Thermo-Thickening Viscoelastic Solutions Formed From a Bicephalous Surfactant Containing a Long Saturated Alkyl Tail

The unique molecular structure of the surfactant is expected to produce solutions with distinctive rheological properties. A novel cationic surfactant, N¹,N¹,N¹,N³,N³-pentamethyl-N³-(3-(3-docosanamidopropanamido)propyl)propane-1,3-diammonium dibromide (C22-β-Ala-DQA), was synthesized. C22-β-Ala-DQA differs from conventional surfactants in that it contains a long saturated hydrophobic tail, two amide groups, and two quaternary ammonium head groups. It exhibits a low Krafft temperature (< 1 °C) and high aqueous solubility at 25 °C. When combined with sodium palmitate (SP), it forms transparent, viscoelastic solutions exhibiting pronounced elasticity at low concentrations across a broad range of molar ratios. Cryo-transmission electron microscopy (Cryo-TEM) imaging confirms the formation of ultralong wormlike micelles with a uniform cross-sectional diameter of ∼7 nm. Notably, the C22-β-Ala-DQA:SP system at a 1:1.5 molar ratio demonstrates significant thermo-thickening behavior between 30 and 80 °C. The zero-shear viscosity (η₀) of a 75 mM solution reaches a maximum of 632.5 Pa·s at 80 °C, which is unusually high for viscoelastic surfactant systems. This behavior is attributed to the dehydration of the large hydrophilic headgroup region of C22-β-Ala-DQA at high temperatures, which promotes further elongation of wormlike micelles. Surfactants with long saturated alkyl tails were used to prepare stable wormlike micellar solutions. These results provide valuable guidance for designing stable wormlike micellar systems using ultralong alkyl tails. Moreover, the proposed system shows potential for applications in fracturing fluids or other smart fluid technologies.