Unsolved Mysteries of Water in Its Liquid and Glass States
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by simulations of what is sometimes called "Computer water." These simula tions are useful because some of the problems associated with doing experi ments on real water can be obviated using Computer simulations.
I would like to begin with a kind of kitchen experiment that any of you can do. Take your favorite drink. For some, this is ice water (Figure 1). Ask a simple question: "Whatshould this thermometer read?" And think for a minute of the implications of the answer to your question. The title of this talk concerns water in two different states: the liquid State and the glass State. We'll organize this talk around three questions: ■ "What is the puzzle of liquid water?" ■ "Why do we care about this puzzle?" ■ "What do we actually do?" The "we" in this case is a rather large number of individuals. TU focus this talk on very recent work that has been published or at least submitted this year. This work was done in collaboration with M.-C. Bellissent-Funel, S.V. Buldyrev, M. Canpolat, M. Meyer, O. Mishima, M.R. Sadr-Lahijany, A. Scala, a n d F.W. Starr. It's also based on earlier research a few years back with C A . Angell, P.G. Debenedetti, A. Geiger, RH. Poole, S. Sastry, F. Sciortino, and J. Teixeira. Any of these 15 valued collaborators could probably give this talk as well as, if not better than, I will. We will organize the answer to our third and principal question in the following way: First, we will attempt to identify, in the spirit of Sherlock Holmes, some interesting clues. Then, we'll formulate a working hypothesis and test it, both by experiments on real water and
Figure 1. A glass ot unstirred ice water with a thermometer reading 4"C at the bottom of the glass. Photograph courtesy of K. Mishima.
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Before beginning, let's note that there are some very good general references on liquid and glassy water. A recent book entitled Metastable Liquids] is a kind of sequel to Skripov's classic on this subject. There's an even more recent book called Supercooled Liquids, published by the American Chemical Society, 2 and there's a very recent seven-page minireview.3 Finally, and perhaps most interestingly, the accomplished science writer Philip Ball has just prepared a book that surveys the entire story of water, f rom the earliest times to the present 4 —responding perhaps to the fact that water is one of the most appealing of the open puzzles in all of science.
What is the Puzzle of Liquid Water? We Start with the first question: "What is the puzzle?" There are many puzzles associated with water. First, water exists in many forms. All of us are familiär with one important control parameter that distinguishes these forms, namely, temperature (Figure 2). Stable water is the form of water that one is familiär with when one discusses biology. In reality, much of biology takes place when water is in a supercooled regime. Why is
Figure 2. Schematic Illustration indicating the various phases of liquid water (color coded) that are found at atmospheric pressure. Courtesy of O. Mishima.
MRS BULLETIN/MAY 1999
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