Interfacial electrostatic potential of polyions as probed by acid‐base indicator dyes covalently attached to the main chain

Abstract

AbstractPolyanions 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 (pKabs) was determined by the spectroscopic pH titration. The interfacial electrostatic potential (ψ) was calculated from pKobs. 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 Å 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.