Determining the Mesh Size of Polymer Solutions via the Pore Size Distribution

V Sorichetti and V Hugouvieux and W Kob, MACROMOLECULES, 53, 2568-2581 (2020).

DOI: 10.1021/acs.macromol.9b02166

In order to determine in polymeric systems the geometrical mesh size we simulate a solution of coarse-grained polymers with densities ranging from the dilute to the concentrated regime and for different chain lengths. We determine the monomer density fluctuation correlation length xi(c) from the monomer structure factor as well as the radial distribution function, showing that the identification xi = xi(c) is not justified outside of the semidilute regime. In order to better characterize xi, we compute the pore size distribution (PSD) following two different definitions, one by Torquato et al. and one by Gubbins et al. We find that the mean values of the two distributions, < r >(T) and < r >(G), display the behavior predicted for xi by scaling theory, and argue that xi can be identified with either one of these quantities. This identification allows to interpret the PSD as the distribution of mesh sizes, a quantity which conventional methods cannot access. Finally, we show that it is possible to map a polymer solution on a system of hard or overlapping spheres, for which Torquato's PSD can be computed analytically and reproduces accurately the PSD of the solution. We give an expression that allows < r >(T) to be estimated with high accuracy in the semidilute regime by knowing only the radius of gyration and the density of the polymers.

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