Lyotropic Liquid Crystalline Phase Behavior Research Articles

Positional Isomers of Linear Sodium Dodecyl Benzene Sulfonate: Solubility, Self-Assembly, and Air/Water Interfacial Activity

Commercial linear alkyl benzene sulfonates (ABS) are a very important class of anionic surfactants that are employed in a wide variety of applications, especially those involving wetting and detergency. Linear ABS surfactants generally consist of a complex mixture of different chain lengths and positional isomers. This diversity and level of complexity makes it difficult to develop fundamental structure-property correlations for the commercial surfactants. In this work, six monodisperse headgroup positional isomers of sodium para-dodecyl benzene sulfonate (Na-x-DBS, x = 1-6) have been studied. The influence of headgroup position and added electrolyte (NaCl) on the solubility and self-assembly (micellar and vesicular aggregation and lyotropic liquid crystalline phase behavior) in the temperature range from 10 to 90 degrees C have been investigated. Additionally, the air-aqueous solution interfacial adsorption at 25 (no added NaCl) and 50 degrees C (from 0 to 1.0 M added NaCl) has been examined. The observed physicochemical behavior is interpreted in terms of local molecular packing constraints, and in the case of the lyotropic liquid crystalline behavior global aggregate packing constraints as well.

Lyotropic Liquid Crystals from Designed Helical β-Peptides

We demonstrate that 14-helical beta-peptides can self-assemble to form lyotropic liquid crystalline (LC) phases in water. beta-Peptides 1-4 were designed to form globally amphiphilic 14-helices of increasing length. Optical microscopy showed that several of these beta-peptides formed LC phases in aqueous solutions at concentrations as low as 2.5 wt % (15 mM). Liquid crystallinity appears to require the adoption of a globally amphiphilic conformation because a scrambled sequence, 5, does not display LC behavior. Thermal stability and reversibility of LC phase formation were assessed by variable temperature 2H NMR spectroscopy and optical microscopy. The LC phase formed by beta-peptide 3 at 10 wt % is disrupted above 40 degrees C in D2O and re-forms within minutes upon cooling. LC phase behavior for solutions of 3 is influenced by concentration and net charge. These studies demonstrate that highly folded 14-helical beta-peptides can produce LC phases at shorter lengths than do alpha-helical alpha-peptide mesogens and can provide a basis for tailoring properties of LC phases for future applications.

Aqueous cholesteric liquid crystals using uncharged rodlike polypeptides.

The aqueous, lyotropic liquid-crystalline phase behavior of the alpha-helical polypeptide, poly(N(epsilon)-2-[2-(2-methoxyethoxy)ethoxy]acetyl-lysine) (1), has been studied using optical microscopy and X-ray scattering. Solutions of optically pure 1 were found to form cholesteric liquid crystals at volume fractions that decreased with increasing average chain length. At very high volume fractions, the formation of a hexagonal mesophase was observed. The pitch of the cholesteric phase could be varied by a mixture of enantiomeric samples L-1 and D-1, where the pitch increased as the mixture approached equimolar. The cholesteric phases could be untwisted, using either magnetic field or shear flow, into nematic phases, which relaxed into cholesterics upon removal of field or shear. We have found that the phase diagram of 1 in aqueous solution parallels that of poly(gamma-benzyl glutamate) in organic solvents, thus providing a useful system for liquid-crystal applications requiring water as solvent.

Cross-linked normal hexagonal and bicontinuous cubic assemblies via polymerizable gemini amphiphiles.

The synthesis and lyotropic liquid-crystalline (LLC) phase behavior of a homologous series of intrinsically cross-linkable gemini surfactants are described. These novel bis(alkyl-1,3-diene)-based phosphonium gemini amphiphiles exhibit "normal" hexagonal (H(I)), Type I bicontinuous cubic (Q(I)), and lamellar (L(alpha)) phases in water, and can be photocross-linked with retention of phase architecture in each case. On the basis of their locations on the phase diagram, their powder X-ray diffraction profiles, and the physical properties of the cross-linked materials, the Q(I) phases formed by these gemini monomers are consistent with four possible bicontinuous cubic architectures with P or I space group symmetry that have been identified previously for small molecule amphiphiles. The extent of polymerization (i.e., the degree of diene conversion) achieved in the LLC phases was determined to be in the 23% to 71% range using UV-vis spectrometry, which is more than sufficient to extensively stabilize the systems. The resulting cross-linked H(I), L(alpha), and Q(I) phases are stable up to 300 degrees C in air. To our knowledge, these reactive amphiphiles constitute the first example of a polymerizable gemini surfactant, and the first example of a cross-linkable amphiphile system that can be polymerized in both the H(I) and a Q(I) mesophase with retention of phase microstructure.

Ordering of quantum dots using genetically engineered viruses.

A liquid crystal system was used for the fabrication of a highly ordered composite material from genetically engineered M13 bacteriophage and zinc sulfide (ZnS) nanocrystals. The bacteriophage, which formed the basis of the self-ordering system, were selected to have a specific recognition moiety for ZnS crystal surfaces. The bacteriophage were coupled with ZnS solution precursors and spontaneously evolved a self-supporting hybrid film material that was ordered at the nanoscale and at the micrometer scale into approximately 72-micrometer domains, which were continuous over a centimeter length scale. In addition, suspensions were prepared in which the lyotropic liquid crystalline phase behavior of the hybrid material was controlled by solvent concentration and by the use of a magnetic field.

How Chain Length, Headgroup Polymerization, and Anomeric Configuration Govern the Thermotropic and Lyotropic Liquid Crystalline Phase Behavior and the Air−Water Interfacial Adsorption of Glucose-Based Surfactants

A matrix of anomerically pure glucose-based surfactants have been synthesized and their thermotropic and lyotropic liquid crystalline phase behavior, and air-aqueous solution interfacial adsorption were investigated. The surfactants, which represent the major components of the Fischer synthesis products, were the n-octyl, n-decyl and n-dodecyl homologues of alkyl α-d- and β-d-glucoside and alkyl β-d-maltoside. The matrix allowed the investigation of the effects of alkyl chain length, headgroup polymerization, and anomeric configuration on the surfactants' physicochemical properties. Increasing the alkyl chain length increases the hydrophobicity and the dispersion interaction between surfactant molecules, as one would expect, resulting in greater thermal stability of thermotropic and lyotropic phases. Phase transition temperatures are influenced significantly by the anomeric configuration in the shorter octyl derivatives, but to a lesser extent in the longer alkyl chain derivatives. The effect of increasin...

A Ferrocene-Containing Carbohydrate Surfactant: Thermotropic and Lyotropic Phase Behavior

A ferrocene-containing carbohydrate surfactant has been synthesized and shown by polarized optical microscopy, differential scanning calorimetry, and X-ray diffraction to exhibit both thermotropic and lyotropic liquid-crystalline phase behavior. This new class of materials should prove useful for the design of redox-active lyotropic liquid crystals, allowing fine electrochemical control of the phase structure and symmetry.

Synthesis of organic polymer gels in microemulsions and lyotropic mesophases

AbstractThe synthesis of fine polymer latices and ordered polymer gels by polymerization in microemulsions and lyotropic mesophases is described. For this purpose, a new class of surfactants based on the coupling of cetyl trimethylammonium groups with organic counterions was developed. Interface activity, critical micelle concentration as well as lyotropic liquid crystalline phase behavior of these surfactants were investigated, and very high efficiency and high phase stability was found.Systems optimized such do not only allow the synthesis of very small polymer latices (Rh≥7.5 nm) in reverse systems, but also the generation of gels with lamellar order. Due to the occurrence of phase transitions during polymerization, direct templating of the original lyotropic phase by the polymer gel is prevented, but the final polymer gels are highly ordered and reflect some of the characteristics of the surfactant template.

Transitional Liquid Crystalline Phases between the Hexagonal and Lamellar Phases in Ternary Cesium N-Tetradecanoate-Water-Additive Mixtures

The effects of added salt (CsOH, CsCl), long-chain carboxylic acid, and long-chain alcohol on the lyotropic liquid crystalline phase behavior in the cesium n-tetradecanoate (CsTD)-water system is reported. The transitional region between the hexagonal (Hα) and lamellar (Lα) phases was the compositional range of focus. Three transitional phases were observed: (i) the ribbon (R) phase, a biaxial phase consisting of cylinders of ellipsoidal cross section; (ii) the viscous isotropic (VI) phase, an isotropic phase thought to consist of interconnected rods on an 1a3d lattice; and (iii) the intermediate (Int) phase, a uniaxial anisotropic phase thought to consist of interconnected rods on a planar lattice. The effect of the additives was to decrease the "interfacial curvature" of the surfactant head group layer by varying head group repulsion and by varying the surfactant tail volume relative to the surfactant head group area. These changes resulted in formation of transitional phases seeming to possess curvature between that of the cylindrical Hα phase and the planar Lα phase. The ionic repulsion between carboxylate head groups was reduced by the addition of CsOH or CsCl, and resulted in destabilization of the VI phase and the formation of the anisotropic Int phase. With the addition of cosurfactants, n-tetradecanoic acid (TDA) and 1-tetradecanol (TDOH), no Int phase was observed. With 7 wt% added TDA the R phase was stabilized up to temperatures of 336 K, above the 330 K temperature limit in the binary CsTD-D2O system. In all four systems, sufficient additive (5-10 wt%) resulted in a transition to the Lα phase, which was stable over a large portion of the compositional range. In order of apparently decreasing mean curvature, the phase sequence is: hexagonal, ribbon, viscous isotropic, intermediate, and lamellar. The inferred structures are remarkably similar to reports in sodium dodecyl sulfate- and alkyl trimethyl ammonium chloride-water binary systems, as well as to liquid crystal formation in block copolymer systems.

Lyotropic liquid crystalline phase behavior of amphiphilic monomers and polymers having a rod-like hydrophobic moiety

Distinct changes in the lyotropic mesophase behaviour of nonionic polyethyleneglycol containing amphiphiles are observed, when rigid, rod-like molecular units are introduced into the hydrophobic part of these amphiphiles, or when the amphiphiles are added as side chains to poly(methylhydrogene siloxane), yielding amphiphilic side chain polymers. Low molar mass amphiphiles with a dominating rigid, rod-like hydrophobic unit form planar-like micelles which aggregate into lamellar mesophases. Compared with their corresponding low molar mass amphiphiles, amphiphilic side chain polymers show a distinct stabilization of mesophases composed of anisometric micelles, i.e. hexagonal H1-phases (built up by rod shaped micelles), and lamellar L α -phases (built up by planarshaped micelles). In addition, several of the polymeric amphiphiles exhibit the formation of a lyotropic nematic Nc-phase regime. Optically isotropic I1-phases composed of approximately spherical-like micelles are, on the other hand, disfavoured by the polymerfixation. Investigations of monodisperse amphiphilic side chain oligomers reveal a linear relationship between the thermal stability of the individual mesophases and the logarithm of the degree of polymerization. Changes in mesophase behaviour, due to the introduction of rigid, rod-like molecular units into the hydrophobic part of the low molar mass amphiphiles, are ascribed to packing restraints of the amphiphiles in the micelles. Alterations in mesophase behaviour which occur as a consequence of polymerfixation are discussed in terms of changes in micellar kinetics, packing restraints, and changes in the interaction between adjacent hydrophobic layers of neighbouring micelles.

Lyotropic liquid crystalline phase behavior of a polymeric amphiphile polymerized via their hydrophilic ends

The reaction of the nonionic low molecular mass surfactant 3, 6, 9, 12, 15, 18, 21, 24-octaoxaoctatriacontane-1-ol (CH3(CH2)13(OCH2CH2)8OH, C14E8) with acryloyl chloride yielded the monomeric amphiphile II (CH3(CH2)13(OCH2CH2)8O2C-(CH:CH2) with the polymerizable group located at the hydrophilic end of the molecule. Using radical polymerization, the polymeric surfactant III is obtained. These three surfactant water systems exhibit lyotropic liquid crystalline phases. The binary phase diagrams are compared with each other. In changing from the monomer-water to the polymer-water system a stabilization of the lyotropic mesophases is observed with amphiphiles which are connected via their hydrophilic ends; it is known for the surfactants to be connected via their hydrophobic ends. The appearance of the inverse mesophases, as expected from the molecular geometry of the polymer, is not observed.

Lyotropic liquid crystalline phase behaviour of a monomeric and a polymeric monosaccharide amphiphile in aqueous solution

Monomeric and polymeric amphiphiles were synthesized which exhibit lyotropic liquid crystalline phases in aqueous solution. The hydrophobic group of the monomeric surfactant is a dodecane-group esterified with acrylic acid. The hydrophilic unit is a monosaccharide derivative. By radical polymerization the monomer (N-D(-)-gluco-N-methyl-(12-acryloyloxy)-dodecane-l-amide) is converted into the corresponding polymeric surfactant. The monomer as well as the polymer exhibit a lyotropic 1.c. phase of lamellar structure. Owing to the polymerization the regime of the lamellar phase is greatly enlarged for the polymer, compared to the monomeric sufactant. These results confirm earlier investigations on non-ionic ethylene-glycol surfactants.