Is glass a solid or a super slow liquid? Physicists create equilibrium glassy phase from rod-shaped particles

Glass appears to be a solid, but in theory it sometimes behaves more like an extremely slow liquid. Physicists in Utrecht now show that glass-like structures can also exist in equilibrium, which is something many theories say should be impossible. The bottom parts of medieval window panes, such as those in old cathedrals, are often thicker than the top. Has the material slowly flowed downward over the centuries, and does this mean that glass actually flows? This is a persistent myth, and the explanation lies in the way glass was produced in the Middle Ages. Because window panes were made by hand, their structure was often irregular and contained thinner and thicker parts. The panes were usually installed in the frame with the thicker side at the bottom, which made them more stable. Still, the story touches on a real physics question. What glass actually is, a solid or a very slow liquid, turns out to be more difficult to answer than it seems.

03.04.19

Chemical pathway unlocks next-generation infrared III–V nanocrystals

A research team led by Professor Sohee Jeong at Sungkyunkwan University has uncovered a key chemical pathway for the controlled synthesis of III–V semiconductor quantum dots, a class of next-generation infrared materials expected to play an important role in autonomous driving sensors, smart sensing systems, night-vision devices, and short-wave infrared optoelectronics. The study was conducted in close international collaboration with Professor Maksym V. Kovalenko's group (SIEST faculty) at ETH Zurich and published in the Journal of the American Chemical Society under the title "Metal–Amide Chemistry Enables Controlled Heavy-Pnictogen Reduction for Colloidal III–V Nanocrystal Synthesis." As infrared-based technologies become increasingly important in daily life, including nighttime object recognition for autonomous vehicles and smart home devices, the demand for high-performance infrared semiconductor materials continues to grow.

Microscopic sensors uncover how liquids turn glassy without structural change

A scientific discovery by researchers at Tel Aviv University's School of Chemistry offers a new perspective on a long-standing scientific mystery: how does a flowing liquid suddenly become a rigid, almost frozen material, without changing its structure? This phenomenon, known as the "glass transition," has puzzled physicists for over a hundred years. The study proposes a new experimental approach to observing this elusive process—by tracking the motion of tiny particles that serve as microscopic "sensors" within the material. The study was conducted by Prof. Haim Diamant and Prof. Yael Roichman of the School of Chemistry at Tel Aviv University, together with the research group of Prof. Stefan Egelhaaf at Heinrich Heine University Düsseldorf. The findings were published in the journal Nature Physics.

A smart fluid that can be reconfigured with temperature

Imagine a "smart fluid" whose internal structure can be rearranged just by changing temperature. In a new study published in Matter, researchers report a way to overcome a long-standing limitation in a class of "smart fluids" called nematic liquid crystal microcolloids, allowing for reconfigurable self-assembly of micrometer-sized particles dispersed in a nematic liquid crystal host. The persistent challenge has been that conventional microparticles can induce strong distortions and topological defects in the liquid crystal, which in turn can drive irreversible sticking and clumping, making it difficult to reach equilibrated, reconfigurable states. Here, the team has developed porous, rod-shaped silica microrods with "slippery" surface treatment that can form dense dispersions that remain fluid-like while reorganizing with temperature.

Researchers combine five metals to build a better nanocrystal

A nanocrystal is an extraordinarily tiny piece of material—composed of anywhere from a few to a few thousand atoms—in which atoms are arranged in a precise, ordered structure. Think of it like taking a piece of gold and shrinking it down to the size of a few hundred atoms. It's still gold, still crystalline, just almost incomprehensibly small. Nanocrystals are in the transistors inside computers and smartphones, in smartphone displays and TV screens, in the gold-nanoparticle sensors that power COVID and pregnancy tests, and in the pipes of your car exhaust system, among countless other innovations. Their small size gives them a dramatically higher ratio of surface area to volume, making them especially useful as catalysts—materials that speed up chemical reactions without being consumed in the process.