

Changes colour when food is too hot for a baby's mouth.

Smart inks change colour with temperature

DEVELOPEMENT OF THERMOCHROMIC COATINGS

Thermochromic coatings change color as a function of the ambient temperature.

For low outdoor temperatures, winter, the coatings may be dark presenting a high absorptivity.

For higher ambient temperatures, summer, the coating becomes white presenting a high reflectivity. Thus, when applied on roofs or walls it may present the best performance all year round.

common

cool

thermochr omic

thermochr omic

cool

common thermochro

mic

thermochro mic


T. Karlessi, M. Santamouris, K. Apostolakis, A.Synnefa I. Livada : Development and Testing of Thermochromic coatings for Buildings and Urban Structures, Solar Energy, 2008

Thermochromism is the reversible colour change of a substance induced by temperature change.

Composition of organic thermochromic dyes

the color former: usually a cyclic ester which determines

the color of the final product in its colored state

the color developer: usually a weak acid that imparts the

reversible color change to the thermochromic material and is responsible for the color intensity of the final product

the solvent: usually an alcohol or an ester, whose melting

point controls the temperature at which the color change occurs

Several thermochromic

coatings have been

developed using

different types of

thermochromic basic

materials


T. Karlessi, M. Santamouris, K. Apostolakis, A.Synnefa I. Livada : Development and Testing of Thermochromic coatings for Buildings and

Urban

Structures, Solar Energy, 2008

0

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(nm)

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%R common %R thermo %R white phase

Brown

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800 1800 2300 1300

w avelength (nm)

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%R thermoblack %R common black %R white phase

Black

Thermochromic coatings present a high reflectivity both in the visible and infrared spectrum, while present very strong

absorption in the near-ultraviolet range of the spectrum.

.



Important problem of ageing


Important problem of ageing. After almost one week, loose their initial optical characteristics. In particular, loose their ability to change color and their reflectivity is stabilised.


Important problem of ageing. When UV Absorbers are added in the thermochromic paints, the optical efficiency is not improving and the ageing problems remain


Thermochromic Coatings present important advantages. Can increase reflectivity during the warm period while present high absorptivity during winter.

Thermochromic coatings have been prepared

and tested in the outdoor environment. Their thermal performance found to be excellent.

However, thermochromic coatings present a very serious problem of optical ageing.

The results of various unsuccessful scientific

efforts to improve their optical performance have been presented. Use of optical filtering techniques have been

employed and the results are very promising.

Chromogenic systems

Chromogenic systems change colour in response to electrical, optical or thermal changes.

These include electrochromic materials, which change their colour or opacity on the application of a voltage (e.g. liquid crystal displays), thermochromic materials change in colour depending on their temperature, and photochromic materials, which change colour in response to light - for example, light sensitive sunglasses that darken when exposed to bright sunlight.


Photochromic lenses become dark when they are exposed to UV radiation.

Once the UV radiation is removed, the lenses gradually return to their normal state.

They can be made of either glass or plastic.

This causes them to undergo a reversible change of colour when exposed to a certain amount of light.

Possible Application.

Energy efficient windows that switch from transparent to opaque

spontaneously upon exposure to increasing levels of sunlight

Reaction lens

Photochromism is the reversible transformation of colour upon exposure to light. This phenomenon is illustrated in sun glasses.

Photochromic pigments reacts to bright light (Ultra Violet).

This T-shirt uses Photochromic inks for decoration purposes. Special pigments change colour when exposed to solar light and reverse back to clear when the light source is removed.

Photochromic lenses are light sensitive lenses that darken on exposure to U V light, protecting the user‟s eyes from harmful radiation.


darkens in bright light

Photochromic, photoluminescence glasses

Electrochromic Materials

Electrochromism is the phenomenon displayed by some materials of reversibly changing colour by using bursts of charge to cause electrochemical redox reactions in electrochromic materials.

Various types of materials and structures can be used to construct electrochromic devices, depending on the specific applications.

Electrochromic

Flip a switch and an electrochromic window

can change from clear to fully darkened or

any level of tint in-between.

The action of an electric field signals the

change in the window's optical and thermal

properties.

Once the field is reversed, the process is

also reversed.

The windows operate on a very low voltage

-- one to three volts -- and only use energy

to change their condition, not to maintain

any particular state.

Electrochromic Materials

Smart Windows are windows which use a glazing material to control the amount of light that is allowed to pass through the glass panes.

The glazing material is often called “switchable glazing”.

These materials change their optical behaviour with application of electrical voltage.

Various Terms for Smart Glass

Types of Smart Glasses

Active Smart Glass

Electrochromic

Suspended particle device (SPD)

Polymer dispersed liquid crystal (PDLC)

Glass-ITO/LixWO3/PEO-LiN(SO2CF3)2/Liy(TiO2 – CeO2)/ITO/glass Glass/ITO/polytoluidine/cellulose –

polyacetate polymer/ Hy(TiO2 – CeO2/ITO/glass

Ability to tune optical transmission from clear to dark.

Low switching speed. Lack complete opacity.

Requires electricity only to change opacity, not to maintain

SPD – Suspended Particle Devices

Microscopic light-absorbing particles are dispersed in droplets within a film.

In the "off" state the particles are suspended randomly, making the window

dark. At moderate voltage is applied the particles align and permit light to

pass through.

PH sensitive polymers

pH sensitive or pH responsive polymers are materials which will respond to the changes in the pH of the surrounding medium by varying their dimensions

Such materials increase its size (swell) or collapse depending on the pH of their environment.

This behavior is exhibited due to the presence of certain functional groups in the polymer chain

pH Sensitive Polymers

The sensor is prepared by entrapping within a polymer matrix a pH sensitive dye that responds, through visible colour changes (see the Figure) to spoilage volatile compounds that contribute to a quantity known as Total Volatile Basic Nitrogen (TVB-N).

Halochromic Materials

Halochromic materials are commonly materials that change their colour as a result of changing acidity.

One suggested application is

for paints that can change colour to indicate corrosion in the metal underneath them.

Magnetorheological

These fluids are composed of iron-like particles.

In their normal state they are fluid.

When placed in a magnetic field the particles are attracted to each other and join up to form a solid.

Currently, these materials are not widely used. It is thought of as a more futuristic smart material.

Magnetorheological fluid (MR fluid) is a type of smart material that has the ability to change state when placed in a magnetic field.

Waterproof clothing (material or structure?)

Goretex® Micro-porous expanded PTFE

(Polytetrafluoroethylene ) discovered in 1969 by Bob Gore

~ 14 x 1012 micropores per m².

Each pore is about 700x larger than a water vapour molecule

Water drop is 20,000x larger than a pore

Waterproof breathable fabric is engineered to handle two tasks simultaneously: repel precipitation and release perspiration vapor.

Blocks wind Used in tents and waterproof walking

gear. Wound care- creates a barrier that

stop moisture going back onto the skin but allows the skin to breathe

microporous breathable fabrics

Electronic paper? Already done at MIT!

A newspaper that change content every day?

EPD (Electronic Paper Display)

Liquid Crystal Displays (LCDs)

Thermotropic Liquid Crystal

Thermotropic liquid crystals (LC) are anisotropic liquids that possess a mesophase (a phase with crystal and liquid properties) within a certain temperature range.

Thermotropic liquid crystals composed of small molecules are finding increasing application as display materials, information storage materials, optical couplers and optical waveguides.

Such materials exist in nematic, smectic and cholesteric states and their microstructures are well known.

It is not generally appreciated that the alignment behaviour in response to moderate electric or magnetic fields, which forms the basis of most display applications, has its origins in the anisotropy of the dielectric or magnetic relaxation processes of the materials.

The action of the applied directing field is to align the local director n in a mesophase either parallel or perpendicular to the field direction depending on the sign of the anisotropy of the susceptibility (i.e. Δɛ = ɛ∥ − ɛ⊥ for the case of applied electric fields).

Transdermal Prescription Drug Patches

Smart Grease Smart grease is a particularly sticky and viscous gel

with almost magical shear characteristics. It can be used in prototype applications to improve

performance or it can be used in novel applications such as wound-up motors to provide uniform speed and torque output.

The example illustrated here is a simple elastic band

motor comprising a pill container, elastic, wheel and securing/winding rod. If, under normal circumstances, the wheel is wound up and released, it will spin rapidly and slow down.

If a tiny amount of smart grease is added between

the friction surfaces, the wheel will turn at a uniform (very slow) speed and the stored energy will be released uniformly.

Smart gels

These are gels that can shrink or swell by several orders of magnitude.

Some of these can also be programmed to absorb or release fluids in response to

a chemical or physical stimulus.

These gels are used in areas such as food, drug delivery, organ replacement and

chemical processing.

Rheological Materials

Material that can change its physical state very quickly in response to a stimulus

Stimulus include

Electrical

Magnetic

Ferromagnets

Magnetic field aligns ferromagnetic molecules in order in order to achieve solid state structure

o Nanoparticles reduce IUT effect (In Use Thickening)

Rheological Materials

These are in liquid phase which can change state instantly through the

application of an electric or magnetic charge. These fluids may find

applications in brakes, shock absorbers and dampers for vehicle seats.

ELECTRIC /MAGNETIC

FIELD APPLIED

ER /MR FLUID

CHANGES LIQUID TO

SOLID

ELECTRIC /MAGNETIC

FIELD

REMOVED

ER /MR FLUID

CHANGES SOLID TO LIQUID

Example of Magnetic Field on Rheological Material

Applications of Rheological Materials

MR materials Structural Support Dampers to minimize vibrational shock from wind and

seismic activity.

Industrial Break fluids

Shock absorbers

Magnetostrictive materials

Material that stretches or shrinks when a magnetic field is applied.

Conversely, when a mechanical force is applied on the material, a magnetic field is induced.

Ferromagnets

Magnetic field can be used to create an electric current

Applications of Magnetorestrictive Materials

More efficient fuel injection system Specific amounts of fuel

Higher frequency

Magnetorheological Fliud (MR Fluid) A magnetorheological fluid is a fascinating smart fluid with the ability to switch

back and forth from a liquid to a near-solid under the influence of a magnetic field.

It is usually used for applications in braking.

The term „‟magnetorheological fluid‟‟ comes from a combination of magneto, meaning magnetic , and rheo, the prefix for the study of deformation of matter under applied stress .

Magnetorheological fluids are not currently in wide use but are considered a futuristic type of materials.

A magnetorheological fliud ( MR Fluid) is a type of smart fluid in a carrier fluid, usually a type of oil.

When subjected to a magnetic field, the fluid greatly increases its apparent viscosity, to the point of becoming a viscoelastic solid.

Importantly, the yield stress of the fluid when in its active („‟on„‟) state can be controlled very accurately by varying the magnetic field intensity. The upshot of which is that the fluid‟s ability to transmit force can be controlled with an electromagnet, which gives rise to its many possible control-based applications.

Magnetorheological Fliud

Material Behavior

To understand and predict the behavior of the MR fluid it is necessary to model the fluid mathematically, a task slightly complicated by the varying material properties (such as yield stress ).

Smart fluids have a low viscosity in the absence of an applied magnetic field, but become quasi-solid with the application of such a field.

In the case of MR fluids (and ER), the fluid actually assumes properties comparable to a solid when in the activated („‟on„‟) state, up until a point of yield (the shear stress above which shearing occurs) .

This yield stress (commonly referred to as apparent yield stress) is dependent on the magnetic field applied to the fluid, but will reach a maximum point after which increases in magnetic flux density have no further effect, as the fluid is then magnetically saturated.

The behavior of a MR fluid can thus be considered similar to a Bingham plastic, a material model which has been well-investigated.

However, a MR fluid does not exactly follow the characteristics of a Bingham plastic.

For example, below the yield stress ( in the activated or „‟on „‟state), the fluid behaves as a viscoelastic material, with a complex modulus, that is also known to be dependent on the magnetic field intensity.

MR fluids are also known to be subject to shear thinning, whereby the viscosity above yield decreases with increased shear rate.

Furthermore, the behavior of MR fluids when in the „‟off‟‟ state is also non-Newtonian and temperature dependent, however it deviates little enough for the fluid to the ultimately considered as a Binbham plastic for a simple analysis.

Magnetorheological Fliud

Common MR Fluid Surfactants MR fluids often contain surfactants including, but not limited to:

Oleic acid Tetramethylammonium hydroxide Citric acid Soy lecithin

These surfactants serve to decrease the rate of ferroparticle settling, of which a high rate is an unfavorable characteristic of MR fluids.

The ideal MR fluid would never settle, but developing this ideal fluid is as highly improbable as developing a perpetual motion machine according to our current understanding of the laws of physics.

Surfactant-aided prolonged setting is typically achieved in one of two ways by: addition of surfactants, and by addition of spherical ferromagnetic nanoparticles.

Common MR Fluid Surfactants

Addition of the nanoparticles results in the larger particles staying suspended longer since to the non-settling nanoparticles interfere with the settling of the larger micrometer-scale particles due to Brownian motion.

Addition of a surfactant allows micelles to form around the ferroparticles.

A surfactant has a polar head and non-polar tail (or vice versa), one of which adsorbs to a nanoparticle while the non-polar tail (or polar head) sticks out into the carrier medium, forming an inverse or regular micelle, respectively, around the particle.

This increases the effective particle diameter.

Steric repulsion then prevents heavy agglomeration of the particles in their settled state, which makes fluid remixing (particle redispersion) occur far faster and with less effort.

For example, magnetorheological will remix within one cycle with a surfactant additive, but are nearly impossible to remix without them.

While surfactants are useful in prolonging the settling rate in MR fluids, they also prove detrimental to the fluid‟s magnetic properties (specifically, the magnetic saturation), which is commonly a parameter which users wish to maximize in order to increase the maximum apparent yield stress.

Whether the anti-settling additive is nonosphere-based or surfactant-based, their addition decreases the packing density of the ferroparticles while in its activated state, thus decreasing the fluids on state/activated viscosity, resulting in a „‟softer‟‟ activated fluid with a lower maximum apparent yield stress.

While the on-state viscosity (the „‟hardness‟‟ of the activated fluid) is also a primary concern for many MR fluid applications, it is a primary fluid property for the majority of their commercial and industrial applications and therefore a compromise must be met when considering an on state viscosity, apparent yield stress, and settling rate of an MR fluid.

Common MR Fluid Surfactants

How it Works

The magnetic particles, which are typically micrometer or nanometer scale spheres or ellipsoids, are suspended within the carrier oil are distributed randomly and in suspension under normal circumstances, as below

When a magnetic field is applied, however, the microscopic particles (usually in the 0.1 – 10 um range) align themselves along the lines of magnetic flux, see below.

When the fluid is contained between two poles (typically of separation 0.5 – 2 mm in the majority of devices), the resulting chains of particles restrict the movement of the fluid, perpendicular to the direction of flux, effectively increasing its viscosity.

How it Works

Importantly, mechanical properties of the fluid in its „‟on‟‟ state are anisotropic.

Thus in designing a magnetorheological (or MR) device, it is crucial to ensure that the lines of flux are perpendicular to the direction of the motion to be restricted.

Modes of Operation and applications

An MR fluid is used in one of three main modes of operation, these being flow mode, shear mode and squeeze-flow mode.

These modes involve, respectively, fluid flowing as a result of pressure gradient between two stationary plates; fluid between two plates moving relative to one another; and fluid between two plates moving in the direction perpendicular to their planes.

In all cases the magnetic field is perpendicular to the planes of the plates, so as to restrict fluid in the direction parallel to the plates.

Flow mode

Electrostrictive Materials • This material has the same properties as

piezoelectric material, but the mechanical change is proportional to the square of the electric field. This characteristic will always produce displacements in the same direction.

Thermoelectrics

Peltier cooling

Thermoelectric generator

Magnetocaloric materials


Hydrochromic Materials

Hydrochromic inks change colour

according to the amount of water they

detect.

Can you think of a use for

HYDROCHROMIC inks?

Click to see video

http://www.youtube.com/watch?v=72fEzgu10ZY


Phosphorescent Materials

Click to see Video

Phosphorescent inks are able to absorb light

during the day and then glow at night.

Can you think of a use for PHOSPHORESCENT

inks?

https://www.youtube.com/watch?v=9I1X6bQY3-w

Conclusion

Today, the most promising technologies for lifetime efficiency and improved reliability include the use of smart materials and structures.

Understanding and controlling the composition and microstructure of any new materials are the ultimate objectives of research in this field, and is crucial to the production of good smart materials.

New and advanced materials will definitively enhance our quality of our life.

It‟s time to be SMART !

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