One Added Molecule Rewires Glass From the Inside as It Melts
Chemists rewired the structure of MOF glass by adding phenanthroline to the melt, lowering its melting point. Here is how it works and what it could lead to.
Chemists in Germany and the UK have found a way to change the inner chemistry of a special kind of glass while it is still liquid. They add one organic molecule, 1,10-phenanthroline, to the starting powder. As the mix melts, the molecule lowers the melting point and also attaches itself to the metal atoms inside, reshaping how those atoms bond to their neighbors.
The study appeared in the journal Nature Materials. It was led by Sebastian Henke of TU Dortmund University, with partners at Paderborn University, the University of Duisburg-Essen and the University of Oxford. The team says the method gives it control over properties such as magnetism and light emission in glasses that would otherwise break down when heated enough to melt.
Glass made from metal-organic frameworks
Ordinary glass forms when a melt cools fast enough that its atoms freeze in a jumble instead of lining up into a crystal. The glasses in this study start from metal-organic frameworks, or MOFs: solids built from metal centers held together by organic molecules. MOF glasses are being studied for gas storage, batteries, optics and catalysis.
Until now, Henke said in a statement from Paderborn University, researchers usually had to live with whatever chemistry the starting material handed them. Some MOFs also start to decompose before they melt, which damages the structure and leaves impurities in the final glass.
How phenanthroline changes the melt
The added molecule has two jobs. As a flux, it brings down the temperature at which the material turns liquid. As a reactant, it binds to the metal atoms and pushes some of the original bonds aside.
Chemists call the arrangement of atoms around a metal its coordination environment. Because phenanthroline grips the metal centers more tightly than the original links, each metal atom ends up with more neighbors. That shift reorganizes the glass network, and the researchers can set how far it goes by changing how much phenanthroline they add.
“The molecule does not simply remain as a filler,” Henke said, adding that it takes part in a reaction while the material is liquid.
Cobalt glasses melted without breaking down
Matthias Bauer of Paderborn University said the cobalt-containing glasses melted at much lower temperatures with the new method and stayed stable, without the harmful decomposition products that form under harsher heating. That matters for magnetism studies, because impurities can blur measurements and hide how the glass itself behaves.
Glass has no repeating atomic pattern, so standard X-ray diffraction reveals little about its structure. The team turned to X-ray absorption spectroscopy, among other methods, to look at the space right around the cobalt atoms. The cobalt kept the same oxidation state, meaning it gained or lost no electrons, but the bonds around it were rearranged to make room for phenanthroline. That result showed the molecule changes the glass chemically and does more than help it melt.
What it means for new glass materials
The method also worked on glasses made from carboxylate-based frameworks, a second family of MOFs, which suggests it could apply to a wider range of materials. Henke described the melt as a space where the team can “program the structure” instead of a fixed in-between stage.
The researchers list possible uses in chemical catalysts, sensors and optoelectronic devices, which work with both light and electricity, as well as glasses built to control magnetic behavior or steer light. These uses remain goals for now. The published work shows the chemistry in laboratory samples, and no products have been announced.
Source: ScienceDaily
