Molecular Dynamics Simulation of Ionic Liquid-type Gemini Imidazolium Surfactants in Aqueous Solutions

The surface activity and the ability of micellization of ionic liquid-type Gemini imidazolium surfactants in aqueous solution were investigated by the molecular dynamics simulation. The simulation results indicate that the surface tension calculated from pressure tensor is lower and need to be corrected by multiplying the modified coefficient. The critical micelle concentration calculated by molecular dynamics simulation is consistent with experimental values, and can be used to discriminate the capacity of micellization of ionic liquid-type Gemini imidazolium surfactants. As the temperature rises, the micellization of ionic liquid-type Gemini imidazolium surfactants becomes more difficult with the aggravation of molecular movement. In addition, we found that ionic liquid-type Gemini imidazolium surfactants with different spacer lengths should follow the various mechanism of micellization. At S <= 6, the self-assembly ball of single molecule begin to form the larger micelle. As the carbon atoms of the alkyl chains on the imidazole increase, the formation ability of the micelles of [C-n-4-C(n)im] is enhanced. But the formation ability of the micelles of [C-10-S-C(10)im] decrease with the longer spacer. However, at S>6, one molecule inserts the crooked spacer into the interspace between the alkyl chains of the other molecule which leads to the formation of the larger micelles. Therefore, the micelle formation ability of [C-10-S-C(10)im] enhances because the repulsion forces decrease and the hydrophobic interactions become stronger with the spacer lengths increasing.