Microstructure and dynamics in lyotropic liquid crystals. Principles and applications of nuclear spin relaxation

Abstract

Nuclear spin relaxation of quadrupolar nuclei provides access to a wide range of properties of lyotropic liquid crystals, ranging from the molecular ordering and dynamics at the interface to the macroscopic viscoelastic behaviour. We emphasize here the unique capability of the spin relaxation method to provide detailed geometric and dynamic information relating to the microstructure of lyotropic liquid crystals, i.e. the metric, curvature, and fluctuations of the dividing interface that separates polar and non-polar regions. This information is conveyed to the spin system via the translational diffusion of surfactants or counterions over the interface. The general principles of the spin relaxation method, as applied to lyotropic liquid crystals, are described, with emphasis on the model-independent information content of the relaxation observables and on the relation to microstructure. Specific results for lamellar, hexagonal, cubic, and nematic phases are also described.     

Structural and dielectric behaviour of non-aqueous lyotropic mixtures: influence of amphiphile chain lengths and counter ions

This study highlights the effects of amphiphile chain length and counter ions on the self-assembly and dielectric behaviour of non-aqueous lyotropic liquid crystals. Two-dimensional hexagonal mesophase is seen for short-chain length sodium dodecyl sulphate, while lamellar and multiwall lamellar mesophases are noticed for long-chain length cetyltrimethylammonium bromide and polyoxyethylene (20) sorbitan monolaurate amphiphiles in the non-aqueous domains of ethylene glycol. A strong influence of amphiphile counter ions is seen on static dielectric constant, loss factor, relaxation frequency and relaxation time of these lyotropic mixtures. Refractive indices of these lyotropic phases are also highlighted.     

Liquid crystal effects on bacterial viability

The primary objective of this research was to test the hypothesis that lyotropic chromonic liquid crystals (neutral grey, red 14, blue 27, cromolyn) are not toxic to bacteria as compared with surfactant-based lyotropic (CPCl and CsPFO) or thermotropic (5CB and E7) liquid crystals. Biocompatibility of most liquid crystals is currently unknown and is required for the development of systems interfacing liquid crystals and biological systems. Potential liquid crystal toxicity was evaluated by two methods. The first examined bacterial survival measured by bacterial growth over 24 hours, after exposure to various liquid crystals. The second toxicity method evaluated liquid crystal effects on bacterial membrane permeability using two fluorescent dyes. Three different types of bacteria were evaluated to assess bacterial structure differences with respect to liquid crystal toxicity. The results of this study indicate that lyotropic chromonic liquid crystals are not toxic to bacteria, whereas thermotropic and surfactant-based lyotropic liquid crystals are toxic to one or more forms of bacteria. We conclude that lyotropic chromonic liquid crystals may be the preferred material in designing liquid crystal-based systems that interact with biological systems, especially in the use of liquid crystal-based biosensors.     

Liquid crystal effects on bacterial viability

The primary objective of this research was to test the hypothesis that lyotropic chromonic liquid crystals (neutral grey, red 14, blue 27, cromolyn) are not toxic to bacteria as compared with surfactant‐based lyotropic (CPCl and CsPFO) or thermotropic (5CB and E7) liquid crystals. Biocompatibility of most liquid crystals is currently unknown and is required for the development of systems interfacing liquid crystals and biological systems. Potential liquid crystal toxicity was evaluated by two methods. The first examined bacterial survival measured by bacterial growth over 24 hours, after exposure to various liquid crystals. The second toxicity method evaluated liquid crystal effects on bacterial membrane permeability using two fluorescent dyes. Three different types of bacteria were evaluated to assess bacterial structure differences with respect to liquid crystal toxicity. The results of this study indicate that lyotropic chromonic liquid crystals are not toxic to bacteria, whereas thermotropic and surfactant‐based lyotropic liquid crystals are toxic to one or more forms of bacteria. We conclude that lyotropic chromonic liquid crystals may be the preferred material in designing liquid crystal‐based systems that interact with biological systems, especially in the use of liquid crystal‐based biosensors.     

Glassy crystalline state and water sorption of alkyl maltosides

A differential scanning calorimetric and sorption calorimetric study of two alkyl maltosides, C8G2 and C10G2, was performed. In the dry state, C8G2 and C10G2 do not form solid crystals but undergo a glass transition upon temperature change. The glass is partly ordered and has the same lamellar structure as the liquid crystals formed by the two maltosides. To reflect the presence of the glass transition and the structure, the terms "glassy crystals" and "glassy liquid crystals" can be used. A mechanism of the relaxation of the glassy crystals based on the results of small-angle X-ray scattering experiments is proposed. Experiments on water sorption showed that the glassy crystals turn into lyotropic liquid crystals upon sorption of water at constant temperature. This isothermal glass transition can be characterized by water content and change of partial molar enthalpy of mixing of water. A method to calculate the phase diagram liquid crystals-glassy liquid crystals is proposed.     

表面活性剂溶致液晶的流变学性质

系统阐述了三种溶致液晶(六角状、立方状和层状液晶)的流变性质,概括了各自的流变性特点并给出了其理论模型,特别对立方相的流变学模型和层状相的剪切诱导转变作用进行了较详细的说明.讨论了因为这种转变而导致的囊泡的形成,并且在表面活性剂和嵌段共聚物中均可观察到剪切诱导的结构转变.     

Ion transport in polymerized lyotropic liquid crystals containing ionic liquid

In this work, we investigate the effect of morphology and segmental dynamics on ion transport in polymerized lyotropic liquid crystals (polyLLCs) containing 1-butyl-3-methylimidazolium tetrafluoroborate as ionic liquid (IL). We demonstrate that two important factors, which affect ion conduction in polyLLCs, are grain size and chain density at the interface. The polyLLC with large grain size (70 nm) shows significant reduction in ion conductivity (one order of magnitude) compared to its homopolymer/IL mixture. However, the polyLLC with small grain size (20 nm) has little difference in ion conductivity compared to its homopolymer/IL mixture. It is observed that decreasing the chain density enhances the interaction of IL with polymer chains and consequently slows the relaxation of polymer chains. In addition, comparing the dynamics of polymer chains in mixtures of homopolymer/IL and templated LLC mesophases shows that the confinement in LLC structure prolongs the relaxation of polymer chains.     

Self-assembly of amphiphilic poly(phenylene ethynylene)s in water-potassium dodecanoate-decanol lyotropic liquid crystals

Poly(phenylene ethynylene)s bearing a high density of branched amphiphilic side-chains self-assemble at the air-water interface and in water-potassium dodecanoate-decanol lyotropic liquid crystals.     

Some Emulsion Features

Traditionally, emulsions have been defined as consisting of two liquids, of which one is dispersed in the other as macroscopic drops, stabilized by mono‐molecular layer of surfactant at the interface. However, a large majority of commercial emulsions are more complex than so and the added elements are essential for the properties of the emulsions including their stability.

With this in mind, this treatment of emulsions is divided into emulsions with mono‐layers and multilayers at the interface. In addition, additional elements in emulsions are described; such as lyotropic liquid crystals, vesicles, microemulsion droplets and solid particles, and their potential influence on the emulsion properties is indicated.     

Narrowing of spontaneous emission and lasing in lyotropic and thermotropic liquid crystals

The narrowing of spontaneous emission and lasing are reported for the first time for a dye-doped lyotropic liquid crystal consisting of a methylbenzylamine solution of polybenzylglutamate (PBLG). Lasing was also studied in twisted nematics based on cholesterol derivatives. PBLG produces a cholesteric liquid crystal (CLC) with selective reflection in the visible region at PBLG concentrations above 55%. A comparison is made of the narrowing of spontaneous emission and lasing in lyotropic vs. thermotropic liquid crystals. In both cases lasing occurs where the selective reflection band overlaps the dye emission band. Thermotropic liquid crystals show a much lower lasing threshold than lyotropic systems. The lasing mechanism and the role of disorder in both systems are discussed.     

Narrowing of spontaneous emission and lasing in lyotropic and thermotropic liquid crystals

The narrowing of spontaneous emission and lasing are reported for the first time for a dye-doped lyotropic liquid crystal consisting of a methylbenzylamine solution of polybenzylglutamate (PBLG). Lasing was also studied in twisted nematics based on cholesterol derivatives. PBLG produces a cholesteric liquid crystal (CLC) with selective reflection in the visible region at PBLG concentrations above 55%. A comparison is made of the narrowing of spontaneous emission and lasing in lyotropic vs. thermotropic liquid crystals. In both cases lasing occurs where the selective reflection band overlaps the dye emission band. Thermotropic liquid crystals show a much lower lasing threshold than lyotropic systems. The lasing mechanism and the role of disorder in both systems are discussed.     

溶致液晶的结构及应用研究进展

本文评述了溶致液晶的相态和结构以及其相态随浓度变化的特点，并着重介绍了溶致液晶在新型纳米材料全盛中的应用，在生物医学中的应用，在化学反应中的催化作用，以及在工业中的作用。     

Molecular simulation of liquid crystals: progress towards a better understanding of bulk structure and the prediction of material properties

This tutorial review covers recent progress in the field of computer simulation of liquid crystals. The development of the main "molecular-based" models for liquid crystals is described. These include lattice models, coarse-grained single site models based on hard and soft interaction potentials, atomistic models and multi-site coarse-grained models. A brief historical review is followed by an assessment of some of the new areas in this field, with an emphasis on understanding of molecular structure in liquid crystal phases and the prediction of bulk material properties. The article also looks to link the field of liquid crystal simulation with important developments in areas such as polymer simulation, lyotropic liquid crystals and model membranes.     

Lyotropic liquid crystal guest–host material and anisotropic thin films for optical applications

We propose a new approach for the production of thin film optical functional materials. The method is based on molecular design whereby two different types of lyotropic liquid crystals (LC), lyotropic LC based on columnar supramolecules and water-soluble rod-like polymer molecules are mixed. The resulting lyotropic guest–host system allows production of optical retardation films with tunable optical anisotropy controlled by composition of the guest–host system. Coatable retarders can be used in modern liquid crystal displays and TVs for optical compensation and enhancement of the LCD's performance.     

仿生溶致液晶体系的构建与掺杂

本文综述了以类脂为基础的仿生溶致液晶体系的构建与掺杂，对掺杂物质与液晶模板之间的相互作用进行了分析，并展望了仿生溶致液晶体系在合成新型功能材料、生物学和医学等领域应用的发展前景。     

Magnetic-field induced biaxiality in nematic liquid crystals. Consequences for nuclear spin relaxation

When a uniaxial nematic liquid crystal is subjected to a magnetic field making a non-zero angle with the C_∞ axis, the uniaxial symmetry is broken. The principal effect is a field-induced biaxiality in the long-wavelength region of the director fluctuation spectrum. Whereas the induced biaxiality has little effect on the mean square director fluctuation amplitudes 〈n²_x〉 and 〈n²_y〉, which are dominated by short-wavelength modes, it can profoundly affect the nuclear spin relaxation behaviour, which is sensitive to long-wavelength modes. Motivated by the increasing number of nuclear spin relaxation studies of director fluctuations in thermotropic, amphiphilic, and polymeric nematic liquid crystals, we present here a theoretical analysis of the effects of field-induced biaxiality on nuclear spin relaxation.     

Spherulite morphology in liquid crystals of polybenzylglutamates. Optical rotatory power and effect of magnetic field

The stepwise growth and emergence of spherulitic structures as isolated entities from lyotropic solutions of polybenzylglutamate liquid crystals is described. Spherulites that form ringed internal structures indicative of a cholesteric organization of macromolecules have large optical rotatory powers. The sense of the rotation is solvent dependent. The morphology of the spherulite is distorted in the presence of a magnetic field. The pitch of the cumulative twist of “onion-shell” molecular layers was measured as a function of field strength and found to follow the theoretical form shown previously to hold for continuous-phase polypeptide liquid crystals.     

纤维素及其衍生物液晶研究近况

就纤维素及其衍生物溶性液晶和热致性液晶的液晶性及其影响因素,和流变性能等方面的研究作了较为详尽的综述。     

壳聚糖在二氯乙酸中的溶致液晶性

制备了不同脱乙酰度和分子量在１－３ ～１５－１ ×１０５ 范围内的壳聚糖样品,并用傅里叶变换红外光谱法（ＦＴＩＲ）和粘度法进行了表征．借助偏光显微镜研究了不同壳聚糖样品在二氯乙酸中的液晶相转变和液晶状态．实验结果表明,分子量在１０５ ～１０６ 范围内的增大使壳聚糖形成液晶相的临界浓度（ Ｃ＊ ） 略有降低;脱乙酰度在７０ ～９０ ％ 范围内,对Ｃ＊ 的影响基本可以忽略．临界浓度的实验值与根据Ｋｈｏｋｈｌｏｖ Ｓｅｍｅｎｏｖ Ｏｄｉｊｋ 理论预示的值比较一致,说明蠕虫链模型可以很好地描述壳聚糖分子链在二氯乙酸中的溶致液晶行为．