arXiv subjects

Rolf Zeißler

Publications and source records attributed to Rolf Zeißler.

6 recordsLinked to original sources

arXiv2026

Ultra-broadband and time-resolved depolarized dynamic light scattering for probing molecular dynamics in supercooled liquids and glasses

Dynamic light scattering (DLS) is a versatile technique for probing microscopic dynamics in soft condensed matter. However, applying DLS to supercooled molecular liquids and glasses demands exceptional experimental performance due to weak depolarized scattering, slow relaxation near the glass transition, and the need for quantitative comparison with complementary spectroscopic techniques. In this tutorial we discuss, how a depolarized dynamic light scattering (DDLS) setup can be tailored to meet these challenges. By combining conventional fiber-optical photon correlation spectroscopy, and multispeckle photon correlation imaging with high-frequency DDLS, such a setup allows to capture rotational dynamics across more than 20 orders of magnitude in time. We detail the experimental design required for high signal-to-noise ratios and long-term optical stability, alongside the treatment of coherence and partial heterodyning effects. As we demonstrate, after proper treatment the different detection schemes yield the same electric-field autocorrelation function, enabling the construction of continuous, ultra-broadband DDLS datasets. Furthermore, multispeckle detection enables time-resolved correlation measurements without temporal averaging, extending DDLS to non-equilibrium systems such as aging molecular glasses. This methodology establishes a unified experimental framework for quantitative investigations of equilibrium and non-equilibrium molecular reorientation dynamics over an exceptionally broad time range.

cond-mat.soft↗

arXiv2026

Non-exponential relaxation without dynamic heterogeneity in van der Waals liquids above the melting point

We investigate the influence of dynamic heterogeneity on the spectral shape of structural relaxation in van der Waals liquids above the melting point by means of depolarized dynamic light scattering. To this end, we study optically anisotropic probe molecules both in the bulk and when diluted in an optically isotropic solvent. Strikingly, the relaxation shape of the probe molecules in dilution is indistinguishable from that of the pure liquid composed of the probe molecules. By contrast, when explicit dynamic heterogeneity is introduced, e.g., through internal degrees of freedom or a distribution of probe molecule sizes, the relaxation shape becomes sensitive to the solvent concentration. These findings indicate that dynamic heterogeneity has a negligible influence on the rotational dynamics of single component van der Waals liquids above the melting point, despite the pronounced non-exponential character of their relaxation shape.

cond-mat.soft↗

arXiv2025

On the Role of Internal Degrees of Freedom in Structural Relaxation of Ring-Tail Structured Liquids Across Temperature Regimes

We investigate how anisotropic molecular rotation and internal molecular flexibility influence liquid dynamics in 1-phenylalkanes. To this end, we combine depolarized dynamic light scattering, nuclear magnetic resonance spectroscopy and molecular dynamics simulations. Our results show that anisotropic rotations and internal molecular flexibility substantially contribute to structural relaxation in the liquid state. However, their influence diminishes on entering the supercooled-liquid regime, where the relaxation behavior develops towards the previously identified generic relaxation shape, likely due to the increasing cooperativity of rotational dynamics. Because 1-phenylalkanes are simple model systems with similarities to many other molecular liquids, this study suggests that effects of anisotropic rotation and internal flexibility are relevant in various liquids with similar molecular complexity, and provides a proof of concept for how these effects can be identified.

cond-mat.soft↗

arXiv2025

A Fresh Perspective on Water Dynamics in Aqueous Salt Solutions

Molecular dynamics in pure water and aqueous salt solutions remain incompletely understood, partly due to the apparent contradictions between results from different spectroscopic techniques. In this work, we demonstrate, by detailed comparison of light scattering and dielectric spectroscopy data for pure water and aqueous lithium chloride solutions, that these apparent contradictions can be resolved by accounting for orientational cross-correlations of neighboring molecules. Remarkably, a single structural relaxation mode with largely temperature- and concentration-independent shape can be identified in all spectra, from room temperature down to the deeply supercooled regime. These results provide a new perspective for the study of molecular dynamics in aqueous salt solutions.

cond-mat.soft↗

arXiv2024

On the Spectral Shape of the Structural Relaxation in Deeply Supercooled Liquids

Structural relaxation in deeply supercooled liquids is non-exponential. In susceptibility representation, $χ^{\prime\prime}(ν)$, the spectral shape of the structural relaxation is observed as an asymmetrically broadened peak with a $ν^{1}$ low- and $ν^{-β}$ high-frequency behavior. In this perspective article we discuss common notions, recent results and open questions regarding the spectral shape of the structural relaxation. In particular, we focus on the observation that a high-frequency behavior of $ν^{-1/2}$ appears to be a generic feature in a broad range of different deeply supercooled liquids. Moreover, we review extensive evidence that contributions from orientational cross-correlations can lead to deviations from the generic spectral shape in certain substances, in particular in dielectric loss spectra. Additionally, intramolecular dynamics can contribute significantly to the spectral shape in substances containing more complex and flexible molecules. Finally, we discuss the open questions regarding potential physical origins of the generic $ν^{-1/2}$ behavior and the evolution of the spectral shape towards higher temperatures.

cond-mat.soft↗

arXiv2022

Glassy Dynamics in Polyalcohols: Intermolecular Simplicity vs. Intramolecular Complexity

Using depolarized light scattering, we have recently shown that structural relaxation in a broad range of supercooled liquids follows, to good approximation, a generic line shape with high-frequency power law $ω^{-1/2}$. We now continue this study by investigating a systematic series of polyalcohols (PAs), frequently used as model systems in glass-science, i.a., because the width of their respective dielectric loss spectra varies strongly along the series. Our results reveal that the microscopic origin of the observed relaxation behavior varies significantly between different PAs: While short-chained PAs like glycerol rotate as more or less rigid entities and their light scattering spectra follow the generic shape, long-chained PAs like sorbitol display pronounced intramolecular dynamic contributions on the time scale of structural relaxation, leading to systematic deviations from the generic shape. Based on these findings we discuss an important limitation for observing the generic shape in a supercooled liquid: The dynamics that is probed needs to reflect the intermolecular dynamic heterogeneity, and must not be superimposed by effects of intramolecular dynamic heterogeneity.

cond-mat.soft↗