Thermodynamics Research Center / ThermoML | Fluid Phase Equilibria

ABSTRACT

Rheological experiments of cetyltrimethylammonium salicylate (C16TASal) solution were carried out on the micellar solutions as a function of surfactant concentration and temperature. This system forms short, rod-like micelles at concentrations of 1-15% as determined by transmission electron microscopy. Rheological behavior at low concentration displays gel-like behavior up to 3%, while it follows Maxwell fluid behavior with a single stress relaxation time above 3%. By the single crystal diffraction experiment, it can be found that the gel-like and Maxwell-like viscoelasticities originate in a three-dimensional net-work formed by hydrogen bond linkages between short rod-like micelles, connecting carboxyl groups of salicylate anions and water molecules. The high viscosity is from the linkages between short rod-like micelles rather than from entangled long micelles. The electronic conductivities of C16TASal solution of dilute solution and semi-dilute solution have been studied. The conductivity-concentration curves of dilute solution show two breaks which correspond to two characteristic concentrations of C16TASal solution. The first break point corresponds to the critical micelle concentration (cmc). The second break point corresponds to the transition concentration (Ct), where the system begins to form rod-like micelles. The conductivity of semi-dilute solution slightly decreases with the increasing temperature.