Smart Materials
What are smart materials?
• Smart materials are materials that
have one or more properties that can
be significantly altered in a controlled
fashion by external stimuli, such as
stress, temperature, moisture, pH,
electric or magnetic fields.
What are the examples?
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Piezoelectric materials
Shape memory alloys
Magnetic shape memory alloys
PH sensitive polymers
Halochromic materials
Chromogenic systems
What are Piezoelectric
materials?
• Piezoelectric materials are materials that
produce a voltage when stress is applied.
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.
• Buzzers are piezoelectric.
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.
What are shape memory
alloys?
• 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.
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 preformed shape which should
hold the structures in place.
Further reading of SMA
• http://en.wikipedia.org/wiki/Shape_memory_alloy
Magnetic SMA
• Magnetic Shape Memory alloys are materials that
change their shape in response to a significant
change in the magnetic field.
PH sensitive polymers
• pH-sensitive polymers are materials which
swell/collapse when the pH of the surrounding
media changes.
• The sensor is prepared by entrapping within a
polymer matrix a pH sensitive dye that responds,
through visible colour changes (see next slide) to
spoilage volatile compounds that contribute to a
quantity known as Total Volatile Basic Nitrogen
(TVB-N).
PH sensitive polymers
• The ‘REF’ sample is outside the package. The others
are all inside. www.dcu.ie/chemistry/asg/pacquita/
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.
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.
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.
Thermochromic
• Kettles that change colour and
signs that glow-in-the-dark are
two recent examples of
products becoming ‘smarter’ as
a result of new materials.
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
Warm
opened up entirely new design
opportunities for
instrumentation, low-level
lighting systems etc.
http://www.mutr.co.uk/catalog/index.php?cPath=79
Cool
Photochromic
• Photochromism is the reversible transformation of colour upon
exposure to light. This phenomenon is illustrated in sun glasses.
QTC
• 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
QTC
QTC
Smart Grease
www.tep.co.uk