Droplets, Micelles, and More Complex Structures of Polyampholyte Aggregates

Polyampholytes are polymers that contain both positive and negative charges, allowing them to self-assemble into various structures under specific conditions. In this study, we investigate the effects of charge sequence on the morphology of polyampholyte aggregates, focusing on chains with a moderate net charge. Using molecular dynamics (MD) simulations, we analyze how the charge sequence influences aggregate formation at varying concentrations. Our findings demonstrate that the charge sequence plays a crucial role in determining the size and morphology of aggregates, with certain sequences forming core-corona structures of the micelle type. In particular, polyelectrolyte-like charged tail sequences predominantly contribute to corona formation, influencing not only aggregate size but also its stability and dynamics. For the range of aggregate sizes explored, the fraction of chain ends participating in the corona increases linearly with the aggregation number. Despite the presence of a kinetic barrier, the equilibrium aggregation number of micelle-type aggregates can be significantly larger than that of the droplets. The presence of charged tails and the magnitude of the central net charge are key factors driving structural diversity, leading to the formation of droplets, micelles, interconnected micelles and droplets, and network-like aggregates. Additionally, charge compensation within the polymer and the condensation of counterions play significant roles in stabilizing aggregates and regulating their growth. Our current simulations do not include salt, which limits direct applicability to biological systems. The effect of the salt is discussed only qualitatively. Nonetheless, these findings enhance our understanding of polymer self-assembly and may aid in the design of polymer-based nanomaterials.