Aggregation Behavior of Surfactants with Different Molecular Structures in Aqueous Solution: DPD Simulation Study

Abstract

The aggregation behavior of surfactants with different molecular structures in aqueous solution was investigated by dissipative particle dynamics (DPD) coarse-grained model simulation. With a simple surfactant model, we investigated how variations in micelle size and structures of surfactants influence their aggregation behavior. The obvious effects on the aggregation properties of surfactants caused by the variation of the hydrophobic or hydrophilic groups and the branch structures were investigated by corresponding structure charts in aqueous solution. The properties such as critical micelle concentration (CMC), cluster size, and density distribution of surfactants were analyzed at the mesoscopic level. Simulation results showed that the CMC value decreases as the length of the hydrophobic tail increases, while the cluster size and the density of tail increase. Conversely, an increase in the size of the head groups was found to enhance the CMC. It is also found that the surfactants with branch in tails are more efficient in forming micelles than linear ones. This is because the stronger excluded volume interactions make branched surfactants require more space at the surface and get more efficient. Additionally, branch in hydrophilic parts, including bola types of surfactant, leads to higher concentration needed to form micelles in aqueous solution and the cluster size are greatly larger than linear ones because of their peculiar structures.

Keywords:

• Cluster size
• critical micelle concentration (CMC)
• density profile
• dissipative particle dynamics
• surfactant

Acknowledgments

This work is supported by the National Natural Science Foundation of China (No. 20803069) and the Science Foundation for Excellent Middle & Young Scientist of Shandong Province (BS2010CL050).