Coarse-grained modeling of peptidic/PDMS triblock morphology

The morphology and chain packing structures in block copolymers strongly impact their mechanical response; therefore, to design and develop high performance materials that utilize block copolymers, it is imperative to have an understanding of their self-assembly behavior. In this research, we utilize coarse-grained (CG) molecular dynamics to study the effects of peptidic volume fraction and secondary structure on the morphological development and chain assembly of the triblocks poly(γ-benzyl-L-glutamate)-b-poly(dimethylsiloxane)-b-poly(γ-benzyl-L-glutamate) (GSG) and poly(dimethylsiloxane)-b-poly(γ-benzyl-L-glutamate)-b-poly(dimethylsiloxane) (SGS). This necessitated developing a complete coarse-grained parameter set for poly(dimethylsiloxane) that closely captures the radial pair distribution of a united atom model and the experimental density at 300 K. These parameters are combined with the MARTINI amino acid CG force field and validated against prior reported values of domain spacing and peptide chain packing for GSG. The combined CG parameter set is then used to model SGS, a triblock currently in development for nature-inspired mechanically enhanced hybrid materials. The results reveal that the peptide side chain strongly influences the final morphology. For instance, lamellar or hexagonally packed cylindrical domain formation can result from the variation in side-chain interactions, namely, side-chain sterics preventing curved interface formation by increasing interfacial free volume. Ultimately, this research lays the foundation for future studies involving systems with dispersity, mixtures of secondary structures, and larger multiblock copolymers, such as polyurethanes and polyureas.