Discover Top Posts Tagged with #ostwald ripening

Gravity Alters the Dynamics of a Phase Transition

An experiment uncovers the role played by gravity in Ostwald ripening, a spontaneous thermodynamic process responsible for many effects such as the recrystallization of ice cream. [...] What do magnets and decaf coffee have in common? Both involve physical systems that belong to the same “universality class.” Ferromagnetic materials are used to make magnets, and supercritical carbon dioxide extracts caffeine from coffee beans. At the critical point, when ferromagnetic and liquid–gas phase transitions occur, these two systems are described by the same critical exponents [1]. By identifying a system’s universality class, one can quantitatively characterize its behavior at the critical point without prior knowledge of microscopic details. Observing macroscopic properties suffices. However, taking that shortcut is often experimentally challenging, not least because many interesting systems are opaque to light. Now Raphael Saiseau of the University of Bordeaux in France and his collaborators have devised an ingenious experiment that enabled them not only to follow a phase transition but also to uncover the subtle and surprising effect of gravity on its dynamics [2].

How do nanoparticles grow? Atomic-scale movie upends 100-year-old theory

For decades, a textbook process known as "Ostwald ripening," named for the Nobel Prize-winning chemist Wilhelm Ostwald, has guided the design of new materials including nanoparticles—tiny materials so small they are invisible to the naked eye.

According to this theory, small particles dissolve and redeposit onto the surface of large particles, and the large particles continue to grow until all of the small particles have dissolved.

But now, new video footage captured by Berkeley Lab scientists reveals that nanoparticle growth is directed not by difference in size, but by defects.

The scientists recently reported their findings in the journal Nature Communications.

Enhancing crystal growth using polyelectrolyte solutions and shear flow

The process of examining characteristics of drug candidates thoroughly is essential for obtaining institutional approvals of new drugs for which high-quality crystallographic data are required. Indeed, growing large crystals of good quality from various substances serves a particular purpose for such processes and analyses. A recent study, affiliated with UNIST has introduced a novel crystal growth method, which enhances crystal growth 10 times faster than the average.

An international joint research team led by Distinguished Professor Bartosz Grzybowski (Schoool of Natural Science) has demonstrated that in the presence of polymers (preferably, polyionic liquids), crystals of various types grow in common solvents, at constant temperature, much bigger and much faster when stirred, rather than kept still. This overturns the idea that mechanical disturbances, such as bumping, swirling, or vibrations, interfere with the production of large and good-quality crystals.

Crystallization method typically begins with the formation of high-quality seed crystals that will be used to grow large single crystals. Thus, producing good-quality crystals of a suitable size is the most important step in the whole crystal structure process. To obtain properly-sized and good-quality crystals more rapidly, it is important to facilitate Ostwald ripening, the process of dissolution of smaller particles and the growth of larger particles at the expense of the smaller particles. It is common knowledge that mechanical disturbance of the crystal growing vessel can result in a large number of very small crystals, instead of a small number of large ones. This, then, hinders the growth of large single crystals.

Ostwald Ripening

Introduction Ostwald Ripening is a phenomenon in physical chemistry named after the German chemist Friedrich Wilhelm Ostwald. It describes the process where smaller particles within a solution dissolve, and the material re-deposits onto larger particles. The process leads to the growth of large particles at the expense of small ones, which results in an increase in the average particle size over…

View On WordPress

#Index #Ostwald Ripening #Surface Tension #Temperature