Dielectric Relaxation in Aqueous Solutions of Hydrazine and Hydrogen Peroxide:  Water Structure Implications

Abstract

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, T g . These solutions behave in a rather simple manner, reminiscent of the diols and diamines of which they are the limiting cases. Their relaxations near T g 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 % N 2 H 4 , the liquid exhibits precise time-temperature-superposition (TTS) behavior. At higher N 2 H 4 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, T 0 , lies close to the Kauzmann temperature, T K , determined earlier from calorimetric studies implying that the thermodynamic and kinetic measures of fragility are very similar. T g values assessed from T(τ)100s) agree well with observed calorimetric, T g 's. Extrapolation of the relaxation time behavior to pure water would imply a T g 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 T g 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. † Part of the special issue "Frank H. Stillinger Festschrift".

Resolving the controversy on the glass transition temperature of water?

“…The relaxation times from microwave measurements of solution of hydrazine mentioned in a previous section [48,49] overlap the bulk water data, as well as the relaxation times deduced from diffusion of bulk water data [83,95]. The lines are VFTH fits to the data of the hydrazine solutions published by Minoguchi et al [20,21]. Immediately above are the dielectric relaxation times of solutions of polyvinylalcohol (PVOH), polyvinylpyrrolidone (PVP) [96], and ethylene glycol (EG) with 90, 80, and 40 wt.% of water respectively.…”

“…open circles and open triangles) from [92,93,79,94] and the relaxation times deduced from diffusion data (cyan solid triangles) [83,95]; just above (green crossed diamonds) the relaxation times from microwave measurements of solution of hydrazine [48,49]. The violet and green lines are VFTH fits to the data of the hydrazine solutions published by Minoguchi et al [20,21]. Immediately above (blue squares) are the dielectric relaxation times of solutions of polyvinylalcohol (PVOH), polyvinylpyrrolidone (PVP) [96], and ethylene glycol (EG) with 30 (red open circles), and 40 wt% (black open circles) of water.…”

“…Their thermodynamic consideration indicates that near its melting point and for T > T H , water is practically the most "fragile" of all liquids. On the other hand, near and above the traditionally accepted T g = 136 K, earlier consideration by Angell [66,20,21] and reiterated by Ito et al has concluded that water is the least fragile. One argument for this is based on the extremely small and broad (relative to T g ) increase in the specific heat C P when glassy water is heated above 136 K, which is a characteristic of a least "fragile" or a very "strong" liquid.…”

“…This deduction supports that the dielectric (calorimetric) T g of pure water cannot be above 137.8 K (144 K). On the other hand, it is hard to rationalize the observed shift of the dielectric T g down to 137.8 K by mixing EG with 40 wt.% of water if the T g of pure water is 165 K or higher [43,44,20,21,22,24]. This is because the dielectric T g of neat EG located at about 150 K [33] is even lower than the hypothesized T g =165 K for water.…”

Transport in Amorphous Solid Water Films: Implications for Self-Diffusivity

“…Some are consistent with T g ≈ 136 K (calorimetry studies, [9][10][11][12][13][14][15][16][17] blunt probe measurements, 18 dielectric studies, 19-23 extrapolation of binary solution data, 3,24 diffusion studies, 25,26 time-of-flight secondary ion mass spectrometry (TOF-SIMS) studies 27,28 ), while others (dielectric studies, [29][30][31] isotope exchange studies, 32 differential scanning calorimetry (DSC) studies/scaling arguments 24,[33][34][35][36] , soft-landed ions 37 ) suggest T g > 160-165 K. 34,35 In the latter case, observation of T g would be masked by crystallization upon heating near T ≈ 150 K. While the "conventional" assignment of water's glass transition temperature is T g ≈ 136 K, this assignment is not universally accepted.…”