FROM MICELLES TO RANDOMLY CONNECTED, BILAYERED MEMBRANES IN DILUTE BLOCK-COPOLYMER BLENDS

As macromolecular surfactants, diblock copolymers order into a variety of morphologies in the presence of a parent homopolymer. Here, we pro be the effects of chemical incompatibility and interfacial rigidity on the morphology of copolymer/homopolymer blends at constant blend comp osition. Five copolymers, each possessing a random-sequence midblock t hat is varied from 0 to 40 wt% of the copolymer molecular weight, have been synthesized for this purpose. While copolymer micelles are repre sentative of dilute (homopolymer-rich) blends, complex bilayered morph ologies, including vesicles and the anomalous isotropic ''sponge'' pha se, are produced upon increasing the midblock fraction. Small-angle ne utron scattering provides a quantitative assessment of characteristic microstructural dimensions, while transmission electron microtomograph y yields the first three-dimensional images of the randomly connected, bilayered membrane comprising the sponge phase.