Liquid Crystalline Phase Behavior Research Articles

Liquid crystal phase behavior of sterically-stabilized goethite

The liquid crystalline phase behavior of sterically-stabilized goethite particles in toluene was studied using small-angle X-ray scattering. The results were compared with those from charged particles in water, with and without magnetic field: similarly rich phase behavior was found. Furthermore, the special magnetic properties were retained after coating the particles with amino-functionalized polyisobutylene chains. A remarkable difference between the aqueous and toluene samples is the latter's tendency to form gels. Smaller domains of the different liquid crystalline phases were observed and the columnar phase does not fully develop, furthermore a higher field is needed to align the full sample.

Charge Reversal of the Rodlike Colloidal fd Virus through Surface Chemical Modification

There is increasing interest in the use of viruses as model systems for fundamental research and as templates for nanomaterials. In this work, the rodlike fd virus was subjected to chemical modifications targeting different solvent-exposed functional groups in order to tune its surface properties, especially reversing the surface charge from negative to positive. The carboxyl groups of fd were coupled with different kinds of organic amines by carbodiimide chemistry, resulting in modified viruses that are positively charged over a wide range of pH. Care was taken to minimize intervirus cross linking, which often occurs because of such modifications. The surface amino groups were also grafted with poly(ethylene glycol) (PEG) end-functionalized with an active succinimidyl ester in order to introduce a steric stabilization effect. By combining charge reversal with PEG grafting, a reversible attraction between positively and negatively charged PEG-grafted fd viruses could be realized, which was tuned by the ionic strength of the solution. In addition, a charge-reversed fd virus forms only a pure nematic phase in contrast to the cholesteric phase of the wild type. These modified viruses might be used as model systems in soft condensed matter physics, for example, in the study of polyelectrolyte complexes or lyotropic liquid-crystalline phase behavior.

Drug release from lipid liquid crystalline phases: relation with phase behavior

Introduction: We studied the release of propranolol hydrochloride (PHCl), a water-soluble amphiphilic drug, from monoolein (MO)/water and phytantriol/water systems. Methods: We related the dissolution profiles with phase behavior and viscosity of the different liquid crystalline phases. Diolein has been added aiming to stabilize the cubic phases and thus preventing formation of less viscous (lamellar) phases. Results: Formulations display first-order release rates and diffusion release mechanism. Some formulations (mostly MO) were close to zero-order release in the first 120 minutes. Discussion: Release mechanism can be influenced by phase changes during dissolution. Conclusions: Both MO and phytantriol show good potential to be used for propranolol hydrochloride sustained drug release.

Preparation and characterisation of liquid crystalline epoxy/epoxy resin composites

A novel liquid crystalline epoxy resin, PHQEP, containing aromatic ester mesogen was synthesised from di(p-hydroxyl benzoic acid) hydroquinone (PHQ) and epichlorohydrin by phase transfer catalysis. The molecular structure of PHQEP was characterised by means of Fourier transformed infrared spectroscopy, hydrogen nuclear magnetic resonance spectroscopy, while its liquid crystalline phase behaviour was observed by a polarised optical microscope. The curing behaviour of PHQEP/diglycidylether of bisphenol A (E-51)/4,4′-diaminodiphenyl sulphone (DDS) system was studied by non-isothermal differential scanning calorimetry. Mechanical performance, thermal stability and dynamic mechanical property of PHQEP/E-51 composites were also investigated. The results revealed that PHQEP is a typical nematic liquid crystalline polymer. Impact strength of 5 wt-% PHQEP/E-51 was 2·6 times higher than that of E-51/DDS, and the initial decomposition temperature was 10°C higher than the value of E-51/DDS. The detailed reasons for the improvement of strength and thermal stability lie in the fact that origination of the mesogenic units of PHQEP was kept in the epoxy networks during the curing process.

Lanthanide Phytanates: Liquid-Crystalline Phase Behavior, Colloidal Particle Dispersions, and Potential as Medical Imaging Agents

Lanthanide salts of phytanic acid, an isoprenoid-type amphiphile, have been synthesized and characterized. Elemental analysis and FTIR spectroscopy were used to confirm the formed product and showed that three phytanate anions are complexed with one lanthanide cation. The physicochemical properties of the lanthanide phytanates were investigated using DSC, XRD, SAXS, and cross-polarized optical microscopy. Several of the hydrated salts form a liquid-crystalline hexagonal columnar mesophase at room temperature, and samarium(III) phytanate forms this phase even in the absence of water. Select lanthanide phytanates were dispersed in water, and cryo-TEM images indicate that some structure has been retained in the dispersed phase. NMR relaxivity measurements were conducted on these systems. It has been shown that a particulate dispersion of gadolinium(III) phytanate displays proton relaxivity values comparable to those of a commercial contrast agent for magnetic resonance imaging and a colloidal dispersion of europium(III) phytanate exhibits the characteristics of a fluorescence imaging agent.

Ordered Nanostructured Amphiphile Self-Assembly Materials from Endogenous Nonionic Unsaturated Monoethanolamide Lipids in Water

The self-assembly, solid state and lyotropic liquid crystalline phase behavior of a series of endogenous n-acylethanolamides (NAEs) with differing degrees of unsaturation, viz., oleoyl monoethanolamide, linoleoyl monoethanolamide, and linolenoyl monoethanolamide, have been examined. The studied molecules are known to possess inherent biological function. Both the monoethanolamide headgroup and the unsaturated hydrophobe are found to be important in dictating the self-assembly behavior of these molecules. In addition, all three molecules form lyotropic liquid crystalline phases in water, including the inverse bicontinuous cubic diamond (Q(II)(D)) and gyroid (Q(II)(G)) phases. The ability of the NAE's to form inverse cubic phases and to be dispersed into ordered nanostructured colloidal particles, cubosomes, in excess water, combined with their endogenous nature and natural medicinal properties, makes this new class of soft mesoporous amphiphile self-assembly materials suitable candidates for investigation in a variety of advanced multifunctional applications, including encapsulation and controlled release of therapeutic agents and incorporation of medical imaging agents.

Predictive synthesis of ordered mesoporous silica with maltoside and cationic surfactants based on aqueous lyotropic phase behavior

Self-assembled nonionic alkyl glycoside surfactants are of interest for creating functional adsorption and catalytic sites at the surface of mesoporous sol-gel-derived materials, but they typically impart poor long-range order when they are used as pore templates. Improved order and control over the functional site density can be achieved by mixing the alkyl polyglycoside surfactant with a cationic surfactant. Here, we investigate the rarely reported lyotropic liquid crystalline (LLC) phase behavior of aqueous solutions of a nonionic disaccharide surfactant, n-dodecyl-beta-d-maltoside (C(12)G(2)/DM), and cetyltrimethylammonium bromide (C(16)TAB) by low-angle powder X-ray diffraction (XRD) and polarized optical microscopy (POM). An approximate ternary phase diagram of the C(16)TAB-C(12)G(2)-water system is developed at 50 degrees C, which includes 2-D hexagonal (P6mm symmetry), bicontinuous cubic (Ia3 d symmetry), lamellar, and rectangular (cmm symmetry) LLC phases. By replacing the volume of water in the phase diagram with an equivalent volume of silica, ordered mesoporous materials are prepared by a nanocasting technique with variable C(12)G(2)/C(16)TAB ratios. For large regions of the phase diagram, this approach is predictive. However, silica materials synthesized with comparatively high C(12)G(2)/C(16)TAB ratios are only poorly ordered in a way that does not correspond to their lyotropic liquid crystalline phase behavior. Also, in contrast with our previous study of mixed C(16)TAB/n-octyl-b-d-glucopyranoside templating [37] the boundary between hexagonal and bicontinuous cubic materials is shifted towards higher surfactant content than in the aqueous LLC system.

Liquid Crystalline Phase Behavior of Protein Fibers in Water: Experiments versus Theory

We have developed a new method allowing the study of the thermodynamic phase behavior of mesoscopic colloidal systems consisting of amyloid protein fibers in water, obtained by heat denaturation and aggregation of beta-lactoglobulin, a dairy protein. The fibers have a cross section of about 5.2 nm and two groups of polydisperse contour lengths: (i) long fibers of 1-20 microm, showing semiflexible behavior, and (ii) short rods of 100-200 nm long, obtained by cutting the long fibers via high-pressure homogenization. At pH 2 without salt, these fibers are highly charged and stable in water. We have studied the isotropic-nematic phase transition for both systems and compared our results with the theoretical values predicted by Onsager's theory. The experimentally measured isotropic-nematic phase transition was found to occur at 0.4% and at 3% for the long and short fibers, respectively. For both systems, this phase transition occurs at concentrations more than 1 order of magnitude lower than what is expected based on Onsager's theory. Moreover, at low enough pH, no intermediate biphasic region was observed between the isotropic phase and the nematic phase. The phase diagrams of both systems (pH vs concentration) showed similar, yet complex and rich, phase behavior. We discuss the possible physical fundamentals ruling the phase diagram as well as the discrepancy we observe for the isotropic-nematic phase transition between our experimental results and the predicted theoretical results. Our work highlights that systems formed by water-amyloid protein fibers are way too complex to be understood based solely on Onsager's theories. Experimental results are revisited in terms of the Flory's theory (1956) for suspensions of rods, which allows accounting for rod-solvent hydrophobic interactions. This theoretical approach allows explaining, on a semiquantitative basis, most of the discrepancies observed between the experimental results and Onsager's predictions. The sources of protein fibers complex colloidal behavior are analyzed and discussed at length.

The effects of fluorescent probes on model membrane organization: photo-induced lipid sorting and soft structure formation

Liquid crystalline phase behaviour in model cell membranes prepared in-vitro has generated an enormous amount of interest in recent years and the phase diagrams of various bio-mimetic mixtures explored. Most recently photo-induced oxidation in fluorescently labelled membranes has been shown to influence these phase diagrams and can be used to generate interesting membrane-based geometries based on differences in membrane composition. In this article the different phases observed in model membranes will be discussed. Methods used to study these systems and recent developments in photo-stimulated phase changes are described along with areas for future investigation.

Size‐Dependent Isotropic/Nematic Phase Transition Behavior of Liquid Crystalline Peptide Nanowires

AbstractWe present size‐tunable assemblies of peptide nanowires and study their liquid crystalline phase behavior. An aromatic peptide molecule of diphenylalanine was rapidly assembled into one‐dimensional nanowires, whose sizes were tunable according to the initial concentration of diphenylalanine in the preparing solution. The stable dispersion of peptide nanowires in an organic solvent exhibited colloidal nematic liquid crystalline phases. The liquid crystalline phase transition was governed by the repulsive electrostatic interaction among peptide nanowires as well as their shape anisotropy and polydispersity. Our work provides an interesting model system to investigate the liquid crystalline phase behaviors of a biomolecular assembly in terms of its assembled morphology and intermolecular interactions.magnified image

Diffusivity of wormlike particles in isotropic melts and the influence of local nematization

Systems of wormlike particles are studied by molecular dynamics computer simulations in the isotropic phase. The particles are modeled as a chain of nine soft repulsive, partially overlapping, spherical sites. These particles are characterized by a varying degree of internal flexibility: from very stiff and rodlike to very deformable and stringlike. Their self-diffusion coefficients have been evaluated at many thermodynamic conditions. Maintaining the temperature constant and sufficiently low, from the stiff rod case and letting the worms become more flexible, the self-diffusion coefficients first steeply increase, then reach a plateau. This behavior is rationalized in terms of local nematic domains. The presence of the latter significantly affects the equation of state of the wormlike particles as well, with the density of the stiffest rods being, respectively, the highest at lower temperatures and the lowest at higher temperatures. This fact might have significant implications for the theory of liquid-crystalline phase behavior in systems of flexible particles. If the density of all systems is fixed at the equilibrium value of the stiffest case, which is a way to single out the effects of flexibility, self-diffusion coefficients may exhibit a moderately nonmonotonic behavior: subsequently to the above-mentioned steep increase, they may reveal a shallow maximum for intermediate degrees of internal flexibility degrees, then gently decrease. This behavior is tentatively associated with the different effects that internal flexibility has on the average length and width of a wormlike particle.

Soft ordered mesoporous materials from nonionic isoprenoid-type monoethanolamide amphiphiles self-assembled in water

The thermal and lyotropic liquid crystalline phase behaviour of a series of amide and monoethanolamide amphiphiles with isoprenoid-type hydrocarbon chains has been investigated. The amphiphilic nature of these molecules combined with their ability to form nanostructured self-assemblies makes them ideal candidates as delivery vehicles of bioactive molecules. For both families of molecules, increased branching in the hydrophobic chain, associated with increasing chain length, results in a decreased melting point. The melting points of the amides are significantly higher than their monoethanolamide homologues. Interestingly, both hexahydrofarnesoyl (H-farnesoyl) and phytanoyl monoethanolamide exhibit a glass transition temperature at around −72 °C to −74 °C. H-Farnesoyl and phytanoyl monoethanolamide form lyotropic liquid crystalline phases in water, whilst H-farnesoyl and phytanoyl amide form a spontaneous emulsion at the amphiphile–water interface. In particular, at room temperature H-farnesoyl and phytanoyl monoethanolamide form the Schwarz diamond (QIID) and the Schoen gyroid (QIIG) bicontinuous cubic phases which are retained down to temperatures as low as 1 °C. Furthermore, phytanoyl monoethanolamide displays a QIID, QIIG and inverse hexagonal phase (HII) at physiological temperature. Both phytanoyl and H-farnesoyl monoethanolamide form mesoporous cubic phases at room temperature that are easily dispersed into cubosomes. The robust nature of the nanostructured phase formation of these two monoethanolamides over a wide range of temperatures makes them ideal candidates for a variety of applications.

METHACRYLATE-BASED SIDE-CHAIN LIQUID CRYSTAL COPOLYMERS CONTAINING BIPHENYL MESOGENS AND CINNAMATE GROUPS

Liquid crystal(LC) polymers have been extensively investigated for their unique properties and many potential applications.Introducing cinnamate functional groups into the polymers can combine the mesogenic properties of LC polymers with the photo-crosslinking ability of the photosensitive groups.In this work,a methacrylate-based monomer(M_1) functionalized with mesogenic biphenyl and cinnamate groups was synthesized via nucleophilic substitution and DCC esterification reactions following a newly designed synthetic route.The overall yield was much higher than that reported before.Another methacrylate monomer(M_2) functionalized with mesogenic biphenyl and n-butyl end group was also synthesized in the same way.The homopolymers of the two monomers and a series of new liquid crystalline copolymers have been synthesized by solution radical polymerization with different feed ratios of the two monomers.The structures of the monomers and the polymers were characterized by~1H-NMR and FT-IR.~1H-NMR results revealed that the contents of M_2 in all of the copolymers were higher than the corresponding feed ratios,which indicateded that M_2 was more reactive than M_1.The liquid crystalline(LC) phase behavior was investigated by differential scanning calorimetry(DSC),polarized optical microscopy(POM) and wide angle and small angle X-ray diffraction(WAXD and SAXD).The monomer with cinnamate group as its end(M_1) exhibited no LC behavior while the monomer with n-butyl as end group(M_2) showed smectic LC behavior.The homopolymer of M_1(P_1) and the homopolymer of M_2(P_9) showed weak anisotropy and thermotropic smectic LC phase,respectively.The copolymers(P_2～P_8 with increasing ratio of M_2 to M_1) all showed thermotropic LC behavior.The copolymers P_2～P_5 exhibited characteristic features of nematic LC phases and P_6～P_9 showed smectic phase behavior.With the increase of the content of M_2 in the copolymers,the glass transition temperature,the melting point and the clearing point increased.As the cinnamate functional groups in the LC polymer can be crosslinked through photo-induced cycloaddition reaction,the polymer can be used to prepare LC elastomers.

Impurities in Commercial Phytantriol Significantly Alter Its Lyotropic Liquid-Crystalline Phase Behavior

The lyotropic liquid-crystalline phase behavior of phytantriol is receiving increasing interest in the literature as a result of similarities with glyceryl monooleate, despite its very different molecular structure. Some differences in the phase-transition temperature for the bicontinuous cubic to reverse hexagonal phase have been reported in the literature. In this study, we have investigated the influence that the commercial source and hence the purity has on the lyotropic phase behavior of phytantriol. Suppression of the phase-transition temperatures (by up to 15 degrees C for the bicontinuous cubic to reverse hexagonal phase transition) is apparent with lower-purity phytantriol. In addition, the composition boundaries were also found to depend significantly on the source and purity of phytantriol, with the bicontinuous cubic phase + excess water boundary occurring at a water content above that reported previously (i.e., >5% higher). Both the temperature and compositional changes in phase boundaries have significant implications on the use of these materials and highlight the impact that subtle levels of impurities can play in the phase behavior of these types of materials.

Liquid Crystalline Phase Behavior of High Molecular Weight DNA: A Comparative Study of the Influence of Metal Ions of Different Size, Charge and Binding Mode

The ability of Li(+), Na(+), K(+), Rb(+), Cs(+), Mg(2+), Ca(2+), Sr(2+), Ba(2+), Cu(2+), Cd(2+), Al(3+), V(4+), Hg(2+), Pd(2+), Au(3+), and Pt(4+) to provoke liquid crystalline (LC) phases in high molecular weight DNA was investigated. The alkali and alkaline earth metal ions provoked typical cholesteric/columnar structures, whereas transition metal ions precipitated DNA into solid/translucent gel-like aggregates. Heavy metal ions reduced viscosity of DNA solution, disrupting rigid, rod-like DNA structure necessary for LC textures. Three-layer quantum mechanical-molecular mechanical (QM/MM) studies of Li(+), Na(+), K(+), Mg(2+), and Ca(2+) binding DNA fragment suggested several possible binding modes of these ions to the phosphate groups. The dianion mode of metal binding, involving the phosphate groups of both strands of DNA, allowed for higher DNA binding affinity of the alkaline earth metal ions. These results have implications in understanding the biological role of metal ions and developing DNA-based sensors and nanoelectronic devices.

Chiral liquid-crystalline copolyacrylates with biphenyl and phenyl benzoate side groups

The phase behavior and structure of liquid-crystalline phases of three series of copolymers with mesogenic units belonging to the families of biphenyls and phenyl benzoates have been studied, with the former mesogenic units containing a chiral center in a flexible spacer. A variation in the isotropization temperature as a function of composition is well described by the additivity rule, whereas the tilt angle of mesogenic groups in smectic layers changes nonlinearly. This angle decreases beginning from homopolymers and attains the minimum value for the copolymers of the equimolar composition, which show the highest ferroelectric activity among the polymer systems under study.

Nanostructured self-assembly materials formed by non-ionic urea amphiphiles

Urea is an extremely versatile molecule that has been widely used for many years in a diverse range of applications. The physicochemical properties of urea have been well studied with respect to the role of hydrogen bonding in biological and chemical systems. Urea-based amphiphiles, in contrast, have received little attention with respect to physicochemical properties. Studies reported in the last few years have demonstrated that specific urea amphiphiles display interesting lyotropic liquid crystalline phase behaviour. These nanostructured self-assembly phases are potential candidates for a number of novel applications. In this work, we review the physicochemical properties of non-ionic urea-based amphiphiles, including those of the solid state, insoluble monolayers residing at the air-water interface, Langmuir-Blodgett films deposited on solid substrates and lyotropic liquid crystalline phases. In addition, we present new data that extends the characterisation of the solid state and lyotropic properties of isoprenoid branched urea surfactants.

From gas-liquid to liquid crystalline phase behavior via anisotropic attraction: A computer simulation study

The partial phase behavior of a continuum molecular model for self-assembling semiflexible equilibrium polymers is studied via Monte Carlo and molecular dynamics simulation. We investigate the transfer from ordinary gas-liquid coexistence to the appearance of liquid crystallinity driven by excluded volume interaction between rodlike aggregates. The transfer between the two types of phase behavior is governed by a tunable anisotropic attractive interaction between monomer particles. The relation to dipolar fluid models, which are also known to form reversible chains, is discussed.

SAFT−LC: An Equation of State for Predicting Liquid-Crystalline Phase Behavior in Carbonaceous Pitches

By adding an orientational free-energy term based on Maier−Saupe theory to the statistical associating fluid theory (SAFT) equation, we have developed a versatile equation of state for describing the phase behavior of carbonaceous pitches, a polydisperse class of discotic nematic liquid-crystalline materials that exhibits both thermotropic and lyotropic behavior. SAFT−liquid crystal (SAFT−LC) can be used to describe the phase behavior of carbonaceous pitches both at conditions where orientational effects are relatively minor (i.e., isotropic liquid−liquid equilibria in the presence of solvent) and at conditions where such effects dominate (e.g., the effect of pitch composition on the isotropic/nematic phase transition). SAFT−LC contains five well-behaved, adjustable parameters: three in SAFT for defining the binary interaction parameters and two in LC for describing the clearing temperature of a pitch pseudocomponent. Predictions of SAFT−LC for phase densities, product yields, and mesophase percentages o...

Binary Mixtures of Hard Rods: A Short Account

Results of recent calculations aimed at predicting the liquid-crystalline phase behavior of binary mixtures of hard spherocylinders are shortly reviewed. These calculations have been made by adopting a simple, re-summed second-virial Onsager-type theory, and include, among the usual isotropic and nematic phases, smectic phases too. The paradigmatic hard spherocylinders with diameter D and length of the cylindrical part equal to 5D have been taken as reference component, to which hard spherocylinders of different geometry are added. The liquid-crystalline phase diagram of the bidisperse mixtures so generated have been traced in all range of composition as a function of pressure. Various phenomena, such as strong demixing, presence of triple, critical and azeotropic points, and smectic phases with different symmetries, have been observed.