Topology and kinetic pathways of colloidosome assembly and disassembly.

Abstract

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.