arXiv subjects

Paul Sotta

Publications and source records attributed to Paul Sotta.

3 recordsLinked to original sources

arXiv2025

Unraveling Specific Conditions for a Repeatable Mpemba Effect

Water exhibits many unique properties compared to other liquids, with some of these explained and others remaining enigmatic. Among them, it was proposed and extensively debated that hot water would freeze faster than cold water. Numerous studies have demonstrated the difficulty of successfully elucidating this effect, making explanations surrounding this phenomenon highly controversial. Here, we demonstrate that when two cups filled with cold and hot water are introduced simultaneously in a freezer saturated with ice-nucleating agents, the hot sample freezes faster and to a greater depth than the cold sample, particularly when the initial temperature difference is high. On the other hand, against some previous beliefs, the time to onset of crystallization is always and logically retarded for hotter samples. Under these conditions, where supercooling is eliminated and temperature recording is precisely controlled, robust experiments follow the same trend,regardless of whether hot versus room temperature (RT) samples or RT versus cold samples are tested.

physics.chem-ph↗

arXiv2015

Connectivity of the Hexagonal, Cubic, and Isotropic Phases of the C$_{12}$EO$_6$/H$_2$O Lyotropic Mixture Investigated by Tracer Diffusion and X-ray Scattering

The connectivity of the hydrophobic medium in the nonionic binary system C$_{12}$EO$_6$/H$_2$O is studied by monitoring the diffusion constants of tracer molecules at the transition between the hexagonal mesophase and the fluid isotropic phase. The increase in the transverse diffusion coefficient on approaching the isotropic phase reveals the proliferation of bridgelike defects connecting the surfactant cylinders. This suggests that the isotropic phase has a highly connected structure. Indeed, we find similar diffusion coefficients in the isotropic and cubic bicontinuous phases. The temperature dependence of the lattice parameter in the hexagonal phase confirms the change in connectivity close to the hexagonal-isotropic transition. Finally, an X-ray investigation of the isotropic phase shows that its structure is locally similar to that of the hexagonal phase.

cond-mat.soft↗

arXiv2015

Dielectric relaxation of thin films of polyamide random copolymers

We investigate the relaxation behavior of thin films of a polyamide random copolymer, PA66/6I, with various film thicknesses using dielectric relaxation spectroscopy. Two dielectric signals are observed at high temperatures, the $α$-process and the relaxation process due to electrode polarization (the EP-process). The relaxation time of the EP-process has a Vogel-Fulcher-Tammann type of temperature dependence, and the glass transition temperature, $T_{\rm g}$, evaluated from the EP-process agrees very well with the $T_{\rm g}$ determined from the thermal measurements. The fragility index derived from the EP-process increases with decreasing film thickness. The relaxation time and the dielectric relaxation strength of the EP-process are described by a linear function of the film thickness $d$ for large values of $d$, which can be regarded as experimental evidence for the validity of attributing the observed signal to the EP-process. Furthermore, there is distinct deviation from this linear law for thicknesses smaller than a critical value. This deviation observed in thinner films is associated with an increase in the mobility and/or diffusion constant of the charge carriers responsible for the EP-process. The $α$-process is located in a high frequency region than the EP-process at high temperatures, but merges with the EP-process at lower temperatures near the glass transition region. The thickness dependence of the relaxation time of the $α$-process is different from that of the EP-process. This suggests that there is decoupling between the segmental motion of the polymers and the translational motion of the charge carriers in confinement.

cond-mat.soft↗