da Rosa Rafaela R, Silva Pedro E S, Saraiva Diogo V, Kumar Anant, de Sousa António P Mendes, Sebastião Pedro, Fernandes Susete N, Godinho Maria Helena
i3N/CENIMAT, Department of Materials Science, NOVA School of Science and Technology, NOVA University Lisbon, Campus de Caparica, Caparica, 2829-516, Portugal.
Centro de Física e Engenharia de Materiais Avançados, Departamento de Física, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, Lisbon, 1049-001, Portugal.
Adv Mater. 2022 Jul;34(28):e2108227. doi: 10.1002/adma.202108227. Epub 2022 Jun 6.
The colloidal suspensions of aqueous cellulose nanocrystals (CNCs) are known to form liquid crystalline (LC) systems above certain critical concentrations. From an isotropic phase, tactoid formation, growth, and sedimentation have been determined as the genesis of a high-density cholesteric phase, which, after drying, originates solid iridescent films. Herein, the coexistence of a liquid crystal upper phase and an isotropic bottom phase in CNC aqueous suspensions at the isotropic-nematic phase separation is reported. Furthermore, isotropic spindle-like domains are observed in the low-density LC phase and high-density LC phases are also prepared. The CNCs isolated from the low- and high-density LC phases are found to have similar average lengths, diameters, and surface charges. The existence of an LC low-density phase is explained by the presence of air dissolved in the water present within the CNCs. The air dissolves out when the water solidifies into ice and remains within the CNCs. The self-adjustment of the cellulose chain conformation enables the entrapment of air within the CNCs and CNC buoyancy in aqueous suspensions.
已知水性纤维素纳米晶体（CNC）的胶体悬浮液在高于特定临界浓度时会形成液晶（LC）体系。从各向同性相开始，已确定类晶结构的形成、生长和沉降是高密度胆甾相的起源，干燥后会形成固体彩虹色薄膜。在此，报道了在各向同性 - 向列相分离时，CNC水性悬浮液中液晶上相和各向同性下相的共存。此外，在低密度LC相中观察到各向同性的纺锤状区域，并且还制备了高密度LC相。从低密度和高密度LC相中分离出的CNC具有相似的平均长度、直径和表面电荷。LC低密度相的存在是由于CNC内部水中溶解有空气。当水凝固成冰时，空气溶解出来并保留在CNC内部。纤维素链构象的自我调节使得空气能够被困在CNC内部，并且使CNC在水性悬浮液中具有浮力。
