We present a molecular coarse-graining approach applied to polystyrene which obtains both the bonded and nonbonded interactions of the coarse-grained model from the sampling of isolated atomistic chains and pairs of oligomers. Atomistic melt properties are not used in the parametrization. We show that the coarse-grained polystyrene model not only predicts melt properties, including the melt packing and the density between 400 and 520 K, in satisfactory agreement with the atomistic model, but also reproduces the local chain conformations of atactic as well as stereoregular polystyrene. The model takes into account and reproduces correlations between neighboring bonded degrees of freedom and therefore reproduces the conformations of detailed atomistic chains in the melt on all length scales.
Many physical phenomena and properties of soft matter systems are characterized by an interplay of interactions and processes that span a wide range of length- and time scales. Computer simulation approaches require models, which cover these scales. These are typically multiscale models that combine and link different levels of resolution. In order to reach mesoscopic time- and length scales, necessary to access material properties, coarse-grained models are developed. They are based on microscopic, atomistic descriptions of systems and represent these systems on a coarser, mesoscopic level. While the connection between length scales can be established immediately, the link between the different time scales that takes into account the faster dynamics of the coarser system cannot be obtained directly. In this perspective paper we discuss methods that link the time scales in structure based multiscale models. Concepts which try to rigorously map dynamics of related models are limited to simple model systems, while the challenge in soft matter systems is the multitude of fluctuating energy barriers of comparable height. More pragmatic methods to match time scales are applied successfully to quantitatively understand and predict dynamics of one-component soft matter systems. However, there are still open questions. We point out that the link between the dynamics on different resolution levels can be affected by slight changes of the system, as for different tacticities. Furthermore, in two-component systems the dynamics of the host polymer and of additives are accelerated very differently.
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