Wormlike Micelles in Mixed Amino Acid‐Based Anionic Surfactant and Zwitterionic Surfactant Systems

Abstract

AbstractThe formation of wormlike micelles in aqueous solutions of an amino acid‐based surfactant, sodium lauroyl sarcosinate (LS) and a zwitterionic surfactant, cocamidopropyl betaine (CAPB) has been investigated. Holding the total concentration of LS and CAPB constant at 12 wt%, the synergistic effects of mass ratio of CAPB and LS and pH of the micelle solution on rheological behaviors of CAPB/LS micelles were studied. The viscosity of CAPB/LS micelle systems with a mass ratio from 4:8 to 9:3 increases to maximum values and then decreases as pH increases from 4.0 to 5.6. The maximum viscosity of the transparent CAPB/LS micelle solution is nearly 5500 mPa·s with a mass ratio of CAPB/LS = 8:4 at pH 5.10. It is suggested that the proper pH for CAPB and LS to form wormlike micelles should be close to the isoelectric point of the CAPB/LS solution. The results of thixotropy measurements show that the appropriate mass ratio of CAPB/LS can improve the stability of the network structure of wormlike micelles. In addition, viscosity curves of CAPB/LS wormlike micelles follow a nonlinear co‐rotational Jeffreys model, and the linear viscoelasticity of CAPB/LS wormlike micelles can be described by a linear viscoelastic Jeffreys model. The network of wormlike micelles is confirmed by Cryo‐TEM images.