Structure and dynamics of colloidal particles on incommensurate substrates
Theoretical Condensed Matter Physics
Final Report Abstract
In the Emmy Noether group we explored the structure and the dynamics of colloidal particles close to structured substrates. In case of colloids that sediment onto a surface, we determined how colloidal quasicrystals can be grown for different substrates. Interestingly, a substrate with 8-fold quasicrystalline symmetry turned out to lead to the largest number of quasicrystalline layers. We employed this system for the first full three-dimensional analysis of the course of dislocation lines in quasicrystals, e.g., we presented examples for forking, annihilation, and bending of defect lines. The deposition on other incommensurate substrates, e.g., substrates that are stretched or compressed, turned out to lead to the formation of islands as well as pyramidal or rim structures. By using a dynamical phase field crystal model we also calculated the growth of twodimensional intrinsic quasicrystal from a seed and observed different modes of growth, including one that can only occur in a quasicrystal. Another interesting property of quasicrystals is the low friction coefficient when a crystal is pulled over the surface of a quasicrystal. We modeled this situation for a colloidal system and confirmed that the friction on quasicrystalline or other incommensurate substrates is much smaller than on commensurate substrates. At the moment, we still explore the differences between periodic and aperiodic substrates in more detail. In our study of the structure of hard sphere systems in the vicinity of a wall we compared our simulation results to calculations obtained by a density functional theory. Concerning the dynamics in this system, the broken isotropy turned out to be an advantage when we studied cage breaking events. We were able to quantitatively analyzed the importance of memory effects for particles that break out of cages close to the wall. In order to generalize the jamming phase diagram we simulated the dynamics of ultrasoft spheres where reentrant glass transitions can occur if the density is increased. We were able to show that if suitable control parameters are considered, the extended jamming phase diagram only possesses monotonous jamming surfaces. Furthermore, we extended our research to a gel-forming colloid-polymer mixture where the colloids effectivly are attractive for short distances. Together with the group of S. Egelhaaf (HHU Düsseldorf) where such gels are studied in experiments, we revealed that a directed percolation of the gel network is closely related to the slowdown of dynamics and the onset of ageing. Furthermore, we observe the detachment of directed percolated gel networks from walls which corresponds to a phenomena called syneresis. Syneresis also causes the formation of slab-like structures if the system is sheared. Our results have been published in Nature Communications. At the moment we explore the glassy dynamics of systems that are driven into nonequilibrium by moving traps. We have demonstrated that with traps moving according to specific patterns one can obtain non-equilibrium steady states without shear bands. Our results are important for many possible applications, e.g., the controlled growth of colloidal clusters on substrates, the production of colloidal quasicrystals by design, or methods how to obtain non-equilibrium colloidal systems without shear bands. We achieved to obtain a deeper insight into phenomena like the mechanisms of quasicrystalline growth, the importance of phasons for the properties of quasicrystals, friction on incommensurate substrates, suitable control parameters to explore and describe jamming, and the relation of glassy dynamics to mean structural quantities.
Publications
- Comparing light-induced colloidal quasicrystals with different rotational symmetries, Journal of Physics: Condensed Matter 24, 284101 (2012)
M. Schmiedeberg and H. Stark
(See online at https://doi.org/10.1088/0953-8984/24/28/284101) - What phasons look like: Particle trajectories in a quasicrystalline potential, Phys. Rev. Lett. 108, 218301 (2012)
J.A. Kromer, M. Schmiedeberg, J. Roth, and H. Stark
(See online at https://doi.org/10.1103/PhysRevLett.108.218301) - Multiple reentrant glass transitions of soft spheres at high densities: Monotonicity of the curves of constant relaxation times in jamming phase diagrams depending on temperature over pressure and pressure, Phys. Rev. E 87, 052310 (2013)
M. Schmiedeberg
(See online at https://doi.org/10.1103/PhysRevE.87.052310) - Course of dislocation lines in templated three dimensional colloidal quasicrystals, Phys. Rev. B 90, 064108 (2014)
M. Sandbrink and M. Schmiedeberg
(See online at https://doi.org/10.1103/PhysRevB.90.064108) - Growth modes of quasicrystals, Phys. Rev. Lett. 112, 255501 (2014)
C.V. Achim, M. Schmiedeberg, and H. Löwen
(See online at https://doi.org/10.1103/PhysRevLett.112.255501) - Particle segregation in a sedimenting bidisperse soft sphere system, Soft Matter 10, 4340 (2014)
M. Kohl and M. Schmiedeberg
(See online at https://doi.org/10.1039/c4sm00140k) - Anisotropic pair correlations in binary and multicomponent hard-sphere mixtures in the vicinity of a hard wall: A combined density functional theory and simulation study, Phys. Rev. E 92, 042310 (2015)
A. Härtel, M. Kohl, and M. Schmiedeberg
(See online at https://doi.org/10.1103/PhysRevE.92.042310) - Effective substrate potentials with quasicrystalline symmetry depend on the size of the adsorbed particles, European Physical Journal E 38, 54 (2015)
F. Rühle, M. Sandbrink, H. Stark, and M. Schmiedeberg
(See online at https://doi.org/10.1140/epje/i2015-15054-y) - Anisotropy and memory during cage breaking events close to a wall, Journal of Physics: Condensed Matter 28, 505001 (2016)
M. Kohl, A. Härtel, and M. Schmiedeberg
(See online at https://doi.org/10.1088/0953-8984/28/50/505001) - Directed percolation identified as equilibrium pre-transition towards nonequilibrium arrested gel states, Nature Communications 7, 11817 (2016)
M. Kohl, R.F. Capellmann, M. Laurati, S.U. Egelhaaf, and M. Schmiedeberg
(See online at https://doi.org/10.1038/ncomms11817)
