PRISM theory comparison with

The predicted nonideal conformational effects can be probed by SANS experiments, and theoretical/experimental comparisons are given elsewhere. A detailed physical picture of the origin of the nonideal conformational behavior in terms of the thermodynamic forces a star experiences has been constructed. Comparison of the self-consistent PRISM theory results with phenomenological scaling, and other coarsegrained polymer physics approaches have also been presented, and distinctive qualitative and quantitative differences have been identified. ... 

Figure 13. Comparison of prediction of the wall-PRISM theory with the hypernetted chain...

The outline of the paper is as follows. In Sect. 2 we describe the basic RISM and PRISM formalisms, and the fundamental approximations invoked that render the polymer problem tractable. The predicticms of PRISM theory for the structure of polymer melts are described in Sect. 3 for a variety of single chain models, including a comparison of atomistic calculations for polyethylene melt with diffraction experiments. The general problem of calculating thermodynamic properties, and particularly the equation-of-state, within the PRISM formalism is described in Sect. 4. A detailed application to polyethylene fluids is summarized and compared with experiment. The develojanent of a density functional theory to treat polymer crystallization is briefly discussed in Sect. 5, and numerical predictions for polyethylene and polytetrafluoroethylene are summarized. 

An example of a comparison by Honnell et al. of PRISM theory with molecular dynamics simulations are shown in Figure 3. Details of the model are given elsewhere. Briefly, a meltlike density was studied for /V = 50-150 unit chains. The linear polymers were modelled as freely jointed beads with a purely repulsive, shifted Lennard-Jones interaction between all segment pairs. The corresponding chain aspect ratio is F-1.4. PRISM theory with the PY closure (plus a standard correction... 

The best test of self-consistent PRISM theory and the different solvation potential approximations is via comparison of its predictions against exact computer simulation studies of the same model. The drawback is that present computer power limits such comparisons to short and intermediate length chains (/V less than roughly 200). Many detailed comparisons have been carried out at all levels of approximation discussed in Section VIII.B. Here we give a few examples along with summarizing remarks. The reader is referred to the original studies for details and a complete discussion. 

Application and generalization of the self-consistent PRISM theory to flexible trimer fluids, and detailed comparison with many molecule simulations, has also been performed by both Grayce and dePablo and Yethiraj. ... 

The PRISM theory can be used to calculate the partial structure factors, which can be input into equation (31) to obtain the SANS chi parameters. In principle, if a molecular model for the polymers is available this comparison could be carried out with no adjustable parameters since the potential parameters can be obtained from fitting to thermodynamic data. Nearly symmetric isotopic blends, where the only difference between the two components is that some of the hydrogen atoms in one component have been substituted with deuterium, are a very good model system because they are fairly easy to model and show interesting behavior, including a strongly composition dependent In most cases... 

The explicit atom potential of Eq. (14) was used for polyethylene in SC/PRISM calculations and MD simulations with the parameters in Table 2. A comparison between theory and simulation is given in Fig. 11 for each of the intermolecular pair... 

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