Coarse-grained models for macromolecular systems

Neutron scattering experiments and simulations are often used as complementary tools in view of revealing the structure and dynamics of molecular and macromolecular systems. For polymeric and self-assembling systems, the simulation of large-scale structures and long-time processes is often achieved by using coarse-grained models which allow to gain some orders of magnitude in space and time scales. By discarding some details of the chains, they also allow a better understanding of the main features of the system that govern its behaviour, such as the sequence of a macromolecule or some interaction that leads to its self-assembly. After a brief introduction on coarse-grained models and associated representations, the approach is illustrated with the case of amphiphilic regularly alternating multiblock copolymers in dilute and semidilute solutions. In this context, a generic HP (H: hydrophobic ; P: hydrophilic, polar) model is used together with a lattice representation of the system and a Monte Carlo algorithm. The simulations give access to the various structures and phases of the system as a function of the energy of interaction between H monomers, the ratio of H monomers in the chain, the length of the blocks and the concentration. In dilute solution structures range from swollen coils in good solvent to chains of micelles and layered structures in poor solvent. In semidilute solution microphase separation and gelation are observed as a function of substitution ratio and concentration