Formation of wormlike micelles with natural-sourced ingredients (sucrose fatty acid ester and fatty acid) and a viscosity-boosting effect induced by fatty acid soap

We have investigated the formation of a viscoelastic wormlike micellar solution with natural-sourced materials such as sucrose monopalmitate (C16SE) and fatty acid (FA). Zero-shear viscosity of 10 wt% aqueous solutions of C16SE and lauric acid (LA) increased with the increase in the C16SE fraction to a certain level but it decreased after a maximum value. Viscous solutions having almost maximum zero-shear viscosity showed non-Newtonian behavior and had Maxwell-type mechanical properties. When a small fraction of LA of the water/C16SE/LA system was substituted with sodium laurate (SL), the maximum zero-shear viscosity increased by nearly one order of magnitude from the original system due to a decrease in the diffusion constant of the wormlike micelles. With further substitutions of LA with SL, the zero-shear viscosity decreased because the highly hydrophilic fatty acid soap makes elongated micelles shorter.