Association of a multifunctional ionic block copolymer in a selective solvent

Response of ionizable block copolymer assemblies to solvent dielectrics: A molecular dynamics study

Ionizable copolymers assembly in solutions is driven by the formation of ionic clusters. Fast clustering of the ionizable blocks often leads to the formation of far-from equilibrium assemblies that ultimately impact the structure of polymer membranes and affect their many applications. Using large-scale atomistic molecular dynamics simulations, we probe the effects of electrostatics on the formation of ionizable copolymer micelles that dominate their solution structure, with the overarching goal of defining the factors that control the assembly of structured ionizable copolymers. A symmetric pentablock ionizable copolymer, with a randomly sulfonated polystyrene center tethered to polyethylene-r-propylene block, terminated by poly(t-butyl styrene), in solvents of varying dielectric constants from 2 to 20, serves as the model system. We find that independent of the solvents, this polymer forms a core-shell micelle with the ionizable segment segregating to the center of the assembly. The specific block conformation, however, strongly depends on the sulfonation levels and the dielectric constant and the polarity of the solvents.

Structured Ionomer Thin Films at Water Interface: Molecular Dynamics Simulation Insight

Controlling the structure and dynamics of thin films of ionizable polymers at water interfaces is critical to their many applications. As the chemical diversity within one polymer is increased, controlling the structure and dynamics of the polymer, which is a key to their use, becomes a challenge. Here molecular dynamics simulations (MD) are used to obtain molecular insight into the structure and dynamics of thin films of one such macromolecule at the interface with water. The polymer consists of an ABCBA topology with randomly sulfonated polystyrene (C), tethered symmetrically to flexible poly(ethylene-r-propylene) blocks (B), and end-capped by a poly(t-butylstyrene) block (A). The compositions of the interfacial and bulk regions of thin films of the ABCBA polymers are followed as a function of exposure time to water. We find that interfacial rearrangements take place where buried ionic segments migrate toward the water interface. The hydrophobic blocks collapse and rearrange to minimize their exposure to water. The water that initially drives interfacial reengagements breaks the ionic clusters within the film, forming a dynamic hydrophilic internal network within the hydrophobic segments.

Soft nanoparticles: nano ionic networks of associated ionic polymers

Directing the formation of nanostructures that serve as building blocks of membranes presents an immense step towards engineering controlled polymeric ion transport systems. Using the exquisite atomic detail captured by molecular dynamics simulations, we follow the assembly of a co-polymer that consists of polystyrene sulfonate tethered symmetrically to hydrophobic blocks, realizing a new type of long lived solvent-responsive soft nanoparticle.