Flexible Coarse-Grained Models

Whittle and Dickinson used a more elaborate model, incorporating harmonic bonds, short-ranged repulsive forces, and a shifted-center Leimard-Jones potential to study aggregates of soft particles typical of food colloids [70]. These authors also studied the failure of a colloidal gel under strain [71]. Similar studies, using either hard spheres or repulsive-core particles, have also been performed by other groups [72-75]. 

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Fig. 8.8 The bond fluctuation model. In this example three bcmds in the polymer arc incorporated into a singk effecti bond between effective moncmers . (Figure adapted from Baschnagel J, K Binder, W Paul, M Laso, U Sutcr, I Batouli [N ]ilge and T Burger 1991. On the Construction of Coarse-Grained Models for Linear Flexible Polymer-Chains -Distribution-Functions for Groups of Consecutive Monomers. Journal of Chemical Physics 93 6014-6025.)...

A suitable approach to the equilibration of an amorphous polymer system at bulk density becomes much more likely when the fully atomistic model in continuous space is replaced by an equivalent coarse-grained model on a lattice with sufficient conformational flexibility. Different strategies, which seek results at different levels of detail, can be employed to create an appropriate coarse-grained model. Section 4 (Doruker, Mattice) describes an approach which attempts to retain a connection with the covalent bonds in the polymer. The rotational isomeric state (RIS) [35,36] model for the chain is mapped into... 

Simulation methods have been proved to be useful in the study of many different molecular systems, in particular in the case of flexible polymers chains [ 14]. According to the variety of structures and the theoretical difficulties inherent to branched structures, simulation work is a very powerful tool in the study of this type of polymer, and can be applied to the general problems outHned above. Sometimes, this utility is manifested even for behaviors which can be explained with simple theoretical treatments in the case of linear chains. Thus, the description of the theta state of a star chain cannot be performed through the use of the simple Gaussian model. The adequate simulation model and method depend strongly on the particular problem investigated. Some cases require a realistic representation of the atoms in the molecular models [10]. Other cases, however, only require simplified coarse-grained models, where some real mon-... 

J. Chem. Phys., 95, 6014 (1991). On the Construction of Coarse-Grained Models for Linear Flexible Polymer Chains—Distribution Functions for Groups of Consecutive Monomers. 

Mapping Atomistically Detailed Models of Flexible Polymer Chains in Melts to Coarse-Grained Lattice Descriptions ... 

Figure 17 A sketch of the rigid units of an oligomeric PFPE molecule (a) the flexible bonds with freely jointed beads and springs for coarse-grained bead-spring model and (b) SRS model with polarity (red arrow).

Another viable method to compare experiments and theories are simulations of either the cell model with one or more infinite rods present or to take a solution of finite semi-flexible polyelectrolytes. These will of course capture all correlations and ionic finite size effects on the basis of the RPM, and are therefore a good method to check how far simple potentials will suffice to reproduce experimental results. In Sect. 4.2, we shall in particular compare simulations and results obtained with the DHHC local density functional theory to osmotic pressure data. This comparison will demonstrate to what extent the PB cell model, and furthermore the whole coarse grained RPM approach can be expected to hold, and on which level one starts to see solvation effects and other molecular details present under experimental conditions. 

The mobility of flexible chains in gels is well described by the biased reptation model [1], which is indicated schematically in Fig. 4. In the model, the fibers of the gel are coarse grained into a reptation tube that confines the chain. The chain thus slithers along the tube contour (the reptation part) under the influence of the electric field, which provides a tendency for the slithering motion to be in the direction of the electric field (the biased part). 

Gelb LD (2007) Simulating Silica Aerogels with a Coarse-Grained Flexible Model and Langevin Dynamics J Phy s Chem C 111 15792-1580... 

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