The synthesis and assembly of mildly fused asymmetric polystyrene/silica dimers confined to gap heights intermediate to an in-plane monolayer and an out-of-plane monolayer are explored. Using real-space confocal microscopy, we show that structures evolve from an oblique two-dimensional (2D) phase to a quasi-2D rotator, and finally to an upright hexagonally close-packed monolayer. The existence of the novel quasi-2D state, where out-of-plane motion is allowed, highlights the critical role that confinement dimensionality plays on the nature of ordering in complex colloidal systems.
Theoretical modeling of the photonic band gap forming properties is reported for the buckled phase of anisotropic particles. These exist between the first and second particulate layers of confined colloidal suspensions. Inspired by the range of non-spherical mushroom-cap building blocks for self-assembly that have been synthesized using seeded emulsion-polymerization, we explore in particular the band structures as a function of toroid shape parameter. The parameter is adjusted to incrementally transform hemispheres to spheres. Additionally, corrugation heights that systematically modulate the slab photonic crystal unit cell from rectangular monolayer to square bilayer are investigated. Polarization independent gaps in the guided modes are determined for direct and inverted structures that exhibit bifurcation in the particle orientation perpendicular to the slab plane. Gaps in the guided modes are observed between the fourth and fifth, twelfth and thirteenth, as well as higher band locales as the particle morphology and lattice aspect ratio vary.
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