Project: Hydrogen Bonding Liquids |
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Using mainly dielectric relaxation experiments [69, 123, 127, 128, 153, 198, 212] and some solvation dynamics results [82, 114, 205], we explore the dynamics of hydrogen-bonding liquids in their viscous regime. The goal is to understand the origin of the large low-frequency Debye-type dielectric polarization and to identify the dielectric signatures of the true structural relaxation. The unusual features of the Debye peak are the differing behaviors compared with typical α-relaxations and the lack of equivalent signals in shear modulus or calorimetric data. |
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Activation traces of the three dielectric loss peaks of 2-ethyl-1-hexanol (2E1H). Symbols
are experimental results, lines are guides only. The inset shows the loss
spectrum at T = 166 K (equivalent to the dashed vertical line in main figure)
and identifies the correlation with the activation traces. [153] |
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Hydrogen-bonded liquids are important materials in many aspects. Therefore, it is of interest to understand the complex relation between thermodynamic and dynamic properties in these systems. The lower graph demonstrates that the main dielectric polarization fluctuates on time scales which differ from those of the calorimetric (and mechanical) processes. Here, this statement is justified by the lack of overlap of the time scales derived from dynamic heat capacity, Cp'', with those of the prominent dielectric loss peak, ε''. However, the Cp'' peak has a corresponding dielectric signal, the smaller 'true' α-process. |
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Comparison of the dielectric and calorimetric susceptibilities in terms of
Cp'' and ε'' for 2-ethyl-1-hexanol (2E1H).
Both quantities are measured at constant temperatures for various frequencies, but only
the 10 Hz results are shown here versus temperature. The dashed lines decompose the dielectric
loss into the Debye and non-Debye contributions. The main observation is that the prominent
dielectric Debye has no corresponding calorimetric signals. [153] |
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Non-linear impedance experiment on 5-methyl-3-heptanol at temperatures at which the Kirkwood correlation
factor gK is near unity, implying a balance of ring and chain structures where the two
species have similar free energies. Accordingly, an electric field should shift the equilibrium constant
towards more chains, resulting in a higher dielectric constant, as demonstrated in this experiment. Field induced relative increase of the non-instantaneous contribution to the permittivity versus frequency, calculated as (ε'hi - ε'lo) / (ε'lo - ε'∞) for 5-methyl-3-heptanol. Here, 'hi' and 'lo' refer to a field of E0 = 254 kV/cm and E0 = 14 kV/cm, respectively. Different curves are for different temperatures as indicated. Lines are fits according to a Debye type frequency dependence. The frequency dependence observed here suggests that structures fluctuate on the Debye time scale, or that the Debye peak of monohydroxy alcohols originates from fluctuations in the value of gK. [206, 212] |
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Reference numbers refer to the list of publications |
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Experimental techniques:
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Selected projects:
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