The puzzle of water solubilities of polyethers solved
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mizing the infiltration process could partially reduce the difference. Optical characterizations also revealed a significant hazing effect, likely due to air pockets in the material. This makes it best suited for applications close to a light source, such as protective display covers, say the researchers. They hope this research will spur efforts to quantify the structure–property relationships of the material, which could lead to enhanced mechanical and optical properties and a wider range of applications. The ETH approach offers a simple and scalable route to bulk materials with
a remarkable combination of transparency, strength, and toughness, according to Flavia Libonati, an expert in the toughening mechanisms of biological structural materials at the Politecnico di Milano. “This work demonstrates the possibilities of implementing microstructural nacre-like toughening mechanisms into glass-based materials, overcoming the intrinsic limitations of such materials, for example, brittle fracture, and offering a valid alternative to silica-based glasses for numerous applications,” she says. Kendra Redmond
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The puzzle of water solubilities of polyethers solved
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he anomalous water solubilities of polyethers have long puzzled researchers. Typically, increasing the oxygen-to-carbon ratio of an organic compound enhances its water solubility. This principle, however, is invalid in the case of polyethers. Polyoxymethylene (POM), a polyether with one carbon atom and one oxygen atom in its repeating unit ([–CH2–O–]n), is entirely insoluble in water. In contrast, poly(ethylene glycol) (PEG), a polyether having two carbon atoms and one oxygen atom in its repeating unit ([–CH2–CH2–O–]n), is infinitely water soluble. The origins of the polyethers’ counterintuitive water solubilities have remained a mystery for decades. Recently, a research team at the University of Amsterdam in The Netherlands led by Bernd Ensing and Sander Woutersen, together with Johannes Hunger and Mischa Bonn of the Max Planck Institute for Polymer Research in Germany, has shed light on this solubility puzzle for polyethers. Combining spectroscopic and computational techniques, the researchers concluded that the difference in the oxygen charge density dictated the water solubilities of polyethers. This was published in the journal Nature Communications (doi:10.1038/ s41467-019-10783-z).
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(a) Atomic charges (the numbers) of poly(ethylene glycol) (PEG) (left) and polyoxymethylene (POM) (right). The blue arrows are directions of electron-withdrawing forces. (b-d) Snapshots of the atom positions of (b) PEG molecules, (c) POM molecules, and (d) POM molecules with oxygen charge equal to that of PEG oxygen. Red, blue, and white spheres represent oxygen, carbon, and hydrogen atoms, respectively. The blue V-shaped sticks are water molecules. Credit: Nature Communications.
Computational simulations indicated that the oxygen atoms in PEG were more negatively charged than those in POM. Due to different electronegativities, oxygen atoms pull valence electr
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