Abstract:

Taking stearic acid as the raw material, N-（2-（dimethylamino） ethyl） stearamide （C18N2N） was synthesized. A new surfactant was prepared by mixing C18N2N and cinnamic acid （TA） with fixed ratio. This surfactant was formed by non-covalent electrostatic interactions, which avoided complicated synthetic procedures. The surface activity and rheological properties of the surfactant were investigated with a surface tensiometer and a rheometer. The critical micelle concentration （cmc） and the surface tension at cmc （γ_cmc） of the surfactant were 0.11 mmol/L and 32.4 mN/m, indicative of strong aggregation and adsorption ability. The maximum amount adsorbed （Γ_max） and the minimum molecular area occupied （A_min） were 2.77 μmol/m² and 0.6 nm². Wormlike micelles were formed at the concentration of 25 mmol/L. When the concentration was over 100 mmol/L, the zero-shear viscosity （η₀） abruptly increased and then reached the maximum value for the surfactant of C18N2N /TA containing 150 mmol/L TA. The solution viscosity was as high as 1 761.38 Pa·s. The effects of temperature on the rheological behavior were also considered. With the increase of temperature, the viscosity gradually increased. And when the temperature reached 40 ℃, η₀ of the solution with the concentration of 100 mmol/L achieved the maximum value of 1 370.386 Pa·s. When the temperature continued to rise, η₀ began to decrease with further increasing temperature. A remarkable viscosity of 305.55 Pa·s was still remained at 50 ℃. The viscoelastic solutions showed good temperature resistance and shear resistance. The surfactant solutions applied as the fracturing fluid were also investigated. This surfactant also showed excellent sand-carrying performance, and the settling rate of the sand was merely 0.26 cm/min. This surfactant could be simply prepared and showed excellent performance, which expanded the preparation and application field of novel surfactants.

Key words: electrostatic interaction, stearic acid, viscoelasticity