Rheology of wormlike micelles in mixed solutions of cocoamidopropyl betaine and sodium dodecylbenzenesulfonate

The interactions between anionic and zwitterionic surfactants have been studied on different compounds systems at varied pH, temperature and concentration of anionic surfactant. These systems contained cocamidopropyl betaine, CAPB(C19H38N2O3), and sodium dodecylbenzenesulfonate, SDBS (C18H29NaO3S) forms wormlike micelles in the concentration range of CAPB equal to 0.083 M and SDBS from 0.057 to 0.072 M. The synergism is significant when the concentrations of CAPB in the solution is 0.083 M and SDBS is 0.063 M. The wormlike micellar solutions show a viscoelastic characteristic and at low shear frequencies can be described by the Maxwell model with a single stress relaxation. A pronounced temperature effect on the wormlike micellar structures can be observed by rheological studies. With an increase in temperature, the samples become less structured due to shortening of the micelles. From measurements at zero shear viscosity eta(0), plateau modulus G(0) and relaxation time tau it is evident that the highest values were achieved for 0.063 M SDBS solution. The rheological behavior of the CAPB/SDBS system strongly depends on the pH of a solution, which reflect the pH-dependence of the structural transformation of wormlike micelles. This is caused by the change in the acidity around the carboxylic acid headgroups as a function of pH. Studies of CAPB/SDBS mixtures at constant molar ratio of both surfactants (1.32) revealed that in the range of CAPB from 0.05 to 0.067 M the wormlike micellar network is formed. Above concentration of CAPB 0.067 M the network is completely constituted, however it disappeared completely below 0.05 M. (C) 2015 Elsevier B.V. All rights reserved.