arXiv subjects

Jan P. Gabriel

Publications and source records attributed to Jan P. Gabriel.

3 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↗

arXiv2024

Dipolar order controls dielectric response of glass-forming liquids

The dielectric response of liquids reflects both, reorientation of single molecular dipoles and collective modes, i.e., dipolar cross-correlations. A recent theory predicts the latter to produce an additional slow peak in the dielectric loss spectrum. Following this idea we argue that in supercooled liquids the high-frequency power law exponent of the dielectric loss $β$ should be correlated with the degree of dipolar order, i.e., the Kirkwood correlation factor $g_K$. This notion is confirmed for 25 supercooled liquids. While our findings support recent theoretical work the results are shown to violate the earlier Kivelson-Madden theory.

cond-mat.soft↗

arXiv2023

Time reversibility during the ageing of materials

Physical ageing is the generic term for irreversible processes in glassy materials resulting from molecular rearrangements. One formalism for describing such ageing processes involves the concept of material time, which may be thought of as time measured on a clock whose rate changes as the glass ages. Experimental determination of material time has so far not been realized, however. Here, we show how dynamic light-scattering measurements provide a way forward. We determined the material time for an ageing sample of the glass-former 1-phenyl-1-propanol after temperature jumps close to the glass transition from the time-autocorrelation function of the intensity fluctuations probed by multispeckle dynamic light scattering. These fluctuations are shown to be stationary and reversible when regarded as a function of the material time. The glass-forming colloidal synthetic clay Laponite and a chemically ageing curing epoxy are also shown to display material-time-reversible scattered-light intensity fluctuations, and simulations of an ageing binary system monitoring the potential energy confirm material-time reversibility. In addition to demonstrating direct measurements of the material time, our findings identify a fundamental property of ageing in quite different contexts that presents a challenge to the current theories of ageing.

cond-mat.soft↗