INTERFACIAL ELECTROSTATIC POTENTIAL OF POLYIONS AS PROBED BY ACID-BASE INDICATOR DYES COVALENTLY ATTACHED TO THE MAIN CHAIN

Polyanions with various charge densities with a solvatochromic acid-base indicator dye attached to the main chain were prepared by the terpolymerization of acrylic acid, acrylamide, and a small mole fraction of 1-(2-methacryloyloxyethyl)-4-(2-(4-hydroxyphenyl) ethenyl) pyridinium bromide. The apparent pK value for the polymer-bound indicator dye (pK(obs)) was determined by the spectroscopic pH titration. The interfacial electrostatic potential (Psi) was calculated from pK(obs). Dielectric contribution to the acid-base equilibrium was taken into account for the calculation. The electrostatic potentials thus obtained were compared with those calculated from the nonlinearized Poisson-Boltzmann equation for a cylinder model. The indicator dye moieties are suggested to be reporting the mean field potential at a distance of about 10 angstrom from the axis of the polyion cylinder. The observed values as a function of the charge density were also discussed in connection with Manning's theory.