Abstract
The last five years’ achievements in the synthesis and investigation of thermotropic ionic liquid crystals are reviewed. The present review describes the mesomorphic properties displayed by organic, as well as metal-containing ionic mesogens. In addition, a short overview on the ionic polymer and self-assembled liquid crystals is given. Potential and actual applications of ionic mesogens are also discussed.
Highlights
The liquid crystalline state is a state of matter in which orientational order is maintained, but, to liquids, gases and amorphous solids, positional order in the molecular arrangement is lost [1]
The calamitic ionic molecules are constructed from a positively charged head and long hydrocarbon tails. This structure favors the formation of smectic lamellar phases via a combination of the electrostatic ion-ion interactions, stabilizing the structure of a layer, and Van-der Waals forces, organizing the arrangement of hydrophobic tails between ionic layers
Among a huge variety of so far obtained ionic mesogens, most of them are derived from the substituted cationic imidazolium framework, ammonium, phosphonium, pyridinium and other charged mesogenic cores have been employed for the design of ionic mesogenic molecules
Summary
The liquid crystalline state is a state of matter in which orientational order is maintained, but, to liquids, gases and amorphous solids, positional order in the molecular arrangement is lost [1]. Incorporation of imidazolium ion functionalities into the paraffinic side-chain termini of a triphenylene derivative resulted in the stabilization of the columnar mesophase (see below) [14] Another unique feature of the liquid crystals, formed by ionic amphiphilic molecules, is their spontaneous homeotropic alignment on a glass surface. The ionic amphiphilic mesogenic molecule consists of a positively charged cationic head and long-chain hydrophobic alkyl substituent. These repulsive and attractive electrostatic forces, Van-der Waals hydrophobic interactions and hydrogen bonding contacts, unique smectic type molecular arrangements are found in ionic liquid crystals. The coefficient after the brackets displays a ratio between an amine dendrimeric core and an acidic second component in a self-assembled system (see Scheme 24)
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