25 August 2017 Effects of size and ligand density on the chirality transfer from chiral-ligand-capped nanoparticles to nematic liquid crystals
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Abstract
Studies of chiroptical effects of chiral ligand-capped gold nanoparticles (Au NPs) are a fascinating and rapidly evolving field in nanomaterial research with promising applications of such chiral metal NPs in catalysis and metamaterials as well as chiral sensing and separation. The aim of our studies was to seek out a system that not only allows the detection and understanding of Au NP chirality but also permits visualization and ranking — considering size, shape and nature as well as density of the ligand shell — of the extent of chirality transfer to a surrounding medium. Nematic liquid crystal (N-LC) phases are an ideal platform to examine these effects, exhibiting characteristic defect textures upon doping with a chiral additive. To test this, we synthesized series of Au NPs capped with two structurally different chiral ligands and studied well-dispersed mixtures in two nematic liquid crystal hosts. Induced circular dichroism (ICD) spectropolarimetry and polarized light optical microscopy (POM) confirmed that all Au NPs induce chiral nematic (N*-LC) phases, and measurements of the helical pitch as well as calculation of the helical twisting power (HTP) in various cell geometries allowed for an insightful ranking of the efficiency of chirality transfer of all Au NPs as well as their free ligands.
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Taizo Mori, Anshul Sharma, Ahlam Nemati, Leah Bergquist, Torsten Hegmann, "Effects of size and ligand density on the chirality transfer from chiral-ligand-capped nanoparticles to nematic liquid crystals", Proc. SPIE 10361, Liquid Crystals XXI, 103610M (25 August 2017); doi: 10.1117/12.2275262; https://doi.org/10.1117/12.2275262
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