arXiv subjects

Jan Philipp Gabriel

Publications and source records attributed to Jan Philipp Gabriel.

12 recordsLinked to original sources

arXiv2026

Time-state superposition in non-equilibrium fluidized granular matter

Despite being intrinsically athermal and strongly driven, granular materials can exhibit remarkably glass-like dynamics. Whether their rheology can be described by the same scaling concepts remains an open question. Here, we investigate the linear viscoelastic response of an air-fluidized granular bed using small-amplitude oscillatory shear over a broad range of fluidization states. We show that the frequency-dependent spectra collapse onto a single master curve when shifted by a state-dependent relaxation time, establishing a time-state superposition principle analogous to time-temperature superposition in molecular glasses. The master curve spans more than five decades in relaxation time and is quantitatively described by a Cole-Davidson relaxation spectrum. By comparison with continuous shear measurements, we identify tribocharging as the origin of history-dependent deviations from universal scaling. Our results demonstrate that fluidization primarily rescales a single structural relaxation time while preserving the underlying relaxation spectrum, establishing a direct connection between the rheology of driven granular matter and molecular glass-forming liquids.

cond-mat.soft↗

arXiv2026

Jamming and Flow in Granular Matter: A Physics Lab Course Experiment

We describe a dynamic light scattering setup that uses diffusing wave spectroscopy (DWS) to investigate the dynamics in sand grains subjected to periodic vertical shaking by a loudspeaker. Along with the setup that is used in the undergraduate physics lab course at TU Darmstadt, the necessary DWS theory is introduced, including the proper treatment of the oscillatory excitation. Some exemplary results are presented that demonstrate the similarity of jamming in an athermal granular medium with the glass transition in thermally driven molecular systems, a relation that has frequently been pointed out but still is poorly understood. Similar, albeit more sophisticated experiments are currently conducted in microgravity environments such as the international space station ISS and the experiment may serve as an introduction to an exciting field of current research.

cond-mat.soft↗

arXiv2025

Towards probing velocity distributions in dense granular matter: Utilizing Fiber Bragg Gratings

Granular gases are commonly characterized through their velocity distribution, which provides access to the granular temperature. In experiments, velocity distributions are typically obtained by particle tracking, which however becomes limited at moderate and high particle densities. As a way forward, we propose a new technique for measuring particle velocities in situ by using a Fiber Bragg Grating (FBG) sensor, which remains applicable at significantly higher particle densities.The FBG sensor detects strain pulses induced by particle-fiber collisions, from which the velocity of the impacting particle can be derived. Applying this method to an ensemble of granular particles allows to extract its velocity distributions as we present for a granular system excited by a vibrational shaker. We validate the extracted velocity distribution against conventional particle-tracking measurements, confirming the reliability of the FBG-based technique.

cond-mat.dis-nn↗

arXiv2025

Molecular dynamics insights into the Debye process of 1-propanol

We reproduce the Debye process in the dielectric response of liquid 1-propanol by all-atom molecular dynamics simulations between 340 K and 200 K. The analysis of dipolar correlations reveals that the $\alpha$ relaxation originates from hydrogen-bond (HB) breaking, while the dominant Debye process results from long-ranged cross-correlations extending over several molecular diameters. By separating intra- and extra-cluster contributions, we demonstrate that HB supramolecular clusters account for the main part of the static dielectric response, with extra-cluster molecules playing only a minor role at low temperatures. Besides, clusters do not preserve connectivity on timescales exceeding the $\alpha$ relaxation time. This indicates that clusters stabilize orientational correlations beyond individual molecular relaxation times by transmitting alignment to newly incorporated molecules. These findings provide microscopic evidence that the Debye relaxation in mono-alcohols arises from the collective dynamics of HB clusters and offer a framework to study dielectric spectra in other hydrogen-bonded liquids.

cond-mat.soft↗

arXiv2025

Competing Supramolecular Structures: Dielectric and Rheological Spectroscopy on Glycerol/Propanol Mixtures

Significant progress has been made in recent years in understanding the dynamics of pure hydrogen-bonded systems by analyzing the spectral shape of various susceptibilities. Monohydroxy- and polyalcohols are currently considered to form transient supramolecular hydrogen-bonded structures in the form of chains, rings, and networks. This complex dynamic behavior has been identified in network-forming glycerol and chain-forming propanol by combining dielectric and light-scattering spectra. We apply these concepts to study the combined dielectric and shear rheological spectral shape of glycerol/propanol mixtures. Glycerol differs from propanol by having two additional hydroxy groups, which leads to significant differences in melting temperatures($ΔT_{\textbf{m}}$\,=\,291\,K\,-\,147\,K\,=\,143\,K) and glass transition temperatures ($ΔT_{\textbf{g}}$\,=\,190\,K-\,98\,K\,=\,92\,K). The strong difference results in two distinct calorimetric glass transitions at a molar glycerol concentration of $χ_{gly}=0.3$, as well as a change in the shear modulus $G_{\infty}$ between $χ_{gly}=0.5$ and 0.7. Performing a comprehensive analysis of the three applied experimental techniques leads to the conclusion that dielectric spectroscopy monitors the evolution of supramolecular chain and network structures and that the mechanical properties depend heavily on the formed hydrogen-bonded network. A strong dynamical heterogeneity is observed and manifests itself in two distinguishable glass transitions in dielectric spectroscopy and calorimetry. The presented chain/network mixture is dynamically highly heterogeneous when compared to the rather narrow dynamical heterogeneity in the network/network mixture Water/Glycerol.

cond-mat.soft↗

arXiv2025

Observing the Glass and Jamming Transitions of Dense Granular Material in Microgravity

The present study investigates a weakly pulsed granular system of polystyrene spheres under long-time microgravity conditions on the International Space Station (ISS). The spheres are measured using Diffusing Wave Spectroscopy (DWS) and are described by mean square displacements (MSDs). Our aim is to use this technique to show the first experimental evidence of glassy dynamics in dense granular media in microgravity and subsequently compare these results with ground-based measurements to see how the nature of these dynamics change without the influence of gravity. Our results show that as we densify the sample in microgravity, glassy dynamics appear at a volume fraction 1.6\% lower than on ground. We also show how the influence of gravity can affect how dense a granular system one can prepare by comparing the final jamming point of our sample on the ISS compared to our ground setup. We show that jamming occurs at a volume fraction 0.5\% lower in space compared to on ground. Showing that we can create denser states when a granular system is in the presence of a stronger gravitational field.

cond-mat.soft↗

arXiv2025

Linear-limit aging times of three monoalcohols

This paper presents data for the physical aging of the three monoalcohols 2-ethyl-1-butanol, 5-methyl-2-hexanol, and 1-phenyl-1-propanol. Aging is studied by monitoring the dielectric loss at a fixed frequency in the kHz range following temperature jumps of a few Kelvin's magnitude, starting from states of equilibrium. The three alcohols differ in the Debye relaxation strength and how much the Debye process is separated from the $α$ process. We first demonstrate that single-parameter aging describes all data well and proceed to utilize this fact to identify the linear-limit normalized aging relaxation functions. From the Laplace transform of these functions, the linear-limit aging loss-peak angular frequency defines the inverse of the linear aging relaxation time. This allows for a comparison to the temperature dependence of the Debye and $α$ dielectric relaxation times of the three monoalcohols. We conclude that the aging response for 5-methyl-2-hexanol and 2-ethyl-1-butanol follows the $α$ relaxation, not the Debye process, while no firm conclusion can be reached for 1-phenyl-1-propanol because its Debye and $α$ processes are too close to be reliably distinguished.

cond-mat.soft↗

arXiv2025

The Dynamics in Vibro-fluidized Beds: A Diffusing Wave Spectroscopy Study

We demonstrate the densification of a granular model system of polystyrene spheres over time by shaking with varying excitation amplitudes or effective temperatures. This densification is quantified by the mean square displacement (MSD), which is measured by diffuse wave spectroscopy (DWS) of a sinusoidally excited vibrating fluidized granular bed. The DWS method also extracts the inherent heterogeneous dynamics of the system in the bulk and at the wall. Through an empirical model-based extraction we obtain the ballistic and diffusive time constants, as well as caging sizes, which were found to depend on temperature and density. The results obtained from this study reveal a sub-diffusive power-law behavior in the MSD, indicating an arrest of motion and potentially a glassy system, especially in cases where the excitation is low to moderate compared to gravity. The extracted MSD caging sizes are two orders smaller than the Lindeman length found in colloidal systems.

cond-mat.soft↗

arXiv2024

Local and Global Expansivity in Water

The supra-molecular structure of a liquid is strongly connected to its dynamics which in turn controls macroscopic properties such as viscosity. Consequently, detailed knowledge about how this structure changes with temperature is essential to understand the thermal evolution of the dynamics ranging from the liquid to the glass. Here we combine infrared spectroscopy (IR) measurements of the hydrogen (H) bond stretching vibration of water with molecular dynamics simulations and employ a quantitative analysis to extract the inter-molecular H-bond length in a wide temperature range of the liquid. The extracted expansivity of this H-bond differs strongly from that of the average nearest neighbor distance of oxygen atoms obtained through a common conversion of mass density. However, both properties can be connected through a simple model based on a random loose packing of spheres with a variable coordination number which demonstrates the relevance of supra-molecular arrangement. Further, the exclusion of the expansivity of the inter-molecular H-bonds reveals that the most compact molecular arrangement is formed in the range $\sim316-331\,\text{K}$ (i.e. above the density maximum) close to the temperature of several pressure-related anomalies which indicates a characteristic point in the supra-molecular arrangement. These results confirm our earlier approach to deduce inter-molecular H-bond lengths via IR in polyalcohols [Gabriel et al. 2021] quantitatively and open a new alley to investigate the role of inter-molecular expansion as a precursor of molecular fluctuations on a bond-specific level.

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↗

arXiv2020

Intra- and Intermolecular Inhomogeneities in the Course of Glassy Densification of Polyalcohols

To test basic assumptions inherent to most theories of molecular liquids and glasses, Infrared spectroscopy is carried out on short polyalcohols at temperatures ranging from far above to far below their glass transition. By analyzing specific vibrations, the thermal expansion of covalent bonds and hydrogen bridges is determined revealing striking differences. A comparison with density verifies the negligibility of \textit{intra}molecular expansion but exposes severe inhomogeneities on \textit{inter}molecular scale. This signals distinct roles in glassy densification and promotes an atomistic understanding.

cond-mat.mtrl-sci↗

arXiv2020

Intermolecular Cross-Correlations in the Dielectric Response of Glycerol

We suggest a way to disentangle self- from cross-correlation contributions in the dielectric spectra of glycerol. Recently it was demonstrated for monohydroxy alcohols that a detailed comparison of the dynamic susceptibilities of photon correlation and broadband dielectric spectroscopy allows to unambiguously disentangle a collective relaxation mode known as the Debye process, which could arises due to supramolecular structures, and the $α$-relaxation, which proves to be identical in both methods. In the present paper, we apply the same idea and analysis to the paradigmatic glass former glycerol. For that purpose we present new light scattering data from photon correlation spectroscopy measurements and combine these with literature data to obtain a data set covering a dynamic range from $10^{-4}-10^{13}\,$Hz. Then we apply the above mentioned analysis by comparing this data set with a corresponding set of broadband dielectric data. Our finding is that even in a polyalcohol self- and cross-correlation contributions can approximately be disentangled in that way and that the emerging picture is very similar to that in monohydroxy alcohols. This is further supported by comparing the data with fast field cycling NMR measurements and dynamic shear relaxation data from the literature, and it turns out that, within the described approach, the $α$-process appears very similar in all methods, while the pronounced differences observed in the spectral density are due to a different expression of the slow collective relaxational contribution. In the dielectric spectra the strength of this peak is reasonably well estimated by the Kirkwood correlation factor, which supports the view that it arises due to dynamic cross-correlations, which were previously often assumed to be negligible in dielectric measurements.

cond-mat.soft↗