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Electro-optical properties of carbon nanotubes doped ferroelectric liquid crystal
Abstract
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.
... In addition, it is observed that the fine-tuning of the tailor-made properties is possible if the FLC mixtures are doped with appropriate nanomaterial. In this context, due to their unique properties, both types of CNTs are found to be the most studied functional dopant to modify the physical properties of FLC/AFLC compounds or mixtures [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31]. ...
... From the analysis of the reported results it is observed that the effects of the doping of SWCNTs/MWCNTs in a pure FLC compound [21,23,[29][30][31] or commercial FLC mixtures with unknown compositions [10][11][12][13]15,17, have mainly been studied by different groups, if we leave aside the studies in achiral systems, especially the nematics. Various display related parameters like FLC/AFLC phase range [17,21], permittivity [11,12,[14][15][16][17][18][19][20][21]23,24], conductivity [12][13][14]21,23,24], spontaneous polarization [11-13,16-19,21,2 3,24], rotational viscosity [11][12][13][15][16][17][18]20,21,24], driving voltage [22], photoluminescence intensity [19] and switching time [11-1 3,15,16,18-21,24] were reported to increase in some systems while decreasing in some other composites [11-13,15,16,18-21,2 4]. ...
... The p electrons also trap the ionic impurities that further decrease the net polarization of the doped mixtures. Similar decrease in spontaneous polarization in FLC-CNT composites had been reported in literature [18,24,27,30,31]. The presence of impurity ions generates a depolarization field (E ion ) opposite to the applied external electric field (E app ) thereby reducing the real or local electric field (E loc = E app -E ion ) [18,27,45]. ...
Doping of different concentrations of single and multi-walled carbon nanotubes (CNTs) is found to influence considerably the dielectric and electro-optical properties of a room temperature FLC mixture. However, the comparative change of such properties between the two types of CNT doped systems is marginal. Dispersion of CNTs produces not enough change in the molecular ordering as revealed by the small decrease in the phase transition temperatures and tilt angles. Spontaneous polarization is also found to decrease due to the screening of the molecular dipole moments by the π–π electron system of the CNTs. Both the dielectric increments and absorption strengths are found to decrease remarkably due to the trapping of ions by the CNTs. Trapping also decreases ac and dc conductivities and the local electric field which in turn fastens the switching time considerably making the CNT-doped systems more suitable for FLC-based applications.
... Although, interaction among MWCNTs may become prominent at higher concentration rather than MWCNTs -FLC interaction or orientation which in turn reduce the optical contrast of the sample. Such interaction amid MWCNTs may also hinder the orientation of the FLC molecules [47,48]. The nanocomposite 0.1wt% MWCNTs doped FLC also depicts reddish, violet, blue and green colours with the application of the externally applied field. ...
... Under applied external field, molecules of the pure FLC material start to orient towards the field direction, however, for the MWCNTs doped FLC nanocomposites, the molecular system responds faster while switching from one position to another. Hence, the obtained results clearly revealed that the FLC-MWCNTs nanocomposites respond considerably faster, i.e. switching of molecules within the device is faster [41,47,48]. ...
... The values of the spontaneous polarisation obtained for nanocomposites are found much smaller than that of non-doped (~90 nCcm −2 ) FLC material; the P s values fall down for more than twice. Such strong decrease of the P s values can be attributed to the interaction between the molecular dipole moment of the FLC and induced polarisation of the MWCNTs which leads to the screening of the spontaneous polarisation vector [47,48]. Secondly, the antiparallel correlation among MWCNTs and FLC molecules could also be the reason for the decrease of polarisation values [41,47,48]. ...
The impact of the size of silica nanoparticles (SNPs) on the properties of ferroelectric liquid crystals (KCFLC 10R) has been investigated by electro-optical and dielectric techniques. We have found that the doping of silica nanoparticles in the host ferroelectric liquid crystal strongly affects the various properties of doped systems. Doping of silica nanoparticles shows a small decrease in spontaneous polarisation and faster switching time. An improvement in permittivity and conductivity with the temperature at a constant frequency was also noticed after dispersion. This dependence is stronger for large size particles (∼40 nm) and weaker for small size particles (~12 nm). The Goldstone mode (GM) shifts towards the higher relaxation frequency. These results would be useful to manufacture better optical and electronic devices for display, switching and beam steering applications.
... Although, interaction among MWCNTs may become prominent at higher concentration rather than MWCNTs -FLC interaction or orientation which in turn reduce the optical contrast of the sample. Such interaction amid MWCNTs may also hinder the orientation of the FLC molecules [47,48]. The nanocomposite 0.1wt% MWCNTs doped FLC also depicts reddish, violet, blue and green colours with the application of the externally applied field. ...
... Under applied external field, molecules of the pure FLC material start to orient towards the field direction, however, for the MWCNTs doped FLC nanocomposites, the molecular system responds faster while switching from one position to another. Hence, the obtained results clearly revealed that the FLC-MWCNTs nanocomposites respond considerably faster, i.e. switching of molecules within the device is faster [41,47,48]. ...
... The values of the spontaneous polarisation obtained for nanocomposites are found much smaller than that of non-doped (~90 nCcm −2 ) FLC material; the P s values fall down for more than twice. Such strong decrease of the P s values can be attributed to the interaction between the molecular dipole moment of the FLC and induced polarisation of the MWCNTs which leads to the screening of the spontaneous polarisation vector [47,48]. Secondly, the antiparallel correlation among MWCNTs and FLC molecules could also be the reason for the decrease of polarisation values [41,47,48]. ...
Functional nanocomposites are designed via doping ferroelectric liquid crystal (FLC) matrix by 0.03wt% and 0.1wt% of functionalised multiwall carbon nanotubes (MWCNTs). Mesomorphic, optical, thermo-optic and electro-optic behaviour of resulting nanocomposites have been studied in the ~5μm thick cells. Effect of applied voltage on the mesomorphic and electro-optic behaviour of ferroelectric liquid crystal has been established. Interestingly, FLC material demonstrates electrically switchable birefringence colours viz. yellow, reddish, violet and green colour, under applied electric field at different temperatures. No considerable perturbation of FLC smectic order has been observed with doping of MWCNTs. However, the MWCNT doping strongly modifies the optical contrast, birefringence, transmission and contrast ratio of the FLC material. The most significant results are obtained for nanocomposite with 0.03wt% MWCNTs concentration. Doping by MWCNTs leads to the generation of new colours in the nanocomposite systems and also effectively reduce the driving voltage for the colour appearance. For the designed nanocomposites, a decrease in the spontaneous polarisation and fastening of the switching time has been detected. Such electrically switchable birefringent MWCNTs/FLC nanocomposites can be effectively utilised for practical applications in the field-sequential colour displays, FLC switches, optoelectronic and photonic devices.
... However, the observed effect was found to be more significant with lower concentration of GNPdecorated MWCNTs. Kumar and Sinha [150] also reported a decrease of about 1-1.5 • C in isotropic temperature and other phase of the investigated FLC (W206E) sample due to the dispersion of MWCNTs. The authors pointed out that this decrease in the phase transition temperature was due to the small change in the order parameter of FLC after the dispersion of MWCNTs. ...
... In contrast, the increase in these parameters was attributed to the charge transfer between SWCNTs and FLC molecules via π-π interaction. Kumar and Sinha [150] reported the effect of dispersion of MWCNTs (0.5 and 1.0 wt%) into the dielectric properties of FLC (W206E). The significant decrease in the dielectric permittivity and conductivity of the FLC matrix by MWCNTs was also observed. ...
The realm of liquid crystals (LCs) has significantly benefited when amalgamated with the exciting features of nanotechnology. Various nanomaterials (NMs) have shown their potentiality in tailoring the display and non-display characteristics of LC materials. Carbon-based nanomaterials (CNMs) such as carbon nanotubes, graphene oxide, graphene flakes, graphene and carbon dots are found to exhibit synergistic interaction with LCs to provide interesting properties such as low switching threshold voltage, faster switching response, reduced ionic conductivity and the formation of localized pseudonematic domains, etc. The network of benzene rings in the CNMs is found to offer π – π stacking of electrons with a benzene-based core of LC molecules which could provide a susceptible pathway for the strong interaction between the LCs and the CNMs. However, the uniform and stable dispersion of CNMs in the LC matrix has been found to be a challenging step in preparation of CNM/LC composites. Herein, we present a detailed review on the recent research work based on CNM-dispersed LC composites with an emphasis on the methods to obtain uniform CNM/LC dispersion and the dielectric, electro-optical, orientation, photophysical properties, etc, of the composites. Moreover, we have critically discussed the pros and cons of these composites and proposed the future scope of research in this exciting field.
... The microstructure, dielectric, and electro-optical properties of MWCNT-ferroelectric (W206E) LC mixtures have been studied [207]. The optical micrographs revealed some topological defects. ...
The current state of the study of different liquid crystalline (LC) systems doped with carbon nanotubes (CNTs) is discussed. An attempt is endeavored to outline the state-of-the-art technology that has emerged after two past decades. Systematization and analysis are presented for the integration of single- and multi-walled carbon nanotubes in thermotropic (nematic, smectic, cholesteric, ferroelectric, etc.) and lyotropic LCs. Special attention is paid to the effects of alignment and supramolecular organization resulting from orientational coupling between CNTs and the LC matrix. The effects of the specific inter-molecular and inter-particle interactions and intriguing microstructural, electromagnetic, percolation, optical, and electro-optical properties are also discussed.
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.
We have studied the formation of topological defects in liquid crystal (LC) matrices induced by multiwalled carbon nanotubes (MWCNTs) and external electric fields. The defects are ascribable to a distortion of the LC molecular director in proximity of the MWCNT surface. The system is analyzed macroscopically using spectroscopic variable angle ellipsometry. Concurrently, confocal micro-Raman spectroscopy is used to study the system state at the microscale. This allows to acquire a three-dimensional, spatially-resolved map of the topological defect, determining scale length variations and orientation topography of the LC molecules around the MWCNT.
We present the results based on dielectric, electro-optical and photoluminescence (PL) measurements of a ferroelectric liquid crystal (FLC) doped with differently functionalised (–COOH, –OH and –NH2 groups) multi-walled carbon nanotubes (MWCNTs). Functional group induced significant modifications in the dielectric permittivity (ε′), dielectric loss factor (tan δ), PL intensity and material parameters of MWCNT/FLC composites have been observed. We found that MWCNTs functionalised with –OH and –NH2 have enhanced the dielectric properties and the PL intensity of FLC material remarkably. The observed results have been explained on the basis of the interaction between FLC material and functionalised MWCNTs. The present study is our sincere attempt to understand the effect of functionalisation of MWCNTs on the FLC properties.
A small quantity of carbon nanotubes (CNT) was doped in a nematic liquid crystal (LC), and the LC+CNT hybrid was found to exhibit a faster field-induced nematic switching compared to that of the pure LC. The field-induced switching time was probed by means of the electro-optic response of the samples. The hybrid system also revealed a reduced rotational viscosity and an enhanced dielectric anisotropy. The results suggest that the hybrid system undergoes a faster field-induced switching, as the CNTs favorably alter the rotational viscosity and the dielectric anisotropy of the nematic matrix.
We demonstrate here the tailoring of electro-optical properties of ferroelectric liquid crystals
(FLCs) by doping different concentrations of Selenium Docosane (SD) capped palladium
nanoparticles (PdNPs). The operating voltage is lowered by �50% in doped FLC as compared to
undoped one. The remarkable increment in optical tilt angle of doped FLC is monitored, which is
concentration-dependent. The steric interactions among alkyl chains of SD capped PdNPs and
FLC molecules could be the probable reason for enhanced optical tilt angle. More importantly,
present investigations on doped FLCs are indicative of their indispensible impact on
next generation FLCs-based electro-optical devices.
The capacitance–voltage (C–V) characteristics of surface-stabilized ferroelectric liquid crystal (SSFLC) cells doped with zinc oxide nanocrystals (nc-ZnO) have been studied and fitted to the Preisach model to reveal the behaviours of dipolar species. To explain the experimental results, we propose a physical picture depicting an interaction of nc-ZnO dipole with surrounding SSFLC dipolar species. Our study shows that doping nc-ZnO into FLC not only increases the contrast ratio of the cells by 10 times but also enhances the dynamic polarization of the beneficial dipolar species while minimizing the polarization response of the species with counter effects.
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.
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.
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.
We present faster display devices based on copper oxide decorated multi-walled carbon nanotubes (MWCNTs) doped ferroelectric liquid crystal (FLC) material. The fastening of the response has been attributed to decrease in rotational viscosity of the FLC material. The ionic impurities were also reduced by doping copper oxide decorated MWCNTs into the FLC material, and the reduction has been attributed to trapping of ions by the guest copper oxide decorated MWCNTs. The observations of fastening the response and reduction of ionic impurities have been verified by experimental data using dielectric and electro-optical studies. The underlying mechanism would certainly help to understand the basic mechanism of interaction of CNTs with FLC molecules and could be applied to fabricate ionic defects free faster display devices.
We have determined the ion trapping coefficients of carbon nanomaterials in liquid crystals through the analysis of capacitance–voltage response. The ion trapping coefficient is defined as the ability to trap impurity ions for each carbon nanomaterial and can be used as a referable value to select proper carbon nanomaterials as dopants in liquid crystals. The characterized nanomaterials include multi-wall carbon nanotubes, carbon nanofibers, carbon nanocoils, single-wall carbon nanotubes and fullerenes, respectively. It is found that the multi-wall carbon nanotubes with a tube length of 5–15μm have the largest ion trapping coefficient and hence serve as the best dopant to suppress the liquid crystal hysteresis.
The preparation of a new type of finite carbon structure consisting of
needlelike tubes is reported. Produced using an arc-discharge
evaporation method similar to that used for fullerene sythesis, the
needles grow at the negative end of the electrode used for the arc
discharge. Electron microscopy reveals that each needle comprises
coaxial tubes of graphitic sheets ranging in number from two up to about
50. On each tube the carbon-atom hexagons are arranged in a helical
fashion about the needle axis. The helical pitch varies from needle to
needle and from tube to tube within a single needle. It appears that
this helical structure may aid the growth process. The formation of
these needles, ranging from a few to a few tens of nanometers in
diameter, suggests that engineering of carbon structures should be
possible on scales considerably greater than those relevant to the
fullerenes.