Full alignment of dispersed colloidal nanorods by alternating electric fields

Mohammadimasoudi, Mohammad; Hens, Zeger; Neyts, Kristiaan

doi:10.1039/c6ra02620f

Cited by 30 publications

(49 citation statements)

References 37 publications

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“…To exploit the linearly polarized emission from QREFs, semiconductor QRs must be unidirectionally aligned, and, therefore, a number of techniques have been explored to achieve the high‐quality alignment for QRs, recently . The electric field assisted alignment, the electro‐spinning technique, and the unidirectional stretching of polymer films embedded with QRs[5d] are among the most popular approaches. Yet another versatile approach is based on the photoalignment of the liquid crystal monomer (LCM) films with embedded QRs 3,4,8.…”

Section: Introductionmentioning

confidence: 99%

Ligand Shell Engineering to Achieve Optimal Photoalignment of Semiconductor Quantum Rods for Liquid Crystal Displays

Zhang

Prodanov

Schneider

et al. 2018

Adv Funct Materials

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The photoalignment process to align semiconductor quantum rods (QRs) in the liquid crystal monomer (LCM) matrix is a flexible technology; however, the optical quality of the resulting enhancement films drops at high concentrations of the QRs. The compatibility between the ligand shell on the QRs and the LCM plays an important role in avoiding this issue. Herein, several kinds of ligand shells on the rod-in-rod CdSe/CdS QRs are designed, without affecting the optical properties of QRs, and their compatibility with LCM molecules is studied. Promesogenic dendritic ligands in combination with relatively short alkylphosphonic acids are found to provide the highest optical quality, without QR aggregation, and so the high brightness of the resulting enhancement films, even at higher concentrations of QRs in LCM, which is perfectly suitable for the application in liquid crystal displays.

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Section: Introductionmentioning

confidence: 99%

Ligand Shell Engineering to Achieve Optimal Photoalignment of Semiconductor Quantum Rods for Liquid Crystal Displays

Zhang

Prodanov

Schneider

et al. 2018

Adv Funct Materials

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“…The electro-optic behavior of colloidal suspensions of nanorods (i.e. rod-like nanoparticles) that show liquidcrystalline phases has raised wide interest in recent years [1][2][3][4][5][6][7][8][9][10][11][12] from both fundamental and applied perspectives.…”

Section: Introductionmentioning

confidence: 99%

“…Aqueous suspensions of anisometric particles are well known for their strong electro-optic response [13][14][15][16][17][18][19], due to a combination of two factors: the strong coupling of the particle orientation with the applied electric field E, and the strong optical anisotropy of the nanoparticles, which is either intrinsic or related to their anisometric shape [9,20].…”

Section: Introductionmentioning

confidence: 99%

“…Indeed, due to their high conductivity, they suffer from fast electrochemical degradation, Joule heating, thermally-and electrophoretically-induced flow and instabilities, as well as increased energy consumption of the devices. To avoid these issues, the electro-optics of colloidal suspensions in polar and apolar organic solvents has been intensively studied in the recent years [1,[4][5][6][7][8][9]. In particular, the possibility of using colloidal suspensions for display devices has been confirmed for dispersions of different types of pigment nanorods in dodecane at high concentrations (> 15 wt% to reach the nematic phase) [26][27][28].…”

Section: Introductionmentioning

confidence: 99%

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Optical and X-ray scattering studies of the electric field-induced orientational order in colloidal suspensions of pigment nanorods

Buluy

Aryasova

Tereshchenko

et al. 2018

Journal of Molecular Liquids

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Under pulsed or a.c. electric fields, colloidal suspensions of nanorods can show strong electro-optic effects, such as the Kerr effect, with fast response times (a few ms), which makes them good candidates for some commercial applications. For this purpose, suspensions of Pigment red 176 nanorods in dodecane were recently developed and their physical properties have been studied. We report here on the investigation of the orientational order induced by electric fields in isotropic suspensions of pigment nanorods by three different techniques: transient electric birefringence, transient electric dichroism, and in-situ small-angle X-ray scattering under electric field ("Electro-SAXS"). We show that, in spite of the apolar character of the solvent, the Maxwell-Wagner-O'Konski mechanism (i.e. the polarization of the counter-ion cloud around each particle) is responsible for the field-induced alignment of the nanorods. Although the particles are only weakly charged and the dielectric constant of dodecane is low, the pigment nanorods effectively behave as metallic particles in an insulating matrix and reach strong values (S~0.5) of the induced nematic order parameter at moderate field amplitudes (~1 V/µm). This study confirms the feasibility of using suspensions of Pigment red 176 nanorods in dodecane for electro-optic applications.

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“…NRs can emit saturated colors and the absorption and emission from these CdSe/CdS nanorods are highly polarized [3]. We have recently shown that NRs can be aligned effectively by applying an electric field [4].…”

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confidence: 99%

Thin Film Polarized Liquid Crystal Backlight

Mohammadimasoudi

Beeckman

Neyts

2015

Symp Digest of Tech Papers

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A thin polarized-light emitting film is fabricated by aligning nanorods in an electric field and subsequent polymerization. A polarization ratio of 0.60 is obtained with this method. The thickness of the film is in the order of a few micrometer, and the method is compatible with largescale processing on cheap, flexible, and transparent substrates. The process can be realized in a roll-to-roll process as in a printing process, when one substrate is flexible and passes over a roll with electrodes.Liquid crystal displays have a limited transmission, on the order of 10%. This is mainly due to the absorbing polarizers and color filters. In a conventional backlight, the emitted light is unpolarized because it originates for LEDs or phosphor materials. Because an LCD is designed to work with polarized light [1], the polarizer typically absorbs half of the light.Light emission is usually the result of a dipole transition in an atom, molecule, or quantum dot. Recently, the development of red and green quantum dots has improved the color saturation of LCDs [2]. Anisotropic emitters can have characteristics that are close to that of a dipole antenna. If the emitters are aligned parallel to the electric field of the light that is transmitted by the polarizer, most of the light that is emitted will pass the polarizer and contribute to the emission of the LCD display as shown in Figure 1. We propose a method for the fabrication of a thin polarized-light emitting film in which an electric field aligns 50-nm long semiconductor nanorods (NRs) in a preferred direction in a polymerized film. Figure 2 shows a photograph of the resulting film with 10 mm thickness.NRs can emit saturated colors and the absorption and emission from these CdSe/CdS nanorods are highly polarized [3]. We have recently shown that NRs can be aligned effectively by applying an electric field [4].Fluorescence microscopy images of thin polarized-light emitting NR film show the emission for the orientation of the polarizer parallel ( Figure 3a) or perpendicular (Figure 3b) to the applied electric field. The ITO electrodes have a width of 6 mm and a spacing of 20 mm. The strongest photoluminescence is observed when the polarizer is parallel to the electric field, indicating that the NRs are aligned along the electric field lines. This is in agreement with earlier polarization measurements on individual NRs and aligned NR arrays [5]. The polarization ratio is defined as:in which I w and I ? are the average photoluminescent intensity over the gap area between two electrodes, when the polarizer is oriented, respectively, parallel and perpendicular to the line electrodes. The polarization ratio for regions with NRs aligned according to the above procedure is about 0.6.

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Full alignment of dispersed colloidal nanorods by alternating electric fields

Cited by 30 publications

References 37 publications

Ligand Shell Engineering to Achieve Optimal Photoalignment of Semiconductor Quantum Rods for Liquid Crystal Displays

Ligand Shell Engineering to Achieve Optimal Photoalignment of Semiconductor Quantum Rods for Liquid Crystal Displays

Optical and X-ray scattering studies of the electric field-induced orientational order in colloidal suspensions of pigment nanorods

Thin Film Polarized Liquid Crystal Backlight

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