Assembly of Liquid Crystalline Cellulose Nanocrystals for Preparation of Anisotropic Aerogels with Ordered Structures

Guang Chu1, Dan Qu2 Eyal Zussman1* and Yan Xu2*

1 Faculty of Mechanical Engineering, Technion-Israel Institute of Technology, Haifa 32000, Israel

2 State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, Jilin University, 2699 Qianjin Street, Changchun 130012, China

KEYWORDS: Freeze casting, Liquid crystal, Cellulose nanocrystal, Anisotropic aerogel

ABSTRACT: Imparting aerogels with structural anisotropy endows these porous materials with direction-dependent properties with promising novel applicability in material science. However, facile fabrication of such anisotropic aerogels under mild conditions still remains a major challenge. Here, we report on the fabrication of anisotropic aerogels from chiral nematic ordered cellulose nanocrystals (CNCs) by a directional freeze-casting process. The resulting CNCs aerogels were millimetre-sized with lamellar mesostructural features and optical anisotropy, exhibiting hierarchical structures perpendicular to the direction of freezing. We show that the birefringence of CNC aerogels arose from the of liquid crystalline CNCs suspensions, rather than from the shape of rod-like nanoparticles. Moreover, the versatility of the directional freezing approach was expanded to a CNC-silica system, resulting in anisotropic silica aerogels with an ordered mesopore-imprinted structure template by the liquid crystalline-ordered CNCs. The highly directional alignment, optical anisotropy, hierarchical porosity and large internal surface area of CNC-based aerogels exhibit bear considerable potential for future fire-resistant, direction-dependent mechanical and electrical insulator applications.