Using chiral tactoids as optical probes to study the aggregation behavior of chromonics

Nayani, Karthik; Fu, Jinxin; Chang, Rui; Park, Jung Ok; Srinivasarao, Mohan

doi:10.1073/pnas.1614620114

Cited by 39 publications

(18 citation statements)

References 48 publications

(84 reference statements)

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“…The transition to the bipolar regime is recognized in the polarizing microscope by the tactoids no longer showing extinction at any orientation, because the optic axis is no longer uniform, hence some parts of the tactoid will always show birefringence. There may be a twist distortion as well, promoted by K 24 [94,95], but this has not yet been investigated for colloidal tactoids to the best of our knowledge.…”

Section: Isotropic-nematic Phase Coexistence and The Nucleation Of Tamentioning

confidence: 99%

From Equilibrium Liquid Crystal Formation and Kinetic Arrest to Photonic Bandgap Films Using Suspensions of Cellulose Nanocrystals

et al. 2020

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The lyotropic cholesteric liquid crystal phase developed by suspensions of cellulose nanocrystals (CNCs) has come increasingly into focus from numerous directions over the last few years. In part, this is because CNC suspensions are sustainably produced aqueous suspensions of a fully bio-derived nanomaterial with attractive properties. Equally important is the interesting and useful behavior exhibited by solid CNC films, created by drying a cholesteric-forming suspension. However, the pathway along which these films are realized, starting from a CNC suspension that may have low enough concentration to be fully isotropic, is more complex than often appreciated, leading to reproducibility problems and confusion. Addressing a broad audience of physicists, chemists, materials scientists and engineers, this Review focuses primarily on the physics and physical chemistry of CNC suspensions and the process of drying them. The ambition is to explain rather than to repeat, hence we spend more time than usual on the meanings and relevance of the key colloid and liquid crystal science concepts that must be mastered in order to understand the behavior of CNC suspensions, and we present some interesting analyses, arguments and data for the first time. We go through the development of cholesteric nuclei (tactoids) from the isotropic phase and their potential impact on the final dry films; the spontaneous CNC fractionation that takes place in the phase coexistence window; the kinetic arrest that sets in when the CNC mass fraction reaches ∼10 wt.%, preserving the cholesteric helical order until the film has dried; the ’coffee-ring effect’ active prior to kinetic arrest, often ruining the uniformity in the produced films; and the compression of the helix during the final water evaporation, giving rise to visible structural color in the films.

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Section: Isotropic-nematic Phase Coexistence and The Nucleation Of Tamentioning

confidence: 99%

From Equilibrium Liquid Crystal Formation and Kinetic Arrest to Photonic Bandgap Films Using Suspensions of Cellulose Nanocrystals

et al. 2020

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“…Because of the subtle balance between the surface tension, the surface anchoring condition and the long-range elasticity of the liquid crystalline phase, the shape and director field configuration of tactoids are very sensitive to a range of chemical and physical factors, such as chiral additives or external forces [23][24][25].…”

Section: Shapes and Director Field Configurations Of Tactoidsmentioning

confidence: 99%

Liquid crystalline tactoids: ordered structure, defective coalescence and evolution in confined geometries

Wang¹,

MacLachlan²

2017

Phil. Trans. R. Soc. A.

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Tactoids are liquid crystalline microdroplets that spontaneously nucleate from isotropic dispersions, and transform into macroscopic anisotropic phases. These intermediate structures have been found in a range of molecular, polymeric and colloidal liquid crystals. Typically only studied by polarized optical microscopy, these ordered but easily deformable microdroplets are now emerging as interesting components for structural investigations and developing new materials. In this review, we highlight the structure, property and transformation of tactoids in different compositions, but especially cellulose nanocrystals. We have selected references that illustrate the diversity and most exciting developments in tactoid research, while capturing the historical development of this field.This article is part of a discussion meeting issue 'New horizons for cellulose nanotechnology'.

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“…The emerging structures and associated functionalities result from an intriguing interplay between bulk elasticity, surface anchoring and intrinsic chirality of the mesogens, dictating the equilibrium configuration of the tactoid 5,6 . Due to this subtle balance of the energy terms, the shape and director field configuration of the tactoid are very sensitive to various chemical and physical factors, such as temperature, chiral and achiral additives, external fields and confinement 7–9 . Confinement-induced reorganization of anisotropic particles in spherical regions is of particular interest, due to the possibility of experimentally generating droplets with controlled curvature for fundamental studies of particle packing, self-assembly, and relaxation of colloidal solutions 10–14 .…”

Section: Introductionmentioning

confidence: 99%

Six-fold director field configuration in amyloid nematic and cholesteric phases

Bagnani

Azzari

Assenza

et al. 2019

Sci Rep

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Chiral liquid crystals, or cholesteric phases, have been widely studied in the last decades, leading to fundamental advances and a multitude of applications and technologies. In general, the rich phenomenology of these systems depends directly on the molecular traits and conditions of the system, imposing precise symmetry to the resulting nematic field. By selecting amyloid fibrils as model filamentous chiral colloids, we report an unprecedented breadth of liquid crystalline morphologies, where up to six distinct configurations of the nematic field are observed under identical conditions. Amyloid-rich droplets show homogeneous, bipolar, radial, uniaxial chiral and radial chiral nematic fields, with additional parabolic focal conics in bulk. Variational and scaling theories allow rationalizing the experimental evidence as a subtle interplay between surface and bulk energies. Our experimental and theoretical findings deepen the understanding of chiral liquid crystals under confinement, opening to a more comprehensive exploitation of these systems in related functional materials.

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Using chiral tactoids as optical probes to study the aggregation behavior of chromonics

Cited by 39 publications

References 48 publications

From Equilibrium Liquid Crystal Formation and Kinetic Arrest to Photonic Bandgap Films Using Suspensions of Cellulose Nanocrystals

From Equilibrium Liquid Crystal Formation and Kinetic Arrest to Photonic Bandgap Films Using Suspensions of Cellulose Nanocrystals

Liquid crystalline tactoids: ordered structure, defective coalescence and evolution in confined geometries

Six-fold director field configuration in amyloid nematic and cholesteric phases

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