Predicting structures for self-assembled colloidal matter

Rao, Abhishek Baindoor (2019). Predicting structures for self-assembled colloidal matter. University of Birmingham. Ph.D.

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Abstract

Colloidal self-assembly provides a bottom-up route to fabricate soft functional materials from simple building blocks. The scope for tuning the interactions between colloidal particles makes colloidal self-assembly programmable to yield the desired structure. This thesis employs a variety of computational techniques to predict and analyse the structures of soft materials that could be self-assembled from designer colloidal building blocks. In this context, the focus is on photonic crystals, which are composite media having periodic variation of dielectric constants, displaying attractive photonic properties.
In this body of work, a computational framework for the prediction of crystal structures was developed and benchmarked by implementing basin-hopping algorithm for global optimisation with fully flexible cell variables in the software GlOSP: A program for Global Optimisation for Structure Prediction. The present implementation can deal with spherical particles interacting via isotropic and/or anisotropic interactions, the latter involving a rigid-body treatment.
This framework was then applied to triblock patchy colloidal particles to find parameter space, which supports cubic and hexagonal tetrastack lattices. A hierarchical selfassembly scheme was then explored to realise these rather open three-dimensional (3D) lattices, which have proven difficult to be accessible via self-assembly pathways. The cubic polymorph was known to have a complete photonic bandgap, which was confirmed by photonic band structure calculations. Furthermore, a complete photonic bandgap was identified for the so-called tetrahedral diamond crystal structure, previously demonstrated to be hierarchically self-assembled from triblock patchy particles via tetrahedral clusters. The photonic band structure calculations were carried out by establishing a platform to subject the crystal structures predicted by GlOSP to photonic band structure calculations by MIT Photonic Bands (MPB) a free and open-source software package. Our findings thus highlight the appealing prospects of realising 3D photonic crystals via hierarchical self-assembly of triblock patchy particles. Finally, a system of asymmetric colloidal magnetic dumbbells was studied in the bulk to investigate emerging helical structures in the presence of an applied magnetic field.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):