Hierarchical self-assembly of elongated patch colloids into photonic crystals

Neophytou, Andreas (2019). Hierarchical self-assembly of elongated patch colloids into photonic crystals. University of Birmingham. M.Sc.

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Abstract

Photonic crystals, dubbed semiconductors for light, provide a platform to control the flow of light, increasingly finding applications in optical communications, lasers and sensors, just to name a few. This thesis presents a body of computational studies undertaken to design novel photonic crystals and devise a bottom-up route to realise them, exploiting a hierarchical self-assembly scheme for elongated triblock colloids. The designer colloidal particles under consideration have a soft repulsive spherocylindrical core, with an attractive patch on each of the hemispherical caps. Using basin-hopping global optimisation, we first predict the low-lying structures for these designer colloidal particles on the crystal energy landscape. We find four isoenergetic structures as the global minima: cubic tetrastack, hexagonal tetrastack, double cubic tetrastack and triple cubic tetrastack. Our photonic band structure calculations then reveal that the cubic and hexagonal tetrastack structures both possess photonic band gaps, which are wider than their spherical counterparts. Additionally, we argue that the local tetrahedral ordering of the particles is vital for the band gaps found for both of these crystal structures. Finally, we explore a hierarchical self-assembly strategy for the colloidal particles to realise these colloidal crystals via a bottom-up route. To this end, we introduce a hierarchy of interaction strengths for the patch-patch interactions so that a two-stage assembly process is followed via the formation of self-limiting tetrahedral clusters. Although such a staged assembly pathway successfully leads to a crystal, a mixed phase of cubic and hexagonal tetrastack structures is observed.

Type of Work:

Thesis (Masters by Research > M.Sc.)

Award Type:

Masters by Research > M.Sc.

Supervisor(s):