Recently our metals lead, Alex, popped into the marketing office with a heaping bowl of ice cream. He brought two spoons along with him too – Was he planning on sharing his delicious ice cream? Unfortunately, he wasn’t – But he did stop in to show us some #CoolScience! As he got a spoon full of ice cream and took a bite, he showed something quite fascinating. The spoon had changed colors from white to blue when coming in contact with the cold ice cream. Our marketing manager stuck the extra spoon in her cup of ice water (which is nowhere near as good as ice cream) and wah-lah a blue spoon!
After doing some research, we learned the reason this happens is a process called thermochromism. Thermochromism simply refers to a material that changes color due to temperature change. Remember being fascinated by mood rings when you were younger? They change colors by using body heat. Many companies rely on thermochromism to create products that appear to magically change colors – but how does this process work?
There are two types of thermochromism inks that make these color changes possible: thermochromatic liquid crystals (TLCs) and leuco dyes. According to How Stuff Works, “liquid crystals are exactly what their name indicates – a substance that has many properties of a liquid crossed with structural elements inherent to crystals.” The properties of TLCs change depending on the surrounding environment. For example, at cooler temperatures TLCs are generally solid, meaning they will not reflect much light and appear black.
The next type of thermochromism ink is leuco dyes. These dyes are a bit different than TLCs. For starters, they feature more “durable” chemistry. A well known way leuco dyes have been used is in Coors Light beer cans. Remember the mountain featured on the can? When the can is at room temperature, the mountains appear white. However, once cooled to around 45 degrees Celsius the mountains turn blue.
Leuco dyes are microcapsulated into droplets three to five microns in size. This prevents them from being damaged from other chemicals. How Stuff Works explained the science behind leuco dyes: “The teensy capsules contain a colorant, an organic acid and a solvent. At lower temperatures the solvent remains in a solid state, keeping the colorant and acid in close proximity to each other — and as a result, they reflect light and create color. As the solvent warms the colorant and the acid separate and there’s no visible color, which in turn exposes underlying inks.” We have to admit – that’s pretty incredible! Leuco dyes aren’t as accurate when it comes to reading temperatures as TLCs are – but they’re the perfect additive to incorporate into a load of fun products!
There are a variety of things to consider when deciding what type of thermochromism ink to incorporate into a product, including the type of product you are creating and durability. Sure, a color changing spoon is a fun way to enjoy ice cream but are there more serious implications for thermochromism technology? Absolutely! This technology can be applied to create indicators for products that require constant temperature verification—like a refrigerator or aquarium tank. Additionally, thermochromism can create safety indicators—such as a rubber ducky for a child’s bath time that changes color when the water is too hot.
Whether a serious or silly application the inner child in us can’t help but be fascinated by color changing polymers—made possible by thermochromism. The good news? Summer’s not over yet—there is still plenty of time for you to grab a bowl of ice cream, kick your feet up on your back deck, and enjoy a tasty treat with a color-changing spoon.