Free-standing mesoporous silica films with tunable chiral nematic structures

Abstract

Chirality at the molecular level is found in diverse biological structures, such as polysaccharides, proteins and DNA, and is responsible for many of their unique properties. Introducing chirality into porous inorganic solids may produce new types of materials that could be useful for chiral separation, stereospecific catalysis, chiral recognition (sensing) and photonic materials. Template synthesis of inorganic solids using the self-assembly of lyotropic liquid crystals offers access to materials with well-defined porous structures, but only recently has chirality been introduced into hexagonal mesostructures through the use of a chiral surfactant. Efforts to impart chirality at a larger length scale using self-assembly are almost unknown. Here we describe the development of a photonic mesoporous inorganic solid that is a cast of a chiral nematic liquid crystal formed from nanocrystalline cellulose. These materials may be obtained as free-standing films with high surface area. The peak reflected wavelength of the films can be varied across the entire visible spectrum and into the near-infrared through simple changes in the synthetic conditions. To the best of our knowledge these are the first materials to combine mesoporosity with long-range chiral ordering that produces photonic properties. Our findings could lead to the development of new materials for applications in, for example, tuneable reflective filters and sensors. In addition, this type of material could be used as a hard template to generate other new materials with chiral nematic structures.

Cellulose Nanocrystals as Advanced "Green" Materials for Biological and Biomedical Engineering

“…The helical liquid crystalline self-assembly of CNCs provides chirality to the added material and more sensitivity to circular polarization. CNCs can also induce similar type of ordering in polymeric macromolecules such as alginate or inorganic materials like silica when mixed together (Shopsowitz et al, 2010;Urena-Benavides et al, 2010). The optical properties of CNC film dispersions can be modulated by controlling the cholesteric pitch, which in turn can be influenced by dispersion composition, polyelectrolyte, temperature, and shear.…”

Chiral Plasmonics Using Twisting along Cellulose Nanocrystals as a Template for Gold Nanoparticles

“…Note that it is opposite to the case when the chiral plasmonic signal is due to nanoparticles templated by the left-handed cholesteric LC phase observed at high CNC concentrations (see schematics in Figure S7, Supporting Information). [2,10,16,25,26] The CNC/AuNP fibrillar superstructures render a CD signal dip-peak magnitude of 1.7 mdeg for our nominal initial aqueous CNC concentration of approximately 2.5 nM (ρCNC = 0.01 mg/mL) (Figure 3b). In comparison, DNA-origami-based right-handed assembly composed of 10 nm AuNPs exhibits a dip-peak value of 1.2 mdeg using 1.5 nM concentration of nanohelixes.…”

“…It allows templating for photonic materials using inorganics, nanoparticles, polymers, and pyrolyzed carbonized matter. [10,12,16,25,26] On the other hand, the CNCs have been suggested to possess a right-handed twist along their nanorod axis to explain the left-handed twist in their chiral LC. [6] Recently, the right-handed twist of individual CNCs and nanocelluloses of three different origins was observed by cryo-electron tomography (cryo-ET), and electron and atomic force microscopy [27,29] supported by molecular dynamics simulations [30−32] .…”

Dye-sensitized photoelectrochemical cell on plasmonic Ag/AgCl @ chiral TiO 2 nanofibers for treatment of urban wastewater effluents, with simultaneous production of hydrogen and electricity

“…One aspect for this enhancement is related to the ability of chiral TiO 2 nanofibers to rotate the incident light in a helical pattern [23][24][25][26] resulting in the removal of the polarization sensitivity effect of plasmonic materials.…”

“…The current-voltage (J-V) 15 characteristics of the 12 cells were measured as described elsewhere [24]. The amount 16 of hydrogen, the concentrations of EE2, TOC, TN and DO were measured as shown 17 our previous studies [4,14,25]. Briefly, the concentration of EE2 was detected by 18 High Performance Liquid Chromatography (HPLC, Agilent 1100).…”