User:LIND2005/sandbox/Thermochromic Ink

Introduction
Thermochromic ink (aka thermochromatic ink) is a specially designed type of dye that changes color in correspondence to a change in its temperature. It was first used in the 1970's within novelty toys like mood rings, but has found some practical uses in things such as thermometers, product packaging, pens. This ink has also found applications within the medical field for specific medical simulations in medical training.

Composition
There are two main variants of the ink; one composed of leuco dyes and one composed of liquid crystals.

Leuco Dyes
The leuco dye variant is typically composed of the leuco dyes with additional chemicals that adds different desired effects. It is the most commonly used type because it is easier to manufacture. They can be designed to react to changes in temperature that range from -15° C to 60° C. Most common applications of the ink has activation temperatures at ~ -10° C (cold), ~ 31° C (body-temperature), or ~ 43° C (warm). When at lower temperatures, the ink is dyed a certain color, and once the temperature increases, the ink becomes either translucent or lightly colored, which allows hidden patterns to be seen. This gives the effect of a change in color, and the process is also reversible as you can bring the temperature down to lower levels to make the original dyed color visible again.

Liquid Crystals
The properties of liquid crystals can change from liquid to solid in response to a change in its temperature. At lower temperatures, the crystals are mostly solid and hardly reflect any light, causing it to look black in this phase. As it gradually increases in temperature, the crystals become more spaced out, causing light to reflect differently and changing the color of the crystals. The temperatures at which these crystals can react range from -30° C to 90° C.

For both types of thermochromic ink, the chemicals need to be micro-encapsulated into extremely small capsules that are around the size of 3 to 5 microns. This protects the dyes and crystals from mixing with other chemicals that might affect the functionality of the ink. This ink contains ions with m/z (grams per charge) levels of 245 m/z, 356 m/z, 467 m/z, 578 m/z, 689 m/z, and 800 m/z. These ions come from a chemical called polyvinylpyrrolidone (PVP) (Chemical formula C6H9NO).

Medical Uses
In medical training, thermochromic ink can be used to imitate human blood because it shares its color changing property. It is currently being tested in medical simulations involving extracorporeal membrane oxygenation (ECMO). In these procedures, a change in color of blood between a dark and light red indicates blood oxygenation and blood deoxygenation, which describes the oxygen concentration levels within a person's blood sample. It's important to accurately identify this change in order to safely and correctly operate the ECMO machines. This has led to simulation-based trainings (SBT) which allows medical students to run simulations that mimic real ECMO machines before using them in serious situations. By using thermochromic ink in these simulations, the color changing effect can be realistically copied and observed without using real human blood or other costly methods.

Artificial blood or animal blood are typically used in these simulations, however there are some advantages in using thermochromic ink as an alternative. It can be reused for multiple simulations with minimal variance in the outcomes and it is more cost effective. There are limitations to using this as the ink does not share any other properties with blood, so it's only practical use is to observe the change in color of blood.

Product Packaging
Product packaging is an important aspect of maintaining the quality of consumer goods. Modern day packaging is split into 2 categories; active packaging and smart packaging. Thermochromic ink has found use in smart packaging, which is the aspect of packaging that deals with monitoring the condition of the products. Since most of the consumer goods are affected by changes in temperature, using thermochromic ink as an indicator of those temperature changes allows consumers to recognize when the quality of a product has changed. It can also be used to tell consumers the right temperatures to consume the product.

Erasable Ink Pen
In 2006, Pilot Pens Inc. developed a pen with erasable ink that utilized thermochromic ink. It was composed of a solvent, a colorant, and a resin film-forming agent. At temperatures below 65° C, the ink stayed in a colored state. Once temperatures went above 65° C, the ink began to melt and became colorless, creating the effect of erasable ink. The ink was able to return to its colored state by cooling the temperature down to below -10° C.