Programmierung adaptiver kolloidaler Suspensionen durch externe Felder
Zusammenfassung der Projektergebnisse
The goal of the project was to expose colloidal particles to an external potential that is coupled to the particle configuration by some function or ‘programme’. Thus, via the external potential, the colloidal suspension reacts to its own configuration through a feedback loop; the suspension becomes adaptive. This was attempted using a combination of experiment, theory and computer simulations. The main task was to implement and test this concept. The susceptibility of colloidal particles to light was exploited to impose external potentials that varied spatially and temporally. The external potential can hence be adapted to the particle configuration to achieve some feedback. The project could build on an available optical set-up that combines a spatial light modulator (SLM) with a pair of galvanometer-mounted mirrors (GMM) and was integrated into an optical microscope. This set-up, however, needed to be considerably adapted, developed further and extensively tested and its control software had to be designed and implemented. In particular, the light patterns created by the initiallyavailable SLM needed to be improved. Although an improvement was planned, the effect of the unwanted random contribution turned out to be much stronger than anticipated. Nevertheless, with a new high-resolution SLM this issue could be resolved so that, with the improved set-up, we could start to illustrate the behaviour of adaptive colloids and explore their properties. Initially, two complementary scenarios were realized. Both, a conventional ‘attractive’ and an inverted ‘repulsive’ harmonic potential located at the previous particle position were implemented. These two potentials restrain or accelerate the motion of the particle and induce subdiffusive or superdiffusive motion respectively. The two examples hence demonstrate that the dynamics of particles can be tuned in a broad range by an external potential and a delayed feedback. Ensembles of adaptive particles were also investigated to explore their cooperative behaviour. We could induce different particle arrangements, including the formation of ‘living’ chains, small clusters and different crystalline arrangements. Their properties, for example the crystal structure and unit cell size, could be controlled through the externallyimposed particle-particle interaction potential. Programmed particles hence provide the opportunity to systematically and quantitatively investigate the relation between particleparticle interactions and particle arrangements, e.g. different crystal symmetries. Furthermore, in contrast to (fixed) templates, an externally-imposed particle-particle interaction potential allows single particles as well as groups of particles to perform large-scale excursions. Our approach thus provides translationally invariant templates. The collective dynamics was investigated with strongly repulsive particles exposed to a feedback potential. This situation was studied by simulations and particle-resolved dynamical density functional theory. Although initially in a disordered fluid state, the particles can exhibit a spontaneous collective self-organization after the interactions are switched on. The particles arrange in a sequence of well-separated empty and crowded regions that move perpendicular to the direction of these bands. Hence they represent ‘traveling bands’. Adaptive colloids could thus successfully be prepared and controlled. Moreover, the examples illustrate the possibilities these systems offer and pave the way for systematic and quantitative investigations of programmed adaptive particles.
Projektbezogene Publikationen (Auswahl)
- Colloids exposed to random potential energy landscapes: From particle number density to particle-potential and particle-particle interactions, J. Chem. Phys. 145, 044905 (2016)
J. Bewerunge, A. Sengupta, R.F. Capellmann, F. Platten, S. Sengupta, S.U. Egelhaaf
(Siehe online unter https://doi.org/10.1063/1.4959129) - Dynamic mode locking in a driven colloidal system: Experiment and theory, New J. Phys. 19, 013010 (2017)
M.P.N. Juniper, U. Zimmermann, A.V. Straube, R. Besseling, D.G.A.L. Aarts, H. Löwen, R.P.A. Dullens
(Siehe online unter https://doi.org/10.1088/1367-2630/aa53cd) - Triple junction at the triple point resolved on the individual particle level, Phys. Rev. Lett. 119, 128001 (2017)
M. Chauduri, E. Allahyarov, H. Lowen, S.U. Egelhaaf, D.A. Weitz
(Siehe online unter https://doi.org/10.1103/PhysRevLett.119.128001) - Dense colloidal mixtures in an external sinusoidal potential, J. Chem. Phys. 148, 114903 (2018)
R.F. Capellmann, A. Khisameeva, F. Platten, S.U. Egelhaaf
(Siehe online unter https://doi.org/10.1063/1.5013007) - Impedance resonance in narrow confinement, J. Phys. Chem. C 122, 21724–21734 (2018)
S. Babel, M. Eikerling, H. Löwen
(Siehe online unter https://doi.org/10.1021/acs.jpcc.8b05559) - Light-controlled assembly of active molecules, J. Chem. Phys. 150, 094905 (2019)
F. Schmidt, B. Liebchen, H. Löwen, G. Volpe
(Siehe online unter https://doi.org/10.1063/1.5079861) - Traveling band formation in feedback-driven colloids, Phys. Rev. E 100, 022609 (2019)
S. Tarama, S.U. Egelhaaf, H. Löwen
(Siehe online unter https://doi.org/10.1103/PhysRevE.100.022609) - Diffusion of anisotropic particles in random energy landscapes – an experimental study, Front. Phys. 7, 224 (2020)
J.P. Segovia-Gutierrez, M.A. Escobedo-Sanchez, E. Sarmiento-Gomez, S.U. Egelhaaf
(Siehe online unter https://doi.org/10.3389/fphy.2019.00224) - Negative resistance for colloids driven over two barriers in a microchannel, Soft Matter
U. Zimmermann, H. Löwen, C. Kreuter, A. Erbe, P. Leiderer, F. Smallenburg
(Siehe online unter https://doi.org/10.1039/D0SM01700K)
