Lipidic Protic Ionic Liquid Crystals

Abstract

Protic ionic liquids (PILs) based on lipidic compounds have a range of industrial applications, revealing the potential of oil chemistry as a sustainable basis for the synthesis of ionic liquids. PILs of fatty acids with ethanolamines are here disclosed to form ionic liquid crystals, and their mixtures with the parent fatty acids and ethanolamines display a lyotropic behavior. Aiming at characterizing their rheologic and phase behavior, four ethanolamine carboxylates and the mixtures used for their synthesis through a Bronsted acid base reaction are investigated. Their phase diagrams present a complex multiphase profile, exhibiting lyotropic mesophases as well as solid liquid biphasic domains with a congruent melting behavior. These PILs present a high self-assembling ability and a non-Newtonian behavior with yield stress in the liquid crystal mesophase. The appearance of lamellar and hexagonal structures, with probably normal and inverted configurations in the mixtures, due to the formation of the PILs is responsible for the high viscoelasticity and notable nonideality that is mainly ruled by hydrophobic/hydrophilic interactions. Considering their renewable origin, the formation of liquid crystalline structures, in addition to the non-Newtonian behavior and ionic liquids properties, and the mixtures here great potential, and numerous applications may be foreseen.