Synthesis and physic-chemical properties of anion–nonionic surfactants under the influence of alkali/salt

This paper presented a series of anion–nonionic surfactants with different hydrophobic tails and hydrophilic head-groups. Changes in physic-chemical properties of these products and their influencing factors were carefully studied. The CMC (critical micelle concentration) ranges from 1.1 × 10−2 mass% for NPS-4 to 4.8 × 10−2 mass% in the case of NPS-10. The values (γcmc) of surface tension at CMC are from 31.62 mN m−1 for NPS-4 to 44.50 mN m−1 for AES-9. Maximum surface excess concentration (Γmax) was more than 0.73 × 10−6 mol m−2and minimum area per molecule at the water/air interface (Amin) was less than 2.270 nm2 molecule−1. Results show that CMC and γcmc were efficiently improved, and the ability of reducing equilibrium interface tension (IFTeq) was weakened due to the increasing of repeat units. The study demonstrated that the detergents with the additional rigid group in the hydrophobic tail had a higher CMC than those with the alkyl chain. In addition, we figured out some IFTeq results of the surfactants solution under the influence of alkaline/salt. Ultra-low IFTeq can be obtained only when the concentration is greater than the optimal value of alkaline/salt. Dynamic interface tension (IFTdy) was analyzed and a hypothetical mechanism was used to explain the interesting phenomena IFTdy.