New developments in nanoparticle-liquid crystal composites: From magic-sized semiconductor nanoclusters to alignment pattern formation via nanoparticle stenciling

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DOIResolve DOI: http://doi.org/10.1117/12.909022
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TypeArticle
Proceedings titleProceedings of SPIE - The International Society for Optical Engineering
ConferenceEmerging Liquid Crystal Technologies VII, 22 January 2012 through 25 January 2012, San Francisco, CA
ISSN0277-786X
ISBN9780819489227
Volume8279
Article number827913
Subjectliquid crystal alignment; nematic; Pattern formation; Quantum Dot; stenciling; Cadmium alloys; Cadmium compounds; Defects; Doping (additives); Electrooptical devices; Energy gap; Glass; Gold; Liquid crystals; Nanocrystals; Nanoparticles; Nematic liquid crystals; Polyimides; Semiconductor doping; Semiconductor quantum dots; Zinc; Alignment
AbstractWe here report on the alignment and electro-optic properties of nematic liquid crystals (LCs) either containing nanoscale particles as additives or featuring particles patterned on substrates. The investigated nematic LCs or LC dispersions are doped or in contact with magic-sized semiconductor CdSe nanocrystals (MSNCs) or silane- and alkylthiol monolayercapped gold nanoparticles. Three single-sized CdSe quantum dots capped with myristic acid exhibiting bright bandgap photoluminescence (PL) at λ max ∼ 463 nm were tested as additives. Two of the quantum dots only vary in the amount of defects as indicated by different bandgap and deep trap PL. The third MSNC sample is compositionally different, doped with Zn. These MSNCs with almost identical sizes were doped at different concentrations (1-5 wt%) into the nematic phase of the 2-phenylpyrimidine-based LC1. Only the Zn-doped MSNCs showed the formation of birefringent stripes surrounded by areas of homeotropic alignment between plain glass slides at all concentrations as observed for many other nanoparticle-doped nematic LCs reported earlier by our group. In polyimide-coated glass slides favoring planar orientation of the nematic director, planar alignment was observed. Similarly, siloxane-coated gold nanoparticle additives with narrow size distribution, but larger size, show homeotropic alignment between plain glass and planar alignment in rubbed polyimide-coated cells. Surprisingly then, we succeeded in creating alignment patterns using smaller, ∼2 nm alkylthiol-capped gold nanoparticles using a process called stenciling that allowed us to generate patterns of homeotropic alignment in a continuum of planar alignment of the nematic LC. Finally, electro-optic investigations on some of these samples revealed that only the Zn-doped magic-sized MSNCs significantly lower the dielectric anisotropy as well as the splay elastic constant of the nematic host, despite identical size and surface functionality of the three used MSNCs, which highlights the tremendous effect of the nanocrystal core composition on the electro-optic properties of the nematic host. © 2012 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE).
Publication date
LanguageEnglish
AffiliationNational Research Council Canada (NRC-CNRC); NRC Steacie Institute for Molecular Sciences (SIMS-ISSM)
Peer reviewedYes
NPARC number21269228
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Record identifier19081b12-0215-41e5-8624-12f78ca9ef17
Record created2013-12-12
Record modified2016-05-09
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