Interfacial dilational properties of betaines and sulfonate mixtures: Effects of alkyl chain length

The dilational rheological properties of anionic/zwitterionic surfactant mixtures of sodium dialkyl sulfosucciantes (SNN10) and three betaines (SB12, SB14 and SB16) have been measured by means of a drop shape analysis method. It is established that SNN10 shows high interfacial activity due to tighter packing of the hydrophobic chains and the film properties of SNN10 is dominated by the in-interface process. When betaines and SNN10 are purposely mixed, the SNN10 molecule would be likely to displace the betaines molecule at the interface, and the displacement depends on the molecular structure of betaines: the shorter the hydrophobic chain, the easier it is to be replaced. In addition, adding SB16 to SNN10 would increase strength of the interfacial film at high surfactant concentrations.