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Microscopic inclusions of aqueous fluids trapped in interstices in quartz and other crystals provide novel systems for the deliberate study of liquids under tension. Liquids under tension should differ in interesting ways from those at ambient pressure or compressed liquids because attractive, rather than repulsive, forces should dominate their behavior. Static tensions in excess of 100 megapascals (~1000 atmospheres) have been obtained reproducibly. Video-recorded observations of the final liquid rupture process, coupled with extrapolations of data at positive pressure, suggest that the homogeneous vapor nucleation point was reached in two of the cases studied. Raman spectra of the fluids at -80 megapascals show that an isothermal volume stretch of -5 percent by volume has only a weak effect on the spectral features and is similar to the effect of isobaric heating.

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ABSTRACT. We review the behavior of a variety of liquids and polymers in which the presence of hydrogen bonding is of special importance to the liquid state properties. In particular we consider the case of a series of disubstituted benzenes in which appropriate changes of substitutents can systematically "turn on" hydrogen bonding between the molecules and the cases of ionic and non-ionic aqueous solutions in which change of water content changes the "fragility" in different directions. Finally we show how in hydrated biopolymers the presence of hydrogen bonding leads to the least fragile behavior yet observed in molecular systems. Where the p;esence of hydrogen bonding has previously been seen as conferring moderately "strong" liquid behavior on molecular liquids, we cite here cases in which either strong or fragile behavior can be seen, and an important case (water) in which there is apparently a transition from fragile to strong behavior as temperature is decreased. IntroductionAmong glass-forming liquids, hydrogen bonded liquids tend to be unusual with respect to their supercooling propensity and their behavior in the supercooled state. We have previously noted( I) that they tend to vitrify more readily than the general rule Tb/T m > 2.0( I ,2) would indicate (e.g. for the classical, widely studied, highly crystallization-resistant case of glycerol, Tb/T m = 1.7) and that in the supercooled liquid state they tend to have large activation energies and relatively small departures from Arrhenius behavior. Also, the liquid ranges, defined by the ratio Tb/T g(3,4), tend to be smaller than for molecular liquids of similar constitution but lacking H-bonds. Crudely, one can observe that for paraffins Tb/T g -4, for M.·C. Bellissent·Funel and J. C. Dore (eds.), Hydrogen Bond Networks, 3-22. © 1994 Kluwer Academic Publishers. 4 aromatics or paraffins with H-bonds , Tb / T g -3, while for aromatics with H-bonds , Tb!T g -->2. Some examples will be given in the course of this paper.In recent times it has become quite common to di scuss departures from Arrhenius behavior and other related propertie s (non-exponentiality and nonlinearity [or state dependence] of re laxation) in terms of the strong/fragile liquids classification, and it is this scheme which we will utilize here to systematize the discussion of several classes of hydrogen bonded liquids including polyalcohols and water, aqueous solutions and hydrated polymers . Strong/Fragile Liquid ClassificationThe strong/fragile classification scheme for liquids< 5,6) is based on a corresponding states representation of the liquid relaxation behavior, which is commonly represented by the widely available property, vi scosity (though generally it is preferable to represent the behavior by a structural relaxation time). The key notion involved is that the glass transiti o n temperature provides an appropriate scaling temperature for corresponding states comparisons. Insert: change in heat capacity observed at the glass transition temperature, also in normalized form....