Dance

Ecology

Biology

Ephemeral key

Visual arts

Business

Finance

Order (exchange)

Proceedings of the National Academy of Sciences

The freezing of a liquid into a crystalline solid is a ubiquitous and familiar phase transition that affects many aspects of our daily life. The crystallization of water, for example, has broad implications for our planet’s climate and geography, and for diverse applications ranging from food and energy production to pharmaceutical formulation (1, 2). Nevertheless, numerous facets of crystallization remain incompletely understood because of the limited ability of experiments to resolve the molecular processes that initiate freezing in liquids. One particularly intriguing mystery is the possible connection between freezing and the dramatic changes observed in the dynamics of liquids cooled below their melting temperature, T m (3, 4). In PNAS, Fitzner et al. (5) report results from computer simulations that offer a revealing glimpse into the microscopic connection between these phenomena in water.The immutable laws of thermodynamics dictate that a liquid will freeze when cooled below T m, but they do not specify how, or on what time scale, this process will occur (1). Our experiences with liquid water, which readily freezes in the environment when cooled below its melting point T m = 0 °C at ambient pressure, may suggest that crystallization is relatively swift. Yet, it is often delayed, or arrested indefinitely, in other scenarios. Without impurities or surfaces to promote crystallization, gentle cooling below T m produces a supercooled liquid phase that can survive in a state of precarious metastable equilibrium (1, 6). Rapid cooling below the glass transition temperature T g ≪ T m, by contrast, produces an amorphous solid known as a glass that will not crystallize on experimentally observable time scales (6, 7). For water, the supercooled liquid has been studied down to −46 °C (8); at atmospheric pressure, it can exist as a glass below T … [↵][1]1Email: jcpalmer{at}uh.edu. [1]: #xref-corresp-1-1

From water’s ephemeral dance, a new order emerges