Molecular Dynamics Simulation Study of a CO₂-Switchable Surfactant

We computed molecular properties of a long-tail amidine surfactant (N'-dodecyl-N,N-dimethylacetamidinium bicarbonate, DDAB) through quantum mechanics (QM) method. We then used molecular dynamics (MD) computations to obtain the properties of DDAB when displaced from the center to the boundary surface. The QM calculation results indicated that the mono-dentate type of bindings between polar head group and HCO^-₃ ion was more likely to be adopted. The MD results indicated that the HCO^-₃ ions could pass the energy barrier surrounding the head groups to form stable ion pairs. Meanwhile, the surfactant molecules aggregated very quickly, and absorbed in a direction pointed from the bulk center to the boundary. These results indicated that hydrophobic correlations of alkyl chains are the driving force for boundary adsorption of DDAB.