Designing colloidal open crystals & empty liquids

Neophytou, Andreas (2024). Designing colloidal open crystals & empty liquids. University of Birmingham. Ph.D.

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Abstract

Because their shape and interactions can be readily controlled, colloidal particles are particularly well suited to act as building blocks for the bottom-up fabrication of complex three-dimensional structures. The self-assembly of sub-micrometre colloidal particles has long been recognised as a promising approach to fabricate photonic materials that operate at visible wavelengths. Cubic diamond-structured colloidal photonic crystals are particularly sought after for their applications in visible light management because of their ability to support a complete photonic band gap at low refractive-index contrasts; however, their realisation via self-assembly pathways has proved to be a long-standing challenge.
In this context, this thesis presents a body of computational studies that devise self- assembly routes for designer triblock patchy colloidal rods and tetrahedral patchy particles to yield colloidal diamond crystals by encoding ring selection rules to circumvent kinetic traps. We show that the photonic band gap of the resulting crystals assembled from the triblock patchy rods is robust to stacking faults, thus circumventing the requirement of polymorph selection in a scalable fabrication method. Additionally, using patterning sym- metry concepts, we present a bottom-up route to an enantiomorphic pair of single gyroid crystals comprising colloidal spheres, and demonstrate their assembly from rationally designed patchy spheres. We show that the single colloidal gyroid, and its inverse structure, supports a wide complete photonic band gap in addition to exhibiting rich chiroptical properties, making them attractive chiral photonic crystals.
Colloids, traditionally seen as “big atoms” and more recently with the development of the concept of “colloidal molecules”, are also perfectly suited to act as model systems for atomic and molecular systems, and provide a window through which we can glean new insight into a number of fundamental problems in condensed matter physics. One such problem is the liquid-liquid phase transition – hypothesised to underpin the anomalous thermodynamic properties of water. We rationally design a colloidal analogue of water using triblock patchy particles, showcasing that this model displays the well-known water thermodynamic anomalies, as well as a liquid-liquid critical point. Using this model, we reveal that the liquid-liquid phase transition of tetrahedral networks can be described as a topological transition between an unentangled low-density liquid and an entangled high-density liquid, the latter containing an ensemble of topologically complex motifs. We show that this topological distinction between the low-density and high-density liquids also holds for molecular water in connection with the liquid-liquid phase transition.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):