Phase behavior and magnetic field response of liquid crystalline block copolymers with labile mesogens

Self-assembly of liquid crystalline block copolymers(LCBCPs) in magnetic fields can yield highly aligned states. The presence of labile mesogens in such systems can modify the field response and phase behavior. We explore a cylinder-forming polylactide(PLA)-based LCBCP blended with labile cyanobiphenyl mesogens. The critical field strength to achieve well-aligned microdomains decreases to sub-1 T values on addition of small amounts of mesogens. At higher mesogen content, the system undergoes a swelling-induced transition to spherical PLA microdomains embedded in a nematic LC matrix. Strikingly, the spherical microdomains order on a rotationally degenerate FCC lattice in which the [001] lattice vector is parallel to the applied field. We systematically explore the system morphology between aligned HEX cylinders and FCC spheres as a function of composition and investigate the effects of field strength and cooling rate on orientational order using in situ X-ray scattering and transmission electron microscopy. Our results demonstrate that the addition of labile mesogens significantly enhances the field response of these materials and provides a pathway to the formation of textured cubic systems that are otherwise not amenable to alignment in a uniaxial magnetic field.