Structure and Organization of Amphiphilic Mikto-Grafted Molecular Brushes at Liquid/Liquid Planar Interfaces

Amphiphilic molecular bottlebrushes provide a rich platform to develop emulsifiers for highly responsive emulsions. An understanding of the effect of the different molecular parameters on the structure, organization, and interfacial properties of bottlebrushes at oil/water interfaces is an important step toward the molecular engineering of advanced bottlebrush surfactants. In this work, extensive numerical simulations were performed to investigate the role of side chain and backbone lengths, as well as polymer surface concentration, on polymer structure, interfacial tension, and the organization of amphiphilic mikto-grafted molecular brushes at planar oil/water interfaces. Simulation results show that the side chain length is an important molecular parameter: long side chains favor extended conformations at low surface concentrations and higher local orientational order at high surface concentrations. In addition, regarding thermodynamic interfacial properties, simulation results predict that bottlebrushes with long side chains and short backbones are better at reducing interfacial tension compared to polymers with long backbones and short side chains, in agreement with previous experimental observations. Several structural descriptors were computed to provide a molecular view of the morphological changes occurring as the polymer surface concentration and molecular parameters were varied. The results reported here provide structure-interfacial property relations that will be useful to have a deeper understanding of how the molecular parameters of amphiphilic mikto-grafted molecular brushes will affect their behavior at oil-water interfaces to create advanced responsive emulsions.