Entropy-driven formation of large icosahedral colloidal clusters by spherical confinement

• Published in: Nature materials Vol. 14; no. 1; pp. 56 - 60
• Main Authors: de Nijs, Bart, Dussi, Simone, Smallenburg, Frank, Meeldijk, Johannes D., Groenendijk, Dirk J., Filion, Laura, Imhof, Arnout, van Blaaderen, Alfons, Dijkstra, Marjolein
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.01.2015; Nature Publishing Group
• Subjects: 639/766/119/1002; 639/925/357/354; Biomaterials; Clusters; Colloids; Condensed Matter Physics; Confinement; Crystallization; Crystals; Entropy; Formations; Icosahedral phase; letter; Long range order; Materials Science; Nanoparticles; Nanostructure; Nanotechnology; Optical and Electronic Materials
• ISSN: 1476-1122; 1476-4660
• DOI: 10.1038/nmat4072

Experiments with colloidal nano- and microparticles and computer simulations show that, unexpectedly, confinement and entropy are sufficient for the formation of icosahedral crystalline clusters of up to about 100,000 particles. Icosahedral symmetry, which is not compatible with truly long-range order, can be found in many systems, such as liquids, glasses, atomic clusters, quasicrystals and virus-capsids 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 . To obtain arrangements with a high degree of icosahedral order from tens of particles or more, interparticle attractive interactions are considered to be essential 1 , 3 , 6 , 7 , 8 , 9 , 10 , 11 , 12 . Here, we report that entropy and spherical confinement suffice for the formation of icosahedral clusters consisting of up to 100,000 particles. Specifically, by using real-space measurements on nanometre- and micrometre-sized colloids, as well as computer simulations, we show that tens of thousands of hard spheres compressed under spherical confinement spontaneously crystallize into icosahedral clusters that are entropically favoured over the bulk face-centred cubic crystal structure 13 , 14 . Our findings provide insights into the interplay between confinement and crystallization and into how these are connected to the formation of icosahedral structures.