Nanoparticles dispersed in liquid crystals: impact on conductivity, low-frequency relaxation and electro-optical performance

Urbanski, Martin; Lagerwall, Jan P. F.

doi:10.1039/c6tc00659k

Cited by 74 publications

(29 citation statements)

References 32 publications

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“…Once the GNP concentration reaches 0.1 wt %, the dielectric loss of the LC mixture increases significantly, because the excess GNP dopant contaminates the LC host with mobile charge carriers, increases the conductivity of the LC mixture [16]. Simultaneously, GNP dopant does not significantly change the measured permittivity, indicating that the trapping of ion impurities on the surfaces of GNPs is negligible under tiny GNP dopant, as shown in Figure 5.…”

Section: Introductionmentioning

confidence: 71%

Electro-optical Effect of Gold Nanoparticle Dispersed in Nematic Liquid Crystals

et al. 2017

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Abstract:The electro-optical performance of nematic liquid crystals (NLCs) dispersed with gold nanoparticles (GNPs) was investigated in this study. The addition of a small amount of GNP dopant decreased the threshold voltage for LC reorientation due to the decreased elastic constant and increased dielectric anisotropy of the LC mixture. The response time of the LC cell was decreased with the addition of tiny amounts of GNPs because of decrease in rotational viscosity of LCs. The doped GNPs also shorten LC reorientation angle during voltage switching, further decreasing the response time of the LC cell. The addition of high amounts of GNPs slowed down the response time of the LC cell, because excess GNPs aggregated and formed networks in the cell, thus disturbing LC alignment and hindering LC reorientation. The measured dielectric spectra of the GNP-LC mixture revealed that the addition of GNPs decreased the relaxation time constant of the LCs. This result confirmed that the GNP dopant decreased the rotational viscosity and elastic constant of the LCs.

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Section: Introductionmentioning

confidence: 71%

Electro-optical Effect of Gold Nanoparticle Dispersed in Nematic Liquid Crystals

et al. 2017

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“…Furthermore, in our measurements the proton Larmor frequency was set to ∼2 MHz. But, the Debye layerʼs charge relaxation rate in LC is typically in the range of kHz [36]. Therefore, due to this wide mismatch of frequencies, the dynamical decoupling method used in our experiment filters out the charge relaxation frequency components slower than MHz.…”

Section: Discussionmentioning

confidence: 99%

Probing phase transitions in a soft matter system using a single spin quantum sensor

et al. 2019

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Phase transitions in soft matter systems reveal some of the interesting structural phenomena at the levels of individual entities constituting those systems. The relevant energy scales in soft matter systems are comparable to thermal energy (k B T∼10 −21 J). This permits one to observe interesting structural dynamics even at ambient conditions. However, at the nanoscale most experimental probes currently being used to study these systems have been either plagued by low sensitivity or are invasive at molecular scales. Nitrogen-vacancy (NV) centers in diamond is emerging as a robust quantum probe for precision metrology of physical quantities (e.g. magnetic field, electric field, temperature, and stress). Here, we demonstrate by using NV sensors to probe spin-fluctuations and temperature simultaneously to obtain information about controlled phase changes in a soft matter material as a function of temperature. The soft matter system chosen for the study is a standard liquid crystalline (LC) material which shows distinct phases close to room temperature. Individual NV centers at depths of a few nm are used as a probe to detect magnetic signals emanating from a few molecular layers of sample on the surface of the diamond. The organization and collective dynamics of LC molecules in nanoscopic volumes are discussed. Our study aims to extend the areas of application of quantum sensing using NV centers to probe the soft matter systems, particularly those exhibiting mesophases and interesting interfacial properties.

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“…By using the measured impedance spectra, each component of the equivalent circuit, such as the resistance and capacitance, can be estimated by the numerical fitting. Several equivalent circuits for LC cell modeling have been reported [32][33][34][35][38][39][40][41][42]. Sprokel has introduced an equivalent circuit model for the low-frequency behavior, including the LCs capacitance and resistance, and electrical double-layer capacitance induced by the space charges near the electrodes.…”

Section: Change In the Impedance Of The Ion-doped Lc Cellmentioning

confidence: 99%

“…To analyze the degradation with time, we fabricated an ion-doped LC cell and measured the haze and impedance. Impedance and dielectric spectroscopic analyses were carried out to extract the impedance parameters, such as the resistance and capacitance of the LCs and physical parameters of the ionic materials in the bulk regions and near the alignment layers [29][30][31][32][33][34][35]. With the increase in time under the applied electric field, the LC cell exhibited nonuniformity with the decrease of the haze, capacitance of the LC cell, and thickness of the diffusion layer, along with the increase of the resistance of the LC cell and surface concentration of the ions.…”

Section: Introductionmentioning

confidence: 99%

Analysis of Optical Performance Degradation in an Ion-Doped Liquid-Crystal Cell with Electrical Circuit Modeling

et al. 2020

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We reported electrical circuit modeling to analyze the optical performance degradation in an ion-doped liquid-crystal (LC) cell, which exhibited advantages, such as excellent optical performance and simple switching process, but suffered from long-term reliability issues. When an electric field was applied to the cell for an extended period of time, the optical performance became nonuniform, and the haze in the opaque state decreased. By measuring the impedance and fitting the measured data by using an equivalent circuit model, we confirmed the changes of the parameters in the electrochemical impedance spectroscopy and electrophysical properties of the ion-doped LC cell with time. According to the measurement of the optical and physical characteristics, the optical performance degradation was caused mainly by the ionic materials.

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Nanoparticles dispersed in liquid crystals: impact on conductivity, low-frequency relaxation and electro-optical performance

Abstract: We show how the contamination with mobile charge carriers caused by nanoparticle doping affects the dielectric response of a nematic host material and deteriorates its electro-optic performance.

Cited by 74 publications

References 32 publications

Electro-optical Effect of Gold Nanoparticle Dispersed in Nematic Liquid Crystals

Electro-optical Effect of Gold Nanoparticle Dispersed in Nematic Liquid Crystals

Probing phase transitions in a soft matter system using a single spin quantum sensor

Analysis of Optical Performance Degradation in an Ion-Doped Liquid-Crystal Cell with Electrical Circuit Modeling

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