Liquid Crystal Nanocomposites Research Articles

Recent advances of core–shell nanocrystals dispersed liquid crystal nanocomposites for their applications in electronic devices: A mini review

Recent advances of core–shell nanocrystals dispersed liquid crystal nanocomposites for their applications in electronic devices: A mini review

Tunable dielectric features of newly synthesized vanadium-doped titanium oxide nanoparticles doped liquid crystal nanocomposites

Tunable dielectric features of newly synthesized vanadium-doped titanium oxide nanoparticles doped liquid crystal nanocomposites

New graphene oxide doped polymer dispersed liquid crystal nanocomposites targeted to eco-friendly and energy-efficient smart windows

Graphene oxide-polymer dispersed liquid crystal (GO-PDLC) composites are proposed as a solution for energy-efficient switchable windows. These composites were prepared by incorporating varying concentrations of graphene oxide (GO) into a mixture of nematic liquid crystal (E7) and a UV–Vis curable resin using the polymerization-induced phase separation technique. The results indicate that the dispersion of GO at an optimum concentration of 0.005 wt% significantly affects the morphology, phase transition temperatures, and electro-optic properties of polymer dispersed liquid crystal (PDLC). In particular, the GO-PDLC composites exhibit a transition from an opaque to a transparent state at a remarkably low voltage (∼11.5 V) compared to pure PDLC cell. Dielectric analysis reveals that adding GO increases the permittivity, conductivity, and dielectric strength of PDLC composites. Moreover, the Cole-Cole plot indicates a non-Debye type relaxation in a higher frequency region. Furthermore, a blue shift in emission wavelength and enhanced photoluminescence intensity suggest alterations in electronic transitions within the composites. This comprehensive study provides valuable insights into optimizing the properties of PDLCs through the dispersion of GO, thereby offering promising prospects for their utilization in various optoelectronic applications.

Influence of polymerisation parameters on the electro-optical properties of polymer-stabilised liquid crystals for smart glass application

ABSTRACT Smart windows are an important application of liquid crystal/polymer nanocomposites. Recently, an original design has been proposed for a window that switches from a scattering to a transparent state under an electric field. By polymerisation, the topological defects of the smectic A phase under hybrid anchoring conditions are stabilised in the nematic phase, making them addressable by the field. Here, we report the impact of the polymerisation parameters on the electro-optical properties and microstructure of the nanocomposites. We have first estimated the polymerisation kinetics and then investigated the influence of the UV-light intensity, monomer concentration, and photoinitiator concentration. UV-light intensity has little effect on the electro-optical properties of the device, although microstructural changes were observed. The monomer concentration has a strong impact on the scattering power in both the on- and off-states. A model is proposed to describe the dependence of the response times on the monomer concentration. Finally, no influence of the photoinitiator concentration on the electro-optical properties was observed. Polymerisation could occur even in the absence of photoinitiator, possibly due to the presence of impurities that could generate radicals under irradiation. Our study should help optimising the formulation of polymer-stabilised liquid crystal nanocomposites for industrial applications.

Two‐Chromatic Printing Creates Skin‐Inspired Geminate Patterns Featuring Crosstalk‐Free Chemical and Physical Colors

AbstractSkin‐inspired optical materials that combine both chemical and physical colors provide enhanced information capacity for potential applications in optical multiplexing and anti‐counterfeiting technologies. However, the existing materials suffer from the limitations of an extremely narrow gamut and incompatibility with universal patterning methods to program dual‐mode images. Here, novel two‐chromatic printing technology is proposed to create full‐color, high‐resolution, and geminate patterns by newly designed fluorescent liquid crystal nanocomposites. Such nanocomposites consist of porous cholesteric liquid crystal networks embedded with core–shell CdSe/ZnS quantum dots to produce extended wide color palettes of both photoluminescence and Bragg reflection. The drop‐on‐demand two‐chromatic printing technology simultaneously enables the construction and patterning of the nanocomposites in a high‐precision way, orthogonally tuning the hues of two color palettes according to Grassmann's and Bragg's law. Therefore, the combination of different color generation mechanisms offers a versatile toolbox, which can be generalized to pigmentary, photonic, and even dynamic optical materials.

Novel nanocomposites based on Tetrazine liquid crystals for energy storage application

Polymethyl methacrylate (PMMA) /Tetrazine liquid crystal (LCTZ12) nanocomposites with different CNTs loadings have been prepared. The prepared nanocomposites were characterized using polarizing light microscope (POM), differential scanning calorimetry (DSC), Fourier transform Infrared Spectroscopy (FTIR) and broadband dielectric spectroscopy (BDS) in the range 10-1-106 Hz respectively. The most commonly observed texture of soft crystal phases was that of a mosaic pattern, as revealed by the POM technique. PMMA alone does not change the polarization states and appeared as isotropic material, but once LCTZ12 is added, crystal growth could be clearly noticed in the needle pattern inside the polymer matrix to compose an amazing structure of soft crystal G texture. The increase of LCTZ12 to about 20 wt% in the PMMA matrix led to more heterogeneous aggregation of liquid crystalline molecules. This ratio addition is enhancing of network connections inside the PMMA. Moreover, the dispersion of carbon nanotubes mounted on catalysts is found to accumulate in segregations in PMMA/ LCTZ12 nanocomposites. However, the location of CNTs is concentrated at bottom of polymer network due to the large difference in densities of LCs, PMMA, and CNTs. DSC is in agreement with the POM result of LCTZ12, which has multi soft crystals or highly self-assembled ordered liquid crystal phases near to room temperature. The FTIR proved that blend PMMA/ LCTZ12 (80/20) has a dramatic increase in the 1387 cm−1 peak of C = C as a response of the rise in the concentration or number of aromatic rings. Additionally, the vibrational scissoring peak located at 1477 cm−1 of methylene CH2 groups is increased significantly and C–H stretching in aliphatic regions at 2850 cm−1 and 2990 cm−1 as well. However, there is no significant change observed after CNTs addition to the PMMA/ 20 wt% LCTZ12 matrix. Regarding dielectric results, it was found that, the polymer dispersed liquid crystals PDLC system composed of (PMMA/20 wt% LCTZ12) possesses the most promising dielectric properties, that is; high dielectric permittivity with low losses compared to the other ratios. The addition of CNTs results in more localization of charge carriers along with mobile ions, causing higher ionic conductivity. The conductivity ranges altered from 3.2 × 10-10 S/cm in pure PDLC system to become 1.7 × 10-3 S/cm for PDLC doped with 10 wt% CNTs nanocomposite. The electrical energy density measurements for 3,6-bis(5-(Dodecyloxy) pyridin-2-yl)-1,2,4,5-tetrazine (LCTZ12) liquid crystals with 6 cationic centers in polymeric matrices proved to be suitable for flexible and efficient electrolytes for energy storage devices.

Enhancement of dielectric and electro-optical characteristics of liquid crystalline material 4'-octyl-4-cyano-biphenyl with dispersed functionalized and nonfunctionalized multiwalled carbon nanotubes.

For recent applications, liquid crystal-carbon nanotube based nanocomposite systems have been proven to be highly attractive. In this paper, we give a thorough analysis of a nanocomposite system made of both functionalized and nonfunctionalized multiwalled carbon nanotubes that are disseminated in a 4'-octyl-4-cyano-biphenyl liquid crystal medium. Thermodynamic study reveals a decrease in the nanocomposites' transition temperatures. In contrast to nonfunctionalized multiwalled carbon nanotube dispersed systems, the enthalpy of functionalized multiwalled carbon nanotube dispersed systems has increased. In comparison to the pure sample, the dispersed nanocomposites have a smaller optical band gap. A rise in the longitudinal component of permittivity and, consequently, the dielectric anisotropy of the dispersed nanocomposites has been observed by dielectric studies. When compared to the pure sample, the conductivity of both dispersed nanocomposite materials has increased by two orders of magnitude. For the system with dispersed functionalized multiwalled carbon nanotubes, the threshold voltage, splay elastic constant, and rotational viscosity all decreased. For the dispersed nanocomposite of nonfunctionalized multiwalled carbon nanotubes, the value of the threshold voltage is somewhat decreased but the rotational viscosity and splay elastic constant both are enhanced. These findings show the applicability of the liquid crystal nanocomposites for display and electro-optical systems with appropriate tuning of the parameters.

Effect of ZnO nanoparticles on liquid crystalline system

Investigations on liquid crystal nanocomposites have been attracting significant attention for decades. Here we describe the results of our recent experimental investigations on different phase transitions when the liquid crystal is dispersed with ZnO NP. Examples discussed involve the least order phase and orthogonal to tilted layered phase transitions.

Magnified charge carrier conduction, permittivity, and mesomorphic properties of columnar structure of a room temperature discotic liquid crystalline material due to the dispersion of low concentration ferroelectric nanoparticles.

Liquid crystal nanocomposites have been a hot topic of research due to optimization of physical properties with such blending. There are several reports on enhancement of physical properties of nematic liquid crystals due to the blending of the nanomaterials. L. M. Lopatina and J. V. Selinger [Phys. Rev. Lett. 102, 197802 (2009)]10.1103/PhysRevLett.102.197802 have even proposed a theory based on experimental results for the enhancement of the properties of the nematic mesophase in the presence of ferroelectric nanoparticles. However, discotic liquid crystal nanocomposites are less studied. In the present experimental work, we have studied the effect of ferroelectric (BaTiO_{3}) nanoparticles on a room temperature discotic liquid crystalline material, namely 1,5-dihydroxy-2,3,6,7-tetrakis(3,7-dimethyloctyloxy)-9,10-anthraquinone. We investigated the physical properties of low concentration ferroelectric nanoparticle dispersed discotic columnar structure, using calorimetric, optical, x-ray diffraction, and dielectric spectroscopy tools. Results show that inclusion of ferroelectric nanoparticles in the discotic matrix consolidates the stability of the columnar matrix of the Col_{h} phase by virtue of their ferroic nature. An enhancement in charge carrier conductivity by several orders of magnitude at ambient conditions has been observed which makes such systems highly appropriate for one-dimensional conductors. Low concentration of BaTiO_{3} nanoparticles substantially enhanced permittivity of the system also. A molecular relaxation mode has been observed in the middle frequency range of the dielectric spectra. Enhancement of these important parameters could be possible due to the ferroelectric nature of the dispersed nanoparticles.

Near-infrared light-responsive intelligent liquid crystal nanocomposites

Near-infrared light-responsive intelligent liquid crystal nanocomposites

Scalable Synthesis of Switchable Assemblies of Gold Nanorod Lyotropic Liquid Crystal Nanocomposites.

A new class of solvent free, lyotropic liquid crystal nanocomposites based on gold nanorods (AuNRs) with high nanorod content is reported. Application of shear results in switchable, highly ordered alignment of the nanorods over several centimeters with excellent storage stability for months. For the synthesis, AuNRs are surface functionalized with a charged, covalently tethered corona, which induces fluid-like properties. This honey-like material can be deposited on a substrate and a high orientational order parameter of 0.72 is achieved using a simple shearing protocol. Switching shearing direction results in realignment of the AuNRs. For a film containing 75 wt% of AuNRs the alignment persists for several months. In addition to the lyotropic liquid crystal characteristics, the AuNRs films also exhibit anisotropic electrical conductivity with an order of magnitude difference between the conductivities in direction parallel and perpendicular to the alignment of the AuNRs.

Analysis of the Temperature Dependence of the Exciton Luminescence Spectra of Cadmium Selenide Quantum Dots Grown in a Liquid Crystal Matrix

The temperature dependences of the positions of maxima of exciton bands in the luminescence spectra of liquid crystal nanocomposites with CdSe quantum dots with sizes of 1.8 and 2.3 nm at T = 77–300 K have been analyzed. The analysis under the theoretical model taking into account the electron–phonon interaction inside quantum dots has made it possible to calculate the values of the Huang–Rhys factor and average phonon energy in nanocrystals under study.

Анализ температурной зависимости спектров экситонной люминесценции квантовых точек селенида кадмия, выращенных в жидкокристаллической матрице-=SUP=-*-=/SUP=-

AbstractThe temperature dependences of the positions of maxima of exciton bands in the luminescence spectra of liquid crystal nanocomposites with CdSe quantum dots with sizes of 1.8 and 2.3 nm at T = 77–300 K have been analyzed. The analysis under the theoretical model taking into account the electron–phonon interaction inside quantum dots has made it possible to calculate the values of the Huang–Rhys factor and average phonon energy in nanocrystals under study.

Multi-walled carbon nanotubes-ferroelectric liquid crystal nanocomposites: effect of cell thickness and dopant concentration on electro-optic and dielectric behaviour

ABSTRACTNanocomposites comprise functionalised multi-walled carbon nanotubes (0.00 wt%, 0.05 wt% and 0.07 wt%) and ferroelectric liquid crystals (FLCs) have been studied in the 5-μm- and 12-μm-thickness cells. Effect of anchoring energy and dopant concentration on the mesomorphic, electro-optic and dielectric behaviour of FLC has been explored. Fast switching time and increase in permittivity of non-doped FLCs and resulting nanocomposites as a function of increased cell thickness (from 5 to 12 μm) can be attributed to the change in the anchoring energy and direct current (DC) conductivity of the non-doped and doped systems. π–π stacking between carbon nanotubes and FLC layers give rise to the spontaneous polarisation of nanocomposites. Effect of cell thickness and anchoring energy on bistability are also discussed.

Recent Advances in Discotic Liquid Crystal-Assisted Nanoparticles.

This article primarily summarizes recent advancement in the field of discotic liquid crystal (DLC) nanocomposites. Discotic liquid crystals are nanostructured materials, usually 2 to 6 nm size and have been recognized as organic semiconducting materials. Recently, it has been observed that the dispersion of small concentration of various functionalized zero-, one- and two-dimensional nanomaterials in the supramolecular order of mesophases of DLCs imparts negligible impact on liquid crystalline properties but enhances their thermal, supramolecular and electronic properties. Synthesis, characterization and dispersion of various nanoparticles in different discotics are presented.

INERA Workshop 2016: Membrane and Liquid Crystal Nanostructures (MELINA 2016)

We are pleased to introduce the Proceedings of the INERA Workshop “Membrane and Liquid Crystal Nanostructures” (MELINA 2016). This meeting was held from 3th to 6th of September 2016 in Varna (Bulgaria) and was organized by the Institute of Solid State Physics, Bulgarian Academy of Sciences (ISSP-BAS) in the frames of the Project INERA “Research and Innovation Capacity Strengthening of ISSP-BAS in Multifunctional Nanostructures” REGPOT-2012-2013-1 NMP (http://www.inera.org). The workshop venue was the “Saints Constantine and Helena” Resort - a beautiful complex on the Bulgarian Black Sea coast within a landscaped park 10 km north of downtown Varna, close to the Euxinograd royal summer palace, park and winery.The aim of this workshop was to bring together researchers with interests in interdisciplinary areas in order to report the recent results of their scientific work, to discuss the state-of-the-art & perspectives and communicate new ideas. Several experimental & theoretical streams in the field of nanostructured liquid crystal systems and nanocomposites; soft and living matter physics; membrane biophysics; nanostructures in polymer and lipid membranes; characterization of soft nanomaterials were merged and directed towards a constructive discussion & solutions of a wide variety of actual problems in these important scientific areas. Participants from 9 countries presented 20 oral and 15 poster presentations in 5 topical areas.INERA Workshop MELINA 2016 provided very good opportunities for direct contacts, interesting discussions and interactive exchange of ideas between the participants. It also became a meeting point where INERA partners could plan and organize their future efficient collaborations and joint research projects of common interest.The editors would like to thank all authors for their high-quality contributions. The papers submitted for publication in the Proceedings were refereed according to the publishing standards of the Journal of Physics: Conference Series. The proceedings of conferences and workshops organized in the frames of INERA Project are regularly published by the Journal of Physics: Conference Series. The Editorial Committee members are very grateful to the journal’s staff for providing us this opportunity, as well as for the continuous support for the publication of these Proceedings.Managing Editor: Assoc. Prof. Dr. Julia GenovaCo-editors:Prof. DSc. Diana NeshevaProf. DSc. Isak BivasAssoc. Prof. Dr. Yordan MarinovAssoc. Prof. Dr. Victoria VitkovaAssoc. Prof. Dr. Georgi Hadjichristov

Helical pitch dependence of the electro-optic characteristics in polymer/cholesteric liquid crystal nanocomposites

The helical pitch (p) dependence of the electro-optic characteristics in low monomer concentration polymer/cholesteric liquid crystal (PChLC) nanocomposites is reported. Four mixtures with different helical pitches were prepared by mixing a ChLC and a mesogenic monomer with a photoinitiator, and polymerized at room (20 °C) or low (−20 °C) temperatures to fabricate samples exhibiting the 'polymer-stabilized' and 'deformation-free' responses, respectively. Reflecting the difference in the electro-optic response modes, the threshold electric field showed different dependencies on the helical pitch. The 'polymer-stabilized' PChLCs showed a p-0.57 dependence on the pitch, which is a consequence of the response being dominated by the Helfrich deformation. The 'deformation-free' samples, on the other hand, showed a smaller dependence on pitch of approximately p-0.33. The decrease in the pitch dependence is described as a consequence of the nano-confined LC molecules undergoing a Fredericks-type reorientation instead of a helix deformation.

Deformation-free switching of polymer-stabilized cholesteric liquid crystals by low-temperature polymerization

We investigate the fabrication of 'deformation-free' polymer/cholesteric liquid crystal (PChLC) nanocomposites by controlling the degree of phase separation in a precursor mixture containing mesogenic monomer and low molecular-weight LC molecules. Scanning electron microscopy investigations reveal that even in mixtures containing only 6.6 wt% of monomer, nano-sized LC domains can be formed by low-temperature polymerization of −20 °C that lead to the 'deformation-free' response. PChLC nanocomposites with reduced monomer concentrations exhibit improved tuning range of the refractive index and a short decay time of about 20 μs, making them more practical for real-life applications.

Pitch-Length Independent Threshold Voltage of Polymer/Cholesteric Liquid Crystal Nano-Composites

Polymer/cholesteric liquid crystal (ChLC) nano-composites consisting of mesogenic monomers and LCs have nano-sized LC domains dispersed in an anisotropic polymer matrix. They exhibit characteristics not observed in conventional ChLCs, such as sub-millisecond and “deformation-free” electro-optic tuning of the selective reflection band; however, their driving voltage is high compared to conventional ChLCs, and is an issue that needs to be solved for the practical use. Here, we investigate the helical pitch dependence of threshold voltage in polymer/ChLC nano-composites. Five samples with different helical pitches were prepared and their electro-optic characteristics were compared before and after photopolymerization. Although the threshold voltage of the unpolymerized samples were inversely proportional to its helical pitch, the threshold voltage of the polymerized samples showed no dependence on the helical pitch. These results are explained to be a consequence of the driving mechanism of the polymer/ChLC nano-composite, in which electro-optic switching is achieved as a consequence of the nano-confined LC molecules reorienting along the electric field, instead of the helical structure becoming unwound. The threshold voltage is independent of pitch length because the pore sizes are similar in all samples.

Dielectric relaxation and electro-optic response in nano-ceria dispersed ferroelectric liquid crystal nanocomposites: effect of structural deformation and lattice straining

The current investigations deal with the effect of concentration of CeO2 nanoparticles (NPs) on physical properties of ferroelectric liquid crystal.