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?

• 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 pre-formed 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 opened up entirely new design opportunities for instrumentation, low-level lighting systems etc.

Warm Cool

http://www.mutr.co.uk/catalog/index.php?cPath=79

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