Keith Radley

Cholesteric Behaviour in Lyotropic Liquid Crystals

Abstract Cholesteric lyotropic liquid crystals prepared from the potassium salts of N-hexadecanoyl-l-proline and N-dodecanoyl-l-alanine have been studied as mixed systems with tetradecyltrimethylammonium bromide. The twist, induced by the chiral centre, was studied as a function of the mole fraction, X, of chiral amphiphile in total amphiphile. It was found that the twist showed a maximum for the neutrally charged mesophases (X = 0.5) and that for the pure chiral systems (X = 1.0) the alaninate system showed a much larger twist than the corresponding prolinate material. The results were discussed in terms of a micelle distortion model for the generation of cholesteric behaviour. Alkali metal ion binding to the carboxylate groups of these amphiphiles was investigated and the results compared to those for the dodecanoate amphiphile. A three site model of binding was used in order to determine the number of liganding amphiphiles in the pure anionic mesophase (X = 1.0). It was found that the number decreased ...

The Interactions of Methylated Ammonium lons in Lyotropic Liquid Crystalline Solution

Abstract The mono-, di- and trimethylammonium ions have been investigated in the lyotropic liquid crystalline system of potasium dodecanoate/alkyltrimethylammonium bromide. The results indicate that non-bonded forces deriving from the anisotropy of the medium contribute little to the alignment of these ions but that forces derving from binding of the ions to the dodecanoate headgroups provide the major mechanism for the imposition of alognment. A three-site model of ion binding was found to be sufficient to describe the change in dipolar couplings as the micellar surface charge was varied. It was also found that anomolous changes in ratios of coupling constants were acconted for by three site model of binding.

A proton NMR study of partially oriented phenylsulphonate in various amphiphilic nematic liquid crystals

Abstract Preliminary proton nmr studies have been made on the partially oriented phenylsulphonate ion (present as the counterion) in various amphiphilic nematic phases. The changes in the sign of the degree of orientation of the phenylsulphonate ion are consistent with the micelle structure and the sign of the diamagnetic anisotropy of the various phases.

A Proton NMR Study of the Methyl Phosphonate lon in an Amphiphilic Nematic Liquid Crystal, when the Sign of the Diamagnetic Anisotropy Changes

Abstract An abrupt change in the proton nmr dipolar couplings in methylphosphate and phenylsulphonate ions is induced in an amphiphilic nematic liquid crystal by the inclusion of the phenylsulphonate ion as the counterion. It is concluded these sign changes are due to a corresponding change in the sign of the diamagnetic anisotropy induced by the aromatic character of the phenylsulphonate ion, and not necessarily ion binding.

Birefringence Measurements in Lyotropic Nematic Phases

Abstract Birefringence measurements have been made on lyotropic nematic phases prepared from the detergent tetradecyl-trimethylammonium bromide. Assignments for the sign of the birefringence of the nematic disk and cylindrical phases of both positive and negative diamagnetic anisotropy have been made. It is suggested the classification of lyotropic nematic phases, based on the sign of the diamagnetic anisotropy or any other physical parameter, should be dropped. Classification should be in terms of thermodynamic properties, i.e. micelle structure.

A Binary Nematic Lyotropic Mesophase in the Decylammonium Bromide/D2O Amphiphilic System

ABSTRACTA binary lyotropic nematic phase is reported for the detergent system of decylammonium bromide with D2O. Deuterium nmr spectroscopy and polarizing microscopy were used to investigate the system. The nematic phase was found to have a disk shaped micelle structure with negative diamagnetic anisotropy.

A Smectic-A Type Lamellar Amphiphilic Lyotropic Liquid Crystal Phase

Abstract Preliminary polar micrographic studies suggest in the binary cesium perfluoro-octanoate/heavy water system more than one smectic type phase exists in the lamellar region. The lamellar phase on the low water side of the nematic was examined and from the micrographic textures it is suggested the structure of the phase is related to the classical thermotropic smectic-A SA mesophase.

The Partial Orientation of 2-Amino-Ethanol in a Mixed Detergent Amphiphilic Nematic Liquid Crystal

AbstractThe proton NMR of 2-amino-ethanol is studied in a mixed detergent amphiphilic nematic liquid crystal. The resulting dipole coupling constants are interpreted in terms of a solute bridge between two detergent head groups in the anionic detergent and the single -OH group interacting with a detergent head group in the cationic detergent.