Surface electric potential on rod‐like polyelectrolyte

The electric potential on the surface of the rod‐like polyelectrolyte with uniform charge distribution or periodically changing charge distribution on the surface is solved numerically by use of a power series method and an electronic computer. The deviation from the Linderstrøm‐Lang's linear relation in the modified pH titration diagram, and the dependence of the surface electric potential on the radius of rod are discussed. Also, the radius of counterion and ionic strength, and the effect of non‐uniformity of charge distribution are considered. Molecular radii were determined by comparing the calculated results with the pH titration data. The molecular radii of stereoregular poly‐(methacrylic acid) and α‐helical poly(glutamic acid) were found to be 5.5 Å and 15.0 Å, respectively, assuming uniform charge distribution. If nonuniform charge distribution was assumed, the molecular radii were calculated to be 5.0 Å and 14.0 Å, respectively. These values are discussed in relation to their molecular structures.