Free-standing mesoporous silica films with tunable chiral nematic structures

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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 properties1. 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 materials2,3,4,5. Template synthesis of inorganic solids using the self-assembly of lyotropic liquid crystals offers access to materials with well-defined porous structures6,7,8,9,10,11,12, but only recently has chirality been introduced into hexagonal mesostructures through the use of a chiral surfactant13,14. 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.

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Figure 1: Schematic of the chiral nematic ordering of NCC crystallites and POM images.
Figure 2: Optical characterization of NCC/silica composite films and the corresponding mesoporous silica films.
Figure 3: Nitrogen and water absorption in a chiral mesoporous silica film.
Figure 4: SEM images of chiral nematic mesoporous silica films and comparison of fingerprint textures in the solid state and liquid crystal phase.

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Acknowledgements

This work was supported by the Natural Sciences and Engineering Research Council (NSERC) of Canada and FPInnovations. K.E.S. is grateful to UBC for a graduate fellowship.

Author information

K.E.S. conducted all of the synthesis and most of the characterization. H.Q. assisted with characterization of the materials. W.Y.H. supplied the NCC and contributed valuable expertise on NCC. M.J.M. initiated and guided this work.

Correspondence to Mark J. MacLachlan.

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The authors declare no competing financial interests.

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The file contains Supplementary Figures 1-9 with legends, Supplementary Tables 1-2 and a Supplementary Discussion. (PDF 1292 kb)

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Shopsowitz, K., Qi, H., Hamad, W. et al. Free-standing mesoporous silica films with tunable chiral nematic structures. Nature 468, 422–425 (2010) doi:10.1038/nature09540

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