Dielectric spectroscopy of isotropic liquids and liquid crystal phases with dispersed graphene oxide

Al-Zangana, Shakhawan; Iliuţ, Maria; Boran, Gökçen; Turner, Michael L.; Vijayaraghavan, Aravind; Dierking, Ingo

doi:10.1038/srep31885

Cited by 48 publications

(21 citation statements)

References 34 publications

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“…The electro-optic and dielectric properties were investigated in detail, also as a function of loading concentration. We use commercial liquid crystal materials 5CB and a ferroelectric Felix mixture, due to their known neat properties and wide use 4,8,19,33,34 in research and applications. Polyimide Kapton tape was used as a protective layer for the central area prior to the immersion of the substrates in hydrochloric acid (30%) for 7min to dissolve the ITO.…”

Section: Reznikov Et Al Have Shown That a Low Concentration Of Ferromentioning

confidence: 99%

A comparison between size dependent paraelectric and ferroelectric BaTiO3 nanoparticle doped nematic and ferroelectric liquid crystals

Al-Zangana

Turner

Dierking

2017

Journal of Applied Physics

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The electro-optic and dielectric properties of barium titanate, BaTiO 3 , nanoparticle (NP) doped nematic and ferroelectric liquid crystal materials were examined with respect to different size and concentration of the NPs. Smaller size paraelectric NPs (≈80nm) are compared to larger, ferroelectric NPs (≈240nm). It is found that for concentrations larger than 0.5vol% the ferroelectric NPs exhibit an increasing effect on the electro-optic response of the nematic liquid crystal, which is demonstrated by the enhancement of the dielectric anisotropy. This could be induced by the coupling of the electrical dipole moments in the spherical NPs with the LC director field. The electro-optical properties of the SmC* phase, like tilt angle Θ, switching time and spontaneous polarisation are found to be independent of the concentration and size of the NPs. The rotational viscosity calculated from response times, polarization reversal current and dielectric properties is comparable for all three methods employed and practically independent of particle concentration and size. The relaxation frequency of the Goldstone mode is higher in the ferroelectric NPs suspensions of 2.0vol% as compared to the smaller paraelectric NPs.

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Section: Reznikov Et Al Have Shown That a Low Concentration Of Ferromentioning

confidence: 99%

A comparison between size dependent paraelectric and ferroelectric BaTiO3 nanoparticle doped nematic and ferroelectric liquid crystals

Al-Zangana

Turner

Dierking

2017

Journal of Applied Physics

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“…Figures 5(a)- (c) show GO textures of the lyotropic nematic phase in GO suspensions for different solvents as a function of concentration and sample thickness. Since the birefringence of the lyotropic nematic LC phase is of the order of 10 −3 [18], the thickness of the samples has to be markedly larger compared to the samples prepared for thermotropic LC phases [41,42]. Here the range of the thickness of the sandwich cells is d = 50-500 µm, and the range of the LC concentrations is c = 0.5-4.0 mg ml −1 for all solvents (DIW, DMSO and DMF).…”

Section: Effect Of Boundary Conditionsmentioning

confidence: 99%

Confinement effects on lyotropic nematic liquid crystal phases of graphene oxide dispersions

et al. 2017

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Graphene oxide (GO) forms well ordered liquid crystal (LC) phases in polar solvents. Here, we map the lyotropic phase diagram of GO as a function of the lateral dimensions of the GO flakes, their concentration, geometrical confinement configuration and solvent polarity. GO flakes were prepared in water and transferred into other polar solvents. Polarising optical microscopy (POM) was used to determine the phase evolution through the isotropic-biphasic-nematic transitions of the GO LC. We report that the confinement volume and geometry relative to the particle size is critical for the observation of the lyotropic phase, specifically, this determines the low-end concentration limit for the detection of the GO LC. Additionally, a solvent with higher polarisability stabilises the LC phases at lower concentrations and smaller flake sizes. GO LCs have been proposed for a range of applications from display technologies to conductive fibres, and the behaviour of LC phase formation under confinement imposes a limit on miniaturisation of the dimensions of such GO LC systems which could significantly impact on their potential applications. LETTEROriginal content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence.

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“…On the other hand, considering the volume fraction for Milli-Q water, equal to V f ∼0.0361 at a weight fraction of 6.5 wt%, we find a value of 2.3 for the dielectric constant of the GO particles in Milli-Q water. Even if the two values found in Milli-Q water and IPA are just estimates of the dielectric constant of the particle, they are still significantly lower than the giant permittivity found in many other papers [7][8][9][10][11][12][13][14][15]30].…”

Section: Resultsmentioning

confidence: 60%

“…As previously observed in the literature, experiments both in Milli-Q water and in 2-Propanol confirm the measurements of very large capacitance at low frequencies. However, our simple modeling also demonstrates that the observed capacitances can be simply explained by polarization of electrodes, without considering neither giant permittivity of GO nor specific relaxation modes related to the rotation of the particles [30]. We therefore conclude that GO is not a high-permittivity material potentially useful for energy storage applications.…”

Section: Introductionmentioning

confidence: 72%

“…Nevertheless, the origin of such large dielectric permittivities remains unclear. Al-Zangana et al [30] have recently investigated dielectric relaxation processes of GO solutions in isotropic fluids or liquid crystals (LCs). Relaxations in 2-Propanol are associated with very large amplitudes, well above 1000 in relative permittivity at 1 kHz.…”

Section: Introductionmentioning

confidence: 99%

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Absence of giant dielectric permittivity in graphene oxide materials

et al. 2019

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Graphene oxide (GO) is considered as a promising component for electronics because of its unique anisotropy, easy processing and sometimes claimed giant permittivity. The latter would arise from an enhanced electronic polarizability due to the presence of functional groups at the surface and edge of GO flakes. As a matter of fact, a number of publications have reported a very large permittivity of GO materials. Nevertheless, the reported values for the intrinsic relative permittivity vary significantly from a few units to several millions. Such variability raises a critical question on the actual and intrinsic permittivity of GO, and on difficulties of measurements due to the polarization of the electrodes. We presently report impedance spectroscopy characterizations of GO solutions with different solvents. We find very large capacitance at low frequencies, in agreement with previous reports. However, we also show that these results can be interpreted without considering a giant permittivity of GO. Actually, a simple equivalent circuit model allows us to confirm that GO does not have a giant permittivity. We conclude that GO can be used as an electrolyte for supercapacitors, or as a precursor for electrically conductive graphene-based materials, but not as an efficient additive to raise the permittivity of solvents or composites for electronics and energy storage applications.

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Dielectric spectroscopy of isotropic liquids and liquid crystal phases with dispersed graphene oxide

Cited by 48 publications

References 34 publications

A comparison between size dependent paraelectric and ferroelectric BaTiO3 nanoparticle doped nematic and ferroelectric liquid crystals

A comparison between size dependent paraelectric and ferroelectric BaTiO3 nanoparticle doped nematic and ferroelectric liquid crystals

Confinement effects on lyotropic nematic liquid crystal phases of graphene oxide dispersions

Absence of giant dielectric permittivity in graphene oxide materials

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