Partitioning of polymers between bulk and porous media: Monte Carlo study of the effect of pore size distribution.

In this paper we investigated the partitioning of polymer chains between bulk solvent and porous stationary phase under conditions appropriate for the chromatography under critical conditions (LCCC) close to the critical adsorption point (CAP). We addressed the concentration effect and the thermodynamic effect of pore-size dispersity (PSD) and their impacts on chromatography, i.e., the topics which surprisingly escaped from the interest of scientists in spite that the hydrodynamic effect of PSD has been a subject of numerous studies. The phase equilibria in narrow pores (as compared with the size of polymer coil) with attractive pores are complex and the enthalpy-to-entropy interplay is very intricate. The chains are attracted into pores and the partition coefficients are larger than 1, which corresponds to the interaction chromatography (IC), but they are strongly confined and deformed. The entropy plays important role and the elution volumes of chains differing in molar mass correspond to the size-exclusion chromatography (SEC). The study thus reveals a new chromatography regime which could be easily overlooked without the awareness of its existence. The unexpected findings are important not only for chromatography, but for understanding the phase equilibria of polymers in porous systems in general.