Asymmetric organic-inorganic hybrid giant molecule: hierarchical smectic phase induced from poss nanoparticles by addition of nematic liquid crystals

Spontaneous vertical alignment (VA) of a nematic liquid crystal medium, 4-cyano-4′-heptyloxybiphenyl (7OCB), was successfully achieved by directely adding a small amount of cyanobiphenyl monosubstituted polyhedral oligomeric silsesquioxane (POSS-CB) giant molecules [Kim, D.-Y.; Kim, S.; Lee, S.-A; Choi, Y.-E.; Yoon, W.-J.; Kuo, S.-W.; Hsu, C.-H.; Huang, M.; Lee, S. H.; Jeong, K.-U. J. Phys. Chem. C 2014, 118, 6300-6306]. The cyanobiphenyl moiety chemically attached to the pristine POSS improved the initial solubility with the 7OCB molecules and alleviated the macroscopic aggregates. However, the phase behavior and structural evolution of the finely tuned POSS-CB giant molecules with 7OCB are still open questions. Based on the thermal, microscopic, and scattering experiments, it was realized that the POSS-based giant molecules strongly interacted with host 7OCB at a molecular level and induced the layered structure. The POSS groups in the POSS-CB giant molecules were laterally close-packed to create the stable two-dimensional (2D) crystalline platforms, where the tethered CB moieties provided the enough empty spaces for 7OCB to crawl into the empty zones. Additionally, the phase behavior of the mixtures was clarified by performing the theoretical calculation based on a combined Flory-Huggins (FH)/Maier-Saupe (MS)/phase field (PF) model.