Frustrated colloidal crystals: order between crystal and gel<!-- notionvc: b5861463-341f-4523-8f4b-59a4434393a6 -->

In recent years, research has shown that anisotropic colloids can self-organize into porous monolayers due to the interplay between bonding sites (referred to as patches) and particle shapes. These monolayers offer valuable micro-scale optical properties and the potential to create auxetic materials, which expand laterally when stretched, with applications in fields like tissue engineering and shock absorption.

Conventionally, it is believed that patchy particles need full bonding with their neighbors for crystal formation, and that if complete bonding was hindered due to patch placement, disordered structures would result. However, our computational study challenges this assumption: we deliberately arranged colloidal platelets with rhombic shapes and four small bonding sites in a way that discouraged full bonding. Surprisingly, instead of gels and glasses, we observed a variety of porous crystallites that were intentionally not fully bonded, with dangling bonds enhancing bonding possibilities. For each patch topology, we identified at least three competing polymorphs, including complex hierarchical structures like porous zig-zagging lattices, multi-porous hexagonal assemblies, and star-like and parallel open lattices. Intriguingly, in most systems, no single polymorph dominated, and the overall crystallinity remained at around 30% over extended simulation times. This leads us to the question posed in the title: Are these frustrated crystals a stable crystalline state, or do they constitute a partially ordered glassy state?

References:

[1] Q. Chen, S. C. Bae, S. Granick, "Nature" (2011), volume 469, pages 381–384.

[2] Y. Suzuki, M. Endo, H. Sugiyama, "Nature Communications" (2015), 6, 1–9.

[3] C. Karner, C. Dellago, E. Bianchi, "Nano Letters" (2019), 19, 7806–7815.<!-- notionvc: 277d96b4-4449-4f61-91de-a2d46ee33aa5 -->