B. Schiener

Nonresonant Spectral Hole Burning in the Slow Dielectric Response of Supercooled Liquids

Large-amplitude, low-frequency electric fields can be used to burn spectral holes in the dielectric response of supercooled propylene carbonate and glycerol. This ability to selectively modify the dielectric response establishes that the non-Debye behavior results from a distribution of relaxation times. Refilling of the spectral hole was consistent with a single recovery time that coincided with the peak in the distribution. Moreover, refilling occurred without significant broadening, which indicates negligible direct exchange between the degrees of freedom that responded to the field. Nonresonant spectral hole burning facilitates direct investigation of the intrinsic response of systems that exhibit nonexponential relaxation.

Dielectric relaxation in the fragile viscous liquid state of toluene

Dielectric measurements were carried out on viscous toluene covering a frequency range from 0.1 Hz to 1 MHz. In order to suppress the pronounced crystallization tendency of this supercooled liquid it was contained in thin walled capillaries with outer diameters of 300 μm. From the temperature dependence of the characteristic dielectric relaxation times it was found that toluene is one of the most fragile low molecular weight glass-forming liquids, with a fragility index m=105. By comparison with time constants available from other experimental techniques it appears that near the glass transition the dielectric relaxation mode is not the slowest one.

Dielectric relaxation in supercooled 1-propanol

Abstract By combining time- and frequency-domain techniques, the dielectric response of 1-propanol has been measured in a spectral range covering eleven decades. In particular it has been demonstrated that the dielectric loss due to the main relaxation in 1-propanol exhibits the Debye width up to timescales of 1000 s. In order to extend the range in which the dynamics of propanol can be exploited to high temperatures, conductivity relaxation due to ionic impurities has been used. The occurrence of high-frequency relaxation processes has been studied in both isomers of propanol. It is shown that the 1-propanol data yield a master curve in a previously suggested scaling representation. However, owing to the presence of the high-frequency excitations, no agreement with the universal scaling form is obtained.

Pulsed dielectric spectroscopy of supercooled liquids

Pulsed dielectric spectroscopy is introduced as a technique for selectively emphasizing specific components of the non-exponential dielectric response of matter. Samples studied include supercooled liquid propanol, propylene carbonate, and poly(lauryl-methacrylate). It is shown that particular sequences of pulses can be used to emphasize the fast response regime, to produce a cross-over or memory effect, or to eliminate the response of selected components. Furthermore, for materials characterized by broad distributions of relaxation times, the technique facilitates the investigation of a relatively narrow band from that distribution. It is also shown that the time domain spectroscopy can be combined with conventional frequency domain techniques to provide the characterization of dielectric response over an extraordinarily broad spectral range.

Dielectric study of supercooled triphenylphosphite and butyronitrile: Comparison with a mesoscopic model

Abstract Dielectric relaxation has been studied in the supercooled liquids triphenylphosphite (TPP) and butyrontrile (BN). BN is relatively strong according to Angells classification and can be characterized by a fragility index m = 47. TPP, on the other hand, appears to be the most fragile non-polymeric liquid studied so far (m = 160). The dielectric response of the two glass-formers exhibits different degrees of non-exponentiality which is analyzed in terms of a mesoscopic model of dynamically correlated domains. The relation of this model to the strong versus fragile liquid classification scheme is discussed.

Dielectric Spectroscopy at High Frequencies on Glass Forming Liquids

Dielectric spectroscopy up to 950 GHz has been performed on various glass formers as glycerol, propylene-carbonate, and Salol. Special attention is given to the dielectric loss, {epsilon}{double_prime}, in the crossover regime from the {alpha}-relaxation to the far-infrared (FIR) response where it can be directly compared to the dynamic susceptibilities obtained by neutron and light scattering techniques. The authors observe a minimum in {epsilon}{double_prime} ({nu}) at high frequencies which cannot be explained by a simple transition from {alpha}-relaxation peak to the FIR bands but has to be attributed to additional fast processes. In all materials investigated, {epsilon}{double_prime} ({nu}) increases significantly sublinear above the minimum. The ratio of the intensity of the {alpha}-process and the fast process as determined from the dielectric experiments is significantly higher compared to the results from the scattering experiments.