Dispersion Of Cholesteric Liquid Crystals Research Articles

Flexible free-standing films morphology characterization: PVA/silica polymer network dispersed cholesteric liquid crystals films by sol-gel method

ABSTRACTA novel flexible free-standing films of polyvinyl alcohol (PVA)/silica polymer network dispersed cholesteric liquid crystals (CLC) have been prepared by the sol-gel process. In the hydrolysis of silicon alkoxides tetraethoxysilane (TEOS) processes, the silica having -OH with the -OH groups on PVA formed polymer networks with Si-O-C bonds by dehydration. The cholesteric liquid crystals were incorporated into the networks. The free-standing films were obtained by the spin-coating method. In order to improve the compatibility and microstructure of the cholesteric liquid crystals with PVA/silica polymer networks, the amphiphilic compound of hexadecyl trimethyl ammonium bromide (HDTMA) was introduced into the forming film solutions. Effects of the different ratios of raw materials on the structure of films were investigated. The microscopic morphology of free-standing films and the uniform dispersion of CLCs in the films have been characterized by polarizing optical microscopy (POM), the field emission scanning electron microscope (FESEM), Fourier transform infrared (FT-IR) spectrometer and atomic force microscope (AFM). The free-standing films exhibiting excellent CLC droplets dispersion, mechanical stability, and good flexibility could be useful for flexible displays, switchable optical elements and smart windows.

Preparation of temperature-response fibers with cholesteric liquid crystal dispersion

Cholesteric liquid crystal (CLC) dispersion was prepared using the mixed emulsifiers composed of Tween 20 and Span 80. The effects of preparation parameters on mean particle size and particle size distribution of CLC dispersion were investigated, demonstrating that the CLC mixture was better dispersed and stabilized above the phase transition temperature, and keeping the HLB at 11.7, emulsifier amount at 1.0%, dispersing speed at 5000 rpm for 60 min, the CLC particle in the dispersion were spherical and had a reversible thermochromic property. This dispersion was then used in the preparation of temperature-response PVP/CLC fibers in a water-based system by electrospinning. Polarized optical microscopy and scanning electron microscopy image reveal that CLC particles were incorporated into the PVP/CLC fibers, protecting the CLC from leaking out. The PVP/CLC fibers exhibited an optical temperature response in the temperature range from 25 to 60 °C.

Erratum to: “On the possibility of determining anthracycline antibiotics in aqueous solutions using optical analytical system (biosensor)”

We propose a version of the theory describing the circular dichroism spectra of cholesteric liquidcrystal dispersion particles of double-stranded DNA. The basis of the theory is the concept of absorption of electromagnetic waves by large molecular systems. The effect of physical parameters of dispersion particles on their circular dichroism is theoretically determined. It is experimentally demonstrated that circular dichroism can be used as a convenient tool for creating an optical analytical system for the determination of biologically active compounds that interact with DNA molecules.

A new nanobiomaterial: particles of liquid-crystalline DNA dispersions with embedded clusters of gold nanoparticles

The effect of gold (Au) nanoparticles with an average size of about 2 nm on double-stranded DNA cholesteric liquid-crystal dispersion (CLCD) particles has been studied. Treatment of DNA CLCD by Au nanoparticles results in two effects: a “disturbance” of the spatial structure of dispersion particles and the induction of the cholesteric → nematic phase transition, as well as the formation of 40.5–53.0 nm linear clusters of Au nanoparticles between neighboring DNA molecules. The efficiency of formation of these clusters and their size depend on the solution properties. Clusters of Au nanoparticles can crosslink neighboring DNA molecules, thus forming “rigid” DNA CLCD particles. The average size of rigid DNA CLCD particles is 450–500 nm, and their height does not exceed 300 nm. Thus, the effect of Au nanoparticles on DNA CLCD leads to the formation of nanobiomaterial in which clusters of Au nanoparticles are formed between DNA molecules fixed in the spatial structure of dispersion particles. This nanobiomaterial has new physicochemical properties (such as a lack of abnormal optical activity and the presence of linear clusters of Au nanoparticles in the structure of DNA CLCD particles, via which the interaction between neighboring DNA molecules is implemented); as a result, it differs from standard nanobiomaterials based on double-stranded DNA molecules.

А Targeted Drug Delivery System of Gd3+ for Neutron Capture Therapy against Cancer is Metalorganic Magnetic Nanoparticles

A method for producing nanoparticles based Cholesteric Liquid Crystal Dispersion (CLCD) of complexed [DNA-Gd] with a high content of gadolinium ions (up to 400 mg/ml). Preparation can be stored in the laboratory for 200 days without changes in the physico-chemical properties. It is shown that the formation of nanoparticles of gadolinium ions bind to DNA molecules by interaction with both phosphate groups, and with the nitrogen bases, breaking the regular the secondary structure of DNA. It was found that the formation of nanoparticles significantly reduced solubility of double-stranded DNA and appears uncompensated positive charge on the surface of the complex, impeding its aggregation. The technique of nanoparticles based on a set CLCD [DNA-Gd], including the processing of the original particles CLCD double-stranded DNA with aqueous GdCl3. The magnetic properties of the nanoparticles, allowing maintain an active neutron diffusion exciting nuclide gadolinium directly on the hearth of a malignant tumor. Immobilization of nanoparticles performed by adsorption on macrophages defines active targeted delivery of gadolinium ions in lesions. The application of the local concentration of nanoparticles gadolinium is ~400 mg/ml, as a carrier for the neutron-exciting therapy of malignant neoplasms.

A neutron activation study of DNA-Gd nanocrystals

The properties of the cholesteric liquid-crystal dispersion containing deoxyribonucleic acid (DNA) molecules and gadolinium ions are investigated using the neutron activation analysis. The cholesteric structure of the DNA-Gd complex is formed by double-stranded DNA molecules and Gd3+ cations in nanoparticles. The DNA concentration in nanoparticles reaches 350 mg/ml. The gadolinium concentration in the DNA-Gd complex is determined using the neutron activation analysis. It is found that the DNA-Gd complex contains approximately 1.5 gadolinium atoms per phosphate group of the DNA molecule. The local gadolinium concentration in the nanoparticle reaches 250 mg/ml.

6.1: Roll-to-Roll Manufacturing Considerations for Flexible, Cholesteric Liquid Crystal (ChLC) Display Media

Roll-to-roll methods and equipment to manufacture a bistable flexible electronic display have been developed. Displays produced with these processes are low-cost, thin, flexible, passively driven, and retain an image without an applied electric field. Using continuous coating techniques and equipment, an aqueous cholesteric liquid-crystal dispersion and a dark layer are deposited onto laser-etched patterned transparent conductors on a polymeric web. Second conductors are printed with a UV-curable polymer thick film ink over the active display layers, followed by slitting and chopping to complete the manufacture of display media in a full roll-to-roll process. Simple seven-segment and matrix displays can be generated using these techniques. This paper will focus on the manufacturing considerations for producing matrix display media.

16.3: Development of a Flexible Electronic Display Using Photographic Technology

AbstractA bistable flexible electronic display has been developed based on photographic technology, processes, and materials. Using photographic film coating techniques, an aqueous cholesteric liquid crystal dispersion, a dielectric layer, and a dark layer were deposited onto patterned transparent conductors on a polymeric web. Second conductors were printed over the active display layers to complete display manufacture in a roll‐to‐roll process. Simple seven‐segment displays and matrix displays have been generated using these techniques. The displays can use contact electronics to eliminate drive cost from the displays. Several prototype applications were demonstrated. Displays produced with these processes were low‐cost, thin, flexible, passively driven, and retained an image without an applied electric field.

Dispersion of Cholesteric Liquid Crystals in Side-Chain Polymer Matrix

Cholesteric formulations (coco-cholesteryl esters:E7) were dispersed in commercial polymethylmethacrylate (PMMA) and in laboratory synthesized side-chain polymers (SCP). The side-chain copolymers were obtained via the ring opening reaction of a commercially available epon resin, ethyleneglycol diglycidyl ether, with the nematic 4-(ω -aminohexyloxy)-4′ -cyanobiphenyl and the twisted nematic cholesteryl 4-aminobutyrate. Switching properties of the resulting dispersions were evaluated. Cells using PMMA as matrix exhibited distinguishable droplet with bipolar and twisted radial configuration. A maximum voltage of 60 volts was needed to transform a 70:30 by weight (LC:PMMA) composite into a transparent state. LC formulations dispersed in the SCP bearing cholesteryl and cyanobiphenyl pendant groups were found to exhibit fingerprint texture. Compared to the LC/PMMA composite, the LC/SCP dispersions required lower voltage for switching.

Some Optical Properties of dispersed Cholesteric Liquid Crystals

Abstract High iridescence has been achieved by the dispersion of cholesteric liquid crystals in polyurethane elastomers. A model based on Frank's disclination theory is proposed whereby the aggregate size and pitch determine a textural change from a spherulitic texture to an “aligned” plane texture as the size of the dispersed aggregate decreases. This is accomplished by the different free energy relationships of radial and surface defects in the dispersed state. Discussion of the model and experimental observations center on the morphological, chemical and physical parameters which determine high iridescence of dispersed cholesteric liquid crystals and hence the effect of these parameters on the topological role of defects in attaining high iridescence.

Measurement of the Infrared Rotatory Dispersion of Cholesteric Liquid Crystals

A polarimeter for the infrared region is described, which is used to measure the optical rotation due to the helical arrangement of molecules in cholesteric mesophases. The rotatory dispersion of mixtures of cholesteric liquid crystals and of liquid crystals in which the cholesteric structure is induced by a small amount of a chiral solute is discussed.

Rotatory Dispersion of Cholesteric Liquid Crystals

Abstract Measurements of rotatory dispersion and circular dichroism of (i) a mixture of nematic p-methoxybenzylidene-p'-butylaniline (MBBA) and spectratherm (ii) a mixture of cholesteryl benzoate and nematic p-azoxyphenetole (PAP) and (iii) cholesteryl cinnamate for different thicknesses have been made. The experimental data on cholesteryl cinnamate are in qualitative agreement with the theoretical predictions of Dreher et al., (1) Chandrasekhar and Shashidhara Prasad(2) and Aihara and Inaba.(3) Also the results of the mixtures are in qualitative agreement with the theoretical predictions, that for thick specimens the circular dichroism plotted as a function of wavelength should exhibit a flat top maximum. An attempt has been made to fit the rotatory dispersion and circular dichroism data of cholesteryl cinnamate. It is found that the same constants can be used to explain our data as well as that due to Mathieu,(4) approximately well.

Theory of Rotatory Dispersion of Cholesteric Liquid Crystals

A theory is developed of the circular dichroism and rotatory power of thin films of cholesteric liquid crystals. It is an extension of the treatment for infinitely thick specimens discussed in a previous paper. The therory predicts that the circular dichroism of a thin film plotted as a function of wave-length should exhibit a principal maximum accompanied by subsidiary maxima, and that the rotatory dispersin should be anomalous. Experimental circular dichroism and rotatory dispersion curves are presented for cholesteric cinnamate, cholesteryl-2-propyn-1-yl carbonate and spectratherm. The results are in qualitative agreement with the theory both inside and outside the region of reflexion. The rotatory dispersion curves are also in accord with the de Vries equation outside the region of reflexion.