TY - JOUR A1 - Koldeweij, Robin B. J. A1 - Kant, Pallav A1 - Harth, Kirsten A1 - Ruiter, Rielle de A1 - Gelderblom, Hanneke A1 - Snoeijer, Jacco H. A1 - Lohse, Detlef A1 - Limbeek, Michiel A. J. van T1 - Initial solidification dynamics of spreading droplets JF - Physical Review Fluids N2 - When a droplet is brought in contact with an undercooled surface, it wets the substrate and solidifies at the same time. The interplay between the phase transition effects and the contact-line motion, leading to its arrest, remains poorly understood. Here we reveal the early solidification patterns and dynamics of spreading hexadecane droplets. Total internal reflection imaging is employed to temporally and spatially resolve the early solidification behavior. With this, we determine the conditions leading to the contact-line arrest. We quantify the overall nucleation behavior, i.e., the nucleation rate and the crystal growth speed and show its sensitivity to the applied undercooling of the substrate. We also show that for strong enough undercooling it is the rapid growth of the crystals which determines the eventual arrest of the spreading contact line. By combining the Johnson-Mehl-Avrami-Kolmogorov nucleation theory and scaling relations for the spreading, we calculate the temporal evolution of the solid area fraction, which is in good agreement with our observations. Y1 - 2021 UR - https://link.aps.org/doi/10.1103/PhysRevFluids.6.L121601 U6 - https://doi.org/10.1103/PhysRevFluids.6.L121601 SN - 2469-990X IS - 12 PB - American Physical Society ER - TY - JOUR A1 - Wang, Jing A1 - Harth, Kirsten A1 - Puzyrev, Dmitry A1 - Stannarius, Ralf T1 - The effect of obstacles near a silo outlet on the discharge of soft spheres JF - New Journal of Physics KW - fluid dynamics Y1 - 2022 U6 - https://doi.org/10.1088/1367-2630/ac8bea VL - 24 PB - IOP ER - TY - JOUR A1 - Missaoui, Amine A1 - Harth, Kirsten A1 - Trittel, Torsten A1 - Klopp, Christoph A1 - Stannarius, Ralf A1 - Lacaze, Emanuelle T1 - Shape instabilities of islands in smectic films under lateral compression JF - Soft Matter Y1 - 2022 U6 - https://doi.org/10.1039/D2SM00144F SN - 1744-6848 VL - 16 SP - 3193 EP - 3205 PB - Royal Society of Chemistry ER - TY - JOUR A1 - Trittel, Torsten A1 - Klopp, Christoph A1 - Harth, Kirsten A1 - Stannarius, Ralf T1 - Stability and Rupture of Liquid Crystal Bridges under Microgravity JF - Crystals KW - smectic liquid-crystals KW - Rayleigh-Plateau instability KW - TEXUS suborbital rocket KW - microgravity Y1 - 2022 U6 - https://doi.org/https://doi.org/10.3390/cryst12081092 VL - 12 IS - 8 PB - MDPI ER - TY - JOUR A1 - Stannarius, Ralf A1 - Harth, Kirsten T1 - The structure of disintegrating defect clusters in smectic C freely suspended films JF - Soft Matter N2 - Disclinations or disclination clusters in smectic C freely suspended films with topological charges larger than one are unstable. They disintegrate, preferably in a spatially symmetric fashion, into single defects with individual charges of +1, which is the smallest positive topological charge allowed in polar vector fields. While the opposite process of defect annihilation is well-defined by the initial defect positions, disintegration starts from a singular state and the following scenario including the emerging regular defect patterns must be selected by specific mechanisms. We analyze experimental data and compare them with a simple model where the defect clusters adiabatically pass quasi-equilibrium solutions in one-constant approximation. It is found that the defects arrange in geometrical patterns that correspond very closely to superimposed singular defect solutions, without additional director distortions. The patterns expand by affine transformations where all distances between individual defects scale with the same time-dependent scaling factor proportional to the square-root of time. Y1 - 2023 UR - https://pubs.rsc.org/en/content/articlelanding/2023/sm/d3sm00808h U6 - https://doi.org/https://doi.org/10.1039/d3sm00808h IS - 19 SP - 6109 EP - 6115 PB - Royal Society of Chemistry ER - TY - JOUR A1 - Klopp, Christoph A1 - Trittel, Torsten A1 - Harth, Kirsten A1 - Stannarius, Ralf T1 - Coalescence of biphasic droplets embedded in free standing smectic A films JF - Soft Matter N2 - We investigate micrometer-sized flat droplets consisting of an isotropic core surrounded by a nematic rim in freely suspended smectic A liquid-crystal films. In contrast to purely isotropic droplets which are characterized by a sharp edge and no long-range interactions, the nematic fringe introduces a continuous film thickness change resulting in long-range mutual attraction of droplets. The coalescence scenario is divided in two phases. The first one consists in the fusion of the nematic regions. The second phase involves the dissolution of a thin nematic film between the two isotropic cores. The latter has many similarities with the rupture of thin liquid films between droplets coalescing in an immiscible viscous liquid. Coalescence of biphasic droplets in free-standing smectic films is controlled in part by the rupture of a thin nematic membrane separating the isotropic droplet cores. Y1 - 2023 UR - https://pubs.rsc.org/en/content/articlelanding/2024/sm/d3sm01549a U6 - https://doi.org/10.1039/d3sm01549a SN - 1744-683X VL - 20 IS - 5 SP - 1036 EP - 1046 PB - Royal Society of Chemistry ER - TY - JOUR A1 - Puzyrev, Dmitry A1 - Torsten, Torsten A1 - Harth, Kirsten A1 - Stannarius, Ralf T1 - Cooling of a granular gas mixture in microgravity JF - npj microgravity N2 - Granular gases are fascinating non-equilibrium systems with interesting features such as spontaneous clustering and non-Gaussian velocity distributions. Mixtures of different components represent a much more natural composition than monodisperse ensembles but attracted comparably little attention so far. We present the observation and characterization of a mixture of rod-like particles with different sizes and masses in a drop tower experiment. Kinetic energy decay rates during granular cooling and collision rates were determined and Haff’s law for homogeneous granular cooling was confirmed. Thereby, energy equipartition between the mixture components and between individual degrees of freedom is violated. Heavier particles keep a slightly higher average kinetic energy than lighter ones. Experimental results are supported by numerical simulations. Y1 - 2024 U6 - https://doi.org/10.1038/s41526-024-00369-5 VL - 10 IS - 1 SP - 1 EP - 9 PB - Springer CY - Brandenburg an der Havel ER - TY - JOUR A1 - Harth, Kirsten A1 - Trittel, Torsten A1 - Mohammadi, Mahdieh A1 - Puzyrev, Dmitry A1 - Enezz, Mohammad A1 - Cruz Hidalgo, Raul A1 - Stannarius, Ralf ED - Alam, M. ED - Das, S.L. ED - Bose, M. ED - Murthy, T.G. ED - Chikkadi, V. ED - Singh, A. ED - Luding, S. T1 - Granular gases of rough spheres: Velocity, rotation and collision statistics from in-situ measurements, optical data and simulations JF - EPJ Web of Conferences N2 - Granular gases are not only of interest in fundamental physics, but they can also serve as a test ensembles for the validity of collision models employed in (loose) granular matter. The theoretical literature mainly addresses spheres under ideal conditions and simulations allow full access to all particle parameters, but experiments cannot fulfill these idealizations. We investigate granular gases of soft, rough spheres by combining microgravity experiments and adjusted simulations. We introduce Smart Particles with embedded autarkic micro-sensors for in-situ measurements of rotation rates and accelerations. Additionally, we extract 3D positions, translations and orientations of the particles from stereoscopic video data using Machine-Learning based algorithms. We address the partition of kinetic energy between the degrees of freedom, the angular and translational velocity as well as collision statistics. A simulation is adjusted to experiment parameters, showing good agreement of translational motion, but qualitative differences in the decay of rotational kinetic energy. Y1 - 2025 U6 - https://doi.org/10.1051/epjconf/202534003012 VL - 340 PB - EDP Sciences ER - TY - JOUR A1 - Puzyrev, Dmitry A1 - Trittel, Torsten A1 - Harth, Kirsten A1 - Sata, Sai Preetham A1 - Stannarius, Ralf A1 - Cruz Hidalgo, Raúl ED - Alam, M. ED - Das, S.L. ED - Bose, M. ED - Murthy, T.G. ED - Chikkadi, V. ED - Singh, A. ED - Luding, S. T1 - AI-aided visual data analysis for granular gases: Complex particles, high density, and other challenges JF - EPJ Web of Conferences N2 - Microgravity experiments with three-dimensional (3D) granular gases, i.e., ensembles of freemoving macroscopic particles which collide inelastically, produce large amounts of stereo video footage which require processing and analysis. The main steps of data treatment are particle detection, 3D matching and tracking in stereoscopic views, and quantification of ensemble statistical properties such as, e.g. mean kinetic energy or collision processes. Frequent overlapping or clustering of particles and their complicated movement patterns require smart software solutions. In recent years, Artificial Intelligence/Machine Learning (AI/ML) methods were successfully used for analysis of granular systems. We have applied such techniques to the granular gases of rod-like particles and developed a software tool which enables a full cycle of semi-automatic experimental data analysis. The approach is now tested on more complex, non-convex particles, shaped as 3D crosses (hexapods). Another challenge is optical analysis of dense granular gases, where individual particles cannot be tracked. We present a preliminary result of application of an ML method for number density profiles extraction in VIP-Gran experiment with dense ensemble of rod-like particles. Y1 - 2025 U6 - https://doi.org/10.1051/epjconf/202534012013 VL - 340 PB - EDP Sciences ER -