| Autor: |
Majoinen J; Department of Bioproducts and Biosystems, Aalto University, Aalto, FI-00076 Espoo, Finland.; Technical Research Centre of Finland VTT, Biomaterial Processing and Products, FI-02150 Espoo, Finland., Gustavsson L; Department of Applied Physics, Aalto University, Aalto, FI-00076 Espoo, Finland., Wani O; Department of Applied Physics, Aalto University, Aalto, FI-00076 Espoo, Finland., Kiefer S; Department of Applied Physics, Aalto University, Aalto, FI-00076 Espoo, Finland., Liljeström V; Nanomicroscopy Center, OtaNano, Aalto University, Aalto, FI-00076 Espoo, Finland., Rojas OJ; Department of Bioproducts and Biosystems, Aalto University, Aalto, FI-00076 Espoo, Finland.; Bioproducts Institute, Department of Chemical and Biological Engineering, Department of Chemistry and Department of Wood Science, University of British Columbia, 2360 East Mall, Vancouver, British Columbia V6T 1Z3, Canada., Rannou P; Université Grenoble Alpes, Université Savoie Mont-Blanc, CNRS, Grenoble INP, LEPMI, 38000 Grenoble, France., Ikkala O; Department of Applied Physics, Aalto University, Aalto, FI-00076 Espoo, Finland. |
| Abstrakt: |
Cellulose nanocrystals (CNCs) are biobased colloidal nanorods that have unlocked new opportunities in the area of sustainable functional nanomaterials including structural films and coatings, biomedical devices, energy, sensing, and composite materials. While selective light reflection and sensing develop from the typical chiral nematic (cholesteric, Nem*) liquid crystallinity exhibited by CNCs, a wealth of technologies would benefit from a nematic liquid crystal (LC) with CNC uniaxial alignment. Therefore, this study answers the central question of whether surfactant complexation suppresses CNC chirality in favor of nematic lyotropic and thermotropic liquid crystallinity. Therein, we use a common surfactant having both nonionic and anionic blocks, namely, oligo(ethylene glycol) alkyl-3-sulfopropyl diether potassium salt (an alcohol ethoxy sulfonate (AES)). AES forms complexes with CNCs in toluene (a representative for nonpolar organic solvent) via hydrogen bonding with an AES' oligo(ethylene glycol) block. A sufficiently high AES weight fraction endows the dispersibility of CNC in toluene. Lyotropic liquid crystallinity with Schlieren textures containing two- and four-point brush defects is observed in polarized optical microscopy (POM), along with the suppression of the cholesteric fingerprint textures. The results suggest a nematic (Nem) phase in toluene. Moreover, thermotropic liquid crystallinity is observed by incorporating an excess of AES, in the absence of an additional solvent and upon mild heating. The Schlieren textures suggest a nematic system that undergoes uniaxial alignment under mild shear. Importantly, replacing AES with a corresponding nonionic surfactant does not lead to liquid crystalline properties, suggesting electrostatic structural control of the charged end group of AES. Overall, we introduce a new avenue to suppress CNC chirality to achieve nematic structures, which resolves the long-sought uniaxial alignment of CNCs in filaments, composite materials, and optical devices. |
