Number 365 (Story #2), April 2, 1998 by Phillip F. Schewe and Ben Stein|
TWO FORMS OF LIQUID WATER MIGHT COEXIST at very low temperatures, possibly shedding light on why water has such unusual properties compared to other liquids. For example, water shrinks when warmed from 0 to 4 degrees Celsius, while most other liquids expand whenever they're heated. At the recent APS March Meeting in Los Angeles, Gene Stanley of Boston University (email@example.com) and Osamu Mishima of the National Institute for Research in Inorganic Materials in Japan (firstname.lastname@example.org) presented a new study of supercooled water, subzero-degree H2O that exists as a liquid because it is particularly pure or under high pressure. (Mishima & Stanley, Nature, 12 March 1998) Working with ice IV, one of the 14 known solid forms of H20, they discovered that melting the sample required drastically different pressures below a temperature of 220 K, consistent with the possibility that the supercooled water may undergo a transition between two liquid structures or "phases." In this scenario, one phase is hypothesized to contain large clusterings of water molecules at short distance scales while the other phase would have smaller congregations of the molecules at these scales. For two phases of supercooled water to coexist would suggest the existence of a "critical point" which could consequently influence the properties of water all the way up to room temperatures and pressures. Alternative explanations exist; for example, perhaps water stays in one form but dramatically changes its density and its entropy (amount of disorder) at decreasing temperature and increasing pressure. Still, recent neutron scattering experiments in supercooled water (M.-C.Bellissent-Funel, email@example.com, Europhysics Letters, 15 April 1998) support the two-phase picture for the liquid.