Phase transition and gelation in cellulose nanocrystal-based aqueous suspensions studied by SANS

Yuan Xu; Elliot P Gilbert; Anna Sokolova; Jason R Stokes

doi:10.1016/j.jcis.2023.12.041

Phase transition and gelation in cellulose nanocrystal-based aqueous suspensions studied by SANS

J Colloid Interface Sci. 2024 Mar 15:658:660-670. doi: 10.1016/j.jcis.2023.12.041. Epub 2023 Dec 12.

Authors

Yuan Xu¹, Elliot P Gilbert², Anna Sokolova², Jason R Stokes³

Affiliations

¹ School of Chemical Engineering, The University of Queensland, Queensland, 4072, Australia. Electronic address: y.xu5@uq.edu.au.
² Australian Centre for Neutron Scattering, ANSTO, Lucas Heights, New South Wales, 2234, Australia.
³ School of Chemical Engineering, The University of Queensland, Queensland, 4072, Australia. Electronic address: Jason.stokes@uq.edu.au.

PMID: 38134674
DOI: 10.1016/j.jcis.2023.12.041

Abstract

Hypothesis: Aqueous suspensions of cellulose nanocrystals (CNC) form a re-entrant liquid crystal (LC) phase with increasing salinity. Phase separation occurs in this LC state leading to a biphasic gel with a flow programmable structure that can be used to form anisotropic soft materials. We term this state a Liquid Crystal Hydroglass (LCH). Defining the mechanisms by which the LCH forms requires detailed structural analysis at the mesoscopic length scale.

Experiments: By utilising Small Angle Neutron Scattering (SANS), we investigated the microstructure transitions in CNC suspensions, with a particular focus on the unique LC re-entrancy and gelation into the biphasic LCH.

Findings: Scattering from LCH gels comprises contributions from a dispersed liquid state and static heterogeneity, characterised using a Lorentzian-Gaussian model of inhomogeneity. This conceptually supports a gelation mechanism (spinodal decomposition) in CNC suspensions towards a biphasic structure of the LCH. It also demonstrates that, with increasing salinity, the non-monotonic variation in effective volume fraction of CNC rods fundamentally causes the LC re-entrancy. This work provides the first experimental characterisation of the LC-re-entrancy and formation of an anisotropic LCH gel. The proposed mechanism can be extended to understanding the general behaviour of anisotropic colloids.

Keywords: Anisotropic soft material; Cellulose nanocrystal; Colloidal phase behaviour; Gelation; Liquid crystal; Nanocrystalline cellulose; SANS; Small angle neutron scattering.