Director field of birefringent stripes in liquid crystal/nanoparticle dispersions

Urbanski, Martin; Kinkead, Brandy; Hegmann, Torsten; Kitzerow, Heinz‐S.

doi:10.1080/02678292.2010.489160

Cited by 37 publications

(25 citation statements)

References 24 publications

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“…Future work will now address the role of electroconvection (or perhaps surface polarization effects 39 ) as described in previous work from our groups using Au NPs in the same N-LC host. 29,37 Finally, images obtained from FCPM studies (x-y scans) confirm the director field in the birefringent stripes, 36 prove homeotropic alignment in the surrounding domains, show that these magic-sized QDs are reasonably well dispersed in the nematic host, and finally that some domains show more significant QD aggregation than others.…”

Section: Discussionmentioning

confidence: 88%

“…dye and QDs), however, prevented us so far from determining the z-distribution of these QDs in contrast to earlier FCPM experiments using larger CdSe QDs, 36 but a more in-depth study is currently underway.…”

Section: Fluorescence Confocal Polarizing Microscopy (Fcpm)mentioning

confidence: 82%

“…Earlier experiments using larger Au NPs have already shown that these birefringent stripes correspond to twist disclinations located at the substrate interface, 36 and established that larger CdSe QDs (4.0 to 4.3 nm in diameter) segregate to the bottom and top interfaces using (x-z) scans.…”

Section: Fluorescence Confocal Polarizing Microscopy (Fcpm)mentioning

confidence: 99%

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Nanocomposites of a nematic liquid crystal doped with magic-sized CdSe quantum dots

Mirzaei

Urbanski

et al. 2011

J. Mater. Chem.

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We here report on the optical, alignment and electro-optic properties of a nematic liquid crystal affected by the presence of semiconductor CdSe magic-sized nanocrystals (MSNCs). Three single-sized CdSe samples were tested, exhibiting bright bandgap photoluminescence (PL) with l max z 463 nm and $10 nm full width at half-maximum (fwhm). The three quantum dot (QD) samples were passivated with a monolayer of myristic acid. Two of them (QD1 and QD2) only vary in the amount of defects as indicated by different bandgap and deep trap PL. The third MSNC sample (QD3) 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 5-n-heptyl-2-(4-n-octyloxyphenyl)-pyrimidine (LC1). Only QD3 showed the formation of birefringent stripes surrounded by areas of homeotropic alignment between plain glass slides at all concentrations as observed for many other nanoparticledoped nematic liquid crystals reported earlier by our group. In polyimide-coated glass slides favouring planar orientation of the nematic director, planar alignment was observed. Surprisingly, only the Zndoped magic-sized QD3 quantum dots (CdSe@Zn) significantly lower the dielectric anisotropy as well as the splay elastic constant of the nematic host, despite identical size and surface functionality, which highlights the tremendous effect of the nanocrystal core composition on the electro-optic properties of the nematic host. In addition, fluorescence confocal (polarizing) microscopy studies show the director field within and around the birefringent stripes and confirm locally elevated concentrations or aggregates of the MCNC that are otherwise randomly distributed in the nematic host.

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Section: Discussionmentioning

confidence: 88%

Section: Fluorescence Confocal Polarizing Microscopy (Fcpm)mentioning

confidence: 82%

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Nanocomposites of a nematic liquid crystal doped with magic-sized CdSe quantum dots

Mirzaei

Urbanski

et al. 2011

J. Mater. Chem.

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“…Predominantly at NP loadings ranging from 0.25 to 2.5 wt% in LC1, large domains of NP-induced homeotropic alignment due to partial segregation of NPs to both glass substrates are observed. These homeotropic domains surround birefringent stripe features (figure 4a-c) frequently observed for many other types of Au NPs and quantum dots [59,60]. We recently investigated these textural features in more detail using fluorescence confocal polarizing microscopy (FCPM) and established both the director field within the stripes and the segregation of NPs causing the induced homeotropic alignment [59].…”

Section: Resultsmentioning

confidence: 99%

Hydrophobic gold nanoparticles via silane conjugation: chemically and thermally robust nanoparticles as dopants for nematic liquid crystals

Mirzaei

Urbanski

Kitzerow

et al. 2013

Phil. Trans. R. Soc. A.

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We examine for the first time how chemically and thermally stable gold nanoparticles (NPs), prepared by a silane conjugation approach, affect both the thermal and the electro-optical properties of a nematic liquid crystal (LC), when doped at concentrations ranging from 0.25 to 7.5 wt%. We find that the octadecylsilane-conjugated gold NPs stabilize both the enantiotropic nematic and the monotropic smectic-A phases of the LC host with a maximum stabilization of 2 ° C for the nematic and 3.5 ° C for the smectic-A phases for the mixture containing 1 wt% of the silanized particles. The same mixture shows the lowest values for the Fréedericksz transition threshold voltage and the highest value for the dielectric anisotropy. Generally, all NP-containing mixtures, except mixtures with NP concentrations exceeding 5 wt%, reduce the threshold voltage, increase the dielectric anisotropy and reduce both rise and decay time; the latter particularly at temperatures at least 10 ° C below the isotropic–nematic phase transition on cooling.

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“…Recently, the impact of nanoscale particles has been highlighted [3]. For example, a small dopant concentration of surface functionalized nanoparticles can improve the electro-optical performance of LCs or cause induced dual alignment effects [3,4]. Nanoparticles surface functionalized with proto-mesogenic ligands may even self-assemble into nanoparticulate thermotropic liquid-crystalline materials [5,6].…”

Section: Introductionmentioning

confidence: 99%

Doping the nematic liquid crystal 5CB with milled BaTiO3nanoparticles

et al. 2012

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The simple nematic mesogen 5CB was doped with milled BaTiO 3 nanoparticles and investigated with x-ray scattering. Doping with BaTiO 3 nanoparticles of 9 nm in diameter led to the formation of crystallites. These crystallites precipitated and formed a wax-like nanodispersion of 5CB and nanoparticles which led to intense x-ray scattering signals characteristic for a multilayer structure. Surprisingly, the multilayers possess unusual interlayer spacing which cannot be explained by simple smectic order of the calamitic molecules.

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Director field of birefringent stripes in liquid crystal/nanoparticle dispersions

Cited by 37 publications

References 24 publications

Nanocomposites of a nematic liquid crystal doped with magic-sized CdSe quantum dots

Nanocomposites of a nematic liquid crystal doped with magic-sized CdSe quantum dots

Hydrophobic gold nanoparticles via silane conjugation: chemically and thermally robust nanoparticles as dopants for nematic liquid crystals

Doping the nematic liquid crystal 5CB with milled BaTiO3nanoparticles

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