Remember
back in the day when your favorite toys would change color underwater
or if you left them out in the sun for too long? As cool as it was back
then, an understanding of the science behind that color-changing
technology lends to a similar sense of amazement as it did so many years
ago. The mechanism behind this change is called thermochromism, wherein
a temperate variation produces a transition between two colors of the
visible spectrum.
Thermochromism is the property of substances to
change color due to a change in temperature. A mood ring is an
excellent example of this phenomenon, but thermochromism also has more
practical uses, such as baby bottles which change to a different color
when cool enough to drink, or kettles which change when water is at or
near boiling point. Thermochromism is one of several types of chromism.
Most
thermochromic materials are based on liquid crystal technology. At
specific temperatures, the liquid crystals re-orientate to produce an
apparent change of color. The liquid crystal material itself is
microencapsulated - 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, with plastics destined for injection molding.
There
are two primary ways to produce a thermochromic effect. The first is
through the use of liquid crystals. Thermochromic crystals have very
specific molecular structures depending on their temperature, and thus
rearrange themselves in different ways as temperature changes. As these
crystals rearrange, so too does the way they reflect light and color.
The other involves chemicals that change color depending on temperature,
wherein microcapsules containing a chemical rupture when passing a
certain thermal threshold before changing color. The mechanism is a
scientific wonder, but the application of such thermochromic elements is
what is both fun and surprising. Here are some of the best applications
of thermochromic material.
These
dyes can be applied to any variety of materials and have a low
threshold for color changes, which make for a very dynamic
transformation. Thermochromic dyes with a low threshold can be printed
on shirts, resulting in color changes depending on body temperature,
exposure to sunlight, etc., producing a tie-dye effect which can be very
visually striking or a more subtle change, depending on the contrast of
the thermochemically activated layer and the original color.
Thermochromism
doesn't always need to be a change between two colors. It can also
consist of a change between color and transparency, which has been
utilized in practical applications such as the new-to-market Print
cards. These cards are marketed for their "personality", wherein
handprints can be left on a surface, exposing a colorful background
against a white foreground. In reality, a thermochromic layer is placed
over an image. The heat of a human hand activates the chemical, which
then shifts to transparency.
Thermochromism isn't just restricted to fun/aesthetic purposes. The thermochromic color
paper proves the business utility of thermochromic materials. Thermal
printers are able to produce a high-resolution image on chemically
treated paper. Thermal barcode printers are the most common application.
The chemically treated paper is fed into the printer before a thermal
head is used to produce an image on the paper.
For More Information Click Here: Color changing pigment
