Effects of the hydrophilicity or hydrophobicity of the neutral block on the structural formation of a block polyelectrolyte/surfactant complex: A molecular dynamics simulation study

The mechanism of how the neutral block in polyelectrolyte (PE) affects the interaction between PE and surfactants is investigated through coarse-grained simulations. We show that the neutral block plays profound roles on the structural formation of the PE/surfactant complex by assessing the adsorption of surfactants on a diblock or triblock PE and the resultant structures. For the diblock PE/surfactant system, adding a hydrophilic neutral block exerts little effect on the structural formation of the complex, while the presence of a hydrophobic neutral block enhances the adsorption of surfactants and facilitates the formation of a tri-layer core-shell structure. In the triblock PE/surfactant systems, two charged blocks located symmetrically at both ends of PE display asymmetric adsorption abilities for the surfactants. In addition, the presence of a charged middle block drives the PE/surfactant complex to form a micelle with two tails due to the hydrophilic blocks at both ends, while the hydrophobic ones drive the formation of a tri-layer core-shell structure with the PE chain showing a looped structure. If one end is hydrophilic and the other is hydrophobic, the complex tends to form a 'tadpole'-like structure in which the head is the tri-layered core-shell sphere, and the tail is the hydrophilic block.