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Hypercolor
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==Principle== Substances that can change color due to a change in temperature are called [[thermochromism|thermochromes]]. There are two common types of thermochromes: [[liquid crystal]]s (used in [[mood ring]]s) and [[leuco dye]]s (used in Hypercolor T-shirts). The color change of Hypercolor shirts is based on combination of two colors: the color of the dyed fabric, which remained constant, and the color of the thermochromic dye. Droplets of the thermochromic dye mixture are enclosed in transparent [[microcapsule]]s, a few micrometers in diameter, bound to the fibers of the fabric. [[Image:Crystal_violet_lactone_reaction.svg|thumb|300px|Transformation between leuco and colored form of crystal violet lactone in response to varying acidity, which is caused by changing temperature]] The thermochromic droplets are actually a mixture of several chemicals—[[crystal violet lactone]] (the color-changing dye itself), [[benzotriazole]] (a [[weak acid]]), and a [[quaternary ammonium salt]] of a [[fatty acid]] (myristylammonium oleate) dissolved in [[Dodecanol|1-dodecanol]] as solvent. Together, these lead to a reversible chemical reaction in response to temperature change that produces a change of color. At low temperatures, the mixture is a solid. The weak acid forms a colored complex with the leuco dye by causing the [[lactone]] ring in the center of the dye molecule to open. At high temperatures, above {{convert|24|–|27|C|F}}, the solvent melts and the ammonium salt [[dissociation (chemistry)|dissociates]], allowing it to react with the weak acid. This reaction increases the [[pH]], which leads to closing of the lactone ring of the dye to convert it to its colorless (leuco) form. Therefore, at the low temperature the color of the shirt is the combination of the color of the encapsulated colored dye with the color of the dyed fabric, while at higher temperatures the capsules become colorless and the color of the fabric prevails.
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