Michael C. Holmes

Intermediate phases of surfactant-water mixtures

Intermediate phases have been identified in some concentrated surfactant-water mixtures between hexagonal and lamellar phases, where usually bicontinuous cubic phases would be expected. It has been shown that they are anisotropic in structure, birefringent and more fluid than bicontinuous cubic phases. There is still discussion in the literature as to which structures are possible. The observed or proposed structures divide topologically into three types, according to symmetry: rectangular or ribbon structures, layered mesh structures and bicontinuous structures. In the past year, structures of mesh phases have been presented together with their epitaxial relationships with adjacent phases.

Novel intermediate phases in an ionic fluorocarbon surfactant/water system

This small angle X-ray scattering study of the lyotropic phases in the binary tetramethylammonium perfluorodecanoate/water system shows that there are no classical lyotropic mesophases present. Much of the liquid crystal region is taken up with a random mesh intermediate phase, Mh1(0) and a phase with rhombohedral symmetry which is probably a rhombohedral mesh intermediate phase, Mh1(R3m). This behaviour is unusual since previously these mesh phases have been associated with hydrocarbon surfactants or diblock copolymer melts. All the mesophases found have non-uniform interfacial curvature and a sufficiently strong inter-layer interaction to ensure the long range correlation of structures in some phases.

Examination of the structural features necessary for mesophase formation with aroylhydrazinato-nickel(II) and -copper(II) complexes

N-Methylidene complexes and a series of N-alkylidene- and N-arylalkylidene-aroylhydrazinato-nickel(II) and -copper(II) complexes were synthesized in high yield and their mesomorphic nature studied. Only the N-methylidene complexes gave mesomorphic compounds as the larger N-alkylidene or N-aralkylidene groups probably prevented mesophase formation due to increased molecular broadening effects. The nickel(II) complexes were found to be highly stable even in the isotropic phase and generally gave wide liquid-crystalline temperature ranges. This contrasted with the very narrow temperature ranges of the copper(II) complexes, which rapidly decomposed in or just before attaining the isotropic phase.

Mesh phases in tetramethylammonium perfluorodecanoate–water ternary systems

The evolution of the phase behaviour and lyotropic phase structures formed in the tetramethylammonium perfluorodecanoate (C10TMA)–water system upon the addition of a third component (tetramethylammonium chloride (TMACl) or 1H, 1H-perfluoro-1-decanol (C10ol)) have been studied using optical polarizing microscope, 2H NMR and small angle X-ray scattering (SAXS) in order to understand the correlated mesh phase with Rm space group. With increasing concentration of both additives, the Mh1(Rm) phase changes to a random mesh phase Mh1(0) via a two phase region. The structure of the Mh1(Rm) phase is essentially unaltered with addition of TMACl or C10ol until the phase change to Mh1(0). With higher additive concentration, the water fraction within a mesh layer of the Mh1(0) phase is decreased. It is proposed that the transition from the Mh1(0) to Mh1(Rm) phases is driven by a reduction in the electrostatic interlayer interaction enabling non-electrostatic repulsive interactions to dominate. This is because of the strong association of the TMA counter ion with the head group region, the increase of water within the mesh layers and the decrease in separation of the mesh layers in the Mh1(Rm) phase. It is also shown that the hydrophobic counter ion has to be small relative to the surfactant for both mesh and correlated mesh to occur.

The thermotropic liquid crystals formed by anhydrous sodium ricinoleate

Abstract The polymorphism of sodium ricinoleate has been examined using differential scanning calorimetry, optical microscopy and low angle X-ray diffraction. There are three low temperature phases, separated by small transition enthalpies, where the molecules are packed in layers with little molecular disorder. At high temperatures (>160°C), two semi-molten mesophases are formed. Both have distinct optical textures under polarizing microscopy, that of the highest temperature phase being the typical fan pattern of a hexagonal phase. X-ray diffraction shows that this phase is comprised of hexagonally packed oblate spheroids arranged in layers according to an ABAB type pattern. It has not been reported previously for surfactants. The head groups form the cores of the spheroids with molten alkyl chains filling the remaining space. In the lower temperature mesophase, the head groups pack into rods joined in fours to give layers of a tetragonal array. The layers stack to give a body centred tetragonal structur...

Hydrophobic counter ion effects on the formation of mesh and reversed phases in the perfluorodecanoate/water system

The tetramethylammonium perfluorodecanoate (C10TMA)/water system forms both random, Mh1(0) and correlated mesh, Mh1(Rm) phases over a wide range of concentration and temperature. Whilst the random mesh phase is found in the ammonium homologue, the extensive correlated mesh phase seems to be a result of the hydrophobic nature of the tetramethylammonium (TMA) counter ion. In order to explore the reasons for the occurrence of these mesh phases and the effects of hydrophobic counter ions on phase structure the counter ion has been substituted by a series of increasing hydrophobicity namely butyltrimethylammonium (BTMA), dibutyldimethylammonium (DBDMA), and methyltributylphosphonium (MTBP). The phases and their structures were identified by small angle X-ray scattering. Increasing counter ion hydrophobicity causes a change from mesh, to lamellar, and finally to reversed phases. All the hydrophobic counter ions are strongly bound to the water/fluorocarbon interface and, in the case of those with butyl chains, there is penetration of between 50 and 60% of the total number of counter ion methyl groups into the fluorocarbon region of the lamellar phase. These bound counter ions reduce the accessibility of the head group region to solvent water. As the number of butyl chains on the counter ion increases the lamellar phase is progressively lost and is replaced by a reversed micelle phase either as a single phase or as part of an extensive two phase region.

Aroylhydrazinatonickel(II) and copper(II) complexes; a new class of metallomesogens

A series of aroylhydrazinato-nickel(II) and -copper(II) complexes have been synthesised in high yield and shown to form a new class of metallomesogens, which form smectic C and nematic phases; the nickel(II) complexes were found to be highly stable even in the isotropic phase, which contrasted with the rapid decomposition of the copper(II) complexes soon after entering the liquid crystalline phase.

Alkyl- and Alkoxy- Aroylhydrazinato Metal Complexes - Unusual X-Ray Diffraction Within the Smectic C Phase

Abstract Two homologous series of novel nickel containing liquid crystalline complexes have been synthesised 1-3. The effect of changing chain length and chain type on phase behaviour is reported here. Optical microscopy, DSC and x-ray scattering is used to identify the phase structures. X-ray scattering from the smectic C phase shows unusual diffraction patterns with the intermolecular scattering larger than would be expected.

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...