Effect of Micelle Structure on the Viscosity of Sulfonate Gemini Surfactant Solution

Abstract

In order to optimize the thickening performance of clean fracturing fluid, a series of sulfonate Gemini surfactants (DSm-s-m) were synthesized and identified by FTIR, $^{1}\hbox {HNMR}$, and $^{13}\hbox {CNMR}$. The surface tension curve was obtained by testing the surface tension of the surfactant at different concentrations, and the viscosity of sulfonate Gemini surfactant solution was measured by rheometer and investigated through changing the molecular structure. The microstructures of the solution were studied by SEM. The experimental results indicated that the CMC of the surfactant decreased with increasing the length of the hydrophobic chain. Moreover, the viscosity of sulfonate Gemini surfactant changed with the carbon number (s or m) of spacer group and hydrophobic chain, and the DS18-3-18 had superior viscosity behavior. The viscosity of the DS18-3-18 solution decreased with the temperature increase but was still $13.25 \hbox { mPa}\cdot \hbox {s}$ at $90\,{^{\circ }}\hbox {C}$. The microstructures of DS18-s-18 solution demonstrated that the micelles of the DS18-s-18 solution changed from spherical to layer like and finally to commixture of spherical/layer like with increasing the carbon number of spacer group ($s=2,3,4$), and the viscosity of the solution increased firstly and then decreased correspondingly. The number of sheet micelles and bulk density in DS18-3-18 solution decreased with the increase of temperature, causing the decrease of the viscosity in solution. However, the intact sheet micelles still existing in solution at $90\,{^{\circ }}\hbox {C}$ meant that the DS18-3-18 had prominent temperature-resistant viscosity behavior. These phenomena illustrated that changing the molecular structure of surfactants could cause changes in their microstructure and finally lead to a change in the viscosity of the solution.