Coarse-grained models of bottlebrush polymers from solutions to melts using a wormlike cylinder model

Bottlebrush polymers are a class of macromolecules composed of densely grafted side chains on a linear polymer backbone. The crowding of side chains leads to steric repulsions, which give the polymer a stiff conformation with molecular thickness. Despite their great engineering potential, particle-based simulation of these materials is challenging due to the large number of monomers needed to describe each molecule. We recently demonstrated that it is possible to describe a bottlebrush as a linear semi-flexible chain based on the wormlike cylinder (WLCy) model, which does not include explicit side chains. These implicit side chain (ISC) models drastically decrease the computational cost by directly mapping to simulations of the conformation of individual bottlebrushes. However, the ISC model is limited to dilute solution, which is far from real functional materials in application in bulk melts or concentrated solutions.

In this study, we expanded the capability of the ISC model to include concentrated solution and melts. First, we show how to adapt the ISC model to semidilute conditions by introducing a concentration-dependent persistence length. We designed a scaling model to parameterize the interaction potential and model parameters, which can be incorporated into molecular dynamics simulations to observe concentration-dependent self-assembly of block bottlebrush polymers. Structural factors and the estimated length scales from the semidilute ISC model are consistent with self-assembly as a function of concentration in experiment. We also consider the limit of the concentrated bottlebrush melts, where we mapped an ISC model of bottlebrush melts from single-chain mean-field (SCMF) simulations. The resulting ISC model was again modeled as a flexible WLCy as a function of different architectures. We describe how the interaction potential is derived in this ISC melts model using structural information.