Lipophilic Tail Architecture and Molecular Structure of Neutralizing Agent for the Controlled Rheology of Viscoelastic Fluid in Amino Acid-Based Anionic Surfactant System

Abstract

The amino acid-based anionic surfactant, N-dodecanoylglutamic acid (designated as LAD), when neutralized with 2-aminoethanol (MEA), 2,2'-iminodiethanol (DEA), or 2,2',2''-nitrilotriethanol (TEA) forms globular type of micelles in aqueous system at 25 °C, and the viscosity of each solution is very close to that of pure water. Addition of cationic surfactants, e.g., tetradecyltrimethylammonium bromide (TTAB) or hexadecyltrimethylammonium bromide (CTAB), induced a sphere-to-rod transition, and the micelles grew axially, resulting in formation of viscoelastic wormlike micelles that could be described by a Maxwell model. The viscosity was ca. 5 orders of magnitude as large as that of water. The viscosity maximum was observed in zero-shear viscosity (η0) curves, and there was a phase separation to liquid crystal phase at higher cosurfactants concentration. The η0 curve shifted toward lower cosurfactant concentration, and the value of maximum viscosity (η0(max)) decreased by reducing lipophilic moiety of cosurfactant. Furthermore, the value of η0(max) decreased with decreasing the number of ethanol content per molecule of neutralizing agent. The η0 decays exponentially with the rise of temperature, following the Arrhenius type of behavior. However, addition of dodecyltrimethylammonium bromide (DTAB) increases viscosity only slightly; viscoelastic wormlike micelles are not formed.