METHODS FOR DETERMINING THE INTRINSIC AND EFFECTIVE CHARGES ON SPHERICAL MACROIONS

The intrinsic number of charges per particle, Z, on particles in a sus pension of monodisperse sulfonated polystyrene latex is found by measu ring steady-state voltammetric transport-limited currents for the redu ction of hydrogen counterion at a Pt disk microelectrode in a suspensi on containing excess supporting electrolyte. limiting currents measure d in deionized latex suspensions yield a corresponding effective charg e, Z. Electrostatic binding of an inner layer of counterions to the p article renders Z < Z, Voltammetrically determined charges agree with the intrinsic and effective Stokes charges as determined by titration and electrophoresis, respectively. zeta- Potentials calculated from t he measured electrophoretic mobility of the particles yield the Loeb c harge number, which agrees more closely with Z than with Z, For exist ing data on spherically charged macroions, Z/Z decreases with increas ing ratio of intrinsic charge to macroion radius, Z/a, This finding is supported by effective charge values calculated from the cell model u sing the nonlinear Poisson-Boltzmann equation with the convention that Z is the charge found between the c(r)/[c] = 1 boundary and the cell wall.