title: Macroscopic control of helix orientation in films dried from cholesteric liquid-crystalline cellulose nanocrystal suspensions.
abstract: The intrinsic ability of cellulose nanocrystals (CNCs) to self-organize into films and bulk materials with helical order in a cholesteric liquid crystal is scientifically intriguing and potentially important for the production of renewable multifunctional materials with attractive optical properties. A major obstacle, however, has been the lack of control of helix direction, which results in a defect-rich, mosaic-like domain structure. Herein, a method for guiding the helix during film formation is introduced, which yields dramatically improved uniformity, as confirmed by using polarizing optical and scanning electron microscopy. By raising the CNC concentration in the initial suspension to the fully liquid crystalline range, a vertical helix orientation is promoted, as directed by the macroscopic phase boundaries. Further control of the helix orientation is achieved by subjecting the suspension to a circular shear flow during drying.
authors.affiliation: Graduate School of Convergence Science & Technology, Nano Science & Technology Program, Seoul National University, 864-1 Iui-dong, Yeongtong-gu, Suwon-si, Gyeonggi-do (Korea).
authors.forename: Ji Hyun
authors.initials: JH
authors.lastname: Park
authors.forename: JungHyun
authors.initials: J
authors.lastname: Noh
authors.forename: Christina
authors.initials: C
authors.lastname: Schütz
authors.forename: German
authors.initials: G
authors.lastname: Salazar-Alvarez
authors.forename: Giusy
authors.initials: G
authors.lastname: Scalia
authors.forename: Lennart
authors.initials: L
authors.lastname: Bergström
authors.forename: Jan P F
authors.initials: JP
authors.lastname: Lagerwall
keywords: film growth; helical structures; liquid crystals; nanocrystalline cellulose; optical properties