Molecular dynamics simulation of four typical surfactants at oil/water interface

ABSTRACT

In the present study, we have performed molecular dynamics simulations to describe the microscopic behaviors of the anionic, nonionic, zwitterion, and gemini surfactants at oil/water interface. The abilities of reducing the interfacial tension and forming the stable interfacial film of the four surfactants have been investigated through evaluating interfacial thickness, interface formation energy and radial distribution function. The results show that the four kinds of surfactants can form in stable oil/water interface of monolayer, and the gemini surfactant can form the more stable monolayer. The results of the above three parameters demonstrate that the gemini surfactant has the best simulation effect in the four surfactants. From the calculated interfacial tension values, the gemini surfactant possess the more powerful ability of reducing the interfacial tension than others, so it is more suitable to be used as the surfactant for flooding. In addition, the effects of different electric field intensities on surfactants were calculated, through the radial distribution function of the hydrophilic group in the surfactant and the oxygen atom in the water. We have found that the adding of the periodic electric field can significantly affect the diffusion behavior of the molecules, and nonionic surfactant has stronger demulsification capability than others.

GRAPHICAL ABSTRACT

KEYWORDS:

• Interfacial tension
• oil/water/surfactant interface
• periodic electric field
• surfactant

Acknowledgments

We thank Professor Yuan Yao (The Academy of Fundamental and Interdisciplinary Sciences, Harbin Institute of Technology, Harbin 150080, and People’s Republic of China) for his fruitful discussions and checking English.

Additional information

Funding

This work is supported by the National Basic Research Program of China [grant number 2012CB723308]; and the National Natural Science Foundation of China [grant number 51337002], [grant number 21201059], [grant number 50977019]. We thank the grid computing server provided by the Chinese Academy of Sciences.