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Closed capsules, such as lipid vesicles, soap bubbles, and emulsion droplets, are ubiquitous throughout biology, engineered matter, and everyday life. Their creation and disintegration are defined by a singularity that separates a topologically distinct extended liquid film from a boundary-free closed shell. Such topology-changing processes are of fundamental interest. They are also essential for intercellular transport, transcellular communication, and drug delivery. However, studies of vesicle formation are challenging because of the rapid dynamics and small length scale involved. We develop fluid colloidosomes, micrometer-sized analogues of lipid vesicles. The mechanics of colloidosomes and lipid vesicles are described by the same theoretical model. We study colloidosomes close to their disk-to-sphere topological transition. Intrinsic colloidal length and time scales slow down the dynamics to reveal colloidosome conformations in real time during their assembly and disassembly. Remarkably, the lowest-energy pathway by which a closed vesicle transforms into a flat disk involves a topologically distinct cylinder-like intermediate. These results reveal aspects of topological changes that are relevant to all liquid capsules. They also provide a robust platform for the encapsulation, transport, and delivery of nanosized cargoes. 

Using a combination of theory and experiments we study the interface between two immiscible domains in a colloidal membrane composed of rigid rods of different lengths. Geometric considerations of rigid rod packing imply that a domain of sufficiently short rods in a background membrane of long rods is more susceptible to twist than the inverse structure, a long-rod domain in a short-rod membrane background. The tilt at the inter-domain edge forces splay, which in turn manifests as a spontaneous edge curvature whose energetics are controlled by the length asymmetry of constituent rods. A thermodynamic model of such tilt-curvature coupling at inter-domain edges explains a number of experimental observations, including a non-monotonic dependence of the edge twist on the domain radius, and annularly shaped domains of long rods. Our work shows how coupling between orientational and compositional degrees of freedom in two-dimensional fluids give rise to complex shapes and thermodynamics of domains, analogous to shape transitions in 3D fluid vesicles.