Investigating the effects of the copolymer architecture on the properties of the polyion complexes by Monte Carlo simulations

Polyelectrolyte complexes constituted by a linear charged homopolymeric chain and oppositely charged copolymers with different topologies are investigated at the stoichiometric charge ratio using Monte Carlo simulations in a coarse-grain model. Highly and weakly charged polyanions as well as a library of copolymers differing in terms of the neutral monomer fraction of the copolymer were examined, and three different architectures (branched vs multiblock vs random) were considered at each copolymer composition. The size and extension of both polyions were characterized by their radius of gyration and asphericity, whereas the morphology of the complexes was investigated by the internal densities of all constituents with respect to the complex center of mass. At strong electrostatic coupling and low neutral monomer fraction, the compaction of polyanion by the branched and multiblock copolymers resulted in a core–shell conformation, and a structureless spherical complex was found in the presence of the random copolymer. As the fraction of neutral monomer increased, a gradual transition from a globular structure to an extended one was encountered only for branched and multiblock copolymers, with the random copolymer providing the largest degree of compaction among the three copolymer types at high fraction of neutral monomer. For weak electrostatic coupling, the internal segregation was not found irrespective of the fraction of neutral monomer, whereas the polyanion compaction degree followed the sequence branched > multiblock ≈ random at given copolymer composition.