The term 'smart materials' has been used more and more over the last few years. It describes materials that have one or two properties that can be altered in a controlled fashion by an external stimuli. It covers materials such as memory shape alloys (usually nitinol), thermochromic paints, pH sensitive polymers and piezoelectric materials.
Many lab suppliers now stock some 'smart materials' that can be used in the classroom.
Nitinol wire can be made to contract when a current is applied or if heated directly. It can therefore be used to make a thermal actuator (a switch which activates when heat is applied) used in some fire alarms. Nitinol springs can contract and lift a significant weight when heated. Nitinol is an alloy of Nickel and Titanium
Memory shape alloys are usually metal wires which when bent, return to their original shape if heated.
Piezoelectric materials produce a small current when stress is applied to them. The opposite effect is also possible where deformation occurs when a current is applied through the material. They are starting to be used in the robotics industries.
Thermochromic paints change colour when heat is applied to them. In practical applications, they are used to paint pipes in industry' If the temperature of the pipe reaches a certain level, the paint warns of the temperature change. Other applications include forehead thermometers and novelty toys.
In schools smart materials are only starting to be used to demonstrate the different properties of these new materials. Nitinol springs can be used to investigate the effects of heating caused by electrical currents on the length of the spring while thermochromic paints can be used to show changes in temperature.