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Title: Programming patchy particles to form complex ordered structures
Author: Tracey, Daniel
ISNI:       0000 0004 7966 4060
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2019
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This thesis explores by numerical simulations the rational use of patchy particles to control material properties, by designing particles to either assemble into or apply internal stress to a target structure. Increasingly complex and fine-tuned patchy-particle assemblies are being reported, which may have a wide range of interesting properties and thus immense value for meso-scale materials, devices, and technologies. Understanding the behaviour of patchy-particle ensembles is also useful for understanding natural systems, such as viruses and condensed matter. I introduce a systematic, rational design scheme for a set of patchy particles to form a unique periodic structure. Torsional restrictions encoded in my patches assist assembly, by controlling second-nearest neighbour bonding. As a proof-of-concept, I demonstrated the robust assembly of five complex, extended, three-dimensional targets. In contrast, previous structures assembled from patchy particles are mostly simple, two-dimensional, and/or finite. I also considered simplified versions of the successful designs (e.g. fewer patches, no torsional interactions), finding them sufficient in some cases but not others. I further extend the structural complexity by assembling three-dimensional dodecagonal quasicrystals, building on earlier two-dimensional work which was recently realised via DNA origami. This is the first demonstration of the self-assembly of any three-dimensional quasicrystal from patchy particles. I use two systems: unary, with wide, non-selective patches; and ternary, with narrower, selective patches. Assembly is more complicated than in two dimensions (e.g. due to de-mixing), but robust nonetheless. I characterised the structures by their diffraction patterns. I unexpectedly observed screw dislocations in the unary system (the ternary system's narrower patches disfavour defects), and in an approximant. Finally, I deliberately introduce internal stress into a helical, tube-like structure via imperfectly aligned patches. Recently, a new mechanism of cholesteric ordering was identified (in DNA origami filaments) - solenoidal shape deformations due to mechanical stress. However, the results for my tubes were inconclusive, with no clear trend in solenoidal shape deformations being yet apparent. This was at least partially due to the tubes' stiffness, which reduced the shape fluctuations, but may also reflect the complex network of axial and lateral interactions controlling the tubes' mechanics.
Supervisor: Doye, Jonathan P. K. Sponsor: Engineering and Physical Sciences Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Chemistry, Physical and theoretical