[OPEN ACCESS] Rod Packing in Chiral Nematic Cellulose Nanocrystal Dispersions Studied by Small-Angle X-ray Scattering and Laser Diffraction

Christina Schütz, Michael Agthe, Andreas B. Fall, Korneliya Gordeyeva, Valentina Guccini, Michaela Salajková, Tomás S. Plivelic, Jan P. F. Lagerwall, German Salazar-Alvarez, and Lennart Bergström
Langmuir 31 (2015) 6507–6513.
DOI: 10.1021/acs.langmuir.5b00924

Abstract

The packing of cellulose nanocrystals (CNC) in the anisotropic chiral nematic phase has been investigated over a wide concentration range by small-angle X-ray scattering (SAXS) and laser diffraction. The average separation distance between the CNCs and the average pitch of the chiral nematic phase have been determined over the entire isotropic–anisotropic biphasic region. The average separation distances range from 51 nm, at the onset of the anisotropic phase formation, to 25 nm above 6 vol % (fully liquid crystalline phase) whereas the average pitch varies from ≈15 μm down to ≈2 μm as ϕ increases from 2.5 up to 6.5 vol %. Using the cholesteric order, we determine that the twist angle between neighboring CNCs increases from about 1° up to 4° as ϕ increases from 2.5 up to 6.5 vol %. The dependence of the twisting on the volume fraction was related to the increase in the magnitude of the repulsive interactions between the charged rods as the average separation distance decreases.

Macroscopic Control of Helix Orientation in Films Dried from Cholesteric Liquid-Crystalline Cellulose Nanocrystal Suspensions

ChemPhysChem, 2014

DOI: 10.1002/cphc.201400062

Ji Hyun Park; JungHyun Noh; Christina Schütz; German Salazar-Alvarez; Giusy Scalia; Lennart Bergström; Jan P. F. Lagerwall

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.