Materials scientists at the University of Michigan have developed a new material which stays liquid at very cold temperatures, but forms yellow crystals when touched that glow under UV light.
The liquid, which bears the catchy name of 'diketopyrrolopyrrole', was created by tweaking the molecular structure of a family of organic molecules commonly used in dyes and electronic devices. Different members of that family crystallise in two ways.
By balancing the two modes of crystallisation, the substance (which normally solidifies at about 133C) was able to remain in a stable 'supercooled' liquid state at temperatures all the way own to 5C - at which point it solidifies into a glass.
More interestingly, at temperatures above 5C the dark red liquid would immediately crystallise when rubbed with a stylus - turning bright yellow in the process. Its creator, Jinsang Kim, was able to write a message to his wife on a film of the liquid.
Its hoped that the unusual properties of the material could guide the development of new electronics and medicines. It's early days yet, but eventually it's hoped could be used in biosensors to reveal the characteristics of living cells, or used as a substitute for computer 'memory' that uses light rather than magnetism.