Rheology of wormlike micelles in mixed solutions of cocoamidopropyl betaine and sodium dodecylbenzenesulfonate
2015
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 0.083M and SDBS from 0.057 to 0.072M. The synergism is significant when the concentrations of CAPB in the solution is 0.083M and SDBS is 0.063M. 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 η0, plateau modulus G0 and relaxation time τ it is evident that the highest values were achieved for 0.063M 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 0.067M the wormlike micellar network is formed. Above concentration of CAPB 0.067M the network is completely constituted, however it disappeared completely below 0.05M.
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