Wormlike micelles and gels reinforced by hydrogen bonding in aqueous cationic gemini surfactant systems

Abstract

The viscoelastic properties of the wormlike micellar solutions of 2-hydroxyl-propanediyl-α,ω-bis(dimethyldodecylammonium bromide) and 2-hydroxyl-propanediyl-α,ω-bis(dimethyltetradecylammonium bromide), abbreviated as 12-3(OH)-12 and 14-3(OH)-14, respectively, have been investigated using steady state and frequency sweep rheological measurements. For comparison, the wormlike micellar solutions of propanediyl-α,ω-bis(dimethyldodecylammonium bromide) (referred to as 12-3-12) were also examined on an identical level. Steady state rheological measurements revealed that at low concentrations, the zero-shear viscosity of the 12-3(OH)-12 system was far higher than that of the 12-3-12 system. From dynamic rheological data, the characteristic parameters were drawn out using the Maxwell fluid model and the viscoelastic rheological behavior was discussed according to the living polymer model proposed by Cates et al. The results showed that 12-3(OH)-12 formed longer wormlike micelles than 12-3-12. With increasing the alkyl tail length, 14-3(OH)-14 produced higher viscoelasticity than 12-3(OH)-12 and even formed a gel-like solid at 50 mmol L⁻¹. These were attributed to the role of the intermolecular hydrogen bonding which occurred between the hydroxyl substituted spacers of m-3(OH)-m, where m represents the number of carbon atoms in the alkyl tail. Increase of the alkyl tail length was favorable for enhancement of the hydrogen bonding interaction and thus greatly promoted the micellar growth.