Project: Dielectric Relaxation |
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With various experimental techniques, we are studying the dielectric properties of liquids, supercooled liquids, polymers, biological materials, and glasses [47, 51, 60, 69, 77, 79, 85, 88, 97, 107, 111, 122, 123, 132, 133, 148, 158, 165, 183, 189, 198, 202, 209, 213]. The dielectric polarization measured as ε*(ω) and as M*(ω) lead to curves which differ in the characteristic time scales and in the way they are affected by electrode polarization [75, 84, 210]. However, the information regarding the motion of dipoles and ions is independent of the applied method [103, 160]. |
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Schematic comparison of the dielectric function ε*(ω) with its equivalent modulus
M*(ω). All curves are based upon the same dielectric properties:
an exponential relaxation process and a low dc- conductivity. |
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Our interest here is to understand the temperature dependence of the relaxation times and its relation to the distribution of relaxation times and to dynamic heterogeneity. We are exploring the dielectric behavior of materials with extremely low dielectric loss, like decalin [107], squalane [111], ααβ -tris-naphthylbenzene [111], and o-terphenyl [132, 141]. |
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Master plot of the dielectric loss ε''(ω) of neat
cis/trans-decahydro-naphthalene (DHN) versus reduced frequency f/fmax
in the range 10-2 ≤ f/fmax ≤ 106.
The data are derived from measurements taken at temperatures in the range 138 K ≤ T ≤ 150 K,
in steps of 2 K. In this series of experiments, the loss tangent tanδ remains below
6×10-4. [107] |
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Example of a simultaneous dual-channel dielectric measurement: Difference of logarithmic relaxation time in terms of log(τCh1) - log(τCh2) versus temperature, with 'Ch1' and 'Ch2' referring to the upper and lower capacitor, respectively. The curves are based upon four measurement, identified by the type of 1-propanol in Ch1 and Ch2, 1-POH or 1-POD. In the order of Ch1/Ch2, the sample configurations were: No.1: 1-POH/1-POH (squares), No.2: 1-POH/1-POD (triangles up), No.3: 1-POD/1-POH (triangles down), and No.4: 1-POH/1-POH (diamonds), with measurement No.1 and No.4 being nominally identical. The upper data (dots with error bars) represent the logarithmic relaxation time difference between 1-propanol-OH and 1-propanaol-OD (deuterated) shown as log(τ1-POD) - log(τ1-POH), and their errors, based on the four measurements. [198] |
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Example of a dual-channel dielectric measurement on an interdigitated electrode cell: (left) Dielectric loss spectra of 600 nm ultrastable IMC films at different times when annealed at Tann = 325.0 K. Loss amplitudes rise with increasing annealing time. The lines are best HN fits using the same relaxation time and shape parameters that describe the conventional IMC supercooled liquid. (right) The relaxation intensity obtained by HN fitting as a function of time for 600 nm ultrastable IMC films annealed at the same sequence of annealing temperatures. The dashed line shows the value of Δε for the completely transformed film, the solid lines are linear fits for Δε(tann) during the transformation, and the area shaded grey indicates the estimated total time scale for the transformation. [207] |
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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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