Tamás Börzsönyi, Ágnes BukaE, Nándor Éber, Katalin Fodor-CsorbaA, Antal Jákli, István JánossyA, Dániel Nagy, Péter Salamon, Ellák Somfai, Balázs Szabó#, Tibor Tóth-Katona
Granular materials – Flow, jamming and segregation phenomena in sheared systems. — Segregation is often observed in granular mixtures due to size or weight difference of the grains. It is well known that heavier or smaller grains migrate downwards in a granular shear flow. We have shown, that grains differing only in surface friction (size and weight is the same) also segregate when sheared, where smooth grains accumulate in the lower regions of the shear zone (Fig. 1). Moreover, when gravity is negligible to other (compressional) forces, the sample still segregates with the smooth grains leaving the shear zone.
Figure 1. A mixture of smooth and rough beads is sheared. Smooth beads migrate to the bottom of the shear zone due to kinetic sieving.
The flow of elongated grains has been also studied in experiments and numerical simulations.
We have experimentally shown, that the flow rate of a hopper is slightly decreased and clogging probability is higher for rod like particles compared to spheres. In numerical simulations, the effective friction of an assembly of frictionless spherocylinders was a non-monotonic, but predominantly decreasing function of the particle aspect ratio.
Two distinct strain amplitudes have been identified in soft glassy materials, such as emulsions, foams, suspensions and pastes, close to the jamming transition. Numerical simulations of oscillatorily sheared soft sphere packings revealed that as the strain amplitude is increased, the initially elastic systems undergo a softening transition, at which both the elastic and loss moduli drop and reach a new plateau. Increasing the strain amplitude further causes yielding, marked by diffusive particle trajectories.
E Professor Emeritus
A Associate fellow
# Ph.D student
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Figure 2. Representative particle trajectories in oscillatory shear. For increasing shear amplitude (left to right), the elliptic trajectory corresponding to linear elasticity becomes non-periodic, but still bounded (softening), then diffusive (yielding).
Liquid crystals. — Tunable optical gratings based on the flexoelectric effect were created in a bent-core nematic liquid crystal. The wavelength of the structure was controlled by the applied d.c. voltage, as demonstrated by polarizing microscopy and light diffraction techniques (Fig. 3): higher voltage yields shorter wavelength. Visibility of the diffraction orders depended on the polarization of the illuminating laser beam (Fig. 4). The dynamical response of the system to switching between voltage levels were also explored. The characteristics and the mechanisms of switching were found to be different, depending on whether the lower voltage level is below or above the threshold of pattern onset. In both cases, the response to increasing voltage levels was much slower than that to decreasing ones.
Figure 3. Microphotographs and diffraction patterns of flexodomain gratings at increasing applied voltages.
Figure 4. Diffraction geometries and the corresponding diffraction images at (a) extraordinary and (b) ordinary illumination.
Liquid crystal composite materials. — Structural transitions under the combined action of magnetic and electric fields have been monitored in 6CHBT and 6CB liquid crystal-based
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ferronematics, obtained by doping the nematics with spherical and rod-like magnetic nanoparticles in low (≤ 10-4) volume concentrations. Based on the experimental data, the type of the anchoring at the liquid crystal‒nanoparticle interface (rigid or soft), as well as the mutual orientation of the magnetic moment of the nanoparticles and the nematic director have been determined.
Studies of the effect discovered the previous year, namely the increase of the alternating current magnetic susceptibility of ferronematics, induced by a dc bias magnetic field applied in the isotropic phase, which vanishes irreversibly when the ferronematic is cooled down to the nematic phase, have been continued. With the optimization of the ferronematic composition, the range of the d.c. bias magnetic field to which the ferronematic is sensitive without saturation was increased by about two orders of magnitude. This finding paves a way to application possibilities such as low magnetic field sensors or basic logical elements for information storage.
Grants
NKFI K 116036: Flow and rheology of non-spherical particles (E. Somfai, 2016-2020) NKFI FK 125134: Tunable topology of confined soft matter (P. Salamon, 2017-2021)
NKFI PD16 121019: Interfacial topology of anisotropic soft matter, (P. Salamon, 2016-2019)
International cooperation
COST Action IC1208: Integrating devices and materials: a challenge for new instrumentation in ICT (Management Committee Member: N. Éber, 2013-2017)
Ecole Supérieure de Physique et de Chimie Industrielles de Paris (France): Rheology of elongated grains and suspensions of fibers (T. Börzsönyi, 2016-2017)
RIKEN (Wako, Japan): Creation, active control, and possible application of topological defects in advanced soft matter systems (Á. Buka, 2016-2018)
Jožef Stefan Institute (Ljubljana, Slovenia): Microfluidic systems based on anisotropic soft matter (P. Salamon, 2016-2018)
Publications
Articles
1. Ashour A, Wegner S, Trittel T, Börzsönyi T, Stannarius R: Outflow and clogging of shape-anisotropic grains in hoppers with small apertures. SOFT MATTER 13:(2) 402-414 (2017)
2. Ashour A, Trittel T, Börzsönyi T, Stannarius R: Silo outflow of soft frictionless spheres.
PHYS REV FLUIDS 2:(12) 123302-1-9 (2017)
3. Boschan J, Vasudevan SA, Boukany PE, Somfai E, Tighe BP: Stress relaxation in viscous soft spheres. SOFT MATTER 13:(38) pp. 6870-6876. (2017)
4. Csach K, Jurikova A, Miskuf J, Tomasovicova N, Gdovinova V, Zavisova V, Kopcansky P, Éber N, Fodor-Csorba K, Vajda A: Kinetics of nematic to isotropic phase transition in liquid crystal doped with magnetic nanoparticles. ACTA PHYS POL A 131:(4) 949-951 (2017)
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5. Dagois-Bohy S, Somfai E, Tighe BP, van Hecke M: Softening and yielding of soft glassy materials. SOFT MATTER 13:(47) 9036-9045 (2017)
6. Gdovinová V, Tomašovičová N, Éber N, Salamon P, Tóth-Katona T, Závišová V, Kováč J, Jadżyn J, Kopčanský P: Ferronematics based on the nematic 6CB in combined electric and magnetic fields. PHASE TRANSIT 90:(8) 780-789 (2017)
7. Gdovinova V, Tomasovicova N, Zavisova V, Éber N, Tóth-Katona T, Royer F, Jamon D, Jadzyn J, Kopcansky P: Low magnetic field response in ferronematics. ACTA PHYS POL A 131:(4) 934-936 (2017)
8. Gillemot K, Somfai E, Börzsönyi T: Szegregáció nyírt, szemcsés keverékekben (Segregation in sheared granular compounds, in Hungarian). FIZIKAI SZEMLE 67:(11) 376-380 (2017)
9. Gillemot KA, Somfai E, Börzsönyi T: Shear-driven segregation of dry granular materials with different friction coefficients. SOFT MATTER 13:(2) 415-420 (2017)
10. May K, Eremin A, Stannarius R, Szabó B, Börzsönyi T, Appel I, Behrens S, Klein S:
Exceptionally large magneto-optical response in dispersions of plate-like nanocrystallites and magnetic nanoparticles. J MAGN MAGN MATER 431: 79-83 (2017)
11. Nagy DB, Claudin P, Börzsönyi T, Somfai E: Rheology of dense granular flows for elongated particles. PHYS REV E 96:(6) 062903/1-5 (2017)
12. Popov P, Mann EK, Jákli A: Thermotropic liquid crystal films for biosensors and beyond. J MATER CHEM B 5:(26) 5061-5078 (2017)
13. Salili SM, Ribeiro de Almeida RR, Challa PK, Sprunt SN, Gleeson JT, Jákli A:
Spontaneously modulated chiral nematic structures of flexible bent-core liquid crystal dimers. LIQUID CRYSTALS 44:(1) 160-167 (2017)
14. Shahsavan H, Salili SM, Jákli A, Zhao B: Thermally active liquid crystal network gripper mimicking the self-peeling of gecko toe pads. ADV MATER 29:(3) 1604021/1-7 (2017) 15. Shahsavan H, Yu L, Jákil A, Zhao BX: Smart biomimetic micro/nanostructures based on
liquid crystal elastomers and networks. SOFT MATTER 13:(44) 8006-8022 (2017) 16. Tomasovicova N, Kovac J, Gdovinova V, Éber N, Tóth-Katona T, Jadzyn J, Kopcansky P:
Y Alternating current magnetic susceptibility of a ferronematic. BEILSTEIN J NANOTECH 8: 2515-2520 (2017)
17. Xiang Y, Jing H-Z, Zhang Z-D, Ye W-J, Xu M-Y, Wang E, Salamon P, Éber N, Buka Á:
Tunable optical grating based on the flexoelectric effect in a bent-core nematic liquid crystal. PHYS REV APPL 7:(6) 064032/1-12 (2017)
18. Török J, Lévay S, Szabó B, Somfai E, Wegner S, Stannarius R, Börzsönyi T: Arching in three-dimensional clogging. EPJ WEB CONF 140: 03076/1-4 (2017) (Powders and Grains 2017 - 8th International Conference on Micromechanics on Granular Media, Montpellier, France, 03-07 July 2017)
19. Börzsönyi T, Somfai E, Szabó B, Wegner S, Ashour A, Stannarius R: Elongated grains in a hopper. EPJ WEB CONF 140: 06017/1-4 (2017) (Powders and Grains 2017 - 8th International Conference on Micromechanics on Granular Media, Montpellier, France, 03-07 July 2017)
20. Somfai E, Nagy DB, Claudin P, Favier A, Kálmán D, Börzsönyi T: Effective friction of granular flows made of non-spherical particles. EPJ WEB CONF 140: Paper 03062. 4 p.
(2017) (Powders and Grains 2017 - 8th International Conference on Micromechanics on Granular Media, Montpellier, France, 03-07 July 2017)
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21. Stannarius R, Fischer D, Börzsönyi T: Heaping and secondary flows in sheared granular materials. EPJ WEB CONF 140: Paper 03025. 4 p. (2017) (Powders and Grains 2017 - 8th International Conference on Micromechanics on Granular Media, Montpellier, France, 03-07 July 2017)
See also: S-L.6, S-L.7
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