@article{WangHarthPuzyrevetal.2022, author = {Wang, Jing and Harth, Kirsten and Puzyrev, Dmitry and Stannarius, Ralf}, title = {The effect of obstacles near a silo outlet on the discharge of soft spheres}, series = {New Journal of Physics}, volume = {24}, journal = {New Journal of Physics}, publisher = {IOP}, doi = {10.1088/1367-2630/ac8bea}, year = {2022}, language = {en} } @article{MissaouiHarthTritteletal.2022, author = {Missaoui, Amine and Harth, Kirsten and Trittel, Torsten and Klopp, Christoph and Stannarius, Ralf and Lacaze, Emanuelle}, title = {Shape instabilities of islands in smectic films under lateral compression}, series = {Soft Matter}, volume = {16}, journal = {Soft Matter}, publisher = {Royal Society of Chemistry}, issn = {1744-6848}, doi = {10.1039/D2SM00144F}, pages = {3193 -- 3205}, year = {2022}, language = {en} } @article{KloppTrittelHarthetal.2022, author = {Klopp, Christoph and Trittel, Torsten and Harth, Kirsten and Stannarius, Ralf}, title = {Smectic free-standing films under fast lateral compression}, series = {Soft Matter}, journal = {Soft Matter}, publisher = {Royal Society of Chemistry}, issn = {1744-683X, 1744-6848}, doi = {10.1039/D1SM01207J}, pages = {146 -- 155}, year = {2022}, abstract = {Smectic films in a collapsing catenoid develop spontaneous wrinkling patterns like solid sheets. Smectic freely-suspended films can wrinkle like solid sheets. This has been demonstrated earlier with shape-fluctuating smectic bubbles. Here, we exploit the collapse of smectic catenoid films with a central equatorial film to expose the latter to rapid lateral compression. Wrinkle formation is observed in the planar film and the thickness dependence of the undulation wavelength is measured. In addition to the central film, its border undergoes an undulation instability as well.}, language = {en} } @article{StannariusHarth2023, author = {Stannarius, Ralf and Harth, Kirsten}, title = {The structure of disintegrating defect clusters in smectic C freely suspended films}, series = {Soft Matter}, journal = {Soft Matter}, number = {19}, publisher = {Royal Society of Chemistry}, doi = {https://doi.org/10.1039/d3sm00808h}, pages = {6109 -- 6115}, year = {2023}, abstract = {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.}, language = {en} } @article{KloppTrittelHarthetal.2023, author = {Klopp, Christoph and Trittel, Torsten and Harth, Kirsten and Stannarius, Ralf}, title = {Coalescence of biphasic droplets embedded in free standing smectic A films}, series = {Soft Matter}, volume = {20}, journal = {Soft Matter}, number = {5}, publisher = {Royal Society of Chemistry}, issn = {1744-683X}, doi = {10.1039/d3sm01549a}, pages = {1036 -- 1046}, year = {2023}, abstract = {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.}, language = {en} } @article{TrittelKloppHarthetal.2022, author = {Trittel, Torsten and Klopp, Christoph and Harth, Kirsten and Stannarius, Ralf}, title = {Stability and Rupture of Liquid Crystal Bridges under Microgravity}, series = {Crystals}, volume = {12}, journal = {Crystals}, number = {8}, publisher = {MDPI}, doi = {https://doi.org/10.3390/cryst12081092}, pages = {16}, year = {2022}, language = {en} } @article{KloppTrittelStannarius2024, author = {Klopp, Christoph and Trittel, Torsten and Stannarius, Ralf}, title = {Coarsening of quasi two-dimensional emulsions formed by islands in free-standing smectic films}, series = {ChemPhysChem}, volume = {25}, journal = {ChemPhysChem}, number = {12}, publisher = {Wiley}, doi = {10.1002/cphc.202400166}, pages = {1 -- 12}, year = {2024}, abstract = {We study the coarsening behavior of assemblies of islands on smectic A freely suspended films in ISS microgravity experiments. The islands can be regarded as liquid inclusions in a two-dimensional fluid in analogy to liquid droplets of the discontinuous phase of an emulsion. The coarsening is effectuated by two processes, predominantly by island coalescence, but to some extend also by Ostwald ripening, whereby large islands grow at the expense of surrounding smaller ones. A peculiarity of this system is that the continuous and the discontinuous phases consist of the same material. We determine the dynamics, analyze the self-similar aging of the island size distribution and discuss characteristic exponents of the mean island growth.}, language = {en} } @article{KloppStannarius2024, author = {Klopp, Christoph and Stannarius, Ralf}, title = {Rupture of thin nematic walls between isotropic droplets of the same mesogenic material}, series = {Liquid Crystals}, volume = {51}, journal = {Liquid Crystals}, number = {5}, publisher = {Taylor \& Francis}, doi = {10.1080/02678292.2024.2325619}, pages = {783 -- 797}, year = {2024}, abstract = {We prepared isotropic droplets surrounded by nematic fringes in smectic A freely suspended films. During their coalescence, a thin nematic film is formed that acts as a barrier and separates the isotropic cores of these droplets. This film ruptures in the course of the droplet merging process. The observation of the film dynamics provides an exceptional opportunity to study the rupture of a thin liquid barrier embedded in a surrounding viscous liquid. A detailed dynamic characterisation of the nematic walls is performed. Qualitatively similar observations have been reported in 3D for oil drops coalescing in water and vice versa, where the rupture of an intermediate thin fluid film retards the merging process. The peculiarity of the system reported here is that the material of the droplets and the membrane is identical.}, language = {en} } @article{PuzyrevTorstenHarthetal.2024, author = {Puzyrev, Dmitry and Torsten, Torsten and Harth, Kirsten and Stannarius, Ralf}, title = {Cooling of a granular gas mixture in microgravity}, series = {npj microgravity}, volume = {10}, journal = {npj microgravity}, number = {1}, publisher = {Springer}, address = {Brandenburg an der Havel}, doi = {10.1038/s41526-024-00369-5}, pages = {1 -- 9}, year = {2024}, abstract = {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.}, language = {de} } @article{TrittelPuzyrevStannarius2024, author = {Trittel, Torsten and Puzyrev, Dmitry and Stannarius, Ralf}, title = {Platonic solids bouncing on a vibrating plate}, series = {Physical Review E}, volume = {109}, journal = {Physical Review E}, number = {3}, publisher = {APS}, doi = {10.1103/PhysRevE.109.034903}, year = {2024}, abstract = {The energy transfer between bouncing particles and rigid boundaries during impacts is crucially influenced not only by restitution coefficients of the material but also by particle shapes. This is particularly important when such particles are mechanically agitated with vibrating plates. Inertial measurement units are able to measure all acceleration and rotational velocity components of an object and store these data for subsequent analysis. We employ them to measure the dynamics of cubes and icosahedra on vibrating plates to study the efficiency of energy transfer into the individual degrees of freedom (DOFs) of the excited object. The rotational DOFs turn out to be much less excited than the vertical translational motion. Most remarkably, there is only little difference between the two Platonic solids in both the absolute energies and the energy partition ratios.}, language = {en} }