In life, the only thing that stays the same is change. The only exception to that rule, of course, is the color of paint on your car. You might really hate that lime green, but there is no way — no way — you’re going through the expensive and time-consuming chore of painting it all over again. You wish that the colors of the things in your life were as dynamic as life itself.
Well, sometimes our possessions and paints really can change color, thanks in part to thermochromic ink technology. Thermochromic inks take advantage of thermochromism, which refers to materials that change their hues in response to temperature fluctuations. Still hate that lime green? Pony up for the right paint and on a warm day, it could morph from a Kermit the Frog hue into a more tolerable sunshine yellow.
Thermochromic inks conjure their magic in different ways. Currently, there are two major categories of these inks: thermochromatic liquid crystals (TLCs) and leuco dyes.
Liquid crystals are exactly what their name indicates — a substance that has many properties of a liquid crossed with structural elements inherent to crystals. Peer through a microscope at a liquid crystal and you’ll see a fluid that exhibits evident textures.
Liquid crystal-based TLCs are a temperamental bunch and rather difficult to incorporate into labels, clothes or other goods. Leuco dye inks, though, feature more durable chemistry that lets product designers employ these inks for all sorts of fun applications.
One of the most famous applications of leuco dyes is on cans of Coors Light beer. These cans feature a graphic of a mountain landscape next to the company’s logo. At room temperature, the mountains appear white. Cool the can to drinking temperature (about 45 degrees Fahrenheit or 7 Celsius), though, and those same mountains turn a vivid, bright blue. As the beer warms in your hand, the graphic again shifts to its original white. This color change can happen over and over again.
Makers of color-morphing products love thermochromic inks, but they have to choose these inks carefully to ensure that they’ll work well in their current manufacturing processes. Usually, companies will acquire samples from ink suppliers and then follow a process of trial and error until the results are stable and visually mesmerizing.
Both types of thermochromic inks have pros and cons. Chemists must weigh the properties of each before choosing an ink that’s best for their application.
Thermochromic inks are more expensive than regular inks, but they still find their way into innovative products, from clothes and cars to papers, paints and bathroom fixtures. Beer and energy drink companies are known for incorporating flashy, temperature-sensitive graphics into their products. Leuco dyes don’t interfere with recycling, so they’re environmentally sound, too.
A company called Moving Color makes color-changing tiles for home decorating. Install the tiles in your shower and watch as the black tile shifts to various bright hues. Or position them near lights and they’ll change in response to heat from the bulbs.