Self-assembly behaviors of zwitterionic heterogemini surfactant at an oil-water interface: A dissipative particle dynamics study

Abstract

The self-assembly behaviors of a battery of zwitterionic heterogemini surfactants C _m H_{2 m +1}-PO^4--(CH₂)₂-N⁺(CH₃)₂-C _n H_{2 n +1}, abbreviated as C _m -P-N-C _n (m, n = 9, 9; 9, 12; 9, 15; 9, 18; 12, 12; 12, 15; 12, 18; 15, 15; 15, 18; 18, 18), have been explored at an oil-water interface by means of the dissipative particle dynamics (DPD) method. Regular oil-water contact together with oil-in-water and water-in-oil emulsions has come into being. Compared with the C _m -P-N-C _n concentration and the oil-water ratio, the hydrophobic chain length plays a less important role in the self-assembly morphology of C _m -P-N-C _n molecules at the interface together with the interfacial morphology. The asymmetry in the molecular structure of C _m -P-N-C _n dominates its critical micelle concentration (CMC) and interfacial efficiency. The C _m -P-N-C _n concentration and its hydrophobic chain length work together to affect the interfacial thickness. What’s more, the dependence of CMC on the C _m -P-N-C _n molecular structure is in qualitative agreement with corresponding experimental findings.

Graphical Abstract

Keywords:

• Self-assembly
• zwitterionic heterogemini surfactant
• dissipative particle dynamics
• oil-water interface

Acknowledgements

We are grateful to the high performance computing center of Shanghai University for providing the Materials Studio software.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work is supported by the National Natural Science Foundation of China (No. 21406136), the Innovation Program of Shanghai Municipal Education Commission (No. 14YZ015), and the Program for Innovative Research Team in University (No. IRT13078).