Alignment of Carbon Nanotubes in Nematic Liquid Crystals

Schoot, Paul van der; Popa-Nita, V.; Kralj, Samo

doi:10.1021/jp712173n

Cited by 135 publications

(92 citation statements)

References 40 publications

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“…This point is crucial to predict the behavior of LC-nanoparticle blends. Coupling of the LC director field to the nanoparticle surface is determined [14] by the so-called penetration length £:…”

Section: Introductionmentioning

confidence: 99%

“…The penetration length is a measure of the distance where the perturbation caused by the introduction of the nanoparticle induces deformations in the previous nematic order [14]. The most relevant conclusion is that the weak anchoring limit leads to negligible deformations while the rigid anchoring may induce topological defects.…”

Section: Introductionmentioning

confidence: 99%

“…This means that CNT doping of LCs should not affect the original order of the LC material, as long as the CNT concentration is kept low enough to avoid interactions between CNTs themselves. It is important to note, however, that the coupling between CNTs and LC molecules is so strong that in practice the CNT induces the alignment of at least a thin layer of LC material, which remains bound to the CNT when electric or magnetic fields are applied, or temperature is modified [14].…”

Section: Introductionmentioning

confidence: 99%

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The peculiar electrical response of liquid crystal-carbon nanotube systems as seen by impedance spectroscopy

García-García¹,

Vergaz²,

Algorri³

et al. 2015

J. Phys. D: Appl. Phys.

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Conductive nanoparticles, especially elongated ones such as carbon nanotubes, dramatically modify the electrical behavior of liquid crystal cells. These nanoparticles are known to reorient with liquid crystals in electric fields, causing significant variations of conductivity at minute concentrations of tens or hundreds ppm. The above notwithstanding, impedance spectroscopy of doped cells in the frequency range customarily employed by liquid crystal devices, 100 Hz-10kHz, shows a relatively simple resistor/capacitor response where the components of the cell can be univocally assigned to single components of the electrical equivalent circuit. However, widening the frequency range up to 1 MHz or beyond reveals a complex behavior that cannot be explained with the same simple EEC. Moreover, the system impedance varies with the application of electric fields, their effect remaining after removing the field. Carbon nanotubes are reoriented together with liquid crystal reorientation when applying voltage, but barely reoriented back upon liquid crystal relaxation once the voltage is removed. Results demonstrate a remarkable variation in the impedance of the dielectric blend formed by liquid crystal and carbon nanotubes, the irreversible orientation of the carbon nanotubes and possible permanent contacts between electrodes.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

The peculiar electrical response of liquid crystal-carbon nanotube systems as seen by impedance spectroscopy

García-García¹,

Vergaz²,

Algorri³

et al. 2015

J. Phys. D: Appl. Phys.

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“…As the CNTs are much thinner than the elastic penetration length, the alignment is driven by the coupling of the unperturbed director field to the anisotropic interfacial tension of the CNTs in the nematic LC matrix [ 12 ]. Thus, the concentration of CNTs in LC is a very important parameter for this alignment process as mono-dispersion without any agglomerates is need.…”

Section: Introductionmentioning

confidence: 99%

Dielectric hysteresis, relaxation dynamics, and nonvolatile memory effect in carbon nanotube dispersed liquid crystal

Basu¹,

Iannacchione²

2009

Journal of Applied Physics

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Self-organizing nematic liquid crystals (LC) impart their orientational order onto dispersed carbon nanotubes (CNTs) and obtain CNT-self-assembly on a macroscopic dimension. The nanotubes-long axis, being coupled to the nematic director, enables orientational manipulation via the LC nematic reorientation. Electric field induced director rotation of a nematic LC+CNT system is of potential interest due to its possible application as a nano-electromechanical system. Electric field and temperature dependence of dielectric properties of an LC+CNT composite system have been investigated to understand the principles governing CNT-assembly mediated by the LC. In the LC+CNT nematic phase, the dielectric relaxation on removing the applied field follows a single exponential decay, exhibiting a faster decay response than the pure LC above a threshold field. The observed dielectric hysteresis on field-cycling in the nematic phase for the composite indicates an improvement in the spontaneous polarization in the nematic matrix due to the dispersed CNTs. Observations in the isotropic phase coherently combine to confirm the presence of anisotropic pseudo-nematic domains stabilized by the LC -CNT anchoring energy. These polarized domains maintain local directors, and respond to external fields, but, do not relax back to the original state on switching the field off, showing non-volatile memory effect.

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“…The CNT alignment mechanism is driven by the coupling of the unperturbed director field (average direction of LC molecules) to the anisotropic interfacial tension of the CNTs in the nematic LC matrix, as individual CNTs (not in bundle) are much thinner than the elastic penetration length [ 8 ]. So, a dilute suspension is stable because dispersed CNTs, without large agglomerates, does not perturb the director field significantly.…”

mentioning

confidence: 99%

Nematic anchoring on carbon nanotubes

Basu

Iannacchione

2009

Applied Physics Letters

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A dilute suspension of carbon nanotubes (CNTs) in a nematic liquid crystal (LC) does not disturb the LC director. Due to a strong LC-CNT anchoring energy and structural symmetry matching, CNT long axis follows the director field, possessing enhanced dielectric anisotropy of the LC media. This strong anchoring energy stabilizes local pseudo-nematic domains, resulting in nonzero dielectric anisotropy in the isotropic phase. These anisotropic domains respond to external electric fields and show intrinsic frequency response. The presence of these domains makes the isotropic phase electric field-responsive, giving rise to a large dielectric hysteresis effect. , due to the alignment with the LC molecules. A dilute suspension of CNTs in an LC matrix is a unique assemblage of an anisotropic dispersion (CNTs) in an anisotropic media (LC), which makes it an important and active area of research for realizing the LC-CNT interactions and the principles governing CNT-assembly through a nematic mediated platform. We observe that the presence of a small concentration of well-dispersed CNTs in an LC matrix produces enhanced dielectric anisotropy in the nematic phase and nonzero dielectric anisotropy in the isotropic phase. In this letter, we report the ac field-induced dielectric (⎯ε ) response for multiwall carbon nanotubes (MWCNTs) dispersed in 4-Cyano-4′-Pentylbiphenyl (5CB) LC in both the nematic and isotropic phases.The nematic phase shows dielectric anisotropy due to the anisotropic nature of the LC molecules where ε || and ε ⊥ are the components parallel and perpendicular to the molecular long axis, respectively. For a positive dielectric anisotropic LC, ε || > ε ⊥ , and so, the director field reorients parallel to an applied electric field. In a uniform homogeneously aligned parallel-plate cell configuration, the nematic director is aligned perpendicular to the applied electric field due to surface anchoring, but the director can reorient parallel to the applied field if the field magnitude is above some critical threshold. This is the essence of a Fréedericksz transition and an ac-capacitive measurement of the ⎯ε reveals ε ⊥ below and ε || above this switching, the exact values depending on frequency. The hybrid LC-CNT mixture was prepared by dispersing 0.005 wt% of MWCNT sample (containing nanotubes < 8 nm in diameter and 0.5-2 μm in length) in 5CB (T nematic-isotropic = 35 o C) host via ultrasonication for 5 hours to reach mono-dispersion of CNTs. Soon after ultrasonication, the mixture was degassed under vacuum at 40 o C for at least two hours. The mixture then was filled into a homogeneous LC cell (5 × 5 mm 2 indium tin oxide (ITO) coated area and 20 μm spacing [ 9 ]) by capillary action. Before performing any dielectric measurements, the CNT doped LC cell was studied under a cross polarized microscope. The micrographs revealed a uniform texture, like a pure LC cell, indicating a uniform nematic director field. There were no indications of phase separation or agglomerates at any temperature. Thus, at least on the ...

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Alignment of Carbon Nanotubes in Nematic Liquid Crystals

Cited by 135 publications

References 40 publications

The peculiar electrical response of liquid crystal-carbon nanotube systems as seen by impedance spectroscopy

The peculiar electrical response of liquid crystal-carbon nanotube systems as seen by impedance spectroscopy

Dielectric hysteresis, relaxation dynamics, and nonvolatile memory effect in carbon nanotube dispersed liquid crystal

Nematic anchoring on carbon nanotubes

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