Lyotropic Liquid Crystal System Research Articles

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.

The Effect of Water on the Flow Orientation Process of Lyotropic Liquid Crystals Cholesterized by D(+)-Mannose

The rheological behavior of cholesteric lyotropic liquid crystals can give information about the chiral forces involved in the formation of the cholesteric arrangement. In the present work, we studied the effect of water availability on the orientation process of a lyotropic liquid crystal system submitted to flow. Different mesophases based on decylammonium chloride were prepared with different amounts of D(+)-mannose added as inductor. It was observed that the flow orientation process on cholesteric lyomesophases is different when occurring in a room atmosphere or a water-saturated atmosphere. For samples sheared in a room atmosphere, the orientation process involves an initial step of destruction of the cholesteric structure caused by shear, leading to the formation of microdomains with different orientations. In a second stage these microdomains orient themselves, forming a new helical structure in the flow direction. When the systems are sheared in a water-saturated atmosphere, the orientation process involves the accommodation of micelles into a new structure seeking the best orientation in the flow direction.

The Influence of Water on the Orientation Process of Cholesteric Lyotropic Liquid Crystals

The rheological behavior of cholesteric lyotropic liquid crystals can give information about the chiral forces involved in the formation of the cholesteric arrangement. In the present work, we studied the effect of water availability on the orientation process of a lyotropic liquid crystal system submitted to flow. We prepared different mesophases based on decylammonium chloride with different amounts of cholesterol added as an inductor. It was observed that the orientation process should involve an initial step of destruction of a cholesteric structure caused by shear that leads to the formation of microdomains. In a second stage these microdomains will orientate themselves, forming a new helical structure in the direction of the flow. Finally, on the third stage, the accommodation of the micelles on a new structure, seeking the best orientation of the system on the flow direction, could be observed. The obtained results showed that the content of water available would determine the existence of fragmentation, rearrange, and accommodation stages.

Undulating membrane structure under mixed extensional-shear flow

We report on studies using a new X-ray extensional flow cell to examine, for the first time, the structure of undulating lamellar lyotropic liquid crystal systems under extensional flow. The extensional component of the flow profile produced within this cell causes the lamellae to orient. We find that, although the intermembrane spacing does not change at low flow rates, it suddenly decreases after a critical flow rate has been attained due to the stretching and straightening of the lamellae. The effects of the shear component of flow on this oriented system have been examined in the context of a theoretical model developed by Ramaswamy.

Temperature dependence of the refractive index near the reentrant-isotropic--calamitic-nematic phase transition.

The laser-induced nonlinear optical response of a lyotropic liquid crystal system in the reentrant-isotropic and calamitic-nematic phases is investigated by the use of the thermal lens technique. The occurrence of an inversion in the temperature coefficient of the ordinary refractive index, dn(radially)/dT, near the reentrant-isotropic-calamitic-nematic phase transition, is discussed. This effect is attributed to the behavior of the electronic polarizability due to the change in micelle shape near the isotropic-nematic transition, and correlated with the results obtained near the nematic-isotropic transition, previously reported.

Rayleigh scattering of a new lyotropic nematic liquid crystal system: crossover of propagative and diffusive behaviour

In this paper we present to our knowledge the first light-scattering measurements on a rather new lyotropic system potassium laurate, decylammonium chloride, H2O. Relative concentrations were chosen in order to obtain the discotic ND phase over a large temperature range. Measurements involve digital recording of the autocorrelation function resulting from selfbeating of the depolarized scattered light. They were carried out at a fixed temperature in the ND phase range, by varying the scattering angle. A strong tendency to oscillations, superimposed on the usual relaxation signal, was found. This behaviour is quite surprising, as special precautions had been taken to minimize any eventual propagative signal. Such precautions have been tested previously, while investigating the older system potassium laurate, decanol, D2O. Nevertheless, we have found that in the new lyotropic system, a propagative component may occur in a significant way, or even become dominant for some particular situations. Actually, the characterization of such situations is the main purpose of the present paper. Based upon a detailed analysis of photocorrelation data, it will be shown that the observed behaviour is consistent with the expected wave vector dependences of propagative and diffusive modes. Finally, a discussion is given on possible causes for the tendency to instability of lyotropic nematic liquid crystals.

Cross-Linkable Liquid Crystal Monomers Containing Hydrocarbon 1,3-Diene Tail Systems

The unprecedented use of polymerizable hydrocarbon tail systems containing 1,3-diene groups for the design of thermotropic and lyotropic liquid crystal (LC) monomers is described. Cross-linkable LC dienes are synthesized by attaching LC core units to modular ω-bromoalka-1,3-diene tails of variable length. These modular diene tails are synthesized by the oxidation of long chain ω-bromoalkan-1-ols to the corresponding ω-bromoalkanals. Reaction of the ω-bromoalkanals with Matteson's reagent, followed by treatment with triethanolamine and deoxysilylation under Peterson elimination conditions, affords the desired ω-bromoalka-1,3-diene tails. The effect of the 1,3-diene group on the mesogenic behavior of certain thermotropic and lyotropic LC systems was determined by examining 1,3-diene analogues of a thermotropic calamitic LC diacrylate and a taper-shaped lyotropic LC triacrylate. Compared to their diacrylate analogues, the thermotropic LC bis(1,3-diene)s exhibit the same progression of nematic and smectic pha...

Nuclear magnetic resonance quantum logic gates using quadrupolar nuclei

The use of nuclei with spin >1/2 and quadrupolar splitting of the spin energy levels has certain advantages over systems of interacting spins 1/2 for building quantum logic gates. Experimental demonstration has been made using 23Na (spin 3/2) NMR in a lyotropic liquid crystal system. The pulse sequences for establishing effective pure quantum states are given, and the resulting NMR spectra are presented.

Comparison of the pitch induced from lamellar and nematic regions in some lyotropic liquid crystal systems

Lamellar phases (Lalpha) composed of decylammonium chloride(DACl), NH4Cl and H2O were doped with cholesteryl-2-ethoxyethoxyethyl carbonate (CEEC) and with (L-MA) or its racemic mixture (DL-MA). Lalpha phases of the novel intrinsic optically active L-serine hydrochloride decylester (L-SDE) and its racemic mixture (DL-SDE) were also prepared. From the chiral Lalpha phases, cholesteric phases (ChD) were induced with increased temperature and it was found that the pitch length shortened as the temperature was raised. This phenomenon is new for micellar cholesterics. The non-chiral Lalpha phases gave pseudo-isotropic and nematic regions with increased temperature. On the basis of these results and those in the literature, a new interpretation of the distorted micelle shape and the formation of the fingerprint texture is presented. The pitches induced from Lalpha regions were always larger than those obtained from nematic regions. From these results it is inferred that the interactions between the micelles in the cholesteric state at room temperature are of 'ideal' type. In addition, the temperature dependence of the pitch in micellar cholesterics is discussed.

Rarely Observed Phase Transitions in a Novel Lyotropic Liquid Crystal System

This Letter presents neutron diffraction data from a novel, biologically relevant, lyotropic membrane system which is highly alignable ( $\ensuremath{\le}1.0\ifmmode^\circ\else\textdegree\fi{}$ mosaic) in a magnetic field and gives rise to a number of well-defined Bragg reflections. The system, composed of two different phosphorylcholine lipids, undergoes a rare nematic $\ensuremath{\rightarrow}$ smectic phase transition upon doping the system with paramagnetic ions (e.g., 2.7 wt % ${\mathrm{Tm}}^{3+}$). In addition, the isotropic phase occurs at a lower temperature than the smectic phase, in contrast to other lyotropic systems and in contrast to the phase behavior predicted by the McMillan model [Phys. Rev. A 4, 1238 (1971)] of smectic ordering.

Simulation of self-assembly and lyotropic liquid crystal phases in model discotic solutions

A prototype model of amphiphilic discotic binary solutions is proposed, and its statistical mechanics investigated by Monte Carlo computer simulation procedures. Data are presented from a large number of simulations, over 50 separate systems in all, carried out at a single relatively low pressure but covering almost the entire temperature-composition range of phase space beyond the melting line, including successful simulations of equilibrated cluster distributions throughout the isotropic solution phase. These data are in agreement with the well known theory of linear aggregation, but a major surprise is found in that the associated equilibrium constant possesses a strong concentration dependence at low temperature. The global aggregation behaviour is described in detail and discussed in the context of the standard state that is usually invoked when applying linear aggregation theory to experimental systems. It is concluded that as the temperature decreases the ideal behaviour of these cluster distribution data shows more and more influence from the nearby infinite polydispersity limit. At sufficiently high surfactant concentration our model discotic solutions melt first into partially ordered states of aligned aggregates (columns of discs) surrounded by liquid solvent. Both a nematic phase and a hexagonally ordered columnar phase are observed. Simulation procedures are used to investigate the phase behaviour and especially the microscopic structure of these lyotropic liquid crystal systems. The thermodynamic behaviour of our prototype molecular model shows a qualitative resemblance to experimental results obtained from aqueous solutions of the discotic amphiphile known as TP6EO2M.

A Study of the Lyotropic Liquid Crystal Phases of Caesium Pentadecafluorooctanoate(CsPFO)/Poly (Ethylene Oxide) (PEO)/Water System

Abstract The binary lyotropic liquid crystal system CsPFO/water is one which has been extensively studied in recent years [1] since the system contains a nematic phase, (ND), over an unprecedented range of temperature and concentration of exceptional stability. This phase is bordered at higher temperatures by an isotropic micellar phase, (L1), and at lower temperatures by a defected lamellar phase (LαH). A non-ionic hydrophilic polymer, poly(ethylene oxide) (PEO), has been added to the system replacing some water molecules. Optical microscopy agrees with previously reported results [2] showing that at 0.9% PEO the lamellar phase is replaced by a phase with a nematic-type texture, (N*). This system is unusual in polymer-surfactant systems in that the polymer addition causes a phase change from a lamellar phase to a magnetically orientatable phase. We have used small angle neutron scattering (SANS), optical microscopy and 2H NMR to investigate both the LαH and N* phases in order to understand the structural...

Characterization of field-ordered aqueous liquid crystals by NMR diffusion measurements

Anisotropic water diffusion in three lyotropic liquid-crystal systems, cesium perfluorooctanoate (CsPFO)/D 2 O, dimyristoylphosphatidylcholine (DMPC)/CHAPSO/D 2 O, and DMPC/Triton X-100/D 2 O, has been measured using the NMR pulsed field gradient spin echo (PFGSE) technique. Field gradients were applied in directions parallel to the magnetic field and perpendicular to the field, in order to obtain very precise water diffusion coefficients along orthogonal directions. The results have been analyzed using a diffusion model in which water molecules move stochastically over fixed sites in a lattice. Micelles which make up the liquid crystal are included as forbidden diskoidal regions of appropriate size and orientation in this lattice

Power-law scattering in fluids with a nonscalar order parameter.

We studied the coarsening behavior of two lyotropic liquid-crystal systems by static light scattering. The samples were quenched from the isotropic phase into either the nematic phase or a region of coexistence between nematic and isotropic phases. In the coexistence region, we observed, in both two and three dimensions, Porod power-law tails of the scattering intensity. Such a behavior is described by S(q)∼q -(d+1) in the limit of large wave vectors q, where S is the scattering intensity, q is the wave vector, and d is the dimension of the system. In addition, the nematic phases displayed novel power-law scaling behavior at large q, namely, S(q)∼q -u , where u=4 in two dimensions and u=6 in three dimensions. These results will be compared to recent theoretical predictions

Shape anisotropy and ordered phases in reversibly assembling lyotropic systems

When a fluid composed of sufficiently asymmetric hard particles is compressed, purely entropic effects give rise to phases possessing long-range orientational and, in some cases, translational order. The various ordered phases observed in conventional lyotropic liquid-crystal systems are commonly described in terms of such a hard-particle model. Here we study the liquid-crystal phases observed in reversibly assembling lyotropics (i.e., systems in which amphiphilic monomers form asymmetric aggregates) within the framework of a hard-particle model. These self-assembling systems are complicated by a variable and polydisperse aggregate size distribution, which is both concentration and temperature dependent, and is coupled to the orientational and translational ordering of the system. Our approach employs a phenomenological description of aggregate assembly, in conjunction with a scaled particle treatment of fluid configurational entropy and a cell description of periodic columnar and smectic density modulations. Cases of rodlike and disklike aggregates are considered. The calculated phase diagram for the rodlike (disklike) system displays a low-temperature nematic phase intervening between a low-concentration isotropic phase and a high-concentration columnar (smectic) phase. With increasing temperature the region of nematic stability narrows and finally terminates at an isotropic-nematic-columnar (smectic) triple point above which there is a direct isotropic to columnar (smectic) transition. This general phase diagram is characteristic of a number of experimental systems in which the aggregates are restricted to either rod- or disklike geometries. The calculated concentration dependence of the aggregate size distribution, orientational order parameter, and periodic columnar and smectic spacings are also reported and compared with specific experimental results.

Lyotropic and Thermotropic Lrquid Crystals Under Shear Flow

AbstractWe describe x-ray scattering studies of the nematic and smectic-A phases of the thermotropic liquid crystal 8CB and the Lα, and L3 (lamellar and sponge) phases of the lyotropic liquid crystal system: SDS, dodecane, pentanol and water. In the thermotropic system a series of orientational states of the nematic director is observed before entering the smectic-A phase where the smectic density wave and nematic director are oriented normal to the shear plane at high shear rates. In the lyotropic system lamellar fluctuations in the sponge phase (L3) become oriented by shear and in the lamellar phase (Lα) at high shear the layers orient preferentially along the velocity-gradient direction, in highly anisotropic cylindrical multilamellar liposome-like structures.

Inosose-Flüssigkristalle / Inosose Liquid Crystals

Six S,S-dialkyl acetals 2a-f of inosose (1), tripodal in structure, have been synthesized, characterized and investigated by optical microscopy and differential scanning calorimetry (d.s.c.). The four S,S-acetals 2c-f with sufficiently long alkyl chains are thermotropic liquid crystalline; 2 e and 2 f are even dithermomesomorphic. Each of these four inosose derivatives 2c-f exhibits monotropically a most likely cubic mesophase (MI); in addition 2e and 2f show enantiotropically a hexagonal mesophase (Hx) with a non-covalent, supramolecular H-bridge architecture. Whereas the nature of the optically isotropic mesophase MI needs further clarification the stable high temperature mesophase Hx of 2 e and 2 f has been established by a miscibility test using a sugar S,S-dialkyl acetal also tripodal in structure and with a Hx phase proved by X-ray diffraction, but in contrast to 2 with an acyclic hydrophilic part. Similarities of structural features between the Hx-phases of 2e and 2f as well as of other thermotropic and lyotropic liquid crystal systems are discussed briefly.

Viscosity and rubber-like properties of isotropic and liquid crystalline solutions of oxypropylcellulose in water

The specific features of the rheological properties of lyotropic liquid crystal systems are demonstrated, using aqueous solutions of propoxycellulose as an example. These properties include the existence of maxima on the plots of viscosity, elastic strain, normal stresses, and dynamic modulus against the concentration. These features are generally observed at concentrations corresponding to the appearance of the liquid crystal phase, although, in the case of elastic strain, the maximum is displaced into the region of higher concentrations. Accumulation of the liquid crystal phase is accompanied by an increase in non-linearity of the mechanical behaviour. The correlation between the static and dynamic characteristics is thus impaired. In the case of completely liquid solution the first difference in the normal stresses becomes negative.

Release Studies from Lyotropic Liquid Crystal Systems

AbstractA temperature-composition diagram of systems containing the nonionic surfactant polyoxethylene (20) isonexadecyl ether (1) and water was established. Three different anisotropic areas existed over the concentration range 33–80% of 1. Release of salicylic acid from liquid crystalline phases of 1 into aqueous buffer across lipoidal barriers was also studied. Rates of transfer as a function of percent loading from a neat mesophase containing 37% of 1 and also from systems with different molecular packing were determined. Apparent activation energies of transfer from an ordered solvent containing 37% of 1 and from an isotropic medium of the same chemical composition were found to be 33.3 and 9.4 kcal/mol, respectively. These findings suggest a pronounced effect of medium structure on the interfacial resistance of the barrier.

Structures and Mechanisms of Phase Transitions in Surfactant Mixtures: Systems Which Induce the Ribbon Phase

Abstract Phase transitions in lyotropic liquid crystal systems made from potassium palmitate/potassium laurate/water (KP/KL/H2O) and potassium palmitate/benzoyl alcohol/water (KP/BZA/H2O) were characterized by time resolved x-ray diffraction done at the SERC Daresbury (U.K.) Synchrotron Laboratory. Hysteretic phase behavior was observed for some of the KP/KL/H2O mixtures but not for any of the KP/BZA/H2O mixtures studied. In addition, the transition between the rectangular and ribbon phases in these systems is described using x-ray diffraction. General trends related to the observation of phase transitions in these systems are discussed. The ribbon phase appears to be more stable in the KP/BZA/H2O system since it retains its structure after the coexisting lamellar phase has transformed into a liquid crystalline bilayer for a larger temperature range than for KP/KL/H2O.