Using an X-ray light source, PETRA III, at Deutsches Elektronen-Synchrotron (DESY), a team of scientists from the Autonomous University of Madrid has developed a 3D printable material that can detect water. The material is cheap, flexible, non-toxic, and can change its color from purple to blue when wet. The development of the material was recently published about in Advanced Functional Materials.
“Understanding how much water is present in a certain environment or material is important,” says Michael Wharmby, co-author of the paper and DESY scientist. “For example, if there is too much water in oils they may not lubricate machines well, whilst with too much water in fuel, it may not burn properly.”
From the DESY article "The functional part of the scientists’ new sensor-material is a so-called copper-based coordination polymer, a compound with a water molecule bound to a central copper atom. 'On heating the compound to 60 degrees Celsius, it changes colour from blue to purple', reports Pilar Amo-Ochoa. 'This change can be reversed by leaving it in air, putting it in water, or putting it in a solvent with trace amounts of water in it.' Using high-energy X-rays from DESY's research light source PETRA III at the experimental station P02.1, the scientists were able to see that in the sample heated to 60 degrees Celsius, the water molecule bound to the copper atoms had been removed. This leads to a reversible structural reorganisation of the material, which is the cause of the colour change.
'Having understood this, we were able to model the physics of this change,' explains co-author José Ignacio Martínez from the Institute for Materials Science in Madrid (ICMM-CSIC). The scientists were then able to mix the copper compound into a 3D printing ink and printed sensors in several different shapes which they tested in air and with solvents containing different amounts of water. These tests showed that the printed objects are even more sensitive to the presence of water than the compound by itself, thanks to their porous nature. In solvents, the printed sensors could already detect 0.3 to 4 per cent of water in less than two minutes. In air, they could detect a relative humidity of 7 per cent."
Read more about the 3D printed color changing water sensor at DESY.