Block copolymer assemblies with cross-link stabilization: From single-component monolayers to bilayer blends with PEO-PLA

Amphiphilic diblock copolymers containing poly(ethylene oxide) (PEO) and saturated polybutadiene (PBD) hydrophobic chains have been cross-linked in both monolayer and bilayer assemblies. For monolayers, the Langmuir isotherm proves consistent with prior measures of density and compressibility for bilayer vesicles, and the monolayers can be macroscopically transferred as Langmuir-Blodgett films. Since the films are inverted (PBD oriented away from the slide) at the air-water interface, they spontaneously reorganize when immersed in water into wormlike micelles. However, this transition is quenched when the film is stabilized by free radical polymerization. Atomic force microscopy shows a stabilized but pitted film, which allows height measurements that prove consistent with a monolayer. With bilayer vesicles, we investigate several additional aspects of cross-linking. Spatial control of membrane cross-linking on the micrometer-scale is demonstrated by dynamic inflation-deflation of a membrane fixed to the end of a micropipet. Complete polymerization of the bilayer renders vesicles resilient to chloroform solubilization, whereas preblending with a non-cross-linkable diblock copolymer of PEO-polylactic acid, undermines vesicle stability in chloroform-water solutions. The results prove miscibility and stable integration of two disparate block copolymers in a membrane, as well as a first-order scheme for controlled release of encapsulants.