Smart Materials: From Hypercolor to the Warfighter

Some may remember the Hypercolor t-shirt of the 1990s. Made of a thermochromic material, the shirts represent an early example of a “smart material.” As the roots of the name suggest, the changes in color (chromic) occur in response to changes in temperature (thermo). Since, smart materials have evolved from a trendy fashion choice to a field with significant implications for warfighters countering emerging threats.

Smart materials are broadly defined as materials that undergo significant changes as a result of external stimuli. These responses can include changes in shape, color, and magnetization in reaction to changes in electric and magnetic fields, temperature, acidity, and light. Examples of smart materials include photomechanical materials, which change shape when exposed to light, and magnetocaloric materials that change temperature in response to a magnetic field. Some smart materials, such as piezoelectrics, exhibit “smart” properties in both directions – changing shape when a voltage is applied and producing a voltage when its shape is changed.