Hydrochromic, Thermochromic, Photochromic or Glow in the Dark. But what do they actually mean in plain English? I will try to explain for those delving for the first time into this colour changing and colour shifting world? All these Smart Materials are affected by the influences of an outside effect or stimulus, that then causes a molecular change and often reversible.
Let us start with Hydrochromic:
When water is applied it loses its opacity. Often used as an ink to hide hidden messages, images or colours. The hydrochromic ink is applied to your chosen surface and appears white in colour. But when water is applied, the hydrochromic ink will become translucent, revealing your hidden layer. Fortunately it is reversible and if by magic, reverses back to its original form repeatedly. Virtually the sky's the limit on the thousands of applications it can be used on. One of the fascinating products that have been produced using this ink is the umbrella that changes colour when it rains!
Sensitive to changes in temperature. Often used in ink that changes colour or becomes transparent at the chosen temperature, revealing a hidden layer. This could be a colour, image or a hidden message. Often Liquid Crystal is the medium used and is often seen in thermometers. Thermochromic ink or pigments have an extremely large number of innovative applications. One of the thermochromic materials we supply called Masterbatch is used in the making of colour changing straws that change colour in cold drinks. These changes are reversible but there are cases in some safety testing products where they are required to be irreversible.
Changes in the sun (UV) by an often dramatic appearance of colour. Again, often used in ink; that when applied to a surface it appears to be without colour. But once subjected to direct sunlight a colour will appear. It always seems to have magical capabilities and can be used for all types of truly amazing applications. The list is almost endless and reverses back to its original form to see over and over again. The most popular and surprisingly common use seen every day, is in the use of transitional eyeglasses that darken in sunlight.
Glow in the Dark:
Probably the most obvious name to describe this effect and with no batteries required! It appears white in colour during the day but leave this ink in daylight and it absorbs light. When the lights are turned off it will emit a bright green glow. This is called photoluminescence and sadly although reversible, is not the answer to permanent rechargeable light, as the frequency of the light emitted is lower than that absorbed. This product can be used for many uses but are often used in safety markers where switches and power boxes can be seen at night in the case of power failures.