Designing self-assembly routes to colloidal gyroids

Flavell, Wesley (2023). Designing self-assembly routes to colloidal gyroids. University of Birmingham. Ph.D.

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Abstract

Colloidal self-assembly has shown great potential as a bottom-up route to the fabrication of functional materials. An area of focus in this regard is the self-assembly of 3D photonic crystals which operate in the visible region of the spectrum. To this end, there has been much work on devising self-assembly routes to cubic diamond-related structures, since they possess some of the largest known 3D photonic band gaps. Largely ignored in this respect, is the single network gyroid structure, which also possesses a large 3D photonic band gap as well as offering additional applications relating to its chirality. Despite its natural appearances, the direct self-assembly of a single gyroid structure remains elusive.

In this thesis, a reverse engineering approach is employed in order to transform the single network gyroid structure into single gyroid colloidal crystal structures built from discrete spherical building blocks. In this approach, the three-fold connectivity of the network is encoded into triblock patchy spheres with two equal-size circular patches. Crystal structure prediction for triblock patchy particles via the basin-hopping technique, then identifies what this thesis refers to as the "single colloidal gyroid'' crystal, in addition to a library of competing trimer-based colloidal crystal structures. Monte Carlo simulations demonstrate, however, that these triblock patchy particles with circular patches are inadequate to self-assemble a single colloidal gyroid crystal. A method of crystal structure selection is then devised based on encoding the selective formation of specific inter-trimer dihedral angles into synthetically reasonable building blocks via the use of rectangular patch coverages at controlled relative orientations. A pair potential is developed in order to model the interactions between such patchy particles. Monte Carlo simulations of these designer chiral patchy spheres then demonstrate the enantiomorphic self-assembly of single colloidal gyroid for a wide parameter space. Alternatively, patchy particles of a fundamentally similar design with four circular patches are also shown to self-assemble single colloidal gyroid in silico. Further simulations demonstrate that both routes are robust, and it is established that an appropriate selection of target patch parameters yields an impressive tolerance for patch dispersity in both coverage and orientation – lending these bottom-up routes to the prospect of experimental realisation. Finally, self-assembly routes to double colloidal gyroid crystals are established in silico, employing racemic mixtures of chiral patchy particles with modified interaction matrices.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):