No abstract

Diblock copolymers are known to spontaneously organize into polymer vesicles. Typically, this is achieved through the techniques of film rehydration or electroformation. We present a new method for generating polymer vesicles from double emulsions. We generate precision water-in-oil-in-water double emulsions from the breakup of concentric fluid streams; the hydrophobic fluid is a volatile mixture of organic solvent that contains dissolved diblock copolymers. We collect the double emulsions and slowly evaporate the organic solvent, which ultimately directs the self-assembly of the dissolved diblock copolymers into vesicular structures. Independent control over all three fluid streams enables precision assembly of polymer vesicles and provides for highly efficient encapsulation of active ingredients within the polymerosomes. We also use double emulsions with several internal drops to form new polymerosome structures.

To investigate whether diblock copolymers with substantial distributions of molecular weight and composition can self-assemble into highly regular microdomain structures, we examine the morphologies of polystyrene-b-poly(acrylic acid), diblock copolymers (PS-PAA) synthesized by controlled radical polymerization in emulsion. Despite diblock polydispersity indices of ca. 2, solvent-cast films of these diblocks, as well as their blends with PS homopolymer of low molecular weight, exhibit well-ordered lamellar or hexagonally packed cylindrical morphologies in the midrange of composition, as shown by small-angle X-ray scattering and transmission electron microscopy. In several specimens, well-ordered regions of lamellae and cylinders appear to coexist. Films of very asymmetric diblocks or blends exhibit spherical microdomains without lattice order.