Using molecular dynamics simulations, we elicit details of the assembly of 3-arm star block copolymers at oil-water interfaces. Each arm consisted of a hydrophilic-hydrophobic block and the hydrophobic blocks were covalently attached to each other forming a core that was modeled so that it becomes protonated when in contact with the aqueous phase. This leads to conformational change of the star at the interface, highlighted by significant stretching of the chains comprising the hydrophilic corona, while the hydrophobic core remains solubilized in the oil phase. The kinetics of anchoring and assembly of the stars at the interface, their lateral assembly, and the subsequent reconfiguration and the change in interfacial tension, as the degree of protonation increases was examined. At low fractions of protonation, the arm cannot fully anchor to the aqueous side of the interface and interacts with other arms in the oil phase. As the degree of protonation increases, more of the hydrophilic arms are dissolved in the solvent changing the conformation from a 3D structure in solution to 2D-like structure at the interface. We further probed the effect of the number of arms, degree-of-polymerization of the arms and arm block sequence on the surface tension for the fully protonated case with 50% hydrophilic segments. Star polymer sequences that have high concentration at the interface had lower interfacial tension. In conclusion, the results provide useful information for decoding interfacial compatibilizer design.

Assembly of charged star block copolymers at the oil-aqueous interface

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