thermochromic materials

Thermochromic and waterproof polyester fabric (image by Inventables)

Heat Reactive Materials
Heat reactive materials change state, shape and/or color when exposed to temperatures above ambient. Naturally, many materials change shape, eg. melt, at high temperatures. What’s special about some of them is that their state, shape and/or color can be altered at relatively low temperatures (provided through hot water, body heat, hair dryers, ambient heaters, ovens, or just a hot summer day), making them easy to use and suitable for DIY projects. In this post I’ll go over thermochromic pigments and a few materials they have been incorporated into, namely paint, fabric, film and glass.

Thermochromic Pigments change color when exposed to heat and turn back to their original color when the temperature drops again. According to TEP:

Most thermochromic materials are based on liquid crystal technology. At specific temperatures the liquid crystals re-orientate to produce an apparent change of colour. The liquid crystal material itself is micro-encapsulated – i.e., contained within microscopic spherical capsules typically just 10 microns in diameter. Billions of these capsules are mixed with a suitable base to make thermochromic printing ink or, for example, plastics destined for injection molding.

These pigments can be mixed with an acrylic base or screen printing ink. At room temperature the pigment appears in its original color, but at temperatures between 27° and 30°C (80° to 86°F) this color disappears, eg, if a black pigment is applied to a white surface, the surface turns from black to white at the change-over temperature. When mixed with an acrylic base each pigment will turn instead into the color of the acrylic base or color blender, eg., if a blue pigment is mixed with a yellow acrylic base the resulting color will be green, but at the change-over temperature the blue will disappear and the green will turn into yellow. The ratio of acrylic base to coloring pigment depends entirely on the application and density of color required. For a detailed explanation of the functioning and applications of thermochromic pigments see the TEP Smart Colors info sheet (PDF) and this little demo animation.

Shi Yuan’s thermochromic wallpaper

Temperature-Sensitive Glass results from the application of thermochromic pigments to glass tiles which change color based on ambient, body or water temperature:

The textured glass surface layer protects and highlights the color-change film on the tile. The base color of the tile can match almost any color, and the temperature change point can be fit to the user’s environment and requirements. The dynamic color change begins at the selected activation temperature and shimmers through three phases, one with each 6–10° rise in temperature. Once the temperature peak is passed, the base color returns and remains the same until the temperature drops.
(source: Inventables)

Temperature-sensitive glass tile (image by Inventables)

Thermochromic Film has adhesive on one side and thermochromic ink on the other. The film is normally black but changes to bright green/blue at temperatures between 29.4 and 33°C (84º – 91º F). Due to its low change-over temperatures, touching a piece of thermochromic film for a few seconds will cause the contact area to change color – it can also be used with nichrome or any other heat source.

Thermochromic film (image by Mindsets)

Suppliers
Body Faders (US) :: thermochromic fabric
Inventables (US) :: thermochromic fabric, thermochromic film, temperature-sensitive glass tiles
Mindsets (UK): thermochromic pigments, thermochromic film
Paint with Pearl (US) :: thermochromic pigment powder
Amazon.com :: thermochromic paint

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