Materiais inteligentes são materiais que possuem uma ou mais propriedades que podem ser alteradas de forma controlada através estímulos externos, tais como: stress mecânico, mudanças de temperatura, de ph, eletricidade, campos magnéticos,etc...
Estes Materiais podem ser aplicados em instalações artísticas, em pequenos projetos científicos, na educação, na moda, na decoração e revestimento de interiores, mas também em aplicações robustas como a engenharia automóvel, conseguindo substituir sistemas mecânicos complexos e até consumos de energia desnecessários.
Com este pequeno tutorial pretendemos apresentar alguns destes materiais e descrever as suas propriedades.
Ferrofluid – a truly magnetic liquid.
Ferrofluid is used commercially in dynamic seals and loudspeakers, but has recently become available for educational investigation.
This consists of micron size magnetic particles (magnetite) in a mineral oil. Particles are coated in a surfactant which prevents them clumping together.
When a magnetic is in close proximity the magnetic particles in the Ferrofluid take up the shape of the magnetic field – a 3-D version of the classic iron fillings on a piece of paper experiment that we used to do in schools.
Electrotextiles are textiles with electrical properties. They're mostly used for electromagnetic shielding, anti-static and heating purposes, and also for soft circuits: electric circuits or sensors made out of a combination of special fabrics, threads, yarns and electronic components.
Many products contain a fluorescent pigment to give the impression of a glowing red, yellow or green glowing surface. The active ingredient in the pigment is a dye that absorbs radiation in the UV region and ‘shifts’ the wavelength(s) to more visible light – hence the glow effect. More light seems to come out than goes in!
The fluorescent dye is microencapsulated to form a water-based solution with the consistency of cream. This can be mixed with acrylic paints or similar media to create fluorescent paints for a graphics work, product design, model prototyping etc.
Polymorph is one of a new generation of commercial polymers set to have a major impact on model making and prototyping. This polymer has all the characteristics of a tough “engineering” material yet it fuses and becomes easily mouldable at just 62°C. It can be heated with just hot water or a hairdryer and moulded by hand to create prototypes and solve manufacturing problems currently outside the capacity of other materials.
Uses for Polymorph include:
• Moulding of handles and orthopaedic aids
• Vacuum forming moulds
• Moulds for batch producing other mouldings
• Prototype mechanical parts
• Armatures / frames for models
• Inserts for compliant products
• Specialised components - e.g. motor mountings
• Moulding of complete products - e.g. torches
• Joining components together
This paint contains ferrite powder suspended in an acrylic latex medium.It will adhere to more or less any surface and provides a base for magnets to cling to.The paint can be built up in coats to accommodate magnets of different strengths. Uses include games, clocks, notice boards etc.
Based on 0.02mm gauge aluminium foil with a matt black polymer coating both sides, it feels and behaves like a metal/paper/plastic hybrid ! The material, which comes from Hollywood in the US, originated in the film industry where it’s used for instant adjustments for spotlights.But it clearly has hundreds of others including:
• Modelling metal structures (it crumples and behaves to scale)
• Making actual models – e.g., the metal equivalent of paper planes
• Protoyping torches and lamps (it is heat resistant)
• Solar heating equipment (it has excellent heat absorption and can literally be wrapped around heat exchanger pipes etc).
• Pin hole cameras and similar optical applications
This polymer-based material has the thickness and flexibility of thin card. It contains a magnetic medium which make its ‘stick’ to any ferrous surface – e.g. tinplate, white goods. It can be passed through an ink jet printer and is an ideal medium for unusual graphics products.
Glow-in-the Dark Film
A flexible self-adhesive plastic film that glows brightly in the dark. Can easily be cut by hand and stuck to a wide range of materials.
Quantum tunnelling composite is a flexible polymer that exhibits extraordinary electrical properties. In its normal state it is a perfect insulator, but when compressed it becomes a more or less perfect conductor and able to pass very high currents. Polymers loaded with carbon are, at best, only partially conductive. In QTC, the change from non-conductor to conductor is dramatic, and a tiny piece measuring 4mm square and 1.5mm thick can pass a current of up to 10 amps when squeezed!
Instead of carbon, QTC contains tiny metal particles, but it does NOT work by percolation. Instead, electrons ‘pass’ through the insulation by a process called quantum tunnelling – hence the name of the material. To explain this effect, we have to appeal to quantum theory and think of the electrons as waves. In classical physics, the electrons cannot pass through an insulation barrier, but according to quantum theory a wave can – and this is what happens in QTC.
Thermocolour / Thermochromic Sheet
A remarkable self adhesive sheet material printed with thermochromic liquid crystal 'ink'. Changes colour (bright blue) when heated from 29.4 to 33°C. Potential applications are many and varied. E.g. temperature indication/warnings, body jewellery, advertising displays (attach a resistance wire to the rear and pass a small current to cause dramatic colour changes to the front 'screen'.
'Smart wire' is a shape memory alloy (SMA) that changes its length with a useful pulling force when a small current is passed through it.A voltage of approx. 3V is sufficient although other values can be used we have not tested for over-heating or other side effects.
ll metals exhibit elastic behaviour before they permanently deform under stress – some more than others. Superelastic wire, as its name suggests, remains elastic even when tied in knots - and handling this material almost defies belief. (Tie it in a knot that you can just undo, and it will come out perfectly straight!)
Superelastic wire is used widely for spectacle frames able to recover their original shape after deformation that would permanently damage other materials. Other uses include ‘impossible’ hinges and deployable structures capable of unfolding and expanding to many times their original size.
Smart Niti Springs
Spring made from shape memory alloy. At room temperature this spring is soft enough to pull out to approximately 50mm by applying a small force. When heated to 70°C by passing an electric current through it, the spring contracts to its original length with a useful pulling force (equivalent to lifting a 0.5kg weight).
Memory spring and memory wire
This nickel/titanium (NiTi) alloy initially ‘remembers’ that it should be straight. If it is bent into a different shape and then dropped in very hot water (90°C), it springs back to its original straight condition. It will repeat this behaviour any number of times. Memory wire has several important medical applications. It is used, for example, to make surgical stents – small woven frames that balloon outwards to open blocked arteries. It is also used for orthodontic braces.
Two-Way Memory Spring
These remarkable springs, based on a brass alloy, ‘remember’ to open up at around 90°C and close again when cool. If immersed in hot water at or around 90°C they will open in a split second and close as quickly if dropped in cold water. Such springs have many industrial applications – e.g., in sprinkler and fire damping systems where they replace expensive single-use only fusible links.
A powder that absorbs 500 times its own weight of water and grows into snow.
• Bouncing putty – a material that suddenly changes from soft to hard if you hit it
• Thermo-film – a plastic film that glows bright blue if you heat it with your hand
• Magic beads – beads that change colour in sunlight
Para mais informações sobre estes e outros materiais e como os encontrar, deixamos os links:
A Fascinating look at Smart Materials [SEP]