Thermodynamics of star polymer solutions: a coarse-grained study

Abstract

We consider a coarse-grained (CG) model with pairwise interactions, suitable to describe low-density solutions of star-branched polymers of functionality $f$. Each macromolecule is represented by a CG molecule with $(f+1)$ interaction sites, which captures the star topology. Potentials are obtained by requiring the CG model to reproduce a set of distribution functions computed in the microscopic model in the zero-density limit. Explicit results are given for $f=6,12$ and $40$. We use the CG model to compute the osmotic equation of state of the solution for concentrations $c$ such that ${\Phi }_p=c/c^{\ast }\lesssim 1$, where $c^{\ast }$ is the overlap concentration. We also investigate in detail the phase diagram for f=40, identifying the boundaries of the solid intermediate phase. Finally, we investigate how the polymer size changes with $c$. For ${\Phi }_p\lesssim 0.3$ polymers become harder as $f$ increases at fixed reduced concentration $c/c^{\ast }$. On the other hand, for ${\Phi }_p\gtrsim 0.3$, polymers show the opposite behavior: At fixed ${\Phi }_p$, the larger the value of $f$, the larger their size reduction is.

29 pages (17 pages main paper, 12 pages supplementary material), 24 figures, 8 tables. Manuscript accepted for publication in J. Chem. Phys

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• Polymer models with optimal good-solvent behavior