J. Phys. Chem. B 2004, 108, 19825-19830
19825
Dielectric Relaxation in Aqueous Solutions of Hydrazine and Hydrogen Peroxide: Water
Structure Implications†
Ayumi Minoguchi, Ranko Richert, and C. Austen Angell*
Department of Chemistry and Biochemistry, Arizona State UniVersity, Tempe, Arizona 85287-1604
ReceiVed: June 29, 2004; In Final Form: October 28, 2004
We report dielectric relaxation studies of aqueous solutions of two water-like molecules, hydrazine and hydrogen
peroxide, in the neighborhood of their glass transition temperatures, Tg. These solutions behave in a rather
simple manner, reminiscent of the diols and diamines of which they are the limiting cases. Their relaxations
near Tg are more nearly exponential than in most other cases, and they show essentially no secondary relaxations.
Supercooled hydrazine solutions are the more stable. At the composition 20 mol % N2H4, the liquid exhibits
precise time-temperature-superposition (TTS) behavior. At higher N2H4 contents, a weak deviation from
TTS appears. The temperature dependence of the relaxation time follows the Vogel-Fulcher-Tammann
(VFT) equation, and the strength parameter, D, is similar to that of glycerol, a liquid of intermediate fragility.
The VFT divergence temperature, T0, lies close to the Kauzmann temperature, TK, determined earlier from
calorimetric studies implying that the thermodynamic and kinetic measures of fragility are very similar. Tg
values assessed from T(τ)100s) agree well with observed calorimetric, Tg’s. Extrapolation of the relaxation
time behavior to pure water would imply a Tg for water of 135-140 K; however, the dielectric behavior of
amorphous solid water in the temperature range 130-160 K is completely different from that of the solutions
showing no sign of the loss peak exhibited by all the solutions. Based on the solution behavior, water
controversially must either remain glassy up until the temperature of crystallization or be an almost ideally
strong liquid above 136 K. Having shown elsewhere how this implies glassy character up to LDA crystallization
and a Tg above 160 K, we now examine the implications for water structure reorganization on dissolution of
solutes, certain glycols excepted. It appears that the water in these solutions behaves like ice III rather than
ice I.
Introduction
The liquids hydrazine and hydrogen peroxide are very waterlike in their melting (-1.6 and 1.9 °C) and boiling (157.9 and
113.6 °C) behavior. In the range above melting, their viscosities
and dielectric constants are also water-like, and it is only in the
supercooled liquid range that more significant differences
appear. The anomalies of supercooled water, such as the famous
density maximum (at 4 °C)1 and the diverging heat capacity,
viscosity, and relaxation times (at -45 °C),2 are not shared by
the others nor by their binary solutions with water. In fact their
binary solutions have been used as a basis for separating the
“anomalous” component of water from the “normal” background
component.3
Aqueous solutions of hydrazine and hydrogen peroxide,
unlike water itself, vitrify quite readily on rapid cooling to liquid
nitrogen temperatures.4 Their glass transition temperatures are
very easy to detect because of the exceptionally large (>100%)
increases of heat capacity that occur on passage through the
glass transition.3 Glass transition temperatures, Tg, for vitrified
solutions were reported a long time ago,4,5 and they have values
in the range 135-140 K. These values are very similar to that
generally attributed to water itself, largely on the basis of
extrapolations of binary solution data.2,4-6
Measurements made directly on the vitreous forms of water
prepared by different methods, on the other hand, have yielded
ambiguous results. These have been reviewed in refs 7 and 8
†
Part of the special issue “Frank H. Stillinger Festschrift”.
and will not be revisited here. The methods of preparation, also
reviewed in refs 7 and 8, range from vapor deposition,9 through
hyperquenching,10 to pressure-induced amorphization,11 where
only the first examples of each type are cited here. In the lowdensity forms, known variously as low-density amorphous solid
water (ASW),12 hyperquenched glassy water (HQGW),13 and
low-density amorphous water (LDA),11 the various preparations
have very similar structures, though subtle differences in their
relaxation behavior have been noted and have lead to the
suggestion that there are actually distinct forms of water (waters
A and B14) of the low-density amorph, even above Tg in the
putative ultraviscous liquid state. Arguments intended to resolve
these sources of confusion by showing that the proposed glass
temperature of pure ambient pressure water actually falls above
the crystallization temperature have been made15,16 but not
generally accepted.17,18
Since the glass transition is a relaxation phenomenon dependent on the motion of molecules on long time scales (order
of minutes at Tg), it would seem reasonable to seek resolution
of phenomenological puzzles by bringing the most precise of
relaxation-sensitive techniques available to bear on the problem.
The most sensitive method available for the study of slow
processes in condensed matter is unquestionably dielectric
spectroscopy. The dielectric relaxation time of a molecular liquid
can now be determined over a range of 20 orders of magnitude,
from times as long as one year19 to values as short as 10-14 s.20
Although dielectic relaxation studies of N2H4-H2O and H2O2H2O solutions near ambient temperature have been made,21,22
10.1021/jp0471608 CCC: $27.50 © 2004 American Chemical Society
Published on Web 11/11/2004