Formation of homogeneous gel-like phases by mixed triblock copolymer micelles in aqueous solution: FCC to BCC phase transition

The phase behavior of mixed block copolymers E99P69E99 and E45B14E45 (with E, P and B being oxyethylene, oxypropylene and oxybutylene, respectively) in aqueous solution is reported for the first time. Homogeneous gel-like structures, formed by the ordered packing of mixed block copolymer micelles, were studied by small-angle X-ray scattering (SAXS). Four different single phases could be identified: mixed solution, body-centered cubic (bcc), face-centered cubic (fcc) and hexagonal. Two fcc to bcc transitions occurred by increasing E99P69E99 concentration or by adding a small amount of E45B14E45 chains to the E99P69E99/water system while keeping the total polymer concentration constant at around 30 wt%.