Liquid crystalline phase behavior of well-defined cylindrical block copolymer micelles using synchrotron small-angle x-ray scattering

The structure and phase behavior of colloidal solutions of monodisperse rod-shaped micelles, of different lengths (ca. 300-2100 nm) and formed from poly(ferrocenylsilane)-block-polyisoprene (PFS-b-PI) diblock copolymers, have been investigated using synchrotron small-angle X-ray scattering. The dimensions of the crystalline PFS core, solvated PI corona, and the overall radial polydispersity were measured, and relationships between the characteristics of the constituent copolymers and the internal structure of the self-assembled micelles have been established. In addition, the effects of micelle length, length distribution, concentration, composition, and block length on the liquid crystalline phase behavior of the micelles have been determined. It was found that micelle dispersions exist in three distinct phases: isotropic, nematic, and hexagonally packed, depending predominantly on their concentration and aspect ratio. The results have also highlighted the importance of the coronal composition and structure in determining the high-concentration behavior of micelle dispersions.