Understanding Water

Posted: August 12, 2009

page 2 of 3

As the temperature of water increases, fewer clumps exist but according to the report, they are always there to some degree, in clumps of a similar size. The researchers also discovered that the disordered regions become more disordered as the temperature rises. This more detailed understanding of the molecular structure and dynamics of liquid water at ambient temperatures mirrors theoretical work on "supercooled" water: an unusual state in which water has not turned to ice although it is far below the freezing point. In this state, theorists believe the liquid is made up of a continuously fluctuating mix of tetrahedral and more disordered structures, with the ratio of the two depending on temperature—just as Nilsson and his colleagues have found in water at ambient temperatures important for life.

This work partially explains water's unusual properties. According to the report, water's density maximum at 4 degrees Celsius can be explained by the fact that the tetrahedral structures are of a lower density, which does not vary significantly with temperature, while the more disordered regions of a higher density become more disordered and thus less dense with increasing temperatures. As water heats, the percentage of molecules in the more disordered state increases, allowing this excitable structure to absorb significant amounts of heat, which leads to water's high heat capacity. Water's tendency to form strong hydrogen bonds also explains the high surface tension that allows insects to walk across it.

According to the report, connecting the molecular structure of water with its bulk properties is important to many fields, ranging from medicine and biology to climate and energy research. "If we don't understand this basic life material, how can we study the more complex life materials—like proteins—that are immersed in water?" added postdoctoral researcher Congcong Huang, who conducted the X-ray scattering experiments, in the press release. "We must understand the simple before we can understand the complex."

How might this research impact the personal care industry? Considering that water is, 9 times out of 10, the first ingredient listed on a product label, it could immensely impact interactions between materials within a formula as well as the formula's long-term stability. As such, an improved understanding of its structure coupled with the knowledge of other material's structures holds the capacity to formulate for improved efficacy. But to Huang's point, the simple must be understood before the complex.

This research was conducted by scientists from SLAC, Stockholm University, Spring-8, University of Tokyo, Hiroshima University, and Linkoping University. The work was supported by the National Science Foundation, the Swedish Foundation for Strategic Research, the Swedish Research Council, the Swedish National Supercomputer Center and the Japanese Ministry of Education, Science, Sports and Culture through a Grant-in-Aid for Scientific Research.