(200h) Predicting Pka Values of Weak Acidic and Basic Polymer Brushes Via Molecular Modeling

Inverted colloidal crystal (ICC) membranes have been proposed as a new porous medium in bioseparation because of their high porosity, narrow pore size distribution, and ability to incorporate a variety of functions. Surface modified ICC membranes can be applied to target specific separations such as proteins and viruses. The pKa value of the membrane ion-exchange groups is a key factor in performance. The pKa values depend on the chain length, chain density and chain conformation of the polymer brush, and also the dielectric properties of the environment. We modeled a number of weak acidic and basic oligomers of DP 2 to 20 by using Car-Parrinello molecular dynamics simulations and solved the Poisson-Boltzmann equation for the electrostatic interactions. The calculated pKa values of the monomers and short oligomers were compared with available experimental data to validate our algorithm. Correlation curve between the pKa value of the polymer brush and chain length and polymer thickness was established.