A strategy is developed for generating equilibrated high molecular-weight polymer melts described with microscopic detail by sequentially backmapping coarse-grained (CG) configurations. The microscopic test model is generic but retains features like hard excluded volume interactions and realistic melt densities. The microscopic representation is mapped onto a model of soft spheres with fluctuating size, where each sphere represents a microscopic subchain with N b monomers. By varying N b a hierarchy of CG representations at different resolutions is obtained. Within this hierarchy, CG configurations equilibrated with Monte Carlo at low resolution are sequentially fine-grained into CG melts described with higher resolution. A Molecular Dynamics scheme is employed to slowly introduce the microscopic details into the latter. All backmapping steps involve only local polymer relaxation thus the computational efficiency of the scheme is independent of molecular weight, being just proportional to system size. To demonstrate the robustness of the approach, microscopic configurations containing up to n = 1000 chains with polymerization degrees N = 2000 are generated and equilibration is confirmed by monitoring key structural and conformational properties. The extension to much longer chains or branched polymers is straightforward.Studying equilibrium and rheological properties of melts of long polymer chains with computer simulations requires the preparation of equilibrated configurations described with microscopic detail. For this purpose, stochastic approaches have been proposed to circumvent the prohibitively large relaxation times in schemes with physically realistic dynamics, resulting from chain entanglements. Among methods addressing directly the microscopic scale, re-bridging (RB) algorithms 1 are the most advanced, modifying the chain connectivity while avoiding significant changes in local monomer packing. Even with their help, the longest melts currently addressed are those of linear polyethylene, corresponding to monodisperse samples with a few C 1000 chains. 1 Introducing polydispersity, increases the acceptance rate of RB moves and longer chains can be modeled. However, the system becomes less well-defined, e.g., for understanding rheological behavior and the samples remain rather small: the longest C 6000 (average length) melt 2 that was realized contained 32 chains. To prove equilibration these studies relied on the decay of conformational correlations. However, recent findings 3 demonstrate that the combination of chain connectivity and limited compressibility affects chain conformations. Since RB moves are largely decoupled from density fluctuations, such subtle effects suggest 3 that to verify unambiguously melt equilibration more sensitive descriptors of chain shape, such as internal distance plots, 3,4 should be considered.To overcome the limitations encountered when 1 arXiv:1610.07511v1 [cond-mat.soft]

Smart polymers are a modern class of polymeric materials that often exhibit unpredictable behavior in mixtures of solvents. One such phenomenon is co-non-solvency. Co-non-solvency occurs when two (perfectly) miscible and competing good solvents, for a given polymer, are mixed together. As a result, the same polymer collapses into a compact globule within intermediate mixing ratios. More interestingly, polymer collapses when the solvent quality remains good and even gets increasingly better by the addition of the better cosolvent. This is a puzzling phenomenon that is driven by strong local concentration fluctuations. Because of the discrete particle based nature of the interactions, Flory-Huggins type mean field arguments become unsuitable. In this work, we extend the analysis of the co-non-solvency effect presented earlier [D. Mukherji et al., Nat. Commun. 5, 4882 (2014)]. We explain why co-non-solvency is a generic phenomenon, which can only be understood by the thermodynamic treatment of the competitive displacement of (co)solvent components. This competition can result in a polymer collapse upon improvement of the solvent quality. Specific chemical details are not required to understand these complex conformational transitions. Therefore, a broad range of polymers are expected to exhibit similar reentrant coil-globule-coil transitions in competing good solvents.

Topological constraints due to chain connectivity and uncrossability greatly impact the long time dynamics and rheology of high molecular weight polymer melts. Computer simulations to study properties of such melts are very advantageous, since perfect control of molecular conformation and melt morphology is available. We present a methodology to prepare well-equilibrated polymer melts which only requires local relaxation. The approach efficiently leads to equilibrated ensembles of bead-spring polymer melts of 1 000 chains of up to 2 000 beads, which correspond to 24 (fully flexible) and 45 entanglement lengths (semi-flexible chains). Entanglements are identified by a primitive path analysis and a master curve of the entanglement lengths for different chain and persistence lengths is presented.

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