Thermochromism

From Freepedia

Thermochromism is the ability of a substance to change colour due to a change in temperature. A mood ring is an excellent example of this, but it has many other uses. Thermochromism is one of several types of chromism.

Inks

Thermochromic inks are temperature sensitive inks, developed in the 1970s, that temporarily change color with exposure to heat. They come in two forms, liquid crystals and leucodyes. Liquid crystals are used in mood rings. Leucodyes are easier to work with and allow for a greater range of applications. These applications include: flat thermometers, battery testers, clothing, and the indicator on bottles of maple syrup that change color when the syrup is warm. The most well-known line of clothing utilizing thermochromics was Hypercolor. The thermometers are often used on the exterior of aquariums, or to obtain a body temperature via the forehead.

Paints

Thermochromic paint is a relatively recent development in the area of color-changing pigments. It involves the use of liquid crystal technology. After absorbing a certain amount of light or heat, the crystal structure of the pigment changes in such a way that it absorbs and emits light at a different wavelength than at lower temperatures. Thermochromic paints are seen quite often as a coating on coffee mugs, whereby once hot coffee is poured into the mugs, the thermochromic paint absorbs the heat and becomes colored or transparent, thus changing the appearance of the mug.

Others

Another good example of this is the color indicators on batteries. The indicator turns green if the battery still possesses a charge. This works by passing the charge of the battery through a small resistor on the battery, and causes the pigment to absorb heat. Once the paint has absorbed enough heat from the current of the battery, it changes from black to green (usually), thus indicating that the battery still has a fair amount of charge left in it.

A simple to make thermochromic compound is zinc oxide this is white at room temperture, but when it is heated to changes to yellow, on cooling the zinc oxide reverts to white. Also lead(II) oxide has a similar colour change on heating. These solids are technically semiconductors, and the colour change is linked to their electronic properties.

External links

• Thermochromic pigments
• Matsui Shikiso Chemical
• Color Change Corporation
• Liquid Crystal Resources LLC
• ALSA Corporation Exotic Paint

 

Chromism  photochromism (light) | thermochromism (heat) | electrochromism (electricity) | solvatochromism (solvent) | ionochromism (ions) | halochromism (pH) | tribochromism (friction) | piezochromism (pressure)