Orientation Relaxation Dynamics in Cellulose Nanocrystal Dispersions in the Chiral Liquid Crystalline Phase

Abstract

A Landau-de Gennes formulation was implemented in dynamic finite element simulations to compare with postshear relaxation experiments that were conducted on cholesteric cellulose nanocrystal (CNC) dispersions. Our study focused on the microstructural reassembly of CNCs in lyotropic dispersions as parameters such as chiral strength and gap confinement were varied. Our simulation results show that homeotropic and/or more complicated three-dimensional helical configurations are possible, depending on the choice of these parameters. We also observed how dynamic banding patterns develop into the hierarchical microstructures that are characterized by an equilibrium pitch length in both the experiments and simulations. This work has immediate relevance for cellulose nanocrystal dispersion processing and provides new insight into fluid phase ordering for tailorable optical properties.

Angular optical response of cellulose nanocrystal films explained by the distortion of the arrested suspension upon drying

“…The presence of such shear is cancelled by symmetry in the central area of the films, whereas it can become significant where the films are affected by the meniscus shape, explaining the usual shift of the optical response at the edge of a dish-cast film. [6,65] On the macroscopic level, the examples of initial ODF illustrated here were either purely isotropic or only biaised by an external field, without the effects of anchoring at the top and bottom interfaces. To complement this, we also proposed an empirical description of the anchoring effect and introduced a crude modeling of the magnitude of its alignment via an adjustable term γ a , introduced as an energy balance between anchoring and thermal energy.…”

“…A similar approach can be developed to account for additional shear experienced near the edge of the drying suspension. [18,65,92] Besides CNC self-assembly, it will be relevant to other liquid crystalline suspensions that recently triggered interest for their ability to form complex structures upon drying, [17] and can be easily adapted to incompressible liquid crystalline systems subject to a unidirectional mechanical strain. [93] The application of these general ideas can also be relevant to understand alternative self-assembly mechanisms involving unidirectional removal of the solvent such as in vacuum filtration or open ended capillaries.…”

“…The alignment of individual CNCs and of their cholesteric domains can be controlled in suspension using various methods such as external fields, [23,[53][54][55][56][57][58][59][60][61], shear, [21,[62][63][64][65] or anchoring. [20,22,49] When the suspension is exposed to a sufficient magnetic field prior to the kinetic arrest transition, the CNCs align with their long axis perpendicular to the field.…”

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.…”