Ion-Induced Formation of Nanocrystalline Cellulose Colloidal Glasses Containing Nematic Domains

Abstract

Controlling the assembly of colloids in dispersion is a fundamental approach toward the production of functional materials. Nanocrystalline cellulose (NCC) is a charged nanoparticle whose colloidal interactions can be modulated from repulsive to attractive by increasing ionic strength. Here, we combine polarized optical microscopy, rheology, and small-angle scattering techniques to investigate (i) the concentration-driven transition from isotropic dispersion to cholesteric liquid crystals and (ii) salt-induced NCC phase transitions. In particular, we report on the formation of NCC attractive glasses containing nematic domains. At increasing NCC concentration, a structure peak was observed in small-angle X-ray scattering (SAXS) patterns. The evolution of the structure peak demonstrates the decrease in NCC interparticle distance, favoring orientational order during the isotropic–cholesteric phase transition. Small amounts of salt reduce the cholesteric volume fraction and pitch by a decrease in excluded volume. Beyond a critical salt concentration, NCC forms attractive glasses due to particle caging and reduced motility. This results in a sharp increase in viscosity and formation of viscoelastic glasses. The presence of nematic domains is suggested by the appearance of interference colors and the Cox–Merz rule failure and was confirmed by an anisotropic SAXS scattering pattern at q ranges associated with the presence of nematic domains. Thus, salt addition allows the formation of NCC attractive glasses with mechanical properties similar to those of gels while remaining optically active owed to entrapped nematic domains.

Adsorption of charged anisotropic nanoparticles at oil–water interfaces

“…This ionic strength allows for sufficient CNC charge screening and intermolecular interactions without inducing aggregation. 12,13 Charge screening accelerated CNC adsorption and resulted in a higher maximum p norm of 0.38 AE 0.01. Charge screening prevents the electrostatic repulsion of CNCs in the bulk and those already adsorbed at the O/W interface.…”

“…The employed CNCs are 79 AE 6 nm long and 5 nm in height with a linear charge density of 0.67 nm À1 . 12,13 The detailed Experimental section is provided in the ESI. †…”

“…12 Their surface charge allows the modulation of CNC interactions from repulsive to attractive by targeted salt addition, making CNCs an interesting model system to investigate the effect of particle interactions on adsorbed nanoparticle layers. 13,14 CNC-stabilized emulsions reveal extraordinary stability against environmental inuences like heat, pH, ionic strength, and even gastric conditions. [15][16][17][18] Despite successful application in O/W emulsions, the adsorption and interactions of CNCs for different oils are mostly unknown.…”

A novel supra coarse-grained model for cellulose

“…The ordering of CNC into chiral nematic phases has been a topic of numerous studies and might be used in applications such as optical encryption, chiral templates or optical sensors (Schütz et al 2015;Surov et al 2017;Liu et al 2019Liu et al , 2018Pospisil et al 2018;Bertsch et al 2019;Parker et al 2016;Yao et al 2017;Park et al 2014;Frka-Petesic et al 2017;Nguyen et al 2013;Parker et al 2018a;Zhang et al 2012;Shopsowitz et al 2010;Kamita et al 2016;Parker et al 2018b). One of the main characteristics of CNC chiral nematic phases is their pitch (p), where often the half pitch (p/2) is reported.…”

“…CNC and CNF can assemble into variety of different configurations (Kontturi et al 2018;Lagerwall et al 2014;Ding et al 2014;Orts et al 1998;Benselfelt et al 2019;Lombardo et al 2019;Honorato-Rios et al 2018). CNC can also self-assemble into chiral nematic phases which possess interesting photonic properties and may have applications as optical material (Schütz et al 2015;Surov et al 2017;Liu et al 2019Liu et al , 2018Pospisil et al 2018;Bertsch et al 2019;Parker et al 2016;Yao et al 2017). The reflected wavelengths of the chiral nematic phases are depended of the pitch (p) of the self-assembled CNC.…”