Measurement of Dynamic and Equilibrium Surface Tension of Surfactant Solutions by the Maximum Bubble Pressure Method

Surfactant solution systems are encountered in many different applications, including as a method to enhance the nucleate boiling performance of water. Characterizing the attendant interfacial phenomena requires precise predictions of their surface tension relaxation behavior. In this study, both the dynamic and equilibrium surface tension behavior of aqueous surfactant solutions has been investigated using the maximum bubble pressure method. The surface tension is measured as a function of concentration at room (23°C) and elevated (80°C) temperatures. The critical micelle concentration (c.m.c.) of each surfactant is calculated from their respective equilibrium adsorption isotherms. The dynamic surface tension measurements are obtained at a surface age of 50 ms, which simulates conditions typically encountered during nucleate boiling of water. Two anionic surfactants, Sodium Dodecyl Sulfate (SDS) and Sodium Lauryl Ether Sulfate (SLES), two cationic surfactants Dodecyl Trimethyl Ammonium Chloride (DTAC) and Ethoquad O12/PG, and one non-ionic surfactant Triton X-100 have been used. SLES, Ethoquad O12/PG and Triton X-100 have, respectively, 3, 2, and 9–10 degrees of ethoxylation, which tends to alter the interfacial rheology. The σ–C isotherms show marked variation based on the surfactant ionic nature and the number of ethoxy groups present, along with the effects of temperature, with considerably less surface relaxation under dynamic conditions compared to those at equilibrium.