Lyotropic Liquid Crystal Phases Research Articles

Optical manipulation of defects in a lyotropic lamellar phase.

Here we study the line defect in a hyperswollen lamellar phase of lyotropic liquid crystal by applying a laser trapping method. We have succeeded in directly measuring the tension of a single isolated line defect and the adhesion energy between two defects. We demonstrate a new possibility of intentional patterning of various defects by direct optical manipulation. Furthermore, local rheological measurements provide information on the membrane organization around a particle and also evidence suggesting that flow in a lamellar phase has a two-dimensional nature.

Construction Of The Full Phase Diagram For The System Of Poly(γ-benzyl-l-glutamate)/dimethylformamide On The Basis Of The Complex Of Literature Data†

The system poly-γ-benzyl-l-glutamate—dimethylformamide (PBG/DMF) is the most-studied of the rodlike polymer-solvent systems. However, up to now there is no satisfactory experimental phase diagram (PD) for this system in the entire range of concentrations. For all studied systems only fragments of the PD are known. Some regions of these fragments agree qualitatively with the theoretical PD for an ensemble of rodlike particles in an isotropic solvent. However, most parts of the PD do not agree with the theoretical ones. A critical analysis of the corresponding experimental data was carried out and on the basis of this analysis a new PD was constructed in the enti re range of concentration. The obtained PD differs essentially from the known theoretical diagram and is very close to the diagram predicted by Papkov taking into account the formation of crystallosolvates. The peculiarities of the phase transitions in the various regions of the PD are considered. It is shown that the so-named lyotropic liquid crystals (LC), on the basis of solved rodlike polymers, are thermotropic LCs diluted by the isotropic solvent. A specific role in the PD are played by the crystallosolvates (CS), which are identified with the phase defined by Luzzati as the “complex phase.” In particular, the phase region LC-CS exists instead of the LC-LC region in the theoretical PDs. Some new concepts of the crystallosolvate defects and on the “limiting” LC phase are discussed. Consideration of the liquidus lines CS/LC and CS/(isotropic liquid) permits us to propose some explanations of the PDs at low polymer concentrations. Most parts of the real PD represent the superposition of different phase equilibria and are complicated by the processes of gelation, crystallization and crystallosolvate formation that cannot be described by the modern theories. The fragments of the PDs in the literature for some rodlike polymers in solution agree well with the general PD for PBG/DMF. Special features of the phase transitions in the different areas of the PD are discussed. On the basis of the principles used in this work for construction of the PD, critical consideration of the PDs published in the literature have been carried out; our understanding of results obtained by other authors are presented. The perspectives of further investigations are considered.

On the Mechanism of Electrophoretic Migration of DNA in Pluronic Gels

Capillary electrophoresis of nucleic acids has recently employed gels of self-assembled uncharged triblock copolymers as sieving media. Pluronic F127 contains poly(ethylene oxide) (EO) and poly(propylene oxide) (PO) with the block structure (EO)106(PO)70(EO)106. Aqueous solutions of 30% w/w of this polymer are liquids at low temperatures, but above 11 °C the polymers assemble to micelles that pack into a locally cubic lattice forming a gel-like lyotropic liquid crystal phase. Here we use linear dichroism spectroscopy to study the orientation dynamics of double-stranded DNA molecules during the electrophoresis. In 30% Pluronic F127, a 5400 bp DNA migrates with substantial perpendicular orientation of the helix axis, which is in contrast to electrophoresis in agarose gels where the helix axis of DNA is aligned parallel to the field direction. Comparison between linear and circular DNA indicates that neither DNA form enters the cubic microcrystals at low fields, and when combined with velocity measurements the kinetics of alignment buildup and relaxation suggests that migration instead occurs in grain boundaries between domains of microcrystals.

NEW LYOTROPIC LIQUID CRYSTALS BASED ON SURFACTANTS

We presented here the phase diagrams and the influence of the external electric field on the lyotropic liquid crystal phase (LLC) for some binary and pseudoternary systems based on surfactants. Binary systems are of the type surfactant/water (S/W) and the pseudoternary systems are of the type surfactant/oil/water (S/O/W). Two surfactants have been used: the lauryl alcohol ethoxilated with 11 molecules of ethylene oxide (LA11EO), which is a nonionic compound, and a mixture of LA11EO with the cationic surfactant named alkyl C12– C14-dimethyl-benzyl ammonium chloride. Based on these two types of surfactants, pseudoternary systems were prepared. Pine oil has been used as the oil. The region where the LLC phase appears depends on the concentration of the surfactant and that of the pine oil, respectively. It is strongly influenced by the nature of the surfactant and by the presence of the pine oil for the same type of surfactant. The influence of the external electric field, investigated by measuring the electric current appearing in the samples for different concentrations of surfactant and pine oil was found to be more important in the case of the systems based on the nonionic-cationic mixture of surfactants. The results are discussed in terms of a theoretical model based on the local thermal equilibrium approach for systems running nonstatic processes.

Aromatic Side Chain-Functionalized Long Chain Acid Salts: Structural Factors Influencing Their Lyotropic Liquid-Crystalline Behavior

The structural factors influencing the self-assembly of aromatic side chain functionalized long chain acid salts into lyotropic liquid crystal (LLC) phases were examined. Two sets of amphiphiles were synthesized containing two different ionic headgroups (i.e., sodium carboxylate and sodium sulfonate) and four different aromatic side chains (i.e., 4-styryl ether, 4-ethylphenyl ether, 1-naphthyl ether, and 4-phenylazophenyl ether) positioned at various locations along the amphiphile backbone. Systematic variation of the type of the aromatic side chain and its relative position on the amphiphile as a function of the two headgroups revealed that the position of the side chain on the amphiphile is the most important structural factor influencing the type and stability of the LLC phases formed. The nature of the aromatic side chain and the nature of the anionic headgroup play much more subtle roles in the LLC behavior of this particular amphiphile structural motif. Noncovalent aromatic−aromatic interactions are known to play important roles in the aggregation behavior of amphiphiles containing aromatic units along the alkyl chains; however, such interactions could not be detected spectroscopically in the LLC phases of our aromatic side chain amphiphiles. We speculate that the differences in alkyl chain interdigitation and packing efficiency arising from having the aromatic unit as a side chain rather than along the alkyl chains are responsible for this discrepancy. Control experiments with aliphatic ether side chain amphiphiles also corroborate the fact that aromatic interactions do not play a significant role in the aggregation behavior of these side chain amphiphiles. Side chain amphiphiles lacking an aromatic unit are still able to form the inverted hexagonal LLC phase, so long as the extent of branching and volume of the aliphatic side chain are sufficient.

Resonance effect in isotropic phase of lyotropic liquid crystal

In this work we present experimental results that show a resonance effect in the isotropic phase of a lyotropic liquid crystal. The lyotropic mixture is made up of Potassium Laurate (KL), Decanol (DeOH) and water with three different relative concentrations: 2.62, 2.79 and 2.90 (C = [KL]/[DeOH], [KL] and [DeOH] in % molar). These mixtures have an isotropic (ISO) phase between two lamellar phases as a function of the temperature. From the transmittance of the sample (I) as a function of the frequency (f) itwas possible to evaluate a characteristic time (tau) in order of magnitude as a function of the temperature (T). The existence of a maximum in tau vs. T around 30ºC indicates the possibility of employing lyotropic liquid crystals in mechanical vibration sensors. We are proposing a mechanical vibration sensor able to measure low mechanical frequencies (f <= 200 Hz).

Amplification of Specific Binding Events between Biological Species Using Lyotropic Liquid Crystals

This paper reports the orientational behavior of lyotropic liquid crystals (LCs) formed from 29.4 wt % potassium laurate and 6.6 wt % decanol (remainder water) that are supported on gold films possessing an anisotropic nanometer-scale topography (wavelength ∼10 nm, amplitude ∼2 nm). The gold-coated surfaces are decorated with biotin-functionalized alkanethiols to which anti-biotin immunoglobulin G (IgG) is specifically bound. Similar to the behavior of thermotropic LCs, we observe the anisotropic topography of these surfaces to cause formation of a single domain of uniform planar or near planar aligned nematic phase of lyotropic LC. However, the relaxation of the lyotropic LC to the uniform alignment is slow (∼30 min) compared to thermotropic phases (∼seconds). When the anti-biotin IgG was bound specifically to the surface functionalized with biotin, the optical appearance (using polarized light) of the lyotropic LC was azimuthally nonuniform and easily distinguished from the appearance of the lyotropic phase in the absence of bound IgG. In contrast, exposure of the surface to anti-streptavidin IgG does not perturb the uniform orientation of the lyotropic LC observed prior to exposure to the aqueous solution of IgG. These results provide new methods to align lyotropic LCs and demonstrate that lyotropic LCs are useful for amplification of specific binding events between biological species.

Ordering effects on the photopolymerization of a lyotropic liquid crystal

The synthesis of polymers bearing the highly ordered nanostructure of lyotropic liquid crystal (LLC) phases has recently been of great interest. This work describes the polymerization behavior and structural evolution of a cationic amphiphile in various LLC phases. The type and degree of LLC phases formed from this monomer depend strongly on the composition and temperature. By adding a nonpolymerizable surfactant a variety of LLC phases are formed including hexagonal, bicontinuous cubic, and lamellar morphologies while maintaining a constant monomer concentration. The highly ordered lamellar LLC phase exhibits the fastest polymerization rate with the slowest occurring in the hexagonal phase. The polymerization rates of the bicontinuous morphology were intermediate to the lamellar and hexagonal phases. The faster polymerization kinetics is due to diffusional limitations imposed on the propagating polymer by the highly ordered lamellar LLC phase. Also, the order of this LLC system has a strong dependence on temperature. At higher temperatures, the degree of LLC order and correspondingly the polymerization rate decrease. The original LLC phase morphology appears to be retained to the greatest extent in the faster polymerizing lamellar phase. The original nanostructure is also retained in the hexagonal and cubic LLC phases but with some slight changes in structure. This LLC structure is preserved at temperatures well exceeding the thermal phase transitions of the unpolymerized LLC samples.

Activation of mandelate racemase via immobilization in lyotropic liquid crystals for biocatalysis in organic solvents: application and modeling

Mandelate racemase from Pseudomonas putida ATCC 12633 could be activated in an organic solvent by immobilization in lyotropic liquid crystals (LC). A theoretical model for a system, that consisted of an organic solvent phase to solve the nonpolar substrate and the LC phase with the immobilized enzyme was developed. The model included the biocatalytic reaction and the mass transfer in-between and within the phases. By means of the finite element method (FEM) this model was transferred into a computer program, which was used as a tool for the simulation of the racemization of d-mandelic acid by mandelate racemase in the organic solvent (di- n-butyl ether). The experimental results at temperatures ranging from 20 to 60°C and starting concentrations of d-mandelic acid between 40 and 80 mmol l −1 in the organic solvent phase could be simulated by the model with high accuracy. Furthermore, the model was used to vary the geometry of the system to minimize mass transfer limitations, which represent a crucial limitation for this system.

Domain Structure in an Unoriented Lamellar Lyotropic Liquid Crystal Phase Studied by2H NMR

The spatial variation of the phase director in an unoriented lamellar lyotropic liquid crystal is investigated by 2H two-dimensional and one-dimensional exchange and PGSE NMR. Exchange NMR probes the single-particle orientational correlation function of D2O molecules that diffuse among regions with different director orientations. The obtained correlation time and the water diffusion coefficient, measured by 2H PGSE NMR, provide the persistence length of director orientation that is defined as domain size. The nature of spatial variation is revealed by the decay of the 2H stimulated echo signal recorded with different evolution times. The persistence length of the director is found to be strongly dependent on the rate of cooling the sample from its isotropic phase.

Growth and shapes of a cubic lyotropic liquid crystal

Monocrystals of the cubic lyotropic liquid crystal phase V1 are studied in droplets of the mixture C 12 EO 6/water surrounded by water vapor of controlled pressure p. Shapes of monocrystals are found to depend on the conditions of growth from the lamellar phase and on the nature of the substrate. After the growth, when the lamellar phase is exhausted and crystals are in equilibrium with water vapors, their shapes are shown to depend on the pressure p. Thermodynamic aspects of these phenomena are discussed.

Photopolymerization Kinetics and Structure Development of Templated Lyotropic Liquid Crystalline Systems

The templating of the ordered nanostructures of lyotropic liquid crystals (LLC) onto organic polymers has recently been of great interest. This work describes the polymerization and segregation behavior of polar and nonpolar monomers in an LLC environment. Nonpolar monomers partition to the oil-soluble domains of the LLC phase, whereas more polar monomers segregate at the interface of the liquid crystals. The polymerization kinetics in both cases are significantly influenced by the LLC phase morphologies although in different ways. The nonpolar monomers exhibit the fastest polymerization rates in micellar aggregates. This behavior is a result of an increase in the rate of propagation, induced by higher local concentrations of monomer in the micelles as compared to other mesophases. For more polar monomers, the opposite polymerization behavior is observed. The fastest polymerizations for these monomers are observed in the highly ordered lamellar mesophase with the minimum polymerization rate observed in th...

14N spin relaxation study in the hexagonal phase of a lyotropic liquid crystal

14N quadrupolar splitting and spin-lattice relaxation times T IZ and T IQ were measured in the hexagonal phase of a binary mixture of dodecyltrimethylammonium chloride and water. The derived spectral densities of motion at seven temperatures together with their corresponding quadrupolar splittings were analysed based on a simple model of ‘classical’ aggregates. Both fast local motion and slower surface self-diffusion about the cylindrical aggregate axis were required to account for the 14N spin relaxation in this phase. The azimuthal correlation time was found to be tens of nanoseconds.

Photopolymerization of Lyotropic Liquid Crystalline Systems: A New Route to Nanostructured Materials

ABSTRACTIn recent years, a considerable amount of research has been dedicated to synthesizing highly ordered nanostructured materials. One way to achieve this is through templated polymerizations. A novel route to fabricating such materials is through the use of lyotropic liquid crystals (LLCs) that possess highly ordered nanostructures. However, LLC phases lack the necessary physical robustness. So, templating LLC phase morphology onto other materials such as organic polymers would give a nanostructure retained as part of a robust polymeric matrix. This study focuses on the photopolymerization behavior and structure retention of hydroxyethyl acrylate (HEA) / dodecyltrimethyl ammonium bromide (DTAB) / water system in a select LC phase. The results suggest that the polymerization behavior is heavily dependent on the type of LLC structure. Specifically, lamellar aggregates polymerize faster than either cubic or isotropic morphologies due to diffusional limitations on the growing polymer chain. Monomer segregation also plays a role in determining the polymerization rates. Results also indicate that the original LLC order of these systems is largely retained upon photopolymerization although some LLC phases do change upon cure. This order would be useful in applications such as ultrafiltration membranes, separation media, and drug delivery systems.

A New Family of Polymerizable Lyotropic Liquid Crystals: Control of Feature Size in Cross-Linked Inverted Hexagonal Assemblies via Monomer Structure

An efficient and versatile synthesis of a series of polymerizable amphiphilic mesogens that affords control over tail length and position of the polymerizable group is described. The synthesis employs a novel and facile method of preparing styrene ethers. The monomers are sodium salts of styrene ether-modified fatty acids that can be used to form cross-linkable inverted hexagonal (HII) lyotropic liquid crystal (LLC) phases at ambient temperature with controllable nanometer-scale dimensions. Examination of a series of regioisomers with the same alkyl chain length but with the styrene ether group at different locations along the chain revealed that the position of the styrene ether has a profound effect on the dimensions of the resulting HII phase at a fixed temperature and composition. Increasing overall monomer tail length also has a significant, although smaller, effect on the unit cell dimensions of the LLC phase. By controlling the structure of the LLC monomer in this manner, cross-linked HII phases wi...

Lyotropic Liquid-Crystalline Phase Behavior of Some Alkyltrimethylphosphonium Bromides

The lyotropic liquid crystal (LLC) behavior of a homologous series of alkyltrimethylphosphonium bromide salts is described. While alkyltrimethylammonium salts are common LLC mesogens that have served in mesoporous materials, phase-transfer catalysis, and polymer−surfactant assemblies, the LLC behavior of the analogous phosphonium salts has been relatively unexplored. Dodecyl- (C12TMPB), tetradecyl- (C14TMPB), and hexadecyltrimethylphosphonium bromide (C16TMPB) were found to exhibit hexagonal, lamellar, and cubic mesophases similar to their ammonium counterparts; however, there is a key difference: Changing to a phosphorus-based headgroup appears to stabilize the cubic phase of C12TMPB and C14TMPB such that the phases extend down to room temperature. Some trends in the lattice parameters of the resulting LLC phases of the alkyltrimethylphosphonium bromides with respect to phase composition and temperature are also discussed. Finally, preliminary use of 31P NMR spectroscopy, as a method of structural chara...

Liquid Crystal Templating of Mesoporous Materials

There is currently great interest in the use of lyotropic liquid crystals as templates for the production of mesoporous inorganic or metallic materials having uniform pore sizes in the range 20-100 Å or greater. Such materials have potential applications as catalysts, molecular sieves or electrodes, and can accommodate molecules which are too large to fit within the pores of conventional zeolites. We have investigated the structure and alignment of mesoporous materials produced using the True Liquid Crystal Templating (TLCT) method. In TLCT, the surfactant forms a lyotropic liquid crystal phase of well defined geometry and dimensions at the start of the synthesis. We have been able to produce hexagonal mesoporous coatings within capillaries, having a specific alignment of the 2-D hexagonal lattice, as probed by X-ray diffraction. We have also followed the structural kinetics of the alignment process. These TLCT mesoporous materials may be functionalized for catalytic applications.

Structural properties of polymerised lyotropic liquid crystals phases of 3,4,5-tris(ω-acryloxyalkoxy)benzoate salts

Nanostructured free-standing films were obtained by polymerisation of lyotropic liquid crystal phases based on the monomer 3,4,5-tris(11′-acryloyloxyundecyloxy)benzoate. The structure of these films was investigated by X-ray diffraction. No change of the lattice due to the polymerisation procedure was observed. The low water content (below 10 wt.-%) of the liquid crystals in combination with the observed hexagonal lattice reveal that a reversed hexagonal structure (H2 phase) is present. Different types of films were investigated, obtained by varying the preparation conditions of the used lyotropic liquid crystals, such as water content, type of metal-counterion and length of the monomer. The lattice constant was found to be independent of the water content. It seems that at low water content of 8 wt.-% the lyotropic structure is still fully hydrated. This unusual behaviour is related to the tapered structure of the monomer which is composed of by a small headgroup and three extended tails for each headgroup. The lattice constant can be changed by using differently charged metal-counterions which are associated with the headgroup, as well as by varying the length of the tails on the monomer. Low resolution electron density maps of the hexagonal lattice give deeper insight in the arrangement of the monomers within the polymerised structure.

Control of Pore Sizes in Mesoporous Silica Templated by Liquid Crystals in Block Copolymer−Cosurfactant−Water Systems

Colloidal silica has been polymerized in the aqueous domain of lyotropic liquid crystal phases in ternary surfactant (Pluronic F127 or P123)−cosurfactant (butanol, pentanol, or hexanol)−water systems to create optically transparent mesostructured surfactant−cosurfactant−silica monoliths. The use of ternary systems enriches phase diagrams of aqueous surfactant systems, which in turn introduces more flexibility and diversity into the designed synthesis of mesoporous materials. Lyotropic surfactant liquid crystal phases are preserved throughout the inorganic polymerization and gelation processes and directly template the formation of inorganic mesophases. The cosurfactant chain length and the cosurfactant/surfactant mass ratio have been used to control the pore size. The large shrinkage of mesopores during calcination can be reduced with hydrothermal treatment prior to calcination. Highly ordered mesoporous silica samples with identical pore sizes, but very different wall thickness, can be prepared. The removal of surfactants and cosurfactants gives periodic hexagonal mesoporous silica with excellent thermal and hydrothermal stability.

The H2-phase of the lyotropic liquid crystal sodium 3,4,5-tris(omega-acryloyloxyundecyloxy)benzoate

The phase behaviour of the lyotropic liquid crystal sodium 3,4,5-tris(omega-acryloyloxyundecyloxy)-benzoate was investigated by small angle X-ray scattering. The water content of the lyotropic liquid crystal phase was varied between 8 and 20wt% and the investigations were performed in a temperature range up to 70oC. A reversed hexagonal structure (H2-phase) as well as the isotropic phase were observed. The lattice constant of the H2-phase was found to be independent of the water content. An extremely small dependence on temperature could be found. Based on the shape of the molecules and the observed structural properties, a model for the arrangement of the molecules within the H2-phase is given. The transition temperature from the H2-phase to the isotropic phase decreases significantly from 60oC for the sample with 8wt% water content to 30oC for the sample with 20wt% water content.