Study of the Synergistic Effect of Sodium Dodecyl Sulfate and Betaine at the Air/Water and Oil/Water Interfaces

Abstract

In this paper, the molecular array behavior of anionic surfactant sodium dodecyl sulfate SDS and zwitterionic surfactant Betaine at the air/water and oil/water interfaces were investigated by molecular simulation approaches, which helped to understand the effects of temperature, salts and the proportion of components on the interfacial activity and foam stability of the mixed binary systems, especially how the multivalent inorganic cations influence the interfacial adsorption behavior of the surfactants and the synergistic effect. The oil/water interfacial tension was not only measured experimentally using TEXAS500 spinning drop interface tension meter, but also calculated theoretically using dissipative particle dynamic (DPD) method. Foam decay method was utilized to determine the foam stability. The array behavior of surfactant molecules at the air/water and oil/water interfaces was described by molecular dynamics (MD) simulation method. It was found that the oil/water interfacial activity of mixed binary system was significantly better than unitary system. The synergistic effect between SDS and Betaine was enhanced when there was Ca 2＋ or Mg 2＋ existed in the solution. The radial distribution function of head groups of surfactants around inorganic ions showed that there was very strong interaction between the Ca 2＋ or Mg 2＋ and the head groups of SDS and Betaine, which not only induced the increase of the maximum interfacial adsorption quantity of the surfactants, but also adjusted the array states of the surfactant molecules in the interface layer. When the proportion of components of SDS/Betaine binary system was 4∶6, the oil/water interfacial activity and foam stability of the binary system both were very good with Ca 2＋ or Mg 2＋ existing, even use sea water as medium, which could be a good candidate system for foam system used under high salinity condition. The co-adsorption behavior of the surfactant molecules in the binary system at oil/water interface and the foam films was found to be similar. The simulation results agreed well with the experiment results. The knowledge about the microscopic character of the mixtures of surfactants at interfaces could provide useful guidance for the design and application of surfactants under the condition of high salinity, such as low tension foam flooding system used in offshore EOR.

Studies on Interfacial Tensions of Ionic Surfactant and Alkyl Sulfobetaine Mixed Solutions

“…Hence, the studies of zwitterionic and ionic surfactant mixed systems for EOR have received the attention of researchers. However, most of the reports focus on surface tensions and the critical micelle concentration (cmc). − Studies on IFT have rarely been reported. , …”

“…The mixed solutions not only avoid the synthesis of complex structures of surfactant molecules but can also obtain ultralow IFT during the wide concentration range. Therefore, it has an important theoretical value and a broad application prospect in EOR. , …”

“…The 10 –5 mN/m magnitude ultralow IFT was obtained because of synergistic interactions between zwitterionic and anionic surfactants. Li et al measured the oil/water IFTs of SDS and betaine mixed solutions. They also simulated the molecular arrangements at air/water and oil/water through molecular simulation approaches and found that there exists a synergistic effect between the anionic surfactant and betaine.…”

“…When different surfactant compounds sort with each other, hybrid systems often perform better. For example, synergy between different types of surfactants in a mixed system can result in lower IFTs. , Another advantage is to reduce costs in two ways: one is to decrease the total amount of surfactants used, and the other is to use a low-cost surfactant mixed with an expensive surfactant to reduce the total cost. For this purpose, we used both n -alkane and crude oil as the oil phase and measured the IFTs of different mixed surfactant solutions against them.…”

Experimental Study on the Stabilization Mechanisms of CO2 Foams by Hydrophilic Silica Nanoparticles

“…This may caused by the decrease of maximum adsorption of surfactant and NPs in Figure . For the NPs/OA-12 system, high salinity or high temperature may make maximum adsorption value decrease; the tendency of foam stability with varied concentration of NPs or surfactant is still consistent, which is in line with the previous works …”