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

Crystals ◽  
2020 ◽  
Vol 10 (3) ◽  
pp. 199 ◽  
Author(s):  
Christina Schütz ◽  
Johanna R. Bruckner ◽  
Camila Honorato-Rios ◽  
Zornitza Tosheva ◽  
Manos Anyfantakis ◽  
...  

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.

Author(s):  
Camilla Honorato-Rios ◽  
Johanna Bruckner ◽  
Christina Schütz ◽  
Sammy Wagner ◽  
Zornitza Tosheva ◽  
...  

Soft Matter ◽  
2021 ◽  
Author(s):  
Yoichi Takanishi

Herein, the local nano-structure in mixtures of cholesteric liquid crystals and a bent-core molecule was analyzed via the small-angle X-ray scattering.


2014 ◽  
Vol 1698 ◽  
Author(s):  
Thomas M. Cooper ◽  
Aaron R. Burke ◽  
Douglas M. Krein ◽  
Ronald F. Ziolo ◽  
Eduardo Arias ◽  
...  

ABSTRACTTo prepare cholesteric liquid crystalline nonlinear optical materials with ability to be vitrified on cooling and form long time stability cholesteric glasses at room temperature, a series of platinum acetylide complexes modified with cholesterol has been synthesized. The materials synthesized have the formula trans-Pt(PR3)(cholesterol (3 or 4)-ethynyl benzoate)(1-ethynyl-4-X-benzene), where R = Et, Bu or Oct and X = H, F, OCH3 and CN. A cholesteric liquid crystal phase was observed in the complexes R = Et, and X = F, OCH3 and CN but not in any of the other complexes. When X = CN, a cholesteric glass was observed at room temperature which remained stable up to 130 °C, then converted to a mixed crystalline/cholesteric phase and completely melted to an isotropic phase at 230 °C. When X = F or OCH3 the complexes were crystalline at room temperature with conversion to the cholesteric phase upon heating to 190 and 230 °C, respectively. In the series X = CN, OCH3 and F, the cholesteric pitch was determined to be 1.7, 3.4 and 9.0 µ, respectively.


Crystals ◽  
2019 ◽  
Vol 9 (4) ◽  
pp. 183 ◽  
Author(s):  
Chia-Hua Yu ◽  
Po-Chang Wu ◽  
Wei Lee

We demonstrated previously that the temperature of a sandwich-type liquid crystal cell with unignorable electrode resistivity could be electrically increased as a result of dielectric heating. In this study, we take advantage of such an electro-thermal effect and report on a unique electric-field approach to the formation of uniform lying helix (ULH) texture in a cholesteric liquid crystal (CLC) cell. The technique entails a hybrid voltage pulse at frequencies f1 and, subsequently, f2, which are higher and lower than the onset frequency for the induction of dielectric heating, respectively. When the cell is electrically sustained in the isotropic phase by the voltage pulse of V = 35 Vrms at f1 = 55 kHz or in the homeotropic state with the enhanced ionic effect at V = 30 Vrms and f1 = 55 kHz, our results indicate that switching of the voltage frequency from f1 to f2 enables the succeeding formation of well-aligned ULH during either the isotropic-to-CLC phase transition at f2 = 1 kHz or by the electrohydrodynamic effect at f2 = 30 Hz. For practical use, the aligning technique proposed for the first time in this study is more applicable than existing alternatives in that the obtained ULH is adoptable to CLCs with positive dielectric anisotropy in a simple cell geometry where complicated surface pretreatment is not required. Moreover, it is electrically switchable to other CLC textures such as Grandjean planar and focal conic states without the need of a temperature controller for the phase transition, the use of ion-rich LC materials, or mechanical shearing for textural transition.


Nanomaterials ◽  
2021 ◽  
Vol 11 (11) ◽  
pp. 2969
Author(s):  
Kazuma Miyagi ◽  
Yoshikuni Teramoto

Wide use of bio-based polymers could play a key role in facilitating a more sustainable society because such polymers are renewable and ecofriendly. Cellulose is a representative bio-based polymer and has been used in various materials. To further expand the application of cellulose, it is crucial to develop functional materials utilizing cellulosic physicochemical properties that are acknowledged but insufficiently applied. Cellulose derivatives and cellulose nanocrystals exhibit a cholesteric liquid crystal (ChLC) property based on rigidity and chirality, and this property is promising for constructing next-generation functional materials. The form of such materials is an important factor because material form is closely related with function. To date, researchers have reported cellulosic ChLC materials with a wide range of material forms—such as films, gels, mesoporous materials, and emulsions—for diverse functions. We first briefly review the fundamental aspects of cellulosic ChLCs. Then we comprehensively review research on cellulosic ChLC functional materials in terms of their material forms. Thus, this review provides insights into the creation of novel cellulosic ChLC functional materials based on material form designed toward the expanded application of cellulosics.


2015 ◽  
Vol 1 (1) ◽  
Author(s):  
D. E. Lucchetta ◽  
F. Simoni ◽  
P. Pagliusi ◽  
G. Cipparrone

AbstractLiquid crystal droplets are widely used in optics and photonics applications. They can act as simple resonators or be arranged in interconnected periodic configurations when their external dimension are similar. In this work we optically analyze and describe the microfluidic generation of liquid crystal droplets in a thermally stabilized environment, namely water, which enables a narrow droplets diameter distribution.We demonstrate a fine control of the droplet dimensions in both nematic and isotropic phases by controlling the ratio between liquid crystal andwater flows. Droplets generated in the isotropic phase show a complex internal structure which reflects their high degree of internal disorder. Moreover, the internal configuration of the droplets also depends on the purity degree of the water in which they grow. In order to investigate their size distribution and their internal structure, a small amount of photo-polymerizable agent (NOA61 optical glue)was added to the liquid crystal to stabilize the droplets structure and to avoid their coalescence. Acting this way, polymer stabilized liquid crystal droplets were created after light induced polymerization, which are stable even after water evaporation. The polarized microscope analysis shows that the bipolar or radial order of the liquid crystal is still preserved inside the droplets depending on the water purity. Moreover an improved size uniformity is reported.


1983 ◽  
Vol 44 (10) ◽  
pp. 1179-1184 ◽  
Author(s):  
M. Vilfan ◽  
R. Blinc ◽  
J. Dolinšek ◽  
M. Ipavec ◽  
G. Lahajnar ◽  
...  

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