Self-assembly and rheological behavior of novel anionic and cationic gemini surfactants

A series of novel carboxylate anionic gemini surfactants SL-n-SL (n = 3, 6, 10) were synthesized, and their rheological properties with a cationic gemini surfactant (12-3(OH)-12) were investigated in this paper. The surface-active properties of SL-n-SL (n = 3, 6, 10) were determined by steady-state fluorescence and a surface tension method. The effect of SL-n-SL on the rheological properties of 12-3(OH)-12 was characterized by steady-state and dynamic rheological measurements. The results indicated that the CMC of SL-n-SL decreased with increased spacer length, and the surfactant with a shorter spacer had a stronger ability to reduce the surface tension of water and had a smaller occupation area at the air/water interface. The addition of SL-n-SL in a 12-3(OH)-12 solution enhanced the viscoelasticity of the 12-3(OH)-12 solution, and worm-like micelles were formed in the mixed solutions. The spacer length had a significant effect on the rheological properties of SL-n-SL/12-3(OH)-12 mixed systems. The SL-n-SL with a shorter spacer had a stronger capacity to promote the formation of worm-like micelles due to the perfect match between the head groups of SL-n-SL and 12-3(OH)-12.