Ionic liquid crystals.

Surfactant-water liquid crystal phases

Molecular self-organization of amphotropic liquid crystals

Data on the synthesis, structures and properties of ionic, coordination, organometallic and organoelement compounds with liquid-crystal properties are surveyed. The substances examined are new in the chemistry of the liquid-crystal compounds. Their potential applications are described. The bibliography includes 211 references.

http://iopscience.iop.org/article/10.1070/RC1993v062n04ABEH000019/pdf

Metal-containing liquid-crystal phases

The thermal behaviour of divalent and higher valent metal soaps: a review

BECAUSE of the strong long range forces acting between the molecules, molten salts constitute a highly distinctive class of liquids. Up to now, however, the variety of stable ionic melts studied has been largely confined to the simplest ions, such as inert gas type halides, nitrates, and network forming oxides and fluorides. Through the establishment of procedures for achieving chemical stability in molten salts with organic anions1,2, the variety of these ionic melts available for investigation and use is potentially greatly increased. Distinctive microstructures and unusual properties might be expected for at least some of these liquids. We illustrate these possibilities here with new observations on liquid crystals, stable over a wide interval of temperatures, formed by melts of sodium isovalerate and related salts. This group of substances differs in several ways from well known classes of liquid crystals, which include chiefly rod-shaped molecules, with long rigid parts3.

Liquid Crystals in Molten Salt Systems

Procedures are described for maintaining good chemical stability in molten alkali-metal carboxylates, up to about 350 degrees C. Valid physical measurements can be made and the fluids can be used up to about this temperature, above which spontaneous decomposition of the anions is difficult to repress. Molten sodium propionate has a useful liquid range of about 60 degrees C and sodium isobutyrate of about 90 degrees C. Sodium n-butyrate transforms into a 'liquid crystal' at about 250 degrees C and into the isotropic liquid at 324 degrees C. For sodium isovalerate corresponding transition points are respectively 188 and 280 degrees C. Thermodynamic measurements are reported of volume and enthalpy changes at transition and melting points. Transport parameters measured include the viscosity and the electrical conductivity. The viscosity of these ionic melts undergoes a steep decrease at the transition from mesomorphic to isotropic liquids. Jumps in ionic conductivity are found both at the melting and clearing points. Even for the isotropic liquids, the ratio of viscosity to electrical conductivity is exceptionally high, compared with the other ionic melts. Mechanisms of melting for these ionic solids are discussed.

Molten Fatty Acid Salts as Model Ionic Liquids. I. Thermodynamic and Transport Parameters of Some Organic Sodium Salts

At their first melting points T f a number of organic salts pass into mesophases which show ‘liquid crystal9 behaviour. Structural studies are described on the mesophases of sodium w-butyrate (mesophase range 252-324 °C) and sodium isovalerate (mesophase range 188- 280 °C). X-ray findings indicate that much of the detailed molecular ordering in the crystalline states of these salts is lost at T f except for the dominant ‘long spacings9 between successive layers of cations. These are probably packed adjacent to charged carboxyl groups. ‘Long spacings9 persist until the second melting point T cl is reached, when optically isotropic melts are formed. Although closely similar in some ways, this pair of salts exhibits interesting differences of thermal behaviour in the mesophases, with respect to the temperature dependence of their long spacings, and with respect to certain optical properties. These characteristics are tentatively interpreted in terms of differences of molecular packing of the alkane ‘tails’ of the anions. Evidence has also been obtained of preferred molecular orientation effects in layers of melt adjacent to walls of Lindemann glass, used to contain the mesophases for X-ray studies. In these layers ordering of the long-spacings persists for a few degrees above the clearing temperatures T cl attributed to the mesophase in bulk.

Structure of Organic Ionic Melt Mesophases

Considerable frequency dispersion of electrical conductivity has been observed in the liquid crystal phases of organic ionic melts, depending on their molecular structure and domain size. Dispersion began to be detectable above about 10000 Hz for sodium isovalerate (in which there are large domains), and above about 2000 Hz for sodium n-butyrate (domains about 0.1 mm across). Neither molten salt showed dispersion in a middle range of frequencies (between 1000 Hz and 100 Hz). Previous researches had shown a marked diamagnetic anomaly of molten organic salts when these are cooled through their mesophases, while applying static magnetic fields. The kind of response observed can be attributed to interaction between 'liquid crystal' domains and the applied fields. A related effect has now been observed when a static magnetic field (approx. 10 kG) was applied in the course of the above measurements of electrical conductivities. With sodium isovalerate melts, a magnetic field applied perpendicular to the electric field reduced by a factor of two the drop in electrical conductivity when the isotropic melt passed into its mesophase. No effect $(\not>2\%)$ was detected with sodium n-butyrate under the same conditions.

Some Novel Electromagnetic Effects in the Conductivity of Molten Organic Salts

Anhydrous sodium propionate melts at 287 °C. In order to investigate model chemical reactions of organic ionic melts generally, decomposition reactions of the propionate ion have been studied under various conditions:

J. J. Duruz

Papers

Liquid Crystals in Molten Salt Systems

Molten Fatty Acid Salts as Model Ionic Liquids. I. Thermodynamic and Transport Parameters of Some Organic Sodium Salts

Structure of Organic Ionic Melt Mesophases

Some Novel Electromagnetic Effects in the Conductivity of Molten Organic Salts

Decomposition reactions of sodium propionate