Figure 1. Overview of the out-of-equilibrium self-assembly approach.

(a) Legend, showing the structure of the PEG-PS block copolymer building block and the colour scale for organic solvents, water and mixtures of the two. (b–d) Scheme of the self-assembly process. (b) Water is slowly (1 ml h⁻¹) added to a solution of PEG-PS in THF/dioxane. (c) Self-assembly of spherical polymersomes occurs with identical internal and external solvent composition. (d) Continued addition of water to the exterior lowers the permeability to water of the polymer membrane and induces osmotic pressure, creating an out-of-equilibrium situation. (e) Three samples with different final water content, showing different equilibration behaviour over time (days). Sample 1 (25% water) remained spherical. Sample 2 (50% water) deflated into prolate shapes after which they inflated back to spheres. Sample 3 (75% water) deflated into discs after which they inflated into stomatocytes.