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Surprises in the Self-Assembly of Particles in Spherical Confinement

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About 6 years ago our group started research at developing methodologies to structure matter at multiple length scales by Self-Assembly (SA). Presently, we see the induced SA of particles inside slowly drying droplets dispersed in an emulsion system and the resulting supraparticles (SPs) as a powerful generally applicable methodology of hierarchical SA. We found that making the shape of the particles the dominant factor in the SA is the most versatile way to use this route also for complex particle shapes and mixtures of particles. One of our first findings by both experiments and computer simulations was that spherical particles self-assembled inside a spherical confinement do not have their equilibrium bulk face centered cubic, close packed, crystal arrangement, but instead adopt an icosahedral symmetry. It turns out this icosahedral symmetry is the lowest free energy state up until roughly 100.000 particles [1]. Icosahedral packings are known not to be able to regularly pack in 3D space and are known e.g. for clusters of atoms interacting through a Lennard-Jones potential. However, it was not known that shape and thus entropy alone would favor this symmetry as well when it is induced by the spherical confinement. In recent work, we have extended our results to include the effects of particles shape (e.g. using rounded cube shaped particles) [2], rod-shaped particles [3], plate-shaped and binary particle systems. We will discuss how these changes affect the SA and how such SPs can be analyzed quantitatively on the single particle level in 3D by electron microscopy tomography [1-4]. We will also show our first more applied work on creating SPs with tunable light emission [5,7], for which the emission properties are modified by Mie Whispering Gallery Modes [6], and that are able to lase as well [7]. For a binary mixture of hard particles that form so-called MgZn2 Laves Phase crystals in bulk we find 3D icosahedral quasicrystals to be induced by the spherical confinement (unpublished work) allowing us for the first time to determine on the single particle level in 3D the structure of a quasicrystal and with computer simulations study how these systems nucleate and grow.

1) Entropy-driven formation of large icosahedral colloidal clusters by spherical confinement, de Nijs, et al., Dijkstra, AvB, Nature Materials 14, 56-60 (2015). 2) Interplay between spherical confinement and particle shape on the self-assembly of rounded cubes, Wang, Murray, Dijkstra, et al., AvB, Nature Comm., 8, 2228 (2018). 3) Determination of the positions and orientations of concentrated rod-like colloids from 3D microscopy data, Besseling, et al, Dijkstra, AvB, J. of Phys: Cond. Mat., 27, 194109 (2015) 4) Quantitative 3D Analysis of Huge Nanoparticle Assemblies, Zanaga, et al., Liz-Marzán, AvB, Batenburg, Bals, van Tendeloo, Nanoscale, 8, 292 (2016). 5) Composite Supraparticles with Tunable Light Emission, Montanarella, et al., Bals, Vanmaekelbergh, AvB, ACS Nano, 11 (9), 9136 (2017). 6) Shape-dependent multi-exciton emission and whispering gallery modes in supraparticles of CdSe/multi-shell quantum dots, Vanmaekelbergh, et al., AvB, ACS Nano, 9, 3942 (2015). 7) Lasing Supraparticles Self-Assembled from Nanocrystals, F. Montanarella, D. Urbonas, L. Chadwick, P.G. Moerman, P.J. Baesjou, R.F. Mahrt, A. van Blaaderen, T. Stöferle and D. Vanmaekelbergh, ACS Nano 12 (12), 12788-12794 (2018).

This talk is part of the Materials Chemistry Research Interest Group series.

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