(687i) Investigation of the Critical Point of Adsorption of Polymer Chains On Porous Adsorbents

Liquid phase chromatography at critical conditions (LCCC) is a widely used technique for the separation of polymeric mixtures of similar molecular weight but different chemical properties.  The critical point of adsorption (CPA) is defined as the point at which adsorption is independent of molecular weight, and is observed experimentally. While theory has been developed to evaluate the CPA for ideal chains, an adequate theoretical description of the CPA of real chains is still lacking.  This work provides a theoretical basis for defining the CPA of a realistic polymer chain based on the free-energy and chemical potential of the chain, and provides model calculations of the CPA on a porous substrate using Gauge Cell Monte Carlo.  In developing the model, several modes of adsorption are considered: adsorption approaching the external surface of an adsorbent particle, complete adsorption within a pore, adsorption of chains tethered to the external surface of the particle, and the adsorption of chains which are partially translocated – called “flower” configurations.  The summation of the Boltzmann-weighted free energies of these configurations are used as the partition function for calculating system variables – notably the partition coefficient and chemical potential of the polymer chain.