Shear Flow Orientation of Cylindrical Microdomain in Liquid Crystalline Diblock Copolymer and its Potentiality as Anchoring Substrate for Nematic Mesogens

We prepared a diblock copolymer composed of polystyrene (PS) and side-chain liquid crystal polymer (LCP) by atom transfer radical polymerization. The weight fraction of the PS segment is 0.22, resulting in a microsegregated structure with PS cylinders hexagonally packed in a matrix of LCP, which forms smectic A, nematic and isotropic phases in order of increasing temperature. Shear flow at nematic temperatures orients well the PS microcylinders, as well as the nematic mesogens of the LCP in the velocity direction. A high degree of orientation of 0.95 is attained for microcylinders while the orientational order parameter of the nematic LC is around 0.5. Interestingly, the nematic LC mesogens recover their initial orientation upon cooling after they have lost the orientational order in the isotropic melt. This spontaneous orientation shows that PS cylinders whose orientation is strongly sustained with a temperature variation acts as an anchoring substrate for the nematic mesogens.