Synthesis and physicochemical investigation of betaine type polyoxyethylene zwitterionic surfactants containing different ionic headgroups

The surfactant solubility in oilfield water and stability under high-salinity/high-temperature reservoirs faces great challenges. The industrially applied surfactants including petroleum sulfonate, alkyl benzyl sulfonate, and polyoxyethylene ether are suffering due to poor performance in high temperature and high salinity environment. In this study, three betaine based polyoxyethylene zwitterionic surfactants having an unsaturated tail with different ionic headgroups (carboxybetaine, sulfobetaine, and hydroxy sulfobetaine) were synthesized. The structures of the synthesized surfactants were elucidated using FTIR and NMR. The surfactants showed excellent solubility in formation water and sear water and no apparent insoluble surfactants were observed. Thermogravimetric analysis results revealed that the degradation temperatures of the synthesized surfactants were above 290 °C. The critical micelle concentration (cmc) of all surfactants was reduced upon enhancing the temperature, however, the surfactant-containing hydroxy sulfonate headgroup showed the lowest cmc (3.35 × 10⁻⁵ mol/L). Similarly, the surface tension at cmc (γ_cmc) also reduced upon enhancing the temperature and the surfactant-containing carboxylate headgroup exhibited lowest surface tension (32.24 mN/m). The excellent surface properties and heat stabilities of the betaine type polyoxyethylene zwitterionic surfactants make them a preferred choice for challenging reservoir conditions.