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Effect of barium titanate nanoparticles of different particle sizes on electro-optic and dielectric properties of ferroelectric liquid crystal
Abstract
A comparative study of two different particle sizes of ferroelectric barium titanate (BaTiO3) nanoparticles as a dopant on the molecular structure, spontaneous polarization and dielectric behavior of a pure ferroelectric liquid crystal 6F6T have been studied. It has been found that there is a remarkable decrease in isotropic temperature of both doped samples as compared to the pure 6F6T sample. The spontaneous polarization also decreases for both the doped samples and the reduction is more pronounced in case of the dopant with large particle size. The dielectric spectroscopy confirms the presence of soft mode as well as Goldstone mode and also shows the decrease in the value of dielectric permittivity ' as a function of frequency for both doped samples. The improvised properties of liquid crystal host doped with BaTiO3 nanoparticles mainly depend upon the synthesis method of nanoparticles and also upon the particle size of dopant.
... No change in the Sm A-Sm C* transition temperature was observed in BaTiO 3 NPs (1 wt% concentration)/FLC LAHS19 composite system [76]. Kumar and Sinha [77] dispersed small amount (0.5 wt%) of ferroelectric NPs BaTiO 3 of two different sizes 5-10 nm and 50-60 nm in FLC 6F6T and studied the size effect of NPs on molecular structure and various other properties. As compared to pure FLC substantial influence of NPs on the phase transition sequence was observed. ...
... Ferroelectric barium titanate BaTiO 3 nanoparticles (BT NPs) of various concentrations and particle sizes have been dispersed in different FLCs and the material parameters and other properties of pure FLCs and dispersed composite systems have been investigated extensively [70,77,108,109]. It has been observed that due to the dispersion of BT NPs in FLCs the value of P s and relative permittivity were reduced as a result of anti-parallel correlation between FLC molecules and BT NPs. ...
... The dispersion of 0.2 wt% BT NPs in FLC was found to be most suitable to obtain the increased PL intensity and faster response of the FLC material. Kumar and Sinha [77] demonstrated that the response of BT NPs on the molecular structure, dielectric and electro-optical behaviour of FLC 6F 6 T material depend mainly on the synthesis method and particle-size of NPs. Dispersion of NPs causes decrease in ordering in LC host leading to about 10 0 decrease in isotropic and crystallization temperatures for both the particle sizes (5-10 nm and 50-60 nm) in dispersed system having 0.5 wt% NPs as compared to pure FLC. ...
In recent years, dispersion of nanomaterials in liquid crystal media has attracted a great deal of attention for their applications in various fields and basic understanding. In this regard, nanocomposites of ferroelectric liquid crystals hold a great promise for technological advancement in displays, sensors, development of hybrid materials for optical applications and others. With the emphasis on the properties of ferroelectric liquid crystals, this paper presents a summarizing overview with critical comments on the progress made in last one decade in understanding the influence of nanoparticles on the ferroelectric liquid crystals. The dispersion of nanoparticles in liquid crystal (host material) significantly influences its properties, thereby making the dispersed material more promising for potential applications. © 2019
... It was found that silica NPs dispersed in FLC result in an improvement of the switching times [28]. The same effect was observed for FLCs doped with ferroelectric barium titanate (BaTiO 3 ) where, additionally, spontaneous polarization of the FLC decreased [29][30][31]. Much attention has been focused on titanium dioxide (TiO 2 ) NPs dispersed in FLCs. ...
This paper describes our recent results on light propagation in photonic crystal fibers (PCFs) partially infiltrated with W212 ferroelectric liquid crystal (FLC) doped with 1–3 nm gold nanoparticles (NPs) with a concentration in the range of 0.1–0.5% wt. Based on our previous results devoted to PCFs infiltrated with nematic liquid crystals (NLCs) doped with gold NPs (GNPs), we extend our research line with FLCs doped with these NPs. To enhance the proper alignment of the NP-FLC nanocomposites inside PCFs, we applied an additional photo-aligning layer of SD-1 azo-dye material (DIC, Japan). Electro-optical response times and thermal tuning were studied in detail. We observed an improvement in response times for NP-FLC nanocomposites in comparison to the undoped FLC.
... Incorporation of AgNPs in the FLC mixture may lower the ordering of the liquid crystal molecules or may decrease the average strength of intermolecular interactions thereby decreasing the transition temperature. Similar decrease of transition temperatures has been observed in FLC/AFLC nanocomposites with various types of nanoparticles [30,34,37,38,40,54,63]. ...
We have investigated the effect of doping of a small amount of silver nanoparticles (AgNPs) on the physicochemical properties of a room temperature ferroelectric liquid crystal mixture. Polarizing optical microscopy, differential scanning calorimetry, synchrotron X-ray diffraction, dielectric and electro-optic studies showed that the inclusion of AgNPs greatly influences the phase transition temperatures, structural, dielectric, and electro-optic properties. Doping slightly decreases the SmC*-SmA* and SmA*-Iso transition temperatures signifying decreased ordering which is also reflected in reduced tilt angles. The Goldstone mode dielectric increment of the nanocomposite increases twofold but the critical frequency decreases slightly. Spontaneous polarization of the mixture also increases significantly in the presence of AgNPs whereas the conductivity decreases indicating trapping of ions by the nanoparticles. Goldstone mode rotational viscosity decreases and as a result of which the switching time also decreases by 88 μs making the nano doped mixture more suitable for practical applications.
... Because the effect of doping of ferroelectric particles on the antiferroelectric phase has not been published so far, our studies can be compared with the results describing the effect of ferroelectric particles on the ferroelectric phase. 59,60 In both mentioned articles, the spontaneous polarization in the ferroelectric phase decreases after doping the liquid crystal compound with ferroelectric particles LiNbO 3 and BaTiO 3 , like in our case in the antiferroelectric phase. We can therefore conclude that the BaTiO 3 admixture reduces the spontaneous polarization in both the ferroelectric and antiferroelectric phases. ...
In this paper, for the first time the influence of the BaTiO3 particles on the antiferroelectric liquid crystalline phase was shown. Low concentrations and two different sizes of BaTiO3 particles (nano– and sub-microparticles) were used. It was found that admixture of the ferroelectric particles causes a decrease in the concentration of free ions in the liquid crystal matrix. Despite the small amount of admixture, a decrease in spontaneous polarization, switching time and rotational viscosity was observed, while the tilt angle of molecules and the smectic layer thickness did not change. It turns out that BaTiO3 particles have a very large impact on the dielectric spectra not only in the antiferroelectric phase but also in the ferroelectric and paraelectric phases of the polymorphic mixture studied. The dopants affect also the complex conductivity. In this paper, we explain why some properties are modified by BaTiO3 particles and others not.
... The threshold voltage has been studied by capacitance-voltage measurements of barium titanate (BaTiO 3 ) NP doped pentylcyanobiphenyl (5CB) liquid crystal [28]. Effect of barium titanate nanoparticles of different particle sizes on electro-optic and dielectric properties of ferroelectric liquid crystal has been investigated [29]. Effects of ferroelectric nanoparticles on free ion concentration in a 5CB liquid crystal have been studied [30]. ...
Hexylcyanobiphenyl liquid crystal was doped with graphene oxide at ratios %0.25GO, %0.5GO, %1GO and %2GO, and the change in physical properties of pristine and the doped liquid crystals has been investigated. The phase transitions of prepared samples were studied by differential scanning calorimeter and polarized optical microscopy. The differential scanning calorimeter and polarized optical microscopy results are in good agreement when examining the nematic–isotropic liquid phase transition temperatures of the hexylcyanobiphenyl. The liquid crystal texture images obtained with polarized optical microscopy reveals that thermal stability of sample changed with graphene oxide concentration, i.e., increased with graphene oxide concentration. Impedance, capacitance, conductivity and real and imaginary dielectric constants of the pure and doped liquid crystals were obtained depending on frequency and voltage at the room temperature by using impedance analyzer. These electrical properties of the pure and the graphene oxide-doped samples showed an increase with increasing the graphene oxide ratio. The voltage-dependent light transmittance experiment revealed that threshold voltage of LC cells decreased for %0.25GO- and % 1GO-dispersed samples, but it was increased at %0.5GO- and %2GO-dispersed samples.
... It has been observed that the incorporation of NPs have influenced their different physical properties without distortion of the directors. For example, the metallic nanoparticle improves the switching time, luminescent properties and conductivity of liquid crystal host [19,20]; ferroelectric NPs change the P s , switching time, transition temperatures [21][22][23][24]; and dielectric NPs change the conductivity, and hence, different electro-optical properties of the LC host [25,26]. The various interesting characteristics of doped LCs as compared to their bulk counterpart have stimulated significant research in this field. ...
We report the effect of dispersion of barium titanate (BaTiO3) nanoparticles (BNPs) in a four ring bent core nematic (BCN) liquid crystal.Polarizing optical microscopy (POM) reveals the presence of a single nematic phase in pure and doped states. Polar switching has been observed in the bent core system and the value of spontaneous polarization (Ps) increases with increase in doping
concentration of BNPs in BCN. Dielectric study shows a lower frequency mode, which can be ascribed to the formation of cybotactic clusters. These clusters are also responsible for the observed polar switching in pure, as well as, in doped BCNs. Another higher frequency mode, observed only in pure BCN, indicates the rotation of molecules about their long molecular axis. The conductivity of doped samples is also found to decrease as compared to the pure BCN. This reduction helps in the minimization of negative effects caused by free ions in LC based devices. This study demonstrates that the interaction between BNPs and BCN molecules improves the Ps, dielectric behaviour, viscosity and reduces the conductivity of pure BCN. Hence, nanodoping in a BCN is an effective method for the enhancement of electro-optic performances and will lead to the development of faster electro-optic devices.
... It has been observed that the doping of small amount of metallic nanoparticles improve the switching time and luminescent properties of ferroelectric liquid crystal (FLC) [3,4]. The doping of ferroelectric nanoparticles in FLC has modified spontaneous polarization, switching time and transition temperature [5]. Semiconducting nanoparticles in FLC can improve the threshold voltage and optical contrast, while the dielectric nanomaterials can change the conductivity by capturing the mobile ions present in LC and hence improve the electro-optical properties [6,7]. ...
The present study is focused on the investigations of possible effects on electro-optical properties of carbon nanotubes (CNTs) doped ferroelectric liquid crystal (FLC), W206E. The optical micrographs of nanocomposite systems reveal some topological defects. The spontaneous polarization of doped systems decreases as compared to the pure FLC. The dielectric permittivity and conductivity are decreased with increasing doping concentration of CNTs in W206E. These decrements can be attributed to the trapping of mobile ions by dopant CNTs in W206E. This study will help in the development of faster display devices based on liquid crystals with better contrast and lower threshold voltage.
... Various research groups have emphasized to study the role of nanomaterials into LCs and gave reasonable theories. Dispersion of nanoparticles like silica, zinc oxide, multiwall carbon nanotubes, singlewall carbon nanotubes [5], ferroelectric [6,7], metal, oxides [8][9][10][11] in nematic LCs as well as in FLCs has been investigated. ...
We have investigated the effect of nickel nanoparticles (NiNPs) in a pure ferroelectric liquid crystal (FLC) mixture. Dielectric spectroscopy was done in the frequency range of 20 Hz–10 MHz. Switching time, spontaneous polarisation, rotational viscosity has been measured using field reversal technique in SmC* phase. The spontaneous polarisation increases for NiNPs-FLC sample which may be due to the induced dipole moments around FLC molecules. Response time decreases with temperature and NiNPs dispersion. The relaxation frequency and dielectric strength of observed mode in SmC* phase is also discussed in pure FLC and NiNPs-FLC samples. The relaxation frequency in NiNPs-FLC sample decreases than pure FLC sample and found ∼120 Hz.
... i.e. (spontaneous polarisation, response time in doped sample) 9nm size < (spontaneous polarisation, response time in doped sample) 26nm size < (spontaneous polarisation, response time in pure FLC mixture). Two different average particle sizes (5-10 and 50-60 nm) of BaTiO 3 were also dispersed in another FLC (6F 6 T) and observe an improvement in EO and dielectric properties [19]. Shukla et al. also consider gold nanoparticles (size 1.77 and 5.5 nm) doped FLC mixture and study EO and dielectric parameters [20]. ...
In the present study, ferromagnetic nickel nanoparticles (NiNPs) of size (~20 nm, 40 nm) into ferroelectric liquid crystal (FLC) mixture has been dispersed and investigated. Effect of size of NiNPs on the electro-optic, dielectric and optical properties of FLC mixture have been studied and discussed. A minor improvement in spontaneous polarisation, rotational viscosity and faster response time in NiNPs-FLC samples than pure FLC is noticed. Goldstone mode of relaxation frequency ~100 Hz is detected in all samples and follow a Debye type relaxation behaviour. In addition, it is observed that size of NiNPs does not have any remarkable effect on relaxation frequency and dielectric strength. A single absorption peak at 363, 362 Hz is also noticed in pure FLC and NiNPs-FLC samples.
... Semiconducting nanoparticles such as zinc oxide when dispersed in FLCs, reduce the threshold voltage and improve the optical contrast of the display devices [11]. Doping of ferroelectric barium titanate (BaTiO 3 ) nanoparticles results in the enhancement of the switching time, transition temperature and decrement in the polarization of FLCs [12,13]. It has been observed that, the impurity ions present in LCs are responsible for the lower contrast, slower response time and high threshold voltage. ...
In the present study, the insulating titanium dioxide (TiO 2) nanoparticles were dispersed in two different concentrations of 0.5 wt % and 1.0 wt % in pure ferroelectric liquid crystal (FLC) mixture, W206E. The effects of different concentrations of dopant TiO 2 in W206E for electro-optical and dielectric properties have been studied. The optical microscopy measurements clearly show the isotropic transition temperature of both the doped samples slightly increases by about 1 ~ 2 0 C as compared to the pure sample. Further, with the increasing concentrations of dopant TiO 2 , the value of spontaneous polarization decreases. The value of dielectric permittivity also decreases for both the doped samples and this decrease in the value of permittivity is more prominent with increasing concentrations of TiO 2 at the lower frequencies. The dielectric measurements also confirm the presence of Goldstone mode in Smectic C* phase in pure as well as in both the doped samples. The conductance measurements confirm the decrease in conductivity of doped samples as compared to the pure W206E FLC. This study may help in improving the transition temperature and reducing the impact of free ionic charge impurities on various physical properties of liquid crystal host by screening the free ions using TiO 2 nanoparticles as dopant.
... Therefore, to improvise the performance of liquid crystal based display devices, the free ionic impurities present in liquid crystal must be minimized before using it for any display application. Doping of different types of nanoparticles such as semiconducting nanoparticle [3,4], metallic nanoparticle [5,6], ferroelectric nanoparticle [7,8] and dielectric nanoparticle [9,10] in liquid crystal has improved the various electro-optical properties of the existing liquid crystals. The insulating nanoparticles are generally used to reduce the free ions present in liquid crystal. ...
In this study, the electrical properties of ferroelectric liquid crystal (W206E) doped with anatase titanium dioxide (TiO2) nanoparticles were studied. The experimental results show that the dopant TiO2 reduces the free ion concentration and therefore the conductivity of doped W206E samples. This reduction in the free ion concentration is due to the trapping of free ions by TiO2 nanoparticles dispersed in W206E. The reduction in the free ion concentration is related to the doping concentration of TiO2. The experimental results show that the higher concentration of TiO2 is more effective in the trapping of mobile ions. This result will help in the development of fast response display devices with better contrast and low threshold voltage.
... Various research groups have emphasized to study the role of nanomaterials into LCs and gave reasonable theories. Dispersion of nanoparticles like silica, zinc oxide, multiwall carbon nanotubes, singlewall carbon nanotubes [5], ferroelectric [6,7], metal, oxides [8][9][10][11] in nematic LCs as well as in FLCs has been investigated. ...
We have investigated the effect of nickel nanoparticles (NiNPs) in
a pure ferroelectric liquid crystal (FLC) mixture. Dielectric spectroscopy
was done in the frequency range of 20 Hz–10 MHz.
Switching time, spontaneous polarisation, rotational viscosity has
been measured using field reversal technique in SmC∗ phase.
The spontaneous polarisation increases for NiNPs-FLC sample
which may be due to the induced dipole moments around FLC
molecules. Response time decreases with temperature and NiNPs
dispersion. The relaxation frequency and dielectric strength of
observed mode in SmC∗ phase is also discussed in pure FLC and
NiNPs-FLC samples. The relaxation frequency in NiNPs-FLC sample
decreases than pure FLC sample and found ∼120 Hz.
... A variety of NPs e.g. carbon nanotubes (CNTs) [7], gold NPs [8,9], graphene [10,11], graphene oxides [12], oxides [13,14], ferroelectric [15,16], quantum dots [17,18], have been dispersed in LCs and studied. It is observed that doping of NPs has considerable effect on enhancement in contrast ratio, transmittance, birefringence, switching time, threshold voltage, polarisation, permittivity, dielectric strength, conductivity and photoluminance. ...
In this work, the effect of Iron nanoparticles (Fe NPs) dispersion in 4′-(Hexyloxy)-4-biphenylcarbonitrile (6OCB) nematic liquid crystal properties has been studied. Inclusion of Fe NPs (0.25 wt. %) in 6OCB liquid crystal (LC) on textures, isotropic–nematic transition temperature (TI–N), electro-optical and dielectric properties have been investigated in planar aligned cell. The threshold voltage (Vth) and TI–N decrease after dispersion of Fe NPs. Dielectric spectroscopy in nematic phase show that relaxation frequency (fr) also decreases after dispersion of Fe NPs in 6OCB. The observed relaxation mode is due to the flip-flop motion of LC molecules about their short axis. The band gap and AC conductivity in case of 6OCB-Fe sample increase over pure 6OCB sample. A decrease in activation energy is also noticed.
... Various research groups have emphasized to study the role of nanomaterials into LCs and gave reasonable theories. Dispersion of nanoparticles like silica, zinc oxide, multiwall carbon nanotubes, singlewall carbon nanotubes [5], ferroelectric [6,7], metal, oxides [8][9][10][11] in nematic LCs as well as in FLCs has been investigated. ...
... 19 For doped 6F 6 T samples apart from screening of external electric field, the anti-parallel dipole-dipole interaction between BaTiO 3 and 6F 6 T molecules is the main reason for the decrease in the value of P s . 5,[20][21][22] The EO response has been measured by placing the cell inside the INSTEC hot stage, and then, this whole system was placed between the crossed polarizer and analyzer. The He-Ne laser light of wavelength 633 nm was incident on one side of the FLC cell through a polarizer and the transmitted laser light is detected on the other side using silicon photodiode (SMO5PD1A from Thorlabs). ...
Nanoparticle (NP) dispersion in liquid crystals
(LCs) results in significant changes in the physical properties of the existing LC mixtures. Two ferroelectric liquid crystals (FLCs), 5F6T and 6F6T, have been studied for analog switching. The 5F6T sample is doped with titanium dioxide (TiO2) NPs of two different concentrations of the same average particle size and another FLC 6F6T is systematically doped with barium titanate (BaTiO3) NPs of two different average particle sizes at the same concentration. The frequency and temperature dependence of the coercive voltage of FLC nanocolloids has been studied. The V-shaped switching was observed in the case of nano-doped FLCs. The value of inversion frequency for the 5F6T+1.0 wt.%
TiO
2
doped sample is 30 Hz while it is 24 Hz for the 6F6T+0.5 wt.%
BaTiO
3 (particle size 5–10 nm) doped sample. The conductivity measurements show that the conductivity of doped samples is higher than the conductivity of their parental FLCs and can be considered the main reason for the V-shaped switching in the FLC nanocolloids, which was initially absent in their parental FLCs.
... [5][6][7][8][9][10] Dispersion of a small amount of numerous types of NPs, e.g. carbon nanotubes (single-/ multi-walled), [11] ferroelectric (Sn 2 P 6 S 6 , BaTiO 3 ), [9,12] metal (Au, Ag, Cu, Si), oxides (MgO, SiO 2 , Y 2 O 3 , Ag, Pd, CdS, Au, Pt), [13][14][15][16] quantum dots (CdSe, CdTe, ZnO, ZnS), [17][18][19] graphene, and NPs in nematic LCs and FLCs, has been considered by different research groups. Doping of such NPs does not induce much distortions in the phases of LCs; however it modifies and improves the response time, photoluminance properties, threshold voltage and contrast of LC devices, which may be beneficial in the designing and fabrication of modern and advanced devices. ...
In the present study, magnetic nanoparticles (NP, nickel ferrite) in different concentrations into ferroelectric liquid crystal (FLC) mixture have been prepared and studied. The effect of nickel ferrite concentration on the electro-optic, dielectric and optical properties of FLC mixture has been studied and discussed. An improvement in spontaneous polarization, response time in nickel ferrite-FLC-doped samples compared to FLC is observed and explained on the basis of dipole moment and anchoring phenomena. The Goldstone mode (GM) is detected in all samples and follows a Debye-type relaxation behaviour. A twofold increase in relaxation frequency for the doped sample rather than the pure sample has been observed. The band gap was found more or less independent of doping concentration. The activation energy (Ea) also decreases on increasing the doping amount.
Despite the great advances, the basic and applied understandings on the behavior of liquid crystals (LCs) continue to have a revolutionary technological impact and consistently pose new challenges. The basic understanding on the properties of liquid crystals (LCs) is poor as compared to other materials. In applied aspects, the subject has achieved respectable positions. There are certain required qualities which LC based devices have to possess. In recent decades, for achieving these requirements the interest and emphasis on the science and technology of LC materials have shifted in two main directions: (i)To synthesize new materials possessing specific characteristics and properties that are appropriate for the applications, and (ii) to prepare a composite system by the dispersion (or doping) of nonmesogenic materials (NMMs) in the host LC and modify its properties so that the dispersed system becomes suitable for the applied applications.
The electro-optic and dielectric behaviors of a four-ring bent core nematic (BCN) liquid crystal (5-2F-2Me-10) in its pristine and two different concentration proportions (0.5 wt.% and 1.0 wt.%) of ferroelectric liquid crystal (W206E) dispersed states, have been studied. Polarized optical microscopy (POM) confirms the presence of a nematic and SmA phases in pure and W206E doped states of BCN. The transition temperatures corresponding to different phases of doped samples decrease as compared to the pure BCN. An interesting ferroelectric like switching has been observed in pure 5-2F-2Me-10 and 5-2F-2Me-10 + 0.5 wt.% W206E samples in their nematic phases. However, it is not significant in the case of 5-2F-2Me-10 + 1.0 wt.% W206E. Dielectric spectroscopy reveals the presence of cybotactic clusters in pure and doped states of BCN, which is considered the main reason for the observed polar switching in these samples in their nematic phases. This study will help to understand the nature of interactions between the host BCN and doped FLC, and gives a direction to understand the effect of doping of FLC in BCN. Further, one major problem commonly associated with BCNs is high clearing temperature, as well as their different LC phases exist relatively at high temperatures, which restricts their potential applications in electro-optic devices. In this regard, the findings of this study are useful in reducing the isotropic temperature and the temperature corresponding to the different phases of a BCN.
We demonstrated the doping effects of titanium silicon oxide (TiSiO4) nanoparticles (NPs) on the characteristics of liquid crystal (LC) system. Simply by adding TiSiO4 to the LC medium, the electro-optical (EO) characteristics of LC cells can be improved. The EO characteristics were improved by increasing the doping concentration. However, it was confirmed that if the doping concentration was too high, the EO characteristics would be deteriorated due to interference with the LC behavior. In addition, TiSiO4 NPs dispersed in the LC mixture captured impurity ions and exhibited hysteresis-free voltage-transmittance (V–T) characteristics. The TiSiO4 NPs doped LC cells also showed higher thermal stability than a pristine LC cell. These results suggest that TiSiO4 NPs doped into an LC system could benefit not only the display industry but also other industrial fields requiring high-performance EO characteristics.
The study of fast response nematic liquid crystal display material mixture and synthesis about compounds has always been an important subject in recent years. In this article, one type of high birefringence liquid crystal based on phenyl-diacetylenes was synthesized by sonogashira coupling reaction. A research is conducted on the effect of electro-optic properties of a widely used nematic liquid crystal mixture doped with the prepared high birefringence liquid crystal molecule which concentrations ranging from 1% to 5 wt%. While the results show that the steepness of electro-optic curves first increase and then decrease with the prepared high birefringence liquid crystal molecule content increasing, when the content of high birefringence liquid crystal molecule reaches 3%, electro-optic properties of the mixture liquid crystals are excellent.
We investigated the physical properties of low concentration ferroelectric nematic colloids, using calorimetry, optical methods, infrared spectroscopy, and capacitance studies. The resulting homogeneous colloids possess a significantly amplified nematic orientational coupling. We find that the nematic orientation coupling increases by \ensuremath{\sim}10% for particle concentrations of 0.2%. A manifestation of the increased orientational order is that the clearing temperature of a nematic colloid increases by up to 40\text{ }\ifmmode^\circ\else\textdegree\fi{}\mathrm{C} compared to the pure liquid crystal host. A theoretical model is proposed in which the ferroelectric particles induce local dipoles whose effective interaction is proportional to the square of the orientational order parameter.
Net spontaneous polarization PS of ferroelectric liquid crystals was obtained by compensat-ing ferroelectric hysteresis loop distortion. The compensated values of PS obey the equation PS=P0(TC − T) β . Effects of experimental condition on parameters TC, P0 and β were investi-gated. These parameters strongly depends on the quality of molecular alignment. In well-aligned cell, TC and β are independent of cell thickness, however, P0 decreases with decreasing cell thickness and with increasing frequency; the decreases of P0 are mainly due to the self-screening effect and partly to the effect of alignment layers fixed on the cell surfaces and the self-screening effect.
A report on the development of a dilute suspension of ferroelectric particles in a nematic liquid-crystal (LC) host was presented. Small ferroelectric particles were obtained using milling large particles as opposed to chemical fabrication. It was found that the LC alignmemt was not disturbed by the submicron particles and the suspension macroscopically appeared similar to a pure LC with no evidence of dissolved particles. It was also found that the suspension possesses enhanced dielectric anisotropy and was sensitive to the sign of an applied electric field.
In the framework of molecular mean-field theory we study the effect of nanoparticles embedded in nematic liquid crystals on the orientational ordering and nematic–isotropic phase transition. We show that spherically isotropic nanoparticles effectively dilute the liquid crystal medium and decrease the nematic–isotropic transition temperature. At the same time, anisotropic nanoparticles become aligned by the nematic host and, reciprocally, improve the liquid crystal alignment. The theory clarifies the microscopic origin of the experimentally observed shift of the isotropic–nematic phase transition and an improvement of the nematic order in composite materials. A considerable softening of the first order nematic–isotropic transition caused by strongly anisotropic nanoparticles is also predicted.
The influence of the size of harvested barium titanate nanoparticles on the properties of ferroelectric liquid crystal (FLC) nanocolloids was investigated by electro-optical and dielectric methods. The spontaneous polarization and the switching time are decreased for the liquid crystalline nanocolloids compared to nondoped FLC mixtures of different dipole strengths; this dependence is stronger for small size particles (9 nm) and weaker for larger size particles (26 nm) by the same concentration in weight. The decrease of the Goldstone mode (GM) relaxation frequency and the decrease of the dielectric GM absorption strength of the nanocomposites compared to the nondoped FLC mixture go stepwise with the increase of the nanoparticles diameter. Results have been interpreted via strong interaction between the FLC dipoles and the dipoles of the highly polar barium titanate nanoparticles.
It is proposed to apply the direct measurement of spontaneous polarization using triangular waves to ferroelectric liquid crystals. The use of the triangular waves allows us to easily subtract the background contribution due to the conductive and the capacitive current and to accurately determine the spontaneous polarization, since a bump due to the polarization realignment appears on a straight base line. Moreover, the experiment with pulsed triangular waves clearly reveals no existence of the threshold voltage for deforming the helix and some characteristic properties of the dynamic reaction of the helix to the field applied.
In scope of this paper, dielectric and electro-optic properties of planar aligned ferroelectric liquid crystals/carbon nanotubes dispersions were investigated. It is demonstrated that even a small concentration of nanotubes greatly affects the performance of the liquid crystal cells. The obtained experimental results are explained by the trapping of ions through the carbon nanotubes, which results in a significant modification of the internal electric field as well as the space charges distribution inside the liquid crystal cells.
In scope of this paper, DSC, small-angle X-ray scattering (SAXS), electro-optic and dielectric studies have been done on BaTiO3 nanoparticles dispersed in a ferroelectric liquid-crystalline (FLC) matrix. Electro-optic studies showed slightly lower spontaneous polarization, faster response time and relatively higher coercive voltage for the nanocomposite as compared to the pure FLC mixture. Dielectric measurements revealed a lower relative dielectric permittivity for the nanocomposite. This paper addresses all the issues starting from the kind of nanoparticles and FLC materials used for the preparation of nanocomposites, the various measurements done and a detailed discussion on the observed results.
Parallel alignment of nanotubes can be obtained by dispersion in a self-organizing anisotropic fluid such as a nematic liquid crystal. Exploiting the cooperative reorientation of liquid crystals, the overall direction of the nanotube alignment can be controlled both statically and dynamically by the application of external fields. These can be electric, magnetic, mechanic, or even optic in nature. Employing multiwall as well as single-wall carbon nanotubes, we show their parallel alignment along a uniform liquid crystal director field and electrically verify their reorientation behavior for two complementary geometries. These demonstrate electrically controlled carbon nanotube OFF– ON and ON–OFF switches. Further applicational potential will be outlined. © 2005 American Institute of Physics.
The aim of this paper is to study the influence of electric field on alignment of para-, ferro- and antiferroelectric phases
in the vicinity of SmA* — SmC* or SmC* — SmC
A
*
phase transitions as to obtain mono-domain cells. Four mixtures studied (W-193B, W-193B-1, W-201, W-204D) show the SmC
A
*
phase in a wide room temperature range. Measurements of the spontaneous polarization versus temperature by using reversal
current method give an answer to the question, what kind of the transitions take place between para-, ferro- or antiferroelectric
phases using the Landau mean field theory. Optimal electrooptic parameters for different compositions of the mixtures such
as tilt angle, spontaneous polarization and saturation voltage have been measured to compare parameters of the mixtures studied.
We report the characterization and photoluminescence (PL) of newly synthesized deformed helix ferroelectric liquid crystal (DHFLC) material having short pitch and high spontaneous polarization. We observed ninefold enhancement in PL intensity in gold nanoparticles doped DHFLC material. This enhancement in the PL intensity has been attributed to the coupling of localized surface plasmon resonance from metal nanoparticles with DHFLC molecules, resulting in the increase in excitation and emission rate of the liquid crystal molecules in the localized electromagnetic field. These studies would provide a cutting edge tool in the realization of enhanced photoluminescent liquid crystal display devices.
It has been observed that the polymeric nanoparticles, copolymer of polybenzene and anthracene (PBA NPs), can induce a homeotropic (HMT) alignment in various ferroelectric liquid crystal (FLC) mixtures. The HMT alignment of various FLCs is attributable to the fact that the anthracene molecules favor an upright orientation (with a little tilt) on the surfaces of indium tin oxide and this upright orientation of anthracene molecules works as a template to align FLC molecules homeotropically. It has been concluded that the addition of ∼0.5 wt % of PBA NPs is enough to induce a HMT alignment in a FLC material Felix 17/100. The influence of the PBA NPs concentrations on the transition temperature, physical constants (such as spontaneous polarization, rotational viscosity, and response time) and dielectric relaxation processes of FLC material (Felix 17/100) has also been investigated.
We present here the dielectric and electro-optical studies of cadmium telluride quantum dots (CdTe QDs) doped ferroelectric liquid crystals (FLCs). It has been observed that the doping of CdTe QDs not only induced a pronounced memory effect but also affected the physical parameters of FLC material (LAHS19). The modifications in the physical parameters and memory effect of LAHS19 are found to depend on the concentration ratio of CdTe QDs. The lower concentration of CdTe QDs (1-3 wt%) enhanced the values of spontaneous polarization and rotational viscosity of LAHS19 material but did not favor the memory effect, whereas a higher concentration of CdTe QDs (>5 wt%) degraded the alignment of LAHS19 material. The doping of ∼5 wt% of CdTe QDs is found to be the most suitable for achieving good memory effect without significantly affecting the material parameters.
The present paper discusses some properties of small, elongated particles suspended in a nematic or cholesteric phase, with low concentrations (typical volume fraction occupied by the particle f ≊ 10-3). We find that in most cases the particle axis should be locked and parallel to the local nematic axis n(r). If such colloidal suspensions could be made successfully with magnetic grains, it should be possible to prepare « ferronematics » or « ferrocholesterics », where locally all particles are magnetized in one direction (colinear to n), and also « compensated » materials with no spontaneous magnetization. These three types of samples should all show remarkable distorsions and phase changes in low external fields H. Similar effects are expected under electric fields with colloidal suspensions of polar rod molecules such as helical polypeptides. On discute certaines propriétés de particules petites et allongées, en suspension dans un cristal liquide, à basse concentration (fraction en volume f ≲ 10-3). On montre que dans la plupart des cas, la direction des particules ne peut pratiquement pas s'écarter de l'axe nématique local n(r). Si l'on parvenait à préparer de telles suspensions avec des grains magnétiques, on pourrait réaliser des suspensions « ferronématiques » ou « ferrocholestériques» dans lesquelles, localement, tous les grains sont aimantés dans une même direction (parallèle à n) et aussi des matériaux « compensés» sans aimantation spontanée. De telles suspensions devraient montrer des distorsions et des changements de phase remarquables en présence de faibles champs extérieurs H. On attend aussi des phénomènes de ségrégation : les grains tendent à se déplacer vers les régions du spécimen où n est parallèle à H. Des effets analogues, sous champ électrique, pourraient en principe être obtenus avec des suspensions colloidales de macromolécules polaires en bâtonnets, par exemple avec des hélices de polypeptides.
Recent experiments have reported that ferroelectric nanoparticles have drastic effects on nematic liquid crystals-increasing the isotropic-nematic transition temperature by about 5 K, and greatly increasing the sensitivity to applied electric fields. To understand these effects, we develop a theory for the statistical mechanics of ferroelectric nanoparticles in liquid crystals. This theory predicts the enhancements of liquid-crystal properties, in good agreement with experiments. These predictions apply even when electrostatic interactions are partially screened by moderate concentrations of ions.
We propose a general approach to the description of the long-ranged interaction between nanoparticles (1-10 nm) of ordinary shape in the paranematic phase, i.e., nematic liquid crystal in the isotropic phase. In general case interaction potential is attractive of Yukawa form with derivatives. But it can be anisotropic despite the isotropy of the paranematic phase. The origin of such anisotropy is the shape of nanoparticles. Particular potentials for spherical and cylindrical particles are considered. For the case of nanocylinders anisotropic part of the interaction potential can lead to the orientational ordering of them in the isotropic phase of nematic liquid crystals.
We investigated the physical properties of low concentration ferroelectric nematic colloids, using calorimetry, optical methods, infrared spectroscopy, and capacitance studies. The resulting homogeneous colloids possess a significantly amplified nematic orientational coupling. We find that the nematic orientation coupling increases by approximately 10% for particle concentrations of 0.2%. A manifestation of the increased orientational order is that the clearing temperature of a nematic colloid increases by up to 40 degrees C compared to the pure liquid crystal host. A theoretical model is proposed in which the ferroelectric particles induce local dipoles whose effective interaction is proportional to the square of the orientational order parameter.
The chemistry, physics, and applications of liquid crystals beyond LCDs Liquid Crystals (LCs) combine order and mobility on a molecular and supramolecular level. But while these remarkable states of matter are most commonly associated with visual display technologies, they have important applications for a variety of other fields as well. Liquid Crystals Beyond Displays: Chemistry, Physics, and Applications considers these, bringing together cutting-edge research from some of the most promising areas of LC science. Featuring contributions from respected researchers from around the globe, this edited volume emphasizes the chemistry, physics, and applications of LCs in areas such as photovoltaics, light-emitting diodes, filed-effect transistors, lasers, molecular motors, nanophotonics and biosensors. Specific chapters look at magnetic LCs, lyotropic chromonic LCs, LC-based chemical sensors, LCs in metamaterials, and much more. Introducing readers to the fundamentals of LC science through the use of illustrative examples, Liquid Crystals Beyond Displays covers not only the most recent research in the myriad areas in which LCs are being utilized, but also looks ahead, addressing potential future developments. Designed for physicists, chemists, engineers, and biologists working in academia or industry, as well as graduate students specializing in LC technology, this is the first book to consider LC applications across a wide range of fields.
Nanocolloids comprising harvested ferroelectric LiNbO3 nanoparticles (≈25 nm) and ferroelectric liquid crystals were prepared and investigated. The impact of the amount of dispersed nanoparticles (0.01 wt%, 0.05 wt%, 0.10 wt%) on the electro-optical, dielectric and material parameters of the ferroelectric liquid crystals (FLCs) has been demonstrated. The dopant strongly influences the switching characteristics and has an effect on the saturation voltage of the FLC materials. Electro-optical measurements demonstrated that a relatively large (0.10 wt%) LiNbO3 dopant concentration decreases the response time and saturation voltage by approximately 40% and 25% respectively, compared with non-doped FLCs. The effect of LiNbO3 nanoparticle concentration on the material and dynamical parameters (i.e. spontaneous polarization, dielectric permittivity, dielectric absorption, dielectric strength, dc conductivity, and rotational viscosity) is presented. The observed behaviours are discussed in terms of capture of impurity ions on the surface of the harvested LiNbO3 nanoparticles. Ion capturing leads to enhancement of the localized electric field inside the smectic layers. The fast switching response and the low operational voltage of these FLC nanocolloids support their application in nanometric scale electronic devices.
Classroom Experiments with Chiral Liquid Crystals.- From a Chiral Molecule to a Chiral Anisotropic Phase.- Chemical Structures and Polymorphism.- Cholesteric Liquid Crystals: Defects and Topology.- Cholesteric Liquid Crystals: Optics, Electro-optics, and Photo-optics.- Blue Phases.- Smectic Liquid Crystals: Ferroelectric Properties and Electroclinic Effect.- Smectic Liquid Crystals: Antiferroelectric and Ferrielectric Phases.- Twist Grain Boundary Phases.- Columnar Liquid Crystals.- Some Aspects of Polymer Dispersed and Polymer Stabilized Chiral Liquid Crystals.- Chirality in Liquid Crystal Elastomers.- Phase Chirality of Micellar Lyotropic Liquid Crystals.- Traveling Phase Boundaries with the Broken Symmetries of Life.
Palladium nanoparticles covered with liquid-crystal molecules were prepared by UV irradiation of an alcohol solution of palladium(II) acetate in the presence of liquid-crystal molecules. The prepared Pd nanoparticles have an average diameter of 2.5 nm. A twisted nematic (TN) liquid-crystal device (LCD) was fabricated by doping with Pd nanoparticles covered with another kind of nematic liquid-crystal molecules. In this device the sign of the dielectric anisotropy (Deltaε) of the liquid-crystal molecules, which cover Pd nanoparticles, is opposite to that of nematic liquid-crystal molecules, which work as the host of the device (DeltaV>0). The TN-LCD cell fabricated in this research exhibits a frequency modulation response to an applied alternative voltage wave form.
The Nematic Phase Nematic Textures Under Planar Boundary Conditions The Nematic Schlieren TextureThe Thread-like TextureThe Marble TextureUniform Planar Nematic SamplesThe Pseudo-Isotropic Texture Under Homeotropic Boundary ConditionsThe Cholesteric Phase Natural Textures of the N* PhaseShort Pitch Cholesterics Planar Boundary Conditions and Selective ReflectionHomeotropic Boundary Conditions and the Flexoelectric EffectLong Pitch Cholesterics Planar Boundary ConditionsHomeotropic Boundary Conditions Nematic Textures Under Planar Boundary Conditions The Nematic Schlieren TextureThe Thread-like TextureThe Marble TextureUniform Planar Nematic SamplesThe Pseudo-Isotropic Texture Under Homeotropic Boundary Conditions The Nematic Schlieren TextureThe Thread-like TextureThe Marble TextureUniform Planar Nematic Samples Natural Textures of the N* PhaseShort Pitch Cholesterics Planar Boundary Conditions and Selective ReflectionHomeotropic Boundary Conditions and the Flexoelectric EffectLong Pitch Cholesterics Planar Boundary ConditionsHomeotropic Boundary Conditions Planar Boundary Conditions and Selective ReflectionHomeotropic Boundary Conditions and the Flexoelectric Effect Planar Boundary ConditionsHomeotropic Boundary Conditions
Dielectric measurements in the frequency range 100 Hz to 100 kHz have been carried out in a short pitch ferroelectric liquid crystal mixture FLC-6430 (Hoffmann-La-Roche) in the SmC* phase aligned in planar orientation. The effects of temperature, frequency and bias voltage on the dielectric properties of this material have been investigated. The relaxation frequency fr, distribution parameter α and the dielectric strength εs, have been determined. The calculated values were found to be ∼0.59 kHz, 0.134 and 427.77 respectively for fr, α and εs at 45°C. A constant DC bias of 0.13 V/μm applied to the sample partially suppresses the Goldstone mode.
We report the reduction of threshold voltage, Vth, of twisted nematic liquid crystal devices by doping the nanoparticles of MgO and SiO2. The results are well explained by inserting the experimentally determined values of elastic constants and dielectric anisotropy in the formula Vth = pi\sqrt{Keff/\varepsilon0Delta\varepsilon}, where both of these quantities decrease due to the existence of these nanoparticles. The Vth decrease approximately as \sqrt{S}, where S being the order parameter. The S is also shown to decrease by doping nanoparticles.
The electrooptic characteristics of a twisted nematic (TN) liquid crystal display (LCD) fabricated by doping Ag nanoparticles protected with NLC, 5CB (K-15, Merck) molecules have been investigated, and it is shown that the device exhibits a unique electrooptic response characteristic that is sensitive to the high-frequency components of the operating voltage together with the conventional root-mean-square voltage response. We call this device frequency modulation (FM) TN-LCD. The FM-TN-LCD is switched by switching the frequency of the operating voltage while its amplitude is kept unchanged. As an example, the frequency switched from 20 Hz to 500 Hz or 50 Hz to 2 kHz, and the switching is performed with the time constant of 21 ms for the rising process and 3 ms for the falling process. This device shows a peculiar response to a burst AC square wave, where the decay time is reduced by several times compared to that of an undoped TN-LCD. The mechanism of the FM-TN-LCD is investigated through the study of its dielectric properties.
Liquid crystals: main types and classification distribution functions and order parameters physical properties of liquid crystals nematic liquid crystals nematic liquid crystals - elastostatics and nematodynamics smectic liquid crystals liquid crystals of disc-like molecules polymer liquid crystals chiral liquid crystals lyotropic liquid crystals defects and textures in liquid crystals.
Broadband dielectric spectroscopy delivers in the frequency range from 10 Hz to 1010 Hz two collective dielectric loss processes (soft and Goldstone modes) and one molecular relaxation (β-relaxation). The soft mode and Goldstone mode are assigned to the fluctuation of the amplitude and the phase of the helical superstructure. The β-relaxation corresponds to the libration (hindered rotation) of the mesogene around its long molecular axis. At the SmA–SmC* phase transition this process does not split or broaden, and the temperature dependence of its relaxation rate does not show any deviation from an Arrhenius-like behavior. Its dielectric strength does not decline at the SmA–SmC* phase transition. These experimental findings are in contrast to the common explanation of the origin of the saturation polarization (“induced spontaneous polarization”), which is based on the existence of a “free” rotation inside the SmA phase and its strong hindrance in the ferroelectric SmC* phase. Furthermore, the high frequency results require a reformulation for the (generalized) Landau theory as applied to the SmA–SmC* phase transition. In comparing low molar mass and polymeric (elastomeric) FLC, the collective and molecular dynamics are qualitatively similar, independent of the molecular architecture (e.g. side-chain, combined main- and side-chain or crosslinked systems).
A simple and robust method to prepare nanoparticle-dispersed liquid crystals is demonstrated. Highly dispersed gold nanoparticle-liquid crystal suspensions are fabricated by simply sputter doping the gold target on the host liquid crystal (see figure). The existence of the nanoparticles is supported by optical extinction measurements, polarization optical microscopy, and transmission electron microscopy. An improvement in the electro-optic response, namely, a decrease in the threshold voltage, is also demonstrated in twist nematic devices fabricated using the nanoparticle-dispersed liquid crystal.
In this work the 4-(trans- 4'-n -hexylcyclohexyl)-isothiocyanatobenzene (6CHBT) liquid crystal was doped with differently shaped magnetite nanoparticles. The structural changes were observed by capacitance measurements and showed significant influence of the shape and size of the magnetic particles on the magnetic Fréedericksz transition. For the volume concentration phi= 2 x 10(-4) of the magnetic particles, the critical magnetic field was established for the pure liquid crystal, and for liquid crystals doped with spherical, chainlike, and rodlike magnetic particles. The influence of the magnetic field depends on the type of anchoring, which is characterized by the density of anchoring energy and by the initial orientation between the liquid crystal molecules and the magnetic moment of the magnetic particles. The experimental results indicated soft anchoring in the case of spherical magnetic particles and rigid anchoring in the case of rodlike and chainlike magnetic particles, with parallel initial orientation between the magnetic moments of the magnetic particles and director.
High-resolution heat-capacity, tilt-angle, and polarization measurements have been carried out in the vicinity of the smectic-A (SmA) -chiral-smectic-C (SmC*) phase transition of p-(n-decyloxybenzylidene)-p-amino-(2-methylbutyl)cinnamate (DOBAMBC). Heat-capacity studies were done on two different samples obtained from two laboratories. Different results were obtained. Almost simultaneous measurements of the tilt angle (theta) and polarization (P) on one of the samples allow us to reveal one surprising temperature dependence of the ratio P/theta. The anomaly in the ratio P/theta seems to be closely related to the anomaly in the helical pitch just below the SmA-SmC* transition.
We calculate the interaction between two spherical colloidal particles embedded in the isotropic phase of a nematogenic liquid. The surface of the particles induces wetting nematic coronas that mediate an elastic interaction. In the weak wetting regime, we obtain exact results for the interaction energy and the texture, showing that defects and biaxiality arise, although they are not topologically required. We evidence rich behaviors, including the possibility of reversible colloidal aggregation and dispersion. Complex anisotropic self-assembled phases might be formed in dense suspensions.