Thermotropic Liquid Crystalline Character and Vesicular Properties of Some Functionalized Long-Chain Di-n-dodecyl Quaternary Ammonium Salts

Abstract

In several reports it has been shown that amphiphilic molecules, including phospholipids, which aggregate in solution to form micelles, vesicles or liposomes also exhibit thermotropic liquid crystalline phases. In conjunction with our recent work on the synthesis and characterization of vesicle-forming monomeric and polymerized allyl and diallyl di-n-alkyl quarternary ammonium salts, a series of analogously functionalized derivatives has been prepared. Di-n-dodecyldimethyl quarternary ammonium bromide was employed as the parent compound. The new quarternary ammonium salts were formed by replacing one or both of the methyl groups in the parent compound by groups such as—CH₂—CH=CH₂,—CH₂CH₂OH,—CH₂COOH,—CH₂CH₂COOH, or—CH₂CH₂CH₂CN. The existence of liquid crystalline phases in these quarternaries was established by optical microscopy while transition temperatures as well as thermodynamic parameters were determined by DSC. Some of these compounds when dispersed in water and sonicated ultimately formed vesicles the structure of which was observed by electron microscopy. The effect of the various functional groups on the liquid crystalline phase behavior of these compounds exhibits a well defined variation. However, no systematic variation has been observed on the ability of these same functional groups to affect vesicles formation.

Keywords:

• thermotropic liquid crystals
• vesicles
• surfactants
• quaternary ammonium salts
• optical microscopy
• differential scanning calorimetry