Iridescent Chiral Nematic Cellulose Nanocrystal/Polymer Composites Assembled in Organic Solvents

Abstract

We describe an approach to prepare polymer composites with chiral nematic photonic structures through the self-assembly of cellulose nanocrystal (CNC) dispersions in organic solvents. Contrary to previous reports, we demonstrate that dispersions of neutralized sulfated CNCs in polar organic media readily form lyotropic chiral nematic liquid crystalline phases. We have investigated the effect of the neutralizing base on the CNC self-assembly, observing chiral nematic ordering for all counterions studied. The self-assembly of the organic CNC dispersions can be exploited to prepare iridescent polymeric composites simply by casting the CNC dispersion with a suitable polymer soluble in the organic solvent. Photonic properties of the composite films can be easily controlled by either varying the ratio of CNCs to polymer or adding salts.

Chiral nematic porous germania and germanium/carbon films

“…34 In fact, iridescent germaniumcontaining composites with chiral nematic ordering can be obtained easily, but the pyrolyzed samples were fragile and we were unable to remove the CNC template by calcination without substantial loss of chirality and structure in the films. 34 In fact, iridescent germaniumcontaining composites with chiral nematic ordering can be obtained easily, but the pyrolyzed samples were fragile and we were unable to remove the CNC template by calcination without substantial loss of chirality and structure in the films.…”

“…These materials have pores about 3-10 nm in diameter that are organized into a layered, helicoidal arrangement. 33 Recently our group 34 and Gray et al 35 demonstrated that lyotropic chiral nematic LC phases can be formed by dispersing neutralized sulfated CNCs in polar organic media such as N,N-dimethylformamide (DMF). It is worth noting that the chiroptical properties of these photonic materials can be tuned by simply changing the length of the helical pitch.…”

“…As the pitch of the helicoidal structure is on the order of the wavelengths of visible light, these films behave as photonic structures 30 and selectively reflect light of a given wavelengththey appear brilliantly iridescent. 34 Germanium, like silicon, is an important semiconductor and has attracted extensive interest in many areas such as optoelectronics, detectors, and solar cells. Therefore, these novel materials are attractive for chiral separation, optical devices, sensors, catalyst supports, and energy-storage materials.…”

Dielectric Characterization of Confined Water in Chiral Cellulose Nanocrystal Films

“…5,6 These attractive properties have motivated numerous endeavors toward fabricating multifunctional CNC nanocomposites using solution casting, melt processing, sol–gel, and template methods, 1,5,7 which may yield the typical low filling fraction nanocomposites (<40 mass %) or highly filled biomimetic composites with cholesteric self-assembled CNCs. 8,9 …”

Liquid Crystals of Cellulosics: Fascinating Ordered Structures for the Design of Functional Material Systems

“…The CNC/polymer hydrogels obtained showed changes in iridescence in response to external stimuli such as solvent, pH, or temperature. Iridescent CNC/polymer composites were also produced solely by slow evaporation of chiral nematic dispersions of CNC (~3.5 wt%) in DMF, which were mixed in advance with a commodity polymer such as polystyrene or poly(methyl methacrylate) [126]. To obtain the stable liquid crystalline suspensions of CNCs in such a polar organic solvent, sulfuric acid-hydrolyzed CNCs were neutralized with a strong base (LiOH, NaOH, KOH, etc.)…”